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Genetic Counseling Boards > Biochemical/Metabolic Genetics > Flashcards

Biochemical/Metabolic Genetics Flashcards

1
Q

Newborn Screening

A
  • heel prick done 24-48 hours after birth
  • RUSP contains 34 core and 26 secondary conditions
  • conditions added based on Wilson and Jungner criteria
  • each state free to choose own NBS panels
  • consent follows opt-out model
  • storage of dried blood spot cards varies from state to state; federally funded research requires parental consent
  • screen positive result = repeat test
  • actionable result = immediate care initiated
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2
Q

Inborn Errors of Metabolism

A
  • deficiency of enzyme prevents something from being broken down/made
  • vast majority are each rare AR conditions; consider consanguinity
  • some more common in certain ethnic groups
  • can be classified as disorders of intoxication, disorders of energy metabolism (including mitochondrial defects), or disorders involving complex molecules
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3
Q

Errors of Protein Metabolism (DI)

A
  • aminoacidopathies
  • organic acidemias
  • urea cycle defects
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4
Q

Aminoacidopathies

A
  • phenylketonuria
  • hyperphenylalaninemia
  • maternal PKU
  • tetrahydrobiopterin deficiency
  • MSUD
  • homocystinuria
  • tyrosinemia
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5
Q

Features of Aminoacidopathies

A
  • elevated amino acid level and/or immediately preceding intermediate before defect
  • neurological and behavioral impact due to build up in brain
  • vomiting, coma, liver failure, thromboembolic complications, FTT, DD, ectopia lentis, cardiomyopathy
  • symptom-free interval
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6
Q

Testing for Aminoacidopathies

A
  • plasma/serum/urine amino acid levels (high)

- enzyme activity tests (little to no activity)

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7
Q

Treatment for Aminoacidopathies

A
  • restrict substrate
  • low protein diet
  • supplement product
  • supplement cofactor
  • substitute enzyme
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8
Q

Organic Acidemias

A
  • propionic acidemia
  • methylmalonic acidemia
  • cobalamin deficiencies
  • isovaleric acidemia
  • 3-MCC deficiency
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9
Q

Features of Organic Acidemias

A
  • low blood pH levels due to build up of organic acids

- vomiting, altered mental status, lethargic, ill appearance, metabolic acidosis, hyperammonemia

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10
Q

Testing for Organic Acidemias

A
  • plasma ammonia (high)
  • venous blood gas (severe metabolic acidosis)
  • urine organic acids (acid metabolites present)
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11
Q

Treatment for Organic Acidemias

A
  • restrict amino acids preceding the organic acid
  • low protein diet
  • provide cofactor
  • provide carnitine for alternate route of elimination
  • pH stabilizer
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12
Q

Urea Cycle Defects

A
  • OTC deficiency
  • arginosuccinate lyase deficiency
  • argininemia
  • later-onset UCDs
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13
Q

Features of Urea Cycle Defects

A
  • neonatal onset

- lethargy, poor feeding, vomiting, seizures, bleeding, hyperventilation, coma, death, hyperammonemia

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14
Q

Testing for Urea Cycle Defects

A
  • ammonia levels (high)
  • arginine levels (low)
  • blood pH (no acidosis)
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15
Q

Treatment for Urea Cycle Defects

A
  • restrict substrate (essentially no protein); essential amino acid formulas
  • provide product (arginine or citrulline)
  • replace enzyme (liver transplant)
  • ammonia scavengers
  • treat secondary effects
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16
Q

Glycogen Storage Diseases

A
  • Hepatic GSDs: GSD 1a (von Gierke), GSD 1b, GSD 3, GSD 4, GSD 6, GSD 9a
  • Muscular GSDs: GSD 2 (Pompe), GSD 5 (McArdle’s), GSD 7 (Tarui)
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17
Q

Features of GSDs

A
  • glycogen stored in liver and in some muscles; some disorders affect one or other
  • accumulation of glycogen, poor feeding, lethargy, hypoglycemia
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18
Q

Testing for GSDs

A
  • not on NBS, except Pompe
  • pyruvate/lactate levels (high)
  • blood glucose (low)
  • triglycerides (high)
  • uric acid (high)
  • enzyme analysis
  • genetic testing
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19
Q

Treatment for GSDs

A
  • feed every 3 hours to prevent brain damage from lack of glucose
  • provide sugar to exercising muscle when heavily used
  • boost WBC count
  • ERT
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20
Q

Disorders of Sugar Metabolism

A
  • galactosemia (emergency)
  • hereditary fructose intolerance
  • fructose 1,6 bisphosphatase deficiency
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21
Q

Features of Sugar Metabolism Disorders

A
  • depends on condition
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22
Q

Testing for Sugar Metabolism Disorders

A
  • fructose metabolism conditions not on NBS
  • enzyme analysis
  • genetic testing
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23
Q

Treatment for Sugar Metabolism Disorders

A
  • restrict intake of offending sugar
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24
Q

Features of CDGs

A
  • infantile onset, DD, heart disease, multiorgan dysfunction, hypoglycemia, protein-losing enteropathy, skin abnormalities (peaux d’orange), neurological abnormalities (stroke-like episodes), abnormal fat distribution, death
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25
Q

Testing for CDGs

A
  • enzyme analysis

- genetic testing

26
Q

Treatment for CDGs

A
  • none
27
Q

Fatty Oxidation Defects

A
  • MCAD
  • LCHAD
  • VLCAD
  • SCAD
  • maternal HELLP syndrome
28
Q

Features of FAODs

A
  • lethargy, coma, hypoglycemia, kypoketosis
29
Q

Testing for FAODs

A
  • acylcarnitine profile (accumulation of fatty acid chains of different sizes)
30
Q

Treatment for FAODs

A
  • no fasting
  • high carb/low fat diet
  • supplement with carnitine if low
31
Q

Disorders of the Carnitine Cycle

A
  • carnitine uptake deficiency
  • CPT-1
  • translocase deficiency
  • CPT-2
32
Q

Features of Carnitine Cycle Disorders

A
  • muscular weakness, cardiomyopathy, exercise intolerance. rhabdomyolysis, hypoglycemia
33
Q

Testing for Carnitine Cycle Disorders

A
  • acylcarnitine profile (build-up of long chain fatty acids)
34
Q

Treatment for Carnitine Cycle Disorders

A
  • provide levocarnitine
  • no fasting
  • low fat diet
35
Q

Features of Peroxisomal Disorders

A
  • elevated VLCFA
36
Q

Testing for Peroxisomal Disorders

A
  • not on NBS, except ALD
  • acylcarnitine profile (elevated VLCFA)
  • plasmalogen analysis (low)
37
Q

Treatment for Peroxisomal Disorders

A
  • management of symptoms

- BMT, hydrocortisone (ALD)

38
Q

Muccopolysaccharidoses

A
  • MPS I (Hurler/Scheie)
  • MPS II (Hunter)
  • MPS III (Sanfilippo)
  • MPS IV (Morquio)
  • MPS VI (Maroteaux-Lamy)
  • MPS VII (Sly)
  • MPS IX (Natowicz)
  • Multiple sulfatase deficiency
39
Q

Features of MPS

A
  • dysfunction in degradation of glycosaminoglycans (GAGs)
  • heparan sulfate found in ECM and has neurological effects
  • keratan sulfate found in bones, collagen, corneas, connective tissue
  • dermatan sulfate found in skin, valves, blood vessels
  • coarse facial features, organomegaly (hepatosplenomegaly), skeletal dysplasia, short stature, cognitive decline, progressive
40
Q

Testing for MPS

A
  • urine GAGs (total GAGs elevated)
  • enzyme analysis
  • genetic testing
41
Q

Treatment for MPS

A
  • BMT
  • ERT
  • supportive treatment
42
Q

Sphingolipidoses

A
  • GM1 gangliosidosis
  • GM2 gangliosidosis (Tay-Sachs)
  • Niemann-Pick A/B
  • Metachromic leukodystrophy
  • Krabbe disease
  • Gaucher disease
  • Fabry disease
43
Q

Features of Sphingolipidoses

A
  • defects in sphingolipid metabolism (important for neuronal cell functioning)
  • several AJ founder mutations
  • progressive neurological/cognitive decline
44
Q

Testing for Sphingolipidoses

A
  • not on NBS, except Krabbe
  • enzyme analysis (beware pseudodeficiency alleles)
  • urine analysis (high sulfatides for MLD)
  • genetic testing
45
Q

Treatment for Sphingolipidoses

A
  • supportive treatment
  • BMT (Krabbe)
  • ERT (Gaucher and Fabry)
46
Q

Porphyrias

A
  • Acute hepatic: AIP, HCP, VP, ADP

- Cutaneous: PCT (cutaneous and hepatic), CEP, EPP, XLP

47
Q

Features of Porphyrias

A
  • Acute hepatic: low penetrance (10-20%), women more commonly affected (80% vs 20%), abdominal pain, nausea, vomiting, pain in extremities/back, muscle weakness, anxiety, depression, dark/reddish urine, hepatocellular carcinoma, photosensitivity
  • Cutaneous: skin blistering, severe photosensitivity, deposition of porphyrin in skin, bones, teeth
48
Q

Testing for Porphyrias

A
  • urine ALA and PBG (high)
  • urine/plasma/fecal porphyrin levels (results depend on type)
  • erythrocyte protoporphyrin levels (elevated in EPP and XLP)
  • free:zinc-chelated erthyrocyte protoporphyrin levels (EPP, XLP)
  • genetic testing
49
Q

Treatment for Porphyrias

A
  • Acute hepatic: intravenous hemin, symptomatic relief, liver transplant, sun protection, siRNA and RNAi, avoid triggers (alcohol, smoking, stress, drugs)
  • Cutaneous: serial phlebotomies/hydroxychloroquinone, blood transfusions, sun/UV protection, BMT/liver transplant, melanin-producing drugs, symptomatic relief, avoid triggers
50
Q

Conditions Involving Purine Salvage/Synthesis

A
  • Lesch-Nyhan disease
51
Q

Conditions Involving Cholesterol

A
  • Niemann-Pick C
  • Antley-Bixler syndrome
  • Smith-Lemli-Opitz syndrome
52
Q

Disorders of Carbohydrate Metabolism (DI, DEM)

A
  • glygocen storage disorders
  • sugar intolerances
  • congenital disorders of glycosylation
53
Q

Disorders of Fat Metabolism (DEM)

A
  • FAODs

- carnitine cycle defects

54
Q

Disorders of Peroxisomal Metabolism (DCM)

A
  • peroxisomal biogenesis disorders

- adrenoleukodystrophy

55
Q

Lysosomal Storage Disorders (DCM)

A
  • mucopolysaccharidoses

- sphingolipidoses

56
Q

Conditions Involving Copper Metabolism

A
  • Menkes syndrome

- Wilson disease

57
Q

Conditions Involving Biotin

A
  • biotinidase deficiency
58
Q

Neurodegeneration with Brain Iron Accumulation

A
  • PKAN (pantothenate kinase-associated neurodegeneration)
  • PLAN/INAD
  • MPAN
  • BPAN
  • FAHN
  • CoPAN
  • KRS
  • ACP
  • NF (not neurofibromatosis)
59
Q

Wilson and Jungner Criteria

A
  • accurate screening test
  • regular review of scientific and medical rationale
  • significant life-challenging risk of morbidity if disorder is untreated
  • total costs of system from diagnosis to follow-up must be reasonably priced
  • significant prevalence of disorder
  • natural history of disease understood
  • consumer involvement, physician and public health acceptance in the decision to mandate screening
  • positive health benefits must outweigh risks and burdens
  • disorder must be treatable and require early treatment
  • resources for and access to confirmatory testing, treatment, and counseling
60
Q

Congenital Disorders of Glycosylation

A
  • CDG 1a

Genetic Counseling Boards (22 decks)

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