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Molecular Foundations of Medicine > Biochemical Genetics and Newborn Screening > Flashcards

Biochemical Genetics and Newborn Screening Flashcards

1
Q

Inheritance of disorders affecting enzymatic proteins

A

typically autosomal recessive

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2
Q

inheritance of disorders affecting structural proteins

A

often autosomal dominant

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3
Q

Phenylketonuria (PKU) clinical presentation

A
  • autosomal recessive
  • normal neonate
  • DD beginning around 3-4 months
  • treated with diet low in protein
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4
Q

mechanism of PKU

A
  • deficiency of enzyme: phenylalanine hydroxylase (PAH)
  • conversion of phenylalanine to tyrosine is blocked
  • buildup of PHE is neurotoxic
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5
Q

Methylmalonic Aciduria presentation

A
  • severe acidosis in first week of life

* treated with diet low in protein

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6
Q

mechanism of methylmalonic aciduria

A
  • lack of enzyme activity: methylmalonyl-CoA mutase

* it converts methylmalonyl-CoA into succinyl-CoA (krebs cycle)

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7
Q

test for PKU

A

phenylalanine elevated on plasma amino acid quantitation

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8
Q

test for methylmalonic aciduria

A

methylmalonic acid elevated on urine organic acid quantitation

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9
Q

important urea cycle defect

A
  • defect in pathway converting toxic ammonia to non-toxic urea
  • ornithine transcarbamylase (OTC) deficiency -> low citrulline
  • ^it is X LINKED
  • severe neurologic damage if not treated rapidly
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10
Q

test for ornithine transcarbamylase (OTC) deficiency

A

low citrulline on plasma amino acid quantitation

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11
Q

other urea cycle defects

A
  • many enzymes; autosomal recessive
  • neurologic damage if not treated rapidly
  • plasma amino acid quantitation will have elevations of a diagnosic aa
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12
Q

treatment for ornithine transcarbamylase (OTC) deficiency

A
  • diet low in protein

* ammonia scavenger medications

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13
Q

hereditary fructose intolerance mechanism

A

•fructoaldolase (aldolase B) metabolized fructose to glucose (gluconeogenesis)

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14
Q

hereditary fructose intolerance presentation

A
  • key: NO fructose in breast milk, symptom onset with introduction of juices
  • ingestion of fructose acutely -> vomiting and hypoglycemia
  • chronic ingestion of fructose -> hepatomegaly and renal dysfunction
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15
Q

diagnosis of hereditary fructose intolerance

A
  • clinical syspicion

* molecular analysis of aldolase B

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16
Q

treatment of hereditary fructose intolerance

A

restricting fruit, vegetables, corn syrup, table sugar

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17
Q

lesch-nyhan disease presentation

A
  • X linked recessive
  • neurologic dysfunction
  • hypotonic
  • self-mutilation behavior
18
Q

mechanism of lesch-nyhan disease

A
  • disorder of purine reclamation

* due to defect in hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity

19
Q

treatment of lesch-nyhan disease

A
  • low purine diet
  • allopurinol
  • medication for neurologic signs and symptoms
20
Q

diagnosis of lesch-nyhan disease

A
  • clinical suspicion
  • elevated uric acid
  • molecular analysis of HGPRT
21
Q

most common fatty acid oxidation disorder

A
  • medium chain acyl-CoA dehydrogenase (MCAD) deficiency

* it is autosomal recessive

22
Q

presentation of MCAD deficiency

A
  • child with lethargy and vomiting following fasting
  • classically presents with hypoketotic hypoglycemia
  • may be entirely asymptomatic
23
Q

other fatty acid oxidation disorders often involve

A

•cardiac and/or hepatic involvement

VLCAD, LCAD, SCAD, LCHAD, SCHAD

24
Q

testing for MCAD deficiency

and other fatty acid oxidation disorders

A
  • elevations of fatty acid oxidation intermediates on urine organic acid quantitation
  • acylcarnitine analysis
25
Q

treatment of MCAD deficiency

and other fatty acid oxidation disorders

A
  • avoidance of fasting

* rapid treatment of hypoglycemia (epinephrine?)

26
Q

biotinidase defect

A
  • results in biotin deficiency

* biotin important in carboxylation reaction

27
Q

presentation of biotinidase defect

A
  • alopecia
  • dermatitis
  • deafness
  • seizures
  • neurologic deterioration starting about 4-6 months of age
28
Q

diagnosis of biotinidase defect

A

enzyme assay of biotinidase

29
Q

treatment of biotinidase defect

A

biotin supplementation

30
Q

Mechanism of Tay-Sachs disease

A
  • autosomal recessive
  • β-hexosaminidase (A isoenzyme) mutation
  • lysosomal storage disease
31
Q

clinical features of tay-sachs

A

hypotonia, spasticity, seizures, blindness

32
Q

hunter syndrome mechanism

A
  • x-linked recessive
  • iduronidate-2-sulfatase defect
  • accumulation of mucopolysaccharides such as dermatan and heparin sulfate
33
Q

diagnosis of hunter syndrome

A

enzyme assay of iduronidate-2-sulfatase

34
Q

treatment of hunter syndrome

A
  • can be treated with enzyme replacement therapy (ERT)
  • an example name is elaprase
  • (enzyme being replaced is iduronidate-2-sulfatase
35
Q

menke disease mechanism

A
  • x-linked recessive
  • inability to absorb copper across intestinal epithelium
  • ^copper deficiency
36
Q

testing for menke disease

A
  • diagnosis suspected by low blood copper and ceruloplasmin

* molecular analysis of ATP7A gene

37
Q

treatment for menke disease

A
  • no real effective treatment

* copper histidinate infusion under investigation

38
Q

presentation of menke disease

A
  • severe neurodegenerative disorder beginning in first year of life
  • copper deficiency
39
Q

Zellweger syndrome

A
  • no peroxisomes formed
  • severe, fatal disease
  • diagnosis: elevation of very long chain fatty acids
  • no effective treatment
40
Q

what are peroxisomes

A

cytoplasmic organelles with variety of biochemical functions:
•peroxide metabolism
•catabolism of very long chain fatty acids
•catabolism of bile acids
•synthesis of complex lipids
(zellweger syndrome=peroxisomal disorder)

41
Q

List of biochemical laboratory tests

A
  • amino acid quantitation
  • urine organic acid quantitation
  • carnitine levels and acylcarnitine analysis
  • ammonia
  • lactic acid
  • urine mucopolysaccharides
  • very long chain fatty acids

Molecular Foundations of Medicine (21 decks)

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