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Path Y > Chemical Pathology - Metabolic Disorders and Screening > Flashcards

Chemical Pathology - Metabolic Disorders and Screening Flashcards

1
Q

Deficiency of which enzyme causes phenylketouria?
what’s its function?

A 
Phenylalanine hydroxylase (PAH)
convert phenylalaine to tyrosine
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2
Q

What builds up in PKU that causes toxicity?

A

phenylalanine

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3
Q

What number must you use when requesting a metabolic screen?

A

OMIM number
Online Mendelian Inheritance in Man

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4
Q

What will be the result of not treating PKU shortly after birth?

A

IQ <50

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5
Q

How is PKU diagnosed?

A

Based on blood phenylalanine level, as >400 different mutations can cause PKU!

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6
Q

How quickly does PKU treatment need to be initiated in order to be effective?

A

First 6 weeks of life

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7
Q

What is the test for cystic fibrosis in the neonate?

A

immunoreactive trypsin test as part of guthrie heel prick test

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8
Q

What is MCADD?

A

medium-chain acyl-CoA dehydrogenase deficiency
AR condition preventing metabolism of fat into energy
prevents production of acetyl CoA and ketones, which permits glucose sparing
may die of hypoglycaemia - classic cause of cot death, as get hypo when not feeding and die

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9
Q

what metabolic defect can cause hyperammonaemia?

A

urea cycle defect

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10
Q

how can hyperammonaemia be treated?

A

remove ammonia w sodium benzoate or sodium phenyl acetate
reduce ammonia production (low protein diet)

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11
Q

what is the typical triad of biochemical findgings for organic aciduria?

A

Hyperammonaemia
Metabolic acidosis
High anion gap

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12
Q

What unusual odour might be smelt on a patient with isovaleric acidaemia?

A

Cheesy and sweaty

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13
Q

What are the typical neurological findings in organic acidurias?

A

truncal hypotonia and limb hypertonia

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14
Q

what condition causes chronic intermittent organic aciduria?

A

reye syndrome = liver and brain injury w hypoglyacaemia and hyperammonaemia

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15
Q

recall 3 drugs that can precipitate symptoms in Reye syndrome

A

Salicylates
Anti-emetics
Valporate

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16
Q

Which inherited metabolic disorder causes a hypoketotic hypoglycaemia?

A

MCADD

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17
Q

What is the most severe & common disorder of galactose metabolism?

A

Galactossaemia

Gal-1-put enzyme deficiency,

can’t convert galactose to glucose, so lots of gal-1-phosphate in blood

Galactose-1-phosphate uridyl transferase

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18
Q

How should Gal-1-Put be treated?

A

avoid galactose (milk - dairy and breast)

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19
Q

what ophthalmological sign may children with Gal-1-put deficiency have?

A

Bilateral cataracts

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20
Q

recall 3 biochemical findings of glycogen storage disease type 1

A

Hypoglycaemia
Neutropaenia
Lactic acidosis

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21
Q

How does Gal-1-Put present in neonates?

A

Diarrhoea & Vomiting
Conjugated hyperbilirubinaemia & hepatomegaly
sepsis (gal-1-phos inhibits the immune response)

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22
Q

When, and in which organ, do mitochondrial disorders present?

A

At any age in any organ!

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23
Q

Recall 3 mitochondrial DNA (mtDNA) disorders

A

BARTH syndrome - presents at birth
MELAS - at age 5-15
Kearns Sayre syndrome - at age 12-30

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24
Q

What abnormal blood results would be suggestive of a mitochondrial disorder?

A

Elevated lactate, even when fasted
Unexplained raised CK

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25
Q

What is the typical muscle biopsy histological finding in mitochondrial disorders?

A

ragged red fibres

26
Q

what 9 diseases are screened for during neonatal heel prick (Guthrie) test?

A

SCD
CF
congenital hypothyroidism

metabolic
PKU
MCADD
homocystinuria
isovaleric academia

glutaric acuduria type , maple syrup disease

27
Q

define sensitivity

A

true positives
correctly identify patients w a disease

= positve test/everyone who has actually the disease(true pos + false neg)

28
Q

define specificity

A

true negatives
correctly identify people without the disease

= people who test neg/people whoa ctually dont have the disease (true neg + false pos)

A specific test helps rule a disease in when positive

29
Q

what 2 specific metabolites accumulate in PKU?

A

phenylpyruvate
phenyl acetic acid (urine)

30
Q

treatment of PKU?

A

diet that eliminated phenylalanine
may be breast fed
avoid protein
avoid aspartame
amino acid supplements

31
Q

what are the symptoms of untreated PKU?

A

lighter skin and hair
musty smell to breath
learning disabilities
epilepsy

at birth may have microcephaly and LBW

32
Q

define PPV and NPV

A

PPV = probability that following a positive test result, that individual will truly have that specific disease.

=true pos/ all postive (true and false)

NPV = negative predictive value is the probability that following a negative test result, that individual will truly not have that specific disease.

= true neg/all neg (true & false)

33
Q

what do you measure as screening for MCADD?

A

C6-C10 Acylcarnitine using tandem mass spectrometry

34
Q

define homocystinuria

A

AR disorder of the metabolism of the amino acid methionine due to a deficiency of methionine synthase

35
Q

give 3 clinical features of homocystinuria

A

Lens dislocation
Mental retardation
Thromboembolism

36
Q

give 4 clinical features of a urea cycle disorder?

A

hyperammonaemia w respiratory alkalosis
neurological encephaloptahy
vomiting without diarrhoea
avoidance of protein or change in diet

37
Q

the urea acid cycle converts what to what?

A

ammonia to urea

38
Q

in high levels of ammonia in the blood, what does the body convert it to?

A

attaches an ammonium group to glutamate to form glutamine

39
Q

what biochemical findings suggest a urea cycle disorder (3)?

A

Serum glutamine is HIGH in hyperammonaemia
Serum amino acids in urea cycle will either be HIGH or ABSENT
Urine orotic acid

40
Q

which urea acid cycle disorder is X linked?

A

OTC
Ornithine Transcarbamylase Deficiency

41
Q

give 3 AR urea acid cycle diseases?

A

Lysinuric protein intolerance
Hyperornithinaemia-Hyperammonaemia-Homocitrullinuria (HHH)
Citrullinaemia type III

all cause high ammonia (toxic)

42
Q

what may precipitate reye’s syndrome?

A

viral infection and aspirin use

43
Q

what 3 biochemical changes are associated w reye’s syndrome?

A

hyperammonaemia
hypoglycaemia
prolonged prothrombin (PT) time

44
Q

what does hyperketotic hypoglycaemia state indicate

A

starvation

45
Q

what does hypoketotic hypoglycaemia state indicate

A

MCADD

46
Q

what does hyperketotic hyperglycaemia state indicate

A

DKA

47
Q

what does hypoketotic hyperglycaemia state indicate

A

HHS

48
Q

what 2 investigations to diagnose gal-1-put deficiency?

A
  • High galactose in urine
  • absence of Gal-1-PUT activity in red cells
49
Q

how do neonates with gal-1-put deficiency present(4)?

A

failure to thrive, jaundice, hepatomegaly and sepsis (e.coli)

50
Q

what are the 3 features of Barth disease?

A

cardiomyopathy, myopathy, neutropenia)

51
Q

what are the 3 features of MELAS?

A

mitochondrial encephalopathy, lactic acidosis and stroke-like episodes

52
Q

what’s the most common enzyme deficiency worldwide? what’s the inheritance?

A

Glucose-6-phosphate dehydrogenase deficiency (G6PDD)
X-linked recessive = defective glucose-6-phosphate dehydrogenase enzyme

53
Q

what’s the function of glucose-6-phosphate dehydrogenase?

A

glucose-6-phosphate dehydrogenase is an enzyme which protects red blood cells
defect causes haemolysis

54
Q

what are 3 clinical features of G6PDD?

A

neonatal jaundice
kernicterus (bilirubin induced brain dysfunction)
haemoglobinuria (red or brown urine)

55
Q

what’s favism?

A

Acute hemolytic anemia in G6PD-deficient people can develop after eating fava/broad beans.

56
Q

define isovaleric acidaemia. what amino acid can’t be processed?

A

AR condition, deficiency in isovaleric acid-CoA dehydrogenase, meaning cant process leucine causing build up of isovaleric acid

it’s a type of organic aciduria/acidaemia

57
Q

define glycogen storage disease type 1. aka?

A

liver being unable to properly break down stored glycogen

also know as von gierke disease

58
Q

what are 2 carbohydrate disorders

A

galactosemia

glycogen storage disease type 1

59
Q

define homocystinuria. what enzyme is deficient?

A

AR condition

inherited disorder of the metabolism of the amino acid methionine due to a deficiency of methionine synthase.

60
Q

whats the treatment of homocystinuria?

A

low protein diet

pryroxidine (vitamin B6)

betaine later in life

61
Q

what are 4 clincical feautures of kearns-sayre?

A

chronic progressive external ophthalmoplegia, retinopathy, deafness, ataxia

62
Q

test & treatment for MCADD

A

blood acylcarnitine

regular carbohydrates

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