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Biochem Disorders Flashcards

1
Q

Orotic Aciduria

- Children –> FTT, developmental delay

A

Defect in UMP synthase –> inability to convert orotic acid to UMP (pyrimidine synthesis pathway)

  • AR
  • megaloblastic anemia refractory to folate and B12
  • orotic acid in urine
  • NORMAL ammonia (opposed to orthinine transcarbamylase def)
  • Rx: uridine monophosphate
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2
Q

Lesch-Nyhan Syndrome
- intellectual disability, self-mutilation, agression, hyperuricemia (orange “sand” sodium urate crystals in diaper), gout, dystonia

A

Absent HGPRT –> can’t convert hypoxanthine to IMP or guanine to GMP –> defective purine salvage –> excess uric acid production and de novo purine synthesis

  • X-linked recessive
  • Rx: allopurinol or febuxostat
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3
Q

Adenosine Deaminase Deficiency

A

No adenosine degradation –> increase in dATP –> toxicity in lymphocytes
- AR SCID

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4
Q 
Lynch Syndrome (HNPCC)
- Colon cancer
A

Defective mismatch repair

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5
Q

Xeroderma Pigmentosum

- Increased risk of skin cancer

A

Defective nucleotide excision repair

- Prevents repair of thymine (pyrimidine) dimers due to UV light exposure

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6
Q

Ataxia Telangiectasia

- Ataxia, poor smooth pursuit with eyes

A

Defective nonhomologous end joining

  • IgA deficiency, elevated alpha fetoprotein
  • sensitive to ionizing radiation
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7
Q

Glycolytic Enzyme Deficiency

- hemolytic anemia

A

Common cause: pyruvate kinase deficiency

- Inability to maintain Na+/K+ ATPase –> cell swelling/lysis –> hemolytic anemia

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8
Q

McArdle Disease (GSD Type V)

  • Painful muscle cramps, myoglobinuria (red urine) with strenuous exercise, arrhythmia from electrolyte abnormalities, second-wind phenomenon during exercise (increased muscular blood flow)
A

Deficient skeletal muscle GLYCOGEN PHOSPHORYLASE

  • Blood glucose levels unaffected
  • McArdle = Muscle
  • Increased glycogen in muscle but muscle cannot break it down –> rhabdomyolysis –> exercise intolerance
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9
Q

VonGierke Disease (GSD Type I)

  • 3-4 mo –> FTT
  • Gout, hepatomegaly
A

Deficient GLUCOSE-6-PHOSPHATASE (no G6P to glucose) –> impaired gluconeogenesis and glycogenolysis –> glucose can’t leave liver –> severe fasting hypoglycemia, increased glycogen in liver
- Increased blood lactate
- Increased triglycerides
- Increased uric acid (gout)
- Hepatomegaly
Rx: frequent oral glucose/corn starch, avoid fructose and galactose

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10
Q

Cori Disease (GSD Type III)

  • Milder form of VonGierke
A

Deficient DEBRANCHING ENZYME (alpha-1,6-glucosidase) –> mild hypoglycemia

  • Normal blood lactate
  • Accumulation of limit dextrin-like structures in cytosol
  • Gluconeogenesis is intact
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11
Q

Pompe Disease (GSD Type II)

  • Infants: cardiomegaly, hypertrophic cardiomyopathy, exercise intolerance, early death (2 yrs)
A

LYSOSOMAL ALPHA-1,4-GLUCOSIDASE with alpha-1,6-glucosidase activity (acid maltase)
- Pompe trashes the pump

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12
Q

Pyruvate Dehydrogenase Deficiency

  • Neuro defects, lactic acidosis
  • Infants
A

No pyruvate –> Acetyl CoA

  • Pyruvate can back up and be converted to lactate ( via LDH) or alanine (via ALT)
  • X-linked or acquired (arsenic poisoning, B1 def. [alcoholics])
  • Increased serum alanine
  • Rx: increase intake of ketogenic nutrients (high fat content or high lysine/leucine)
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13
Q

Chronic Granulomatous Disease

  • Increased susceptibility to catalase+ organisms
A

Defect of NADPH OXIDASE –> less ROS and no respiratory burst in neutrophils

  • X-linked recessive most common
  • Catalase positive organisms (neutralize environmental H2O2): Nocardia, Pseudomonas, Listeria, Aspergillus, Candida, E. coli, Staph, Serratia, B. cepacia, H. pylori
  • Abnormal dihydrorhodamine (flow cytometry, green)
  • Nitroblue tetrazolium dye reduction test is colorless
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14
Q

G6PD Deficiency

- hemolytic anemia

A

Deficient GLUCOSE-6-PHOSPHATE DEHYDROGENASE –> can’t make NADPH –> can’t keep glutathione reduced –> can’t detoxify free radicals and peroxides –> hemolytic anemia due to poor RBC defense against oxidizing agents

  • Oxidizing agents: fava beans, sulfonamides, primaquine, dapsone, chloroquin, nitrofurantoin, antituberculosis drugs
  • Also precipitated by infection (most common cause) –> inflammatory response produces free radicals that diffuse into RBCs
  • X-linked recessive
  • Most common human enzyme deficiency
  • More prevalent among AA (malarial resistance)
  • Heinz bodies (denatured Hb due to oxidative stress)
  • Bite cells (from splenic macs)
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15
Q

Essential Fructosuria

- benign, asymptomatic

A

Defect in FRUCTOKINASE (no fructose to F1P) –> can still metabolize fructose by converting to F6P via hexokinase –> pyruvate and glycogen

  • AR
  • Fructose appears in blood and urine
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16
Q

Fructose Intolerance

- hypoglycemia, jaundice, cirrhosis, vomiting following consumption of fruit, juice, honey

A

Defect in ALDOLASE B (no F1P metabolism) –> F1P builds up –> metabolic sink (P gets trapped) –> no ATP for glycolysis or ATP synthase –> inhibits glycogenoysis and gluconeogenesis –> severe hypoglycemia

  • Urine dipstick will be negative (only tests for glucose)
  • Reducing sugar detected in urine
  • Rx: decrease intake of fructose and sucrose (glucose + fructose)
17
Q

Galactokinase Deficiency

  • Infants start feeding, infantile cataracts, failure to track objects, failure to develop social smile
A

Deficiency of GALACTOKINASE –> no galactose to galactose-1-P –> more galactose to galactitol (via aldose reductase)

  • AR
  • Sx begin when infant begins feeding (lactose present in breast milk and formula)
  • Galactosemia, galactosuria, infantile cataracts
18
Q

Classic Galactosemia

  • FTT, jaundice, hepatomegaly, infantile cataracts, intellectual disability
A

Deficiency of GALACTOSE-1-PHOSPHATE-URIDYLTRANSFERASE –> no galactose-1-P to glucose-1-P –> accumulation of toxic substances (including galactitol)

  • Can lead to E. coli sepsis in neonates
  • Rx: exclude galactose and lactose (galactose + glucose) –> strikingly alters course of DZ
19
Q

Lactase Deficiency

  • Bloating, cramps, flatulence, osmotic diarrhea
A

Insufficient LACTASE –> no brush border digestion of lactose into glucose and galactose –> osmotic diarrhea, bacteria produce gas

  • Primary: age-dependent decline after childhood (Asian, African, NA)
  • Secondary: loss of brush border due to gasteroenteritis (rotavirus), AI DZ
  • Congenital: rare
  • Stool –> decreased pH
  • Breath –> increased hydrogen
  • NORMAL MUCOSA
  • Rx: avoid dairy, add lactase pills
20
Q

Abetalipoproteinemia

  • steatorrhea, ataxia, nightblindness
A
  • Deficient ApoB-48 and ApoB-100
  • AR mutation in MTP gene –> decreased chylomicron and VLDL synthesis and secretion
  • Decreased absorption of fat soluble vitamins
  • Bx: enterocytes swollen with triglycerides
  • Peripheral smear: acanthocytosis of RBCs (“spikes”) due to alteration in membrane lipids
  • Rx: Vit E (restores lipoproteins)
21
Q

Hyperchylomicronemia (Type I Dyslipidemia)

- Pancreatitis, hepatosplenomegaly, eruptive/pruritic xanthomas

A

AR defect in LIPOPROTEIN LIPASE or APO-CII

  • Elevated chylomicrons, TGs, cholesterol
  • NO RISK FOR ATHEROSCLEROSIS
  • Creamy layer in supernant
22
Q 
Familial Hypercholesterolemia (Type IIa Dyslipidemia)
- Hyperlipidemia, MI before age 20, tendon xanthomas (Achilles), corneal arcus
A

AD absent/defective LDL RECEPTORS (bind Apo-B100)

  • Elevated LDL and cholesterol
  • Heterozygotes –> cholesterol = 300
  • Homozygotes –> cholesterol = 700
  • ACCELERATED ATHEROSCLEROSIS (MI before age 20)
23
Q

Hypertriglyceridemia (Type IV Dyslipidemia)

- Hypertriglyceridemia, acute pancreatitis

A

AD hepatic overproduction of VLDL

  • Elevated VLDL, TG
  • TG > 1,000
24
Q

Carnitine Deficiency

- weakness, hypotonia, hypoketic hypoglycemia

A

Inherited defect in transport of LCFAs into mitochondria –> toxic accumulation

25
Q

Phenylketonuria

- intellectual disability, growth retardation, seizures, fair skin, eczema, musty body odor

A

Decreased PHENYLALANINE HYDROXYLASE or TETRAHYDROBIOPTERIN COFACTOR (no Phe –> Tyr)

  • Tyrosine becomes essential
  • Increased Phe –> excess phenylketones in urine (phenylacetate, phenyllactate, phenylpyruvate)
  • Screened 2-3 d after birth
  • Rx: decreased Phe and increased Tyr, BH4 supplementation, avoid aspartame
  • Lack of proper dietary therapy during pregnancy –> microcephaly intellectual disability, growth retardation, congenital heard defects
26
Q

Ornithine Transcarbamylase Deficiency

  • Lethargic, unwilling to eat, poorly controlled RR and body temp, seizures
  • First few days of life
A
  • Most common urea cycle disorder
  • X-linked recessive
  • Can’t do urea cycle –> buildup of nitrogen and ammonia in the body –> orotic acid in blood and urine
  • BUN decreased (can’t make urea)
  • Hyperammonemia
27
Q

Hyperammonemia

  • slurring of speech, somnolence, vomiting, cerebral edema, blurring of vision
A

Acquired (liver disease) or hereditary (urea cycle enzyme deficiencies)

  • Excess NH3 –> depletes alpha-KG –> inhibition of TCA cycle
  • Rx: limit protein, lactulose (acidify GI tract and trap NH4), rifaximin (wipe out colonic ammoniagenic bacteria), benzoate/phenylacetate/phenylbutyrate (bind NH4 and lead to excretion)
28
Q

Alkaptonuria

- bluish-black CT and sclerae (ochronosis), urine turns black on prolonged exposure to air, debilitating arthralgias

A
  • Congenital deficiency in HOMOGENTISATE OXIDASE
  • Can’t degrade tyrosine to fumarate –> pigment forming homogentisic acid accumulates in tissue
  • AR
  • Usually benign
29
Q

Albinism

A
  • TYROSINASE deficiency or defective tyrosine transport

- No melanin

30
Q

Homocystinuria

  • intellectual disability, osteoporosis, marfanoid habitus, kyphosis, lens subluxation (downward and inward), thrombosis, atherosclerosis (stroke and MI)
A
  • AR
  • CYSTATHIONE SYNTHASE deficiency –> no homocysteine to cystathione (supplement cysteine/B12/folate, reduce methionine in diet)
  • Decreased affinity of cystathione synthase for pyridoxal phosphate (Rx: supplement B6 and cysteine)
  • METHIONINE SYNTHASE deficiency –> no homocysteine to methionine (rx: supplement methionine)
31
Q

Cystinuria

- Recurrent precipitation of hexagonal cystine stones

A

Hereditary defect of renal PCT and intestinal AA transporter than prevents reabsorption of CYSTINE, ORNITHINE, LYSINE, and ARGININE (COLA)

  • Rx: urinary alkalinization (potassium citrate, acetazolamide), chelating agents (penicillamine)
  • AR
  • Urinary cyanide-nitroprusside test to dx
32
Q

Maple Syrup Urine Disease

  • Severe CNS defects, intellectual disability, death
  • Vomiting, poor feeding, urine smells like maple syrup/burnt sugar
A

Deficiency in BRANCHED-CHAIN ALPHA-KETOACID DEHYDROGENASE –> can’t degrade branched AA (isoleucine, leucine, valine) –> increased alpha-ketoacids in blood (esp. leucine)

  • Rx: restriction of isoleucine, leucine, and valine; thiamine supplementation
  • AR
33
Q

Hartnup Disease

  • Diarrhea, dementia (and hallucinations), dermatitis (“broad collar” rash, hyperpigmentation of sun exposed limbs)
A
  • AR deficiency of neutral AA transporters in proximal renal tubular cells and on enterocytes –> neutral aminoaciduria and decreased absorption from gut –> decreased tryptophan for conversion to niacin (B3) –> pellagra = DERMATITIS, DIARRHEA, DEMENTIA
  • Rx: high-protein diet, nicotinic acid

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