Biochemical Genetics 2 Flashcards
Carbohydrate metabolism and Fatty acid oxidation disorders
How are classic and clinical variant galactosemia detected on NBS
primarily based on the quantification of (may be dependent on state):
total content of the erythrocyte galactose-1-phosphate and blood galactose concentration AND/OR
erythrocyte GALT activity
requires f/u testing in a biochem genetics lab
DIETARY INTERVENTION NEEDS TO BEGIN IMMEDIATELY
What are the biochemical differences between classic and clinical galctosemia
Classic galactosemia
erythrocyte galactose-1-phosphate is high
plasma free galactose is usually high
GALT enzyme activity is absent or barely detectable
Clinical variant galactosemia
erythrocyte galactose-1-phosphate is usually high
Plasma free galactose may be high
Erythrocyte GALT enzyme activity is close to or above 1% of control values but probably never >10-15%
In certain pops (AA with hypomorphic alleles including p.Ser135Leu/Ser135Leu) erythrocyte GALT enzyme activity may be absent or barely detectable but is often much higher in liver and in intestinal tissue
How can the dx of galactosemia be established
Detection of elevated erythrocyte galactose-1-phosphate concentration, reduced erythrocyte galactose-1-phosphate uridylytransferase (GALT) enzyme activity, and/or biallelic PVs in GALT
What molecular (Genetic) testing approach should be taken to identify galactosemia
sequence analysis of GALT first then gene-targeted del/dup
targeted analysis for common PVs can be performed first in individuals of European or African ancestry
What are the clinical features of classic galactosemia
Within days of ingesting breast milk or lactose-containing formulas develop life-threatening complications including feeding problems, FTT, hypoglycemia, hepatocellular damage, bleeding diathesis, and jaundice
if classic galactosemia is not tx, sepsis with E coli, shock, and death may occur
extreme variability in symptoms
What is the long term outcome of those with classic galactosemia
cataracts, speech defects, poor growth, poor intellectual function, neurological deficits (extrapyramidal findings with ataxia), hypergonadotropic hypogonadism or premature ovarian insufficiency (both in females)
greater incidence of DD among individuals who were not tx until after age 2mo
What are the clinical features of individuals with clinical variant galactosemia
What populations is this most commonly seen in, and what molecular considerations need to be taken into account for this condition
early cataracts, liver dz, mild ID with ataxia, growth restriction
can result in life threatening complications including feeding problems, FTT, hepatocellular damage (cirrhosis), and bleeding
occurs in AA and native Africans in S. Africa with a p.Ser135Leu/Ser135Leu genotype
may be missed in NBS bc the hypergalactosemia is not as marked as in classic galactosemia
if lactose restricted diet is provided in the first ten days of life, severe acute neonatal complications usually do not occur
What are the common variants associated with classic galactosemia
Q188R/Q188R (p.Gln188Arg/Gln188Arg)
~70% of alleles in persons with GALT deficiency of northern European ancestry; associated with increased risks for POI and childhood apraxia of speech
K285N/K285N (p.Lys285Asn/Lys285Asn)
prevalent in southern Germany, Austria, and Croatia; associated with poor prognosis for neurologic and cognitive function, considered classic galactosemia
L195P/L195P (p.Leu195Pro/Leu195Pro)
delta 5.2kb del/ delta 5.2kb del (seen in AJ pop)
What is the variant associated with clinical variant galactosemia
p.Ser135Leu/Ser135Leu
S135L/S135L
prevalent in Africa
if therapy is initiated, have a good prognosis; generally not prone to E coli sepsis or chronic complications when tx from infancy
What are the variants associated with biochemical galactosemia
Duarte: c.940A>G;-16_1119delGTCA
(4bp 5’ del + N314D/Q188R)
enzyme activity is reduced by 50%; generally exhibit no signs and symptoms of dz, only biochemical perturbations
LA: identical to duarte but does not have the deletion
What is the enzymatic difference between the three types of galactosemia
classic: severe GALT deficiency with absent or barely detectable activity in erythrocytes and liver
clinical variant: 1-10% residual GALT activity in erythrocytes and/or liver
biochemical variant: 15-33% residual GALT activity in erythrocytes
What are some DD for galactosemia
hereditary fructose intolerance
tyrosinemia type 1
Alagille syndrome
Niemann-Pick dz type C
Galactokinase deficiency
What are the recommended evals following a galactosemia dx
consultation with metabolic physician and specialist metabolic dietician
gastro/nutrition/feeding team eval
eval for hepatocellular dz
developmental assessment
consultation with neurologist
consultation with ophthalmologist
infectious dz
consultation with social worker/psychologist
consider assessment for ovarian dysfunction
What is the recommended tx for galactosemia
remove all milk products from diet which should continue throughout life, replace infant formulas with isomil or Prosobee
standard tx for cataracts
standard tx for POI
stimulation with FSH for some to induce ovulation
supplements of vitamin D and K for diminished bone mineral density
What is the schedule for individuals with galactosemia to have a biochemical genetics visit
q3mo for the first yr of life or as needed
q6mo during the second yr of life
yearly thereafter
What should individuals with galactosemia avoid
breast milk, infant formula with lactose, cows milk, dairy products, casein or whey containing foods
meds with lactose or galactose
How is carrier testing done for galactosemia
measuring erythrocyte GALT enzyme activity:
~50% of control values in carriers of classic galactosemia
~50% of control values in carriers of p.Ser135Leu-related clinical variant galactosemia; different than those in the homozygous state whcih will show 1-10% of GALT enzyme activity
What is the molecular pathogenesis of galactosemia? Mechanism of dz?
catalyzes the converstion of galactose 1 phosphate and UDP glucose to UDP galactose and Clu-1-P in a bi-bi molecular rxn
when GALT activity is deficient, galactose-1-phosphate, galactose, and galactitol accumulate
LOF
In which population is galactokinase deficiency high
Romani population, carrier frequency is 1 in 47
Describe the pathophysiology associated with galactokinase deficiency (galactosemia type 2)
block of the pathway (galactose metabolism) leads to accumulation of galactitol in the lens, causing osmotic swelling of the lens fibers, rupture of the cell membrane, and protein denaturation causing cataracts; reversible only if galactose is withdrawn from food before the rupture of the cell membrane
gal-1-phosphate does NOT accumulate, unlike galactosemia type 1
What are the clinical features of galactokinase deficiency
usually produces no dramatic dz in the first weeks to months of life
unexplained hyperbilirubinemia, bilateral cataracts, pseudotumor cerebri, high risk of dyspraxia, ID, motor delays, hypergonadotropic hypogonadism, microcephaly, FTT, seizures, bilateral deafness, hypoglycemia, hypercholesterolemia, and hepatomegaly, ovarian failure common
What are carriers for galactokinase deficiency at risk for
presenile cataracts
What is the recommended tx/managements for pts with galactokinase deficiency
dietary galactose restriction with calcium supplementation is essential
cataracts that are too dense or mature may require sx
long term management includes measurements of galactose (especially galactitol in the RBCs), routine ophthalmologic exam by slip lamp, neuroimaging to monitor for pseudotumor cerebri, blood sugar checks for hypoglycemia
What are some DD for galactokinase deficiency
classic galactosemia, Duarte galactosemia, epimerase deficiency galactosemia
How is galactokinase deficiency tested for
after positive NBS, GALT enzyme activity measured – if normal and clinical suspicion is high (GALT level is high but GAL1P levels are normal), galactokinase enzyme assay should be initiated
can also do full gene sequencing followed by del/dup, no targeted mutation testing
What are the three different versions of epimerase deficiency galactosemia
Generalized: enzyme activity is profoundly decreased in all tissues tested
Peripheral: enzyme activity is deficient in RBC and circulating WBCs but normal or near normal in all other tissues
Intermediate: enzyme activity is deficient in RBC and circulating WBCs and less than 50% of normal levels in other cells tested
What are suggestive lab findings consistent with a dx of GALE deficiency
elevated RBC hemolysate gal-1P concentration
urinary galactose concentrations high
elevated urinary galactitol concentration
generalized aminoaciduria
normal GALT, GALK, and GALM concentrations
What do the NBS results suggest for someone with GALE deficiency
in states in which the NBS program includes measurements of both total galactose and GALT enzyme activity: total galactose is elevated and GALT enzyme activity is normal
in states where total galactose is only measured if GALT activity is low, results for NBS will be normal
How is the dx of GALE deficiency established biochemically
ONE OR MORE of the following:
reduced GALE enzyme activity in RBC as determined by traditional spectrophotometric assay
reduced GALE enzyme activity in RBC using liquid chromatography/mass spec
GALE enzyme activity can be measured in fibroblasts or lymphoblasts to help distinguish between the generalized, peripheral, and intermediate forms but is not currently offered on a clinical basis
How is the dx of GALE deficiency established with molecular testing
biallelic PVs in GALE
sequence analysis of GALE is performed first followed by gene targeted del/dup analysis
What are the clinical features associated with generalized epimerase deficiency galactosemia
hypotonia, vomiting, weight loss, jaundice, hepatomegaly, liver dysfunction, aminoaciduria, cataracts, renal dysfunction
SNHL, physical and cognitive DD and/or learning difficulties
What clinical features are associated with peripheral epimerase deficiency galactosemia
usually asymptomatic even on a regular milk diet
appear to remain asymptomatic even if maintained on a normal milk diet
What clinical features are associated with intermediate epimerase deficiency galactosemia
usually asymptomatic even on a regular milk diet and are only identified through NBS
tx by dietary galactose/lactose, at least in infancy, and thus far those who have been followed appear to remain clinically well
What are the recommended evals following a dx of GALE deficiency
neurologic eval, developmental assessment, orthopedics, PT/OT, nutrition and feeding eval, liver function tests, urinalysis, ophthalmologic eval, audiologic eval
What are some DD for epimerase deficiency galactosemia
GALT deficiency (classic galactosemia, clinical variant galactosemia, duarte variant galactosemia)
GALK deficiency
What are the recommended treatments following a dx of GALE deficiency
switch from breast milk or milk-based formula to one with trace levels of galactose or lactose; dietary restriction involves continued restriction of dairy products
standard tx for contractures/clubfoot
feeding therapy for poor weight gain/FTT
sx removal of cataracts if they do not resolve with dietary restriction
hearing aids for hearing loss
those with peripheral GALE deficiency, do not need tx
Can carriers for GALE deficiency be detected via enzymatic analysis? prenatal testing?
although biochemical testing to detect carriers is also a possibility, the ranges for control and carrier GALE enzyme activity overlap, thus making molecular genetic testing the preferred method for carrier detection
theoretically, prenatal testing can be accomplished via amniocytes/CVS but due to lack of GALE reference range for the relevant sample type, it is not usually done on a clinical basis
What is the molecular pathogenesis of GALE deficiency? Mechanism of dz?
GALE catalyzes an essential step in the galactose metabolism converting UDP-galactose to UDP-glucose
cataracts associated with epimerase deficiency galactosemia are believed to be caused by galactitol accumulation in the ocular lens
LOF
Describe the features of a pt with fructokinase deficiency
benign condition, usually detected incidentally on NBS
fructose in the urine
no tx necessary
What are the laboratory findings consistent with hereditary fructose intolerance (fructosemia)
hypoglycemia
lactic acidemia
hypophosphatemia
hyperuricemia
hypermagnesemia
hyperalanemia
When is the dx of hereditary fructose intolerance (fructosemia) made
established in a proband with the following after exposure to fructose, sucrose, sorbitol, and/or sucralose
biallelic PVs in ALDOB on molecular genetic testing (sequence analysis first then del/dup)
deficient hepatic fructose 1-phosphate aldolase (aldolase B) on liver bx
Fructose tolerance testing (“fructose challenge”) can be hazardous for dx and should not be used
How can the dx of hereditary fructose intolerance (fructosemia) made via liver bx`
fructose-1-phosphate aldolase B enzyme assays and fructose assay enzyme panels on frozen liver tissue may be important options
while molecular genetic testing is the first line dx test for HFI, assay of aldolase B activity on liver bx is more invasive but more sensitive than molecular genetic testing
What are the clinical features associated with hereditary fructose intolerance
nausea, bloating/ascites, vomiting, sweating, abdominal pain, enlarged liver, growth delays, lethargy, seizures, progressive coma, recurrent/profound hypoglycemia, metabolic acidosis, liver dysfunction (hepatomegaly despite fructose restriction, hepatic adenoma and fibrosis), and/or renal insufficiency (proximal tubular dysfunction); coagulopathy
acute hypoglycemia which can lead to death; ONE OF THE FEW INBORN ERRORS OF METABOLISM THAT HYPOGLYCEMIA OCCURS IN THE IMMEDIATE STATE AFTER EATING
What is the prognosis of pts with hereditary fructose intolerance
when dietary fructose, sucrose, sorbitol, and/or sucralose restriction is implemented early in life and adherence is maintained, prognosis for individuals with HFI is excellent
Do carriers of hereditary fructose intolerance present with symptoms
yes, predisposed to gout/crystal arthropathy
increases in plasma uric acid concentration in response to fructose ingestion compared to controls
What are some DD for hereditary fructose intolerance
Neonatal hemochromatosis
infectious hepatitis, sepsis
FAODs
Disorders of gluconeogenesis (Fructose 1,6 Bisphosphate deficiency)
Organic acidemias
Type 1 congenital disorders of glycosylation (HFI causes a secondary disorder of glycosylation)
What are the recommended initial evals for someone with hereditary fructose intolerance
baseline status by biochemical geneticist
dietary management by dietician
ophthalmologic involvement
assess liver enzymes to assess hepatic involvement
assess renal function by measuring related analytes and electrolytes
What are the recommended txs for those with hereditary fructose intolerance in the acute inpatient setting
IV glucose
fresh frozen plasma or exchange transfusion for hepatic insufficiency
tx of metabolic acidosis
immediate and complete elimination of fructose and supplement with glucose, maltose, and cornstarch
What are the recommended txs for those with hereditary fructose intolerance
dietary restriction of fructose, sucrose, and sorbitol
remove sources of fructose to control hepatomegaly and renal involvement
ensuring adequate vitamin supplementation in the setting of reduced fruit and vegetable intake is imperative
What should be avoided in those with hereditary fructose intolerance
fructose tolerance testing to dx HFI
vaccine for rotavirus vaccine in the US which is routinely administered prior to the discovery of HFI in an infant and contains a high amount of sucrose per dose
What is the molecular pathogenesis of Hereditary fructose intolerance (fructosemia)? Mechanism of dz?
aldolase B participates in fructose metabolism, mostly in the liver, renal cortex, and intestinal mucosa
normally aldolase B rapidly coverts IV fructose to glucose, resulting in hyperglycemia; fructose may also be converted to lactate, provoking metabolic acidosis
LOF of enzyme aldolase B
In what populations is hereditary fructose intolerance most commonly seen
Turkey, Spain, Central Europe, France, US, Italy
What are the metabolic findings consistent with Fructose-1,6-Bisphosphatase deficiency
strong clinical suspicion for:
hypoglycemia, high anion-gap metabolic acidosis (lactic acidemia with possible elevate lactate:pyruvate ratio, hyperalanemia), ketosis, pseudo-hypertriglycemia, hyperuricemia, increased free FAs in some cases
HIGH GLYCEROL 3-PHOSPHATE IS AN IMPORTANT BIOMARKER ON URINE ORGANIC ACID ANALYSIS
How is the dx of Fructose-1,6-Bisphosphatase deficiency established
identification of biallelic PVs on molecular genetic testing (perform sequence analysis first then gene-targeted del/dup analysis); dels of exons as well as whole gene dels have been reported
deficient fructose-1,6-bisphosphatase 1 activity in liver or mononuclear WBCs (while enzymatic activity in leukocytes and liver is very specific, testing is not widely available)
What are the clinical features associated with Fructose-1,6-Bisphosphatase deficiency
episodic due to lactic acidosis and ketotic hypoglycemia which are often triggered by fasting or febrile infections or increased fructose levels
most frequent in early life and subsequently decrease in frequency
nearly half present in the first 4d of life with an acute crisis, results from hypoglycemia due to deficient glycogen stores
episodes of hyperventilation, apneic spells, seizures, coma, hepatomegaly, hypotonia, transient liver dysfunction, irritability, lethargy, dyspnea
in between crises, children are asymptomatic and majority experience normal growth and psychomotor development
continued catabolism leads to multiorgan failure (liver, brain, later heart), morbidity/mortality are high, sepsis, blindness, Reye syndrome like presentation have been reported
What are some DD for Fructose-1,6-Bisphosphatase deficiency
Hereditary fructose intolerance
glycogen storage dz type 1
FAODs
mitochondrial respiratory chain disorders and krebs cycle disorders
What are the recommended evaluations following initial dx of Fructose-1,6-Bisphosphatase deficiency
consultation with metabolic physician and specialist metabolic dietician
abdominal u/s, baseline liver function tests, baseline serum lipid panel, baseline serum uric acid to assess for hepatomegaly
developmental assessment
What is the emergency outpatient tx of pts in crisis with Fructose-1,6-Bisphosphatase deficiency
restriction of fructose, sucrose, glycerol, and sorbitol
increased frequency of carb feedings
intake of glucose polymers
ketonuria is an early indicator of impending crisis
prevent hypoglycemia by slowly absorbed carbs such as uncooked cornstarch at bedtime to prevent nocturnal hypoglycemia
What is the acute inpt tx of pts in crisis with Fructose-1,6-Bisphosphatase deficiency
IV glucose for hypoglycemia
administer sodium bicarbonate and restrict fructose, glycerol, sucrose, and sorbitol for metabolic acidosis
hepatomegaly and elevated transaminases resolve spontaneously
What should pts with Fructose-1,6-Bisphosphatase deficiency avoid
avoid food with fructose, sucrose, glycerol, and/or sorbitol
fructose tolerance testing (fructose challenge) can be hazardous and should not be performed
If a person with Fructose-1,6-Bisphosphatase deficiency were to have a pregnancy, what recommendations should they follow
pre pregnancy: prevent hypoglycemia and monitor for early detection
pregnancy: close monitoring for hypoglycemia, maintenance of glycemic control by taking uncooked cornstarch at night as needed; increase in dietary intake and glucose monitoring as needed
during labor: continuous glycose infusion to remain euglycemia
biochemical testing is not a reliable method for prenatal dx as FBP1 enzyme activity has been reported to be low in the human placenta
What is the molecular pathogenesis of Fructose-1,6-Bisphosphatase deficiency? Mechanism of dz?
deficiency impairs glucose production from all gluconeogenic precursors, including dietary fructose
LOF of fructose-1,6-bisphosphatase 1 function
What are the laboratory findings consistent with glycogen storage dz type 1 (Von Gierke)?
hypoglycemia
mildly elevated aspartate aminotransferase (AST) and alanine aminotransferase (ALT)
high blood lactate
high uric acid
hyperlipidemia (triglycerides and cholesterol)
How is the dx of GSD1 established
biallelic PVs in G6PC1 (GSD Ia) or SLC37A4 (GSD Ib) on molecular testing
deficient hepatic enzyme activity (glucose-g-phosphatase catalytic activity [GSD Ia]) from liver bx; glucose-6-phosphate exchanger activity (GSD Ib) is no longer clinically available
How is the dx of GSD1 established using molecular testing
concurrent gene testing of sequence and gene-targeted del/dup analysis of G6PC1 and SLC37A4
Targeted analysis for PVs can be performed FIRST in individuals of AJ or Amish ancestry
How is the dx of GSD1 established using enzyme activity assay
sample needs to be frozen liver bx
most individuals with GSD Ia will have enzyme activity <10% of normal; in rare individuals with milder clinical manifestations, enzyme activity can be higher
MOLECULAR GENETIC TESTING IS INCREASINGLY THE PREFERRED CONFIRMATORY TEST COMPARED TO INVASIVE LIVER BX
What are the clinical features associated with GSD1
poor growth (leading to short stature), hepatomegaly and nephromegaly (due to accumulation of glycogen and fat). lactic acidosis, hyperuricemia, hyperlipidemia, hypertriglyceridemia, hypoglycemic seizures, doll-like facies, full cheeks, thin extremities, protuberant abdomen, possible splenomegaly during infection IN TYPE 1B, eruptive xanthomas, diarrhea, acquired von Willebrand dz (bleeding tendency, epistaxis, easy bruising)
What are some long term complications of untx GSD1
poor growth and stature in adulthood; frequent fractures and osteopenia are common; delayed puberty (can be normal w tx), some progress to ESKD and need a kidney transplant, gout can develop after puberty due to hyperuricemia, systemic HTN in second decade of life due to kidney dz progression
development of hepatic adenomas with more females having them, can turn into hepatocellular carcinoma; pancreatitis due to severe hypertriglyceridemia, variable degrees of gliosis and encephalomalacia in brain, anemia (GSD1A due to hepatic adenoma, GSD1b due to enterocolitis and inflammatory bowel dz), GSD1B assocaited with chronic neutropenia and impaired neutrophil and monocyte function (recurrent infections), polycystic ovaries in some females, thyroid autoimmunity and hypothyroidism caused by abnormal T cell function
What are phenotype correlations noted in GSD1
In G6PC1 (associated w GSD1A)
better improvement of bone mineral density is seen with optimized diet and vitamin D supplementation
severe anemia often associated with hepatic adenomas, with kidney failure, persistent, menorrhagia, poor nutrition, and often multifactorial
in SLC37A4 (GSD 1b)
severe neutropenia and related enterocolitis and intestinal mucosal inflammation may occur leading to severe anemia
risk for thyroid autoimmunity and hypothyroidism is increased
In what populations is GSD1 most prevalent
AJ (carrier frequency for most common PV (p.Arg83Cys) is 1.4%
c.648G>T identified in 88% of affected individuals with Japanese ancestry and c.379_380dupTA in 50% with Hispanic Americans
What are some DD for GSD1
Fructose-1,6-bisphosphatase deficiency
Gaucher dz
Niemann-Pick dz type B (chronic visceral ASMD)
Describe the recommended evals following initial dx of GSD1
conc. of glucose, lactic acid, uric acid, lipids; liver imaging and liver functioning all to asses hepatomegaly
measurements of growth and eval of nutritional status
measure bone density and serum hydroxyvitamin D for skeletal at 10yo
echo, lipid panel with triglycerides for cardio at 10yo
kidney function tests
neurodevelopmental assessment and assessment for evidence of seizures
eval for anemia, platelet aggregation studies, von Willebrand factor and antigen activity
CBC to evaluate for neutropenia
Assess gastro system for signs of enterocolitis and/or bowel ulcers
What is the recommended tx for pts with GSD1
includes care from metabolic specialist, metabolic dietician, hepatologist, GI specialist, social worker, GC, and psychologist
medical nutrition therapy: uncooked cornstarch (often started between 6mo-1yo, amylase required to digest cornstarch and may not be produce enough until 2yo); meals and snacks q3-4hrs that are rich in complex carbs; nasogastric or gastrostomy tube for continuous feeding; diet with ~60% complex carbs, 10-15% protein, and 25-30% fat that is limited in trans fat and saturated fat; supplementation with calcium and vitamin D, complete multivitamin with minerals (especially iron and zinc)
hepatic adenomas tx with surgery, ethanol injections, and radiofrequency ablation. liver transplant considered when those fail or if rr is suspicious of malignant transformation
take HMG-CoA reductase inhibitors and fibrate (Lipitor, gemfibrozil) for hyperlipidemia
ACE inhibitors to tx renal dz
allopurinol to prevent gout, should be discontinued when a women is planning a pregnancy
antifibrinolytics and DDAVP for bleeding diathesis
human granulocyte colony-stimulating factor (G-CSF) may be helpful preventing infections in those with GSD T1B
thyroid hormone supplementation for tx of hypothyroidism
Gene therapy are currently being developed
What should individuals with GSD T1 avoid
sucrose, galactose, fructose, and products with those ingredients in them, sorbitol
combined oral contraception should be avoided due to negative effects on hepatic adenomas
progestin-only contraceptives can be considered, but potential to risk low bone mineral density and osteoporosis
metformin and lactate containing infusions (Ringer’s lactate)
amoxicillin/clavulanic acid associated with increased risk of diarrhea
glucagon should not be used to tx hypoglycemia bc it is ineffective and may increase the risk of lactic acidosis
How should pregnancy be managed for someone with GSD T1
avoid low blood glucose and stress importance of monitoring glucose
baseline u/s of liver and kidneys prior to pregnancy
consider MFM consultation
exposure to ACE inhibitors int he second and third trs can cause fetal damage and death
high dose allopurinol have been shown to interfere with embryo development in animals
lipid lowering drugs may lead to adverse fetal effects and should be avoided
What is the molecular pathogenesis of GSD T1? Mechanism of dz?
G6PC1 encodes G6Pase, a multicomponent enzyme system localized in the ER, helps catalyze terminal rxn of glucogenolysis and gluconeogenesis in hepatocytes and renal cells
SLC37A4 encodes a transporter protein that helps transport G6P into the lumen of the ER expressed ubiquitously in tissues such as liver, kidney, large intestine, small intestine, skeletal muscle, and to a lesser extent the brain and heart, unlike G6Pase
LOF
How is GSD2 (Pompe) identified using NBS
Sensitive analysis of acid alpha-glucosidase (GAA) enzyme activity can be performed on dried blood spots using mass spec
confirmation is recommended by molecular testing
Countries with NBS for Pompe: Taiwan, Austria, Japan, US (NY, Missouri, Kentucky, Illinois)
What are the laboratory findings suggestive of GSD T2
deficient GAA enzyme activity
elevated creatine kinase in all individuals with infantile onset and some with late onset
elevation of urinary glucose (tetrasaccharide)
How is the dx of GSD II established
proband with deficiency of acid alpha glucosidase enzyme
biallelic PVs in GAA
sequence analysis followed by del dup; pseudodeficiency allele (p.Gly576Ser) which is common in Asian pops, interferes with interpretation of enzyme testing in NBS programs
targeted analysis can be performed for the following: AA with IOPD (50-60% have the PV p.Arg854Ter); Chinese with IOPD (40-80% have the PV p.Asp645Glu); Adults with LOPD (50-85% have the PV x.-32-13T>G in the compound heterozygous state
Dx of Infantile onset can be established rapidly after + NBS result when physical exam, echo, and elevated CPK support the dx; recommended that dx be confirmed with molecular testing or measurement of GAA in another tissue such as isolated lymphocytes or mixed leukocytes
How does enzyme activity correlate with dz presentation for GSD II
the lower the activity, the earlier the age of onset of dz
complete deficiency of GAA enzyme activity (<1% of normal controls) is associated with infantile onset
partial deficiency of GAA (2-40% of normal controls) is associated with late onset
What are the clinical features associated with infantile onset GSD II
generally recognized at 4mo
hypotonia/muscle weakness, cardiomegaly, hepatomegaly, left ventricular hypertrophy, cardiomyopathy, respiratory distress, murmur, macroglossia, feeding difficulties, FTT, absent deep tendon reflexes, normal cognition, SNHL
w/out tx, death occurs in the first 2yrs of life from cardiopulmonary insufficiency; death from ventilatory failure typically occurs in childhood
What are the clinical features associated with late onset GSD II
male sex, severity of skeletal muscle weakness, and duration of dz are all risk factors for severe respiratory insufficiency
may present from the first decade to as late as the seventh decade
can mimic limb-girdle muscular dystrophy
progressive proximal muscle weakness, respiratory insufficiency, exercise intolerance, orthopnea, sleep apnea, scoliosis, hepatomegaly, macroglossia, difficulty chewing and swallowing, GI issues, chronic pain, increased respiratory infections, decreased deep tendon reflexes, Gower sign, joint contractures
What are genotype-phenotype correlations seen in GSD II
biallelic PVs that produce no enzyme activity result in infantile onset dz, are likely to have two null variants
age of onset and progression are most likely directly proportional to the residual GAA enzyme activity
PVs missense and splicing variants may result in either complete or partial absence of GAA enzyme activity
What are some DD for infantile and late onset GSD II
infantile: SMA 1, Danon dz
late onset: limb-girdle muscular dystrophy, duchenne-becker muscular dystrophy, GSD V
Describe the initial evals following dx of infantile and late onset GSD II
IOPD
Nearly all affected infants have cardiomegaly on chest x-ray
majority of affected infants have left ventricular hypertrophy and many have biventricular hypertrophy (EKG)
most have varying degrees of respiratory insufficiency yet objective assessment of pulmonary functions in infants is difficult at best
evaluate for possible feeding difficulties, assessment of growth is appropriate, all should be eval for GERD
baseline hearing eval including tympanometry
LOPD
baseline radiographic evaluation is indicated but only rarely reveals cardiomegaly
recommended Holter monitoring at initial eval
affected individuals should be evaluated with formal pulmonary function tests (which show pulmonary insufficiency)
assessment of nutritional status is recommended
Describe the tx following dx of infantile and late onset GSD II
ERT (Myozyme and Lumizyme) should be initiated as soon as the dx of IOPD or symptomatic Pompe dz is established. Gene therapy is being looked into
24hr Holter monitoring is useful in characterizing the type and severity of rhythm disturbance
PT, may need aggressive management for those with contractures of the pelvic girdle in infants and children
speech therapy
specialized diets and max nutrition with some requiring gastric feedings for IOPD; Those with LOPD often managed on a soft diet
respiratory support including CPAP and BiPAP may be required; macroglossia and severe respiratory insufficiency in the infantile form may necessitate tracheostomy
What are circumstances someone with GSD II should avoid
infections need to be aggressively managed, immunizations need to be kept current; anesthesia only when necessary bc reduced cardiovascular return and underlying respiratory insufficiency pose significant risks
use of digoxin, ionotropes, diuretics, and afterload-reducing agents may worsen left ventricular outflow obstruction, although they may be indicated in the later stages of the dz
hypotension and volume depletion should be avoided
Can you detect heterozygotes with biochemical testing for GSD II?
unreliable for carrier determination bc of significant overlap in residual enzyme activity levels between obligate carriers and the general populations
Is there concordance among family members with GSD II
sib pair concordance in IOPD is high in children with null PVs. Age and severity of manifestations in LOPD may vary between affected FMs
Describe test findings associated with suspected GSD V (McArdle)
high resting serum creatine kinase activity
cycle and walking tests are physiological exertion tests to detect the pathognomonic heart rate response of the second wind phenomenon seen in those with GSDV
Forearm non-ischemic exercise test detects low values of post-exercise plasma lactate to ammonia ration and has high sensitivity and specificity
How can the dx of GSD V be established
sequencing of PYGM (most PVs are detected in sequencing) then del dup
myophosphorylase is the muscle isoenzyme of glycogen phosphorylase; qualitative histochemistry or quantitative biochemical analysis in a muscle bx or muscle homogenate is dx (residual activity is virtually undetectable); cannot be done on fetal tissue since this is expressed only in differentiated muscle cells
What are the clinical features associated with GSD V
metabolic myopathy in the first decade of life; ~10% have mild manifestations and remain virtually asymptomatic during daily activities of life, in some instances progressive weakness in the sixth or seventh decade of life
exercise intolerance, myalgia, fatigue, are all typically relieved by rest (any skeletal muscle can be affected), difficulty with mastication, dysphagia, oral motor function; rhabdomyolysis and myoglobinuria, hx of dark urine
What is the second wind phenomenon and what condition is it associated with
GSD V
relief of myalgia and rapid fatigue after a few minutes of rest due to increased supply of blood-borne glucose and free fatty acids as exercise progresses (aerobic exercise is favored for these individuals)
What evals need to be done following initial dx of GSD V
Physical exam with emphasis on muscle strength/weakness
Basal serum CK activity
Consultation with genetics
How is GSD V tx
simple healthy lifestyle interventions in diet and regular low impact exercise is the most effective means of preventing and managing exercise intolerance in GSD V
Tx that shows some benefit is oral sucrose, carbohydrate-rich diet, ramipril, and low dose creatine
What should individuals with GSDV avoid
exercises including static muscle contractions, dynamic high-intensity exercises, high involvement of muscle contractions (jumping), very intense dynamic aerobic exercise
general anesthetics due to risk of acute muscle damage that may cause muscle ischemia and rhabdomyolysis
Describe the molecular pathogenesis of GSD V
lack or deficiency of muscle glycogen phosphorylase, which catalyzes the breakdown of glycogen into glucose-1-phosphate in this tissue
LOF; skeletal muscle shows lack or deficiency of glycogen phosphorylase
What are the laboratory findings associated with dx of GLUT1 deficiency
single most important lab observation is hypoglycorrhachia (reduced CSF glucose concentration)
How is the dx of GLUT1 deficiency established
normal blood glucose concentration with high CSF glucose concentration
identification of a heterozygous PV (rarely biallelic PVs) in SLC2A1 by molecular genetic testing
single gene analysis followed by del dup
if molecular genetic testing does not detect a PV, consider performing erythrocyte glucose uptake assay (abnormally low assay implies abnormality in SLC2A1)
Describe the erythrocyte 3-O-mrthyl-D-glucose uptake assay. What genetic condition is it used for
GLUT1 deficiency
functional measure of glucose transport across the cell membrane; have abnormal levels that range from 35-75% of controls which confirms the dx
viewed as the diagnostic gold standard for this dz
What are the clinical features associated with classic GLUT1 deficiency
~90% of individuals
appear normal at birth, commonly experience infantile-onset epileptic encephalopathy refractory to anticonvulsants and associated with delayed neurologic development; acquired microcephaly, ataxia, dystonia, and spasticity, seizures between 6mo and 1yr often the first indication of brain dysfunction, multifocal spike discharges on EEG, varying degrees of speech and language impairment, varying degrees of cognitive impairment/ID, gait disturbances, diffuse hypometabolism of the cerebral cortex and regional hypometabolism of the cerebellum and thalamus
What are the clinical features associated with non-classic GLUT1 deficiency
intermittent ataxia, choreoathetosis, dystonia, alternating hemiplegia, varying degrees of cognitive impairment/ID, varying degrees of speech and language impairment, gait disturbances, diffuse hypometabolism of the cerebral cortex and regional hypometabolism of the cerebellum and thalamus
Describe the pathophysiology of GLUT1 deficiency
glucose is the principal fuel source for brain metabolism; the glucose transporter, Glut1, the protein product of SLC2A1, is the fundamental vehicle that facilitates glucose entry into the brain
erythrocyte glucose uptake assay is a functional surrogate measure of residual Glut1 transporter function. Absence of Glut1 transporter expression is embryonic lethal
Describe the phenotype/genotype correlations seen in GLUT1 deficiency? Mechanism of dz?
missense variants in mild and moderate cases
splice site and nonsense variants and indels and exon deletions occurred almost exclusively with moderate and severe dz
complete gene dels cluster in those with severe dz
LOF
What is the penetrance for those with GLUT1 deficiency
inherited in an AD manner is complete
asymptomatic parent harboring the variant implies a mosaic state
What evals should someone undergo after initial dx of GLU1 deficiency
EEG, brain imaging including FDG-PET in selected individuals, neuropsychological assessment
Describe the tx for someone with GLUT1 deficiency
ketogenic diet which provides an alternative fuel for brain metabolism, highly effective in controlling the seizures and improving gait disturbance
antiepileptic drugs are generally ineffective
alpha-lipoic acid has been shown to facilitate glucose transport in Glut4-dependent cultured skeletal muscle cells
L-carnitine supplementation to avoid carnitine deficiency
avoidance of carb containing foods, IV fluids, and meds that will interrupt the state of ketosis
therapies under investigation: triheptanoin and gene therapy
What are some agents/circumstances that someone with GLUT1 deficiency should avoid
barbiturates aggravate the Glut1 transport defect in erythrocytes of individuals with Glut1
methylxanthines (caffeine) are known to inhibit transport of glucose by Glut1
clinical consequences of valproic acid cannot be predicted so should be avoided
What are some genetic counseling considerations needing to be acknowledged for pts with GLUT1 deficiency
~10% of individuals have an affected parent, the other 90% represent sporadic cases and have the disorder as the result of de novo PVs in SCL2A1
What is the typical role of carnitine in the body
plays a role in lipid metabolism and intermediary metabolic pathways
helps in transporting the LCFAs from the cytoplasm to the mitochondrial matrix
more than 95% of the body’s carnitine is found in skeletal muscle; liver, heart, and kidneys have the rest
What causes primary carnitine deficiency? What does this cause the pt to have? carriers?
due to a carnitine transport defect of the OCTN2 carnitine transporter system encoded by the SLC22A5 gene (AR)
pts may lose up to 95% of the filtered carnitine in the urine.
The parents of a child with PCD may lose 2x-3x the levels of normal urinary excretion
Describe the clinical features of someone with OCTN2 deficiency (primary carnitine deficiency)
if age of onset is bwn 3mo-2yrs
hepatic encephalopathy characterized by poor feeding, lethargy, and irritability; hepatomegaly, nonketotic or hypoketotic glycemia, lactic acidosis, hyperammonemia, and elevated hepatic enzymes
if age of onset is btwn 2-4yo
hypotonia, skeletal muscle weakness, exercise intolerance, episodes of rhabdomyolysis, myoglobinuria, elevated creatine kinase
sudden cardiac death remains a risk in adults
What biochemical feature is consistent with a dx of OCTN2 deficiency? How is this confirmed with genetic testing?
low plasma free carnitine levels
sequence analysis of SLC22A5 gene followed by aCGH if sequence analysis is not conclusive; if that does not identify PVs, functional assay of the cultured skin fibroblasts is the preferred test
How is OCTN2 deficiency detected on NBS
by tandem mass spec, low plasma free carnitine levels are detected in newborns. due to placental transfer of carnitine from the mother to the fetus, low fetal plasma creatinine levels shortly after birth can reflect maternal plasma carnitine levels
if NBS is positive, both the baby and mother are re-tested 2wks later to determine who has the PCD
What follow up care should someone undergo following dx of primary carnitine deficiency? Treatment?
Echo, electrocardiogram, serum creatine kinase, serum transaminases, blood sugar levels
lifelong tx with high dose oral L-carnitine
acute episodes of hypoglycemia is tx promptly with 10% dextrose and tx of accompanying metabolic abnormalities including immediate carnitine supplementation
What are the laboratory findings consistent with a dx of CPT1A deficiency
hypoketotic hypoglycemia
elevated liver enzymes (AST/ALT)
hyperammonemia
elevated total serum carnitine
elevated ratio of free carnitine to acylcarnitine species (C0/C16+C18)
elevated C12 dodecanedioic acid on urine organic acids
ELEVATION OF TOTAL CARNITINE AND HYPOKETOTIC HYPOGLYCEMIA SHOULD INCREASE SUSPICION FOR CONDITION
How can the dx of carnitine palmitoyltransferase 1A deficiency be established
sequence analysis of CPT1A is performed first followed by del dup analysis (rarely variants here)
targeted analysis may be considered first for the PVs p.Pro479Leu in populations with a very high frequency of the allele (Alaska, Inuit pop, Siberians) OR
carnitine palmitoyltransferase 1A deficiency on cultured skin fibroblasts (residual enzyme activity btwn 1-5%)
Describe the clinical features of carnitine palmitoyltransferase 1A deficiency
onset of symptoms is typically rapid
fetal CPT1A deficiency has been associated with acute fatty liver of pregnancy typically in the third trimester
fasting-induced encephalopathy in early childhood, potentially a fatal presentation
can also initially present later in life
appear developmentally and cognitively normal unless previous metabolic decomp has resulted in neurologic damage
long term liver damage as a result of recurring hepatosteatosis
renal tubular acidosis
What is the molecular pathogenesis of CPT1A deficiency
CPT I is a mito membrane protein that converts long chain fatty acid acyl-CoA molecules to their corresponding acylcarnitine molecules, provides an alternative source of fuel when glycogen reserves are significantly reduced and fuels ketogenesis for metabolism in peripheral tissues that cannot oxidize fatty acids
in the reduced activitiy of CPT1 caused by biallelic PVs, FAs cannot enter the mito for energy production; CPT1A is expressed in the liver, kidney, leukocytes, and skin fibroblasts
Give 3 DD for carnitine palmitoyltransferase 1A deficiency
MCAD deficiency
CPT II deficiency
VLCAD deficiency
What initial evals need to be made following a CPT1A deficiency dx? What tx needs to be started?
in affected individuals with profound and/or prolonged exposure to hypoglycemia: a complete neurologic eval to detect secondary neurologic damage
those who present with acute hypoglycemia, sufficient amounts of IV fluid containing 10% dextrose should be provided as quickly as possible
high carb diet (70% of calories) that is low in fat (<20% of calories, 1/3 should be medium chain triglycerides) is recommended, supplementation of essential FAs may be necessary
frequent feeding, cornstarch overnight to prevent hypoglycemia
What should people with CPT1A deficiency avoid?
prolonged fasting especially during febrile or gastro illness
potentially hepatotoxic agents such as valproate and salicylate should be avoided
How is VLCAD identified on NBS
primarily based on quantification of acylcarnitine levels (C14:1, C14:2, C14, C12:1) and their ratios
C14:1 level > 1umol/L on NBS very strongly suggests dx; those with a level >0.8umol/L suggests the dx although this can also occur in carriers and some healthy individuals with no PV ACADVL PVs
a significant number of individuals with an abnormal NBS have one PV are are likely carriers who have been detected bc of the low specificity of the initial NBS acylcarnitine screening assay
What medical interventions need to begin immediately following suspicion of VLCAD on NBS
Admission to the hospital, fluid resuscitation, infusion of IV glucose, nutritional eval, institution of enteral nutrition with supplementation of medium chain fat, cardiac eval
How is VLCAD deficiency dx established
single gene testing with sequence analysis first and del dup second (only one reported variant) in ACAVDL
analysis of FA beta oxidation in cultured fibroblasts: typically accumulate excess tetradecanoyl (C14) carnitine, whereas individuals with less severe phenotypes may shift accumulation toward dodecanoyl (C12) carnitine
analysis of VLCAD enzyme activity: measurement in leukocytes, cultured fibroblasts, liver, heart, skeletal muscle, or amniocytes by the electron transfer flavoprotein or ferricenium reduction assay can be used to confirm the dx
Describe the three clinical presentations associated with VLCAD deficiency
most individuals identified by NBS are asymptomatic
- severe early onset cardiac and multiorgan failure form
presents in the first months of life with HCM or DCM, pericardial effusion, and arrhythmias, as well as hypotonia, hepatomegaly, and intermittent hypoglycemia. Cardiomyopathy and arrythmias are often lethal - hepatic or hypoketotic hypoglycemic form
presents during early childhood with hypoketotic hypoglycemia without cardiomyopathy, poor feeding in newborn period - late onset myopathic form
most common phenotype, presents with intermittent rhabdomyolysis provoked by exercise, muscle cramps, and/or pain and/or exercise intolerance
What are the notable genotype/phenotype correlations in VLCAD deficiency
severe dz associated with no residual enzyme activity, often resulting from null variants. ~81 are truncating variants
specific homozygous missense PV p.Cys237Arg is associated with cardiac dz
common p.Val283Ala variant is typically associated with the non-cardiac phenotypes
What are some DD for VLCAD deficiency
MCAD deficiency like the hepatic hypoglycemic form
Intermittent rhabdomyolysis like McArdle Dz
What initial evals should a neonate/infant with VLCAD deficiency undergo
fasting precautions should begin immediately, breast milk without supplemental medium chain triglycerides can continue as long as fasting precautions are taken
consultation with metabolic physician/specialist metabolic dietician
baseline lab studies: serum creatine kinase concentrations, liver transaminases, blood glucose concentrations
electrocardiogram: assess for arrythmias
echo: assess for cardiomyopathy and cardiac dysfunction
nutrition/ feeding team eval
What initial evals should an older child or adult with VLCAD deficiency undergo
consultation with metabolic physician and specialist metabolic dietician
baseline lab studies: serum creatine kinase and liver transaminases
physical exam of abdomen to assess for hepatomegaly
developmental assessment
How should individuals with VLCAD be tx routinely
use of IV glucose, monitor for cardiac rhythm disturbance, monitor rhabdomyolysis, avoid triggers (fasting, long chain fats, irritation of the myocardium
cardiac dysfunction may be reversible with early, intensive supportive care and diet modification
Triheptanoin (C7): an odd medium chain FA that can correct the secondary depletion of TCA cycle intermediates occurring in these disorders
restriction of LCFAs, frequent feeding and prevention of catabolism from overnight fasting, avoidance of severe exercise in older persons, supplement with L carnitine for secondary carnitine deficiency
speech/PT/rehab therapy for speech/gross motor delays
How should individuals with VLCAD be tx in the acute inpt setting
administer high-energy fluids w electrolytes to decrease catabolism from a stressor
standard tx for cardiomyopathy/cardiac failure
ample hydration and alkalization of urine for rhabdomyolysis
What should ppl with VLCAD avoid
fasting, myocardial irritation, dehydration, high-fat diet (long-chain fats) including ketogenic or carbohydrate-restricted diets for the purpose of weight loss, volatile anesthetics that contain high doses of long-chain fatty acids such as propofol and etomidate
How should someone with VLCAD be managed in pregnancy
placental and fetal beta oxidation may temporize or improve maternal FA beta oxidation but labor and postpartum period are catabolic states and place the mother at higher risk for rhabdomyolysis and subsequent myoglobinuria
monitor labs: plasma carnitine panel, creatine kinase level, plasma acylcarnitine profile, RBC or plasma essential fatty acids, vitamins A, D, and E, CBC, ferritin level, comprehensive metabolic panel
cardiomyopathy: echo and assessment by cardio/MFM
What is the molecular pathogenesis of VLCAD deficiency? Mechanism of dz?
VLCAD is a homodimer associated with the inner mito matrix; controls a critical point in the supply of electrons to the respiratory chain, and also provides a pathway permissive to the production of ketones
LOF
How is MCAD deficiency detected on NBS
based on the results of a quantitative acylcarnitine profile on dried blood spot cards
elevations of C8-acylcarnitine with lesser elevations of C6- and C10-acylcarnitine values above the cutoff reported by the screening lab are considered positive
f/u testing include plasma acylcarnitine analysis, urine organic acid analysis, and urine acylglycine analysis
PPV is currently considered to be very high for tandem mass spec, although false negatives have been reported in newborns with low free carnitine levels
A NEWBORN WHOSE BLOOD SAMPLE HAS BEEN SUBMITTED FOR NBS MAY BECOME SYMPTOMATIC BEFORE THE SCREENING RESULTS ARE AVAILABLE. SEVERE LETHAL PRESENTATIONS IN THE FIRST WK OF LIFE HAVE BEEN REPORTED
How can the dx of MCAD be established with biochemical testing
plasma acylcarnitine analysis (characterized by the prominent accumulation of C8- with lesser elevations of C6-, C10-, and C10:1- acylcarnitines; decreased levels of free carnitine and acetylcarnitine may be seen with carnitine deficiency)
urine organic acid analysis: medium-chain dicarboxylic acids are elevated with characteristic pattern- hexanoylglycine > octanoylglycine> decanoylglycine- while ketones are inappropriately low; during acute episodes, suberylglycine and dicarboxylic acids may be elevated
urine acylglycine analysis will detect urinary n-hexanoylglycine, 3-phenylpropionylglycine, and suberylglycine. More sensitive and specific for the identification of asymptomatic individuals and those with mild or intermittent biochemical phenotypes that may be missed by organic acid analysis alone
How can the dx of MCAD be established with genetic/molecular testing
sequence analysis of ACADM followed by del/dup analysis
targeted analysis for common northern European PVs may be performed first in those with northern European backgrounds OR those with Japanese backgrounds of which certain variants account for ~60% of alleles examined in the Japanese pop
How can the dx of MCAD be established with enzyme analysis testing
analysis of FA beta oxidation in cultured fibroblasts involves acylcarnitine analysis
accumulation of C6- C10 acylcarnitines as described for plasma analysis confirms the dx
noninvasive testing using palmitate in individuals with suspected FAODs
Describe how MCAD can be detected postmortem
collect postmortem blood and bile spots on filter paper cards of the type used for NBS for subsequent acylcarnitine analysis
What are the clinical features associated with MCAD deficiency
A KNOWN CAUSE OF SIDS
appear normal at birth and historically have presented between the age 3-24mo
hypoketotic hypoglycemia may begin with or accompanied by seizures; metabolic stress can lead to vomiting and lethargy, quickly progressing to coma and death
hepatomegaly, increased anion gap, hyperuricemia, elevated liver transaminases, and hyperammonemia
sudden and expected death was historically common as the first manifestation of MCAD deficiency; early death before the return of NBS results still occurs
cerebral edema, fatty infiltration of the liver, kidneys, and heart
loss of developmental milestones, acquired aphasia, ADHD, chronic muscle weakness, fatigue, muscle pain, and reduced exercise tolerance, risk for obesity, prolongation of the QTc interval, chronic kidney dz
Describe the pathophysiology associated with MCAD deficiency? Mechanism of dz?
disorder of mitochondrial fatty acid B oxidation
medium and short chain fatty acids passively diffuse across the mito membrane independent of carnitine transport and are activated to CoA esters in the mitochondrial matrix
impairs the energy supply to peripheral tissues through ketogenesis and increases glucose dependency and utilization; results in hypoketotic hypoglycemia, metabolic acidosis, liver dz, and lethargy, which progresses to coma and death when glycogen stores are depleted
LOF
What are the genotype/phenotype correlations in MCAD deficiency
most individuals are compound heterozygous for the c.985A>G PV and another deletion or PV or homozygous for the above variant
individuals homozygous for the common variant above had the highest C8 NBS values and were most likely to have neonatal symptoms
individuals who are compound heterozygotes for the above variant and c.600-18G>A have a mild phenotype and may not be detected by NBS due to residual MCAD enzyme activity
What are some DD for MCAD deficiency
SCAD deficiency
VLCAD deficiency
LCHAD deficiency and TFP deficiency
systemic primary carnitine deficiency
CPT1A deficiency
What initial evals should a newborn undergo after NBS positive for MCAD deficiency
plasma acylcarnitine analysis, plasma free and total carnitine levels, urine acylglycine analysis, urine organic acid analysis, consultation w genetics
What initial evals should a symptomatic individual undergo dx for MCAD deficiency
blood glucose concentration, liver function tests, blood gas analysis, ammonia, lactic acid, CBC w differential, electrolytes, and blood cultures (in case of fever)
What is the recommended tx for pts with MCAD deficiency
most impt: reversal of catabolism and prevention of hypoglycemia by providing simple carbs by mouth or IV fluids if the individual is unable to receive sufficient oral intake to maintain anabolism; IV administration of glucose should be initiated immediately followed by 10% dextrose with appropriate electrolytes
infants require feeding q2-3hrs; overnight feeds, a bedtime snack, or uncooked cornstarch to ensure sufficient glucose supply; normal healthy diet containing no more than 30% of total energy from fat may be followed; overfeeding should be avoided bc of the risk for obesity
low dose L-carnitine supplementation when free carnitine levels are below the normal range
What should individuals with MCAD deficiency avoid
hypoglycemia should be avoided to prevent catabolism
high-fat/low-carb diets
alcohol consumption (particularly binge drinking) elicits metabolic decomp
aspirin exacerbates MCAD deficiency
How is SCAD deficiency dx
presence of increased butyrylcarnitine (C4) concentrations in the plasma and/or increased ethylmalonic acid (EMA) concentrations in urine UNDER NON-STRESSED CONDITIONS
biallelic PVs in ACADS
How is SCADD identified on NBS
primarily based on acylcarnitine analysis by tandem mass spec to detect elevated blood C4 (butyrylcarnitine)
How is the dx of SCADD established with biochemical analysis
acylcarnitine profile testing is used to confirm C4 elevations
urine acylglycines detect elevated ethylmalonic acid as confirmatory testing for NBS or dx testing
urine organic acids detect EMA and dicarboxylic acid
2 common variants can lead to a biochemical phenotype but are not clinically relevant
How is SCADD dx established with molecular testing
perform sequence analysis first then del dup (no dels or complex arrangements have been reported)
c.511C>T and c.625G>A result in biochemical abnormality when in trans with a PV but is not associated with clinical manifestations of SCADD
Describe the clinical spectrum seen in individuals with SCADD
severe dysmorphic facial features, feeding difficulties/FTT, metabolic acidosis, ketotic hypoglycemia, lethargy, DD, seizures, hypotonia, dystonia, and myopathy
also reported in individuals with no symptoms
What is the tx for someone with SCADD
no need for tx since it is viewed more as a biochemical phenotype and less of a dz
avoid fasting longer than 12 hrs and an age appropriate heart-healthy diet
What prenatal testing is available for SCADD
PGT/prenatal testing is unnecessary and not recommended due to generally benign phenotype
What is the molecular pathogenesis of SCADD
most individuals do not present with the classic picture of metabolic acidosis and hypoketotic hypoglycemia characteristic of FAODs
most PVs are missense that lead to protein misfolding which has been postulated to cause pathologic cellular effects of SCAD
How is LCHAD/TFP deficiency detected on NBS
primarily based on quantification of the analyte 3-hydroxypalmitoyl carnitine (C16-OH) and 3-hydroxyoleoylcarnitine (C18:1-OH) on dried blood spots (above the cutoff is considered + and need f/u plasma acylcarnitine and urine organic acid profiles
medical interventions need to begin immediately
What are the specific biochemical findings indicative of LCHAD/TFP deficiency
elevation of 3-hydroxy derivatives of C16, C18, and C18:1 is highly suggestive
elevations of 3-hydroxy-dicarboxylic acids and lactic acid
How is the dx of LCHAD and TFP deficiency established? How do you tell the difference between the 2 dx’s?
LCHAD deficiency: elevation of long-chain 3-hydroxyacylcarnitine species in plasma and/or increased excretion of 3-hydroxy-dicarboxylic acids in urine in combo with biallelic PVs in HADHA; distinguishing requires identification of isolated long chain 3 hydroxyacyl-CoA dehydrogenase deficiency on enzymatic assay in lymphocytes or skin fibroblasts
TFP deficiency: same as above in addition to biallelic PVs in HADHA and/or HADHB and requires identification of deficient in all three TFP enzymatic activities in lymphocytes or skin fibroblasts
an in vitro probe analysis on skin fibroblasts can be assayed for acylcarnitine after 96hrs of incubation: there is substantial accumulation of C16-OH for those with the conditon
How is the dx of LCHAD/TFP deficiency identified with molecular genetic testing? Mechanism of dz?
perform sequence analysis of HADHA first, perform gene targeted del/dup analysis; if HADHA testing is negative, perform sequence analysis of HADHB then del/dup analysis
LOF
Describe the general features associated with LCHAD/TFP deficiency
dilated cardiomyopathy (seen in those with severe neonatal presentation), hypoketotic hypoglycemia, liver dysfunction, liver failure, cardiomyopathy, hypotonia, muscle weakness, exercise intolerance, episodic muscle pain and myoglobinuria, peripheral neuropathy, retinopathy resulting in vision loss
Describe the neonatal presentation of LCHAD/TFP deficiency
the severe/cardiac presentation is more common in individuals with TFP deficiency than those w LCHAD
encephalopathy, hypoketotic hypoglycemia, hepatomegaly, hepatosteatosis, lactic acidosis, liver failure, lethargy, poor feeding, seizures, apnea, coma, progressive dilated cardiomyopathy
Describe the infantile onset presentation of LCHAD/TFP deficiency
the intermediate/hepatic presentation
most common presentation in LCHAD deficiency and relatively uncommon in TFP deficiency
vomiting, lethargy, poor feeding, hepatomegaly, muscle weakness, hypotonia, long QT intervals, DD, FTT
Describe the late onset presentation of LCHAD/TFP deficiency
the mild/neuromyopathic presentation
typical of mild TFP deficiency and rare in LCHAD
muscle weakness, exercise intolerance, hypotonia, episodic rhabdomyolysis, diffuse muscle pain, profound weakness, myoglobinuria, and elevations of serum CK, peripheral neuropathy
What are the long term complications of LCHAD/TFP deficiency
peripheral neuropathy is a unique long term complication, age of onset ranges from infancy to adulthood, progressive and sensorimotor in nature
retinopathy is more common in those with LCHAD than those with TFP; progressive and correlates with dz severity
What are some pregnancies complications that need to be monitored in those pregnant with a fetus with LCHAD/TFP deficiency
HELLP syndrome and acute fatty liver of pregnancy are seen in about 15-25% of pregnancies in women carrying a fetus affected with LCHAD/TFP
What are the genotype/phenotype correlations seen in those with LCHAD/TFP deficiency
homozygous c.1528G>C variants are associated with LCHAD. Most with LCHAD will have at least one allele with this variant. Few individuals who were compound hetero for this variant and another PV in HADHA were reported to have TFP deficiency; enzyme assay is needed to distinguish btwn these conditions
individuals with HADHB missense PVs present with milder phenotypes than those with premature termination or frameshift variants. ~ 1/2 with HADHA PVs present with a severe/lethal phenotype, while ~70% of individuals with HADHB PVs have a milder phenotype
What are some DD for LCHAD/TFP deficiency
MCAD
VLCAD
CPT1A deficiency
What are the recommended clinical evals for someone dx with LCHAD/TFP deficiency
consult with metabolic physician/specialist metabolic dietician
analysis
for metabolic decomp surveillance: Blood gas, ammonia, lactic acid, glucose, liver transaminases, electrolytes with bicarbonate, BUN, creatinine, CK, CBC w differential, plasma and total free carnitine, plasma acylcarnitine profile, urine organic acids, consider cardio consult and echo, consider neuro consult, consider ophthalmology consult, development assessment
What is the recommended tx/management for someone with LCHAD/TFP deficiency
avoidance of fasting, MCT supplementation (low fat diet (30%) of which 7-15% are from long chain fast and 15-25% are from MCT, triheptanoin to tx long chain FAODs
L carnitine for secondary carnitine deficiency
feeding therapy for FTT/poor weight gain
developmental specialist as needed
cardiac and neurologist interventions as needed for cardiac dysfunction and peripheral neuropathy, interventions per ophthalmologist
What is the acute inpt tx for someone with LCHAD/TFP deficiency
IV fluid w high dextrose to maintain blood glucose for hypoglycemia
initiate bicarbonate therapy for severe metabolic acidosis
hyperammonemia self resolves with reversal of catabolism
start IV fluid with dextrose and electrolytes for rhabdo
manage cardiac failure due to cardiomyopathy in collab with cardiologist
What should be avoided in those with LCHAD/TRP deficiency
fasting, inadequate caloric provision during stressors, inadequate calories following vaccination (vaccination is safe), dehydration, high-fat diet, administer IV intralipids during an acute metabolic crisis (propofol, etomidate)
What are some genetic counseling considerations for those with a fh or personal hx of LCHAD/TFP deficiency
significant intrafamilial clinical variability may be observed between sibs who inherit the same biallelic HADHA or HADHB PVs; variability stems primarily from diet and severity of infection triggering metabolic decomp
