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MoD > L14 - Inborn Errors of Metabolism > Flashcards

L14 - Inborn Errors of Metabolism Flashcards

1
Q

Which substances often act as cofactors?

A

Vitamins (B12m B6)

trace elements (Mg Zinc)

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2
Q

Why can deficiency of vitamins and trace elements cause problems?

A

Vitamins and trace elements are often cofactors - lack of cofactors can lead to lack of activation of important enzymes

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3
Q

Accumulation of a toxin can be a mechanism of disease. What accumulates in patients with urea cycle defects?

A

Ammonia (NH3) - very toxic

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4
Q

What are the clinical effects of acute hyperammonaemia toxicity?

A
  • lethargy
  • poor feeding
  • vomiting
  • tachypnoea (metabolic alkalosis)
  • convulsions
  • coma
  • death
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5
Q

What is porphyria?

A

Disease in which there is abnormal metabolism of haemoglobin

Get accumulation of porphyrins

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6
Q

What are the 2 types of porphyria?

A
  • acute porphyria

- photosensitive porphyria

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7
Q

What are the steps in the pathway between ALA and HAEM?

A

ALA

PBG

Uroporphyrin

Coproporphyrin

Protoporphyrin

Haem

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8
Q

What are the signs of acute porphyria?

A
  • severe abdominal pain
  • pain in chest, legs, back
  • constipation or diarrhoea
  • vomiting
  • insomnia
  • palpitations
  • hypertension
  • anxiety or restlessness
  • seizures
  • mental changes
  • breathing problem
  • muscle pain/tingling/weakness/paralysis
  • red or brown urine
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9
Q

What are the signs of photosensitive porphyria?

A
  • sensitivity to light
  • sudden painful erythema and oedema
  • blisters taking weeks to heal
  • itching
  • fragile skin
  • increased hair growth
  • red or brown urine
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10
Q

Fatty acid oxidation results in what product?

A

Acetyl CoA

Goes on to make ketones or enter the TCA cycle

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11
Q

Fatty acid oxidation occurs in which organelle?

A

Mitochondria

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12
Q

What is androgen insensitivity syndrome?

A

AIS is when a person who is genetically male (who has one X and one Y chromosome) is resistant to male hormones (androgens) - and so the person has some physical traits of a female, but the genetics a male.

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13
Q

What does the basic urine metabolism screen consist of?

A
  • spot tests
  • organic acids
  • amino acids
  • sugar chromatography
  • oligosaccharides/sialic acids
  • mucopolysaccharides
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14
Q

How can amino acids be tested?

A

By amino acid TLC (thin layer chromatography)

  • can identity argininosuccinic acid which is a product of urea cycle defects
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15
Q

What is homocystinuria?

A

A disorder of methionine metabolism, leading to an abnormal accumulation of homocysteine and its metabolites in urine

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16
Q

What are the clinical problems of homocystinuria?

A
  • mental retardation
  • marfinoid habitus
  • ectopia lentis
  • osteoporosis
  • thromboembolism
17
Q

What is hyperhomocystinaemia?

A

Medical condition characterised by an abnormally high level of homocysteine in the blood, conventionally described as above 15 µmol/L

18
Q

What percentage of the general population have hyperhomocystinaemia?

A

5%

19
Q

There is increased incidence of hyperhomocystinaemia in patients with which diseases?

A
  • stroke
  • peripheral vascular disease
  • coronary artery disease
20
Q

What are the 3 classic organic acidaemias?

A
  • propionic acidaemia
  • isovaleirc acidaemia
  • methyl malonic acidameia
21
Q

What are the benefits of diagnosis of IEMs?

A
  • treatment, improve prognosis
  • identify cause of clinical problem
  • genetic counselling
  • IEM act as models for other disorders
22
Q

How are neural tube defects diagnosed?

A
  • maternal serum and amniotic fluid AFP

- ultrasound scan at 16 weeks

23
Q

How is down syndrome diagnosed?

A

1st trimester - PAPA, HCG and nuchal translucency

2nd trimester - maternal serum AFP, HCG, inhibin and estriol

Test on the ascent: free foetal DNA

24
Q

Enzyme deficiencies cause problems clinically due to what 3 outcomes?

A
  • accumulation of metabolites prior the enzyme
  • reduction in new products of the enzyme
  • spontaneous production of new compounds due to inc accumulation (can be toxic)
25
Q

how is co-factor deficiency treated?

A

cofactor supplementation

26
Q

what is a common urea cycle defect?

A

OTC
Ornithine transcarbamylase deficiency

X-linked

27
Q

how is an acute Ornithine transcarbamylase deficiency patient treated?

A
  • reduced protein intake
  • not fasting for too long

Low protein diet; dialysis; liver transplant

28
Q

what is the porphyrins pathway?

A

biosynthetic pathway to make haem

29
Q

what happens if there is a complete block of the porphyrins pathway?

A

Complete block of this pathway is incompatible with life (no Hb for oxygen delivery)

can’t sustain life

30
Q

what happens if there is a partial block at the top of the porphyrins pathway?

A

accumulation of ALA and PBG

presenting acute porphyria.

31
Q

what happens if there is a partial block at the bottom of the porphyrins pathway?

A

accumulation of porphyrin

molecules, presenting photosensitive porphyria.

32
Q

how can an enzyme deficiency cause an energy deficiency?

A

if an enzyme is missing from:

  • oxidative phosphorylation
  • glycolysis
  • fatty acid oxidation
  • TCA cycle
33
Q

what does a partial defect in androgen insensitivity syndrome
result in?

A

ambiguous genitalia

34
Q

what is the presentation of androgen insensitivity syndrome?

A

primary amenorrhoea, infertility [only resent in puberty]

35
Q

how is androgen insensitivity syndrome treated?

A

surgical resection of residual gonads

36
Q

how is androgen insensitivity syndrome treated?

A

surgical resection of residual gonads

37
Q

how are inborn errors of metabolism diagnosed\/

A
  • pre-symptomatic screening

- investigation of symptomatic individuals

38
Q

how do you investigate a symptomatic individual for inborn errors of metabolism?

A

● test body fluids for abnormal metabolites

● measure enzyme activities [more demanding and time consuming]

● histochemical / immunochemical staining

● DNA analysis

MoD (19 decks)

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