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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
What is the typical muscle biopsy histological finding in mitochondrial disorders?
ragged red fibres
26
what 9 diseases are screened for during neonatal heel prick (Guthrie) test?
SCD CF congenital hypothyroidism metabolic PKU MCADD homocystinuria isovaleric academia glutaric acuduria type , maple syrup disease
27
define sensitivity
true positives correctly identify patients w a disease = positve test/everyone who has actually the disease(true pos + false neg)
28
define specificity
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
what 2 specific metabolites accumulate in PKU?
phenylpyruvate phenyl acetic acid (urine)
30
treatment of PKU?
diet that eliminated phenylalanine may be breast fed avoid protein avoid aspartame amino acid supplements
31
what are the symptoms of untreated PKU?
lighter skin and hair musty smell to breath learning disabilities epilepsy at birth may have microcephaly and LBW
32
define PPV and NPV
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
what do you measure as screening for MCADD?
C6-C10 Acylcarnitine using tandem mass spectrometry
34
define homocystinuria
AR disorder of the metabolism of the amino acid methionine due to a deficiency of methionine synthase
35
give 3 clinical features of homocystinuria
Lens dislocation Mental retardation Thromboembolism
36
give 4 clinical features of a urea cycle disorder?
hyperammonaemia w respiratory alkalosis neurological encephaloptahy vomiting without diarrhoea avoidance of protein or change in diet
37
the urea acid cycle converts what to what?
ammonia to urea
38
in high levels of ammonia in the blood, what does the body convert it to?
attaches an ammonium group to glutamate to form glutamine
39
what biochemical findings suggest a urea cycle disorder (3)?
Serum glutamine is HIGH in hyperammonaemia Serum amino acids in urea cycle will either be HIGH or ABSENT Urine orotic acid
40
which urea acid cycle disorder is X linked?
OTC Ornithine Transcarbamylase Deficiency
41
give 3 AR urea acid cycle diseases?
Lysinuric protein intolerance Hyperornithinaemia-Hyperammonaemia-Homocitrullinuria (HHH) Citrullinaemia type III all cause high ammonia (toxic)
42
what may precipitate reye's syndrome?
viral infection and aspirin use
43
what 3 biochemical changes are associated w reye's syndrome?
hyperammonaemia hypoglycaemia prolonged prothrombin (PT) time
44
what does hyperketotic hypoglycaemia state indicate
starvation
45
what does hypoketotic hypoglycaemia state indicate
MCADD
46
what does hyperketotic hyperglycaemia state indicate
DKA
47
what does hypoketotic hyperglycaemia state indicate
HHS
48
what 2 investigations to diagnose gal-1-put deficiency?
* High galactose in urine * absence of Gal-1-PUT activity in red cells
49
how do neonates with gal-1-put deficiency present(4)?
failure to thrive, jaundice, hepatomegaly and sepsis (e.coli)
50
what are the 3 features of Barth disease?
cardiomyopathy, myopathy, neutropenia)
51
what are the 3 features of MELAS?
mitochondrial encephalopathy, lactic acidosis and stroke-like episodes
52
what's the most common enzyme deficiency worldwide? what's the inheritance?
Glucose-6-phosphate dehydrogenase deficiency (G6PDD) X-linked recessive = defective glucose-6-phosphate dehydrogenase enzyme
53
what's the function of glucose-6-phosphate dehydrogenase?
glucose-6-phosphate dehydrogenase is an enzyme which protects red blood cells defect causes haemolysis
54
what are 3 clinical features of G6PDD?
neonatal jaundice kernicterus (bilirubin induced brain dysfunction) haemoglobinuria (red or brown urine)
55
what's favism?
Acute hemolytic anemia in G6PD-deficient people can develop after eating fava/broad beans.
56
define isovaleric acidaemia. what amino acid can't be processed?
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
define glycogen storage disease type 1. aka?
liver being unable to properly break down stored glycogen also know as von gierke disease
58
what are 2 carbohydrate disorders
galactosemia glycogen storage disease type 1
59
define homocystinuria. what enzyme is deficient?
AR condition inherited disorder of the metabolism of the **amino acid methionine** due to a deficiency of **methionine synthase.**
60
whats the treatment of homocystinuria?
low protein diet pryroxidine (vitamin B6) betaine later in life
61
what are 4 clincical feautures of kearns-sayre?
chronic progressive external ophthalmoplegia, retinopathy, deafness, ataxia
62
test & treatment for MCADD
blood acylcarnitine regular carbohydrates

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