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Clinical Genetics > Inborn errors of metabolism > Flashcards

Inborn errors of metabolism Flashcards

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1
Q

What happens to urine in alkaptonuria(AR)?

A

Urine turns black on standing

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2
Q

What deficiency is present in alkaptonuria(AR)?

A

Homogentisic acid oxidase deficiency

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3
Q

What replacement is needed as the patient with alkaptonuria gets older?

A

Need to have joint/valve replacements as you get older

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4
Q

What happens in cystinuria?

A

Defective transport of cystine and dibasic AAs through epithelial cells of renal tubule and intestinal tract

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5
Q

Why do dibasic acids form stones?

A

Dibasic acids are insoluble so form stones

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6
Q

What does a low solubility of cysteine cause the formation of in renal tract?

A

Cystine has low solubility -formation of calculi in renal tract

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7
Q

What mutations cause cystinuria and how can we see this?

A
  • Mutations of SLC3A1 aa transporter gene (Chr 2p) & SLC7A9 (Chr 19)
  • Infrared spectroscopy can be done to see this
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8
Q

How do we treat a patient with cystinuria?

A

Treat this by making sure the patient remains hydrated

-3L of water everyday to stop stones forming

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9
Q

What is albinism a defect of?

A

Defect of metabolism of tyrosine

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10
Q

What is the phenotype of albinism?

A

Pink eyes, white hair

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11
Q

Tyrosinase negative albinism

A
  • Type 1a - complete lack of enzyme activity due to production of inactive tyrosinase
  • Type 1b - reduced activity of tyrosinase
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12
Q

Tyrosinase positive albinism

A

Type II

  • AR, biosynthesis of melanin reduced in skin hair and eyes
  • most individuals do acquire a small amount of pigment with age
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13
Q

What do patients with pentosuria excrete in urine?

A

Excrete 1-4g pentose sugar L-xylulose daily in urine

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14
Q

State of pentosuria

A

Benign

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15
Q

What is the one gene one enzyme concept?

A

Each gene directly produces a single enzyme, which consequently affects an individual step in a metabolic pathway

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16
Q

What are inborn errors of metabolism caused by?

A

Inborn errors of metabolism are caused by mutations in genes which then produce abnormal proteins whose functional activities are altered

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17
Q

What are the 5 mechanisms of inheritance?

A
  • Autosomal recessive
  • Autosomal dominant
  • X-linked
  • Codominant
  • mitochondrial
18
Q

What is the most common form of inheritance?

A

Autosomal recessive

19
Q

What does consanguinity do in autosomal recessive inheritance?

A

Consanguinity increases risk of autosomal recessive conditions

20
Q

What are the chances in carrying mutation in autosomal dominant?

A

50% chance of carrying mutation

21
Q

What is X-linked inheritance characterised by?

A

Characterised by carrier females passing on condition to their affected sons

22
Q

Transmission in X-linked inheritance

A

No male to male transmission

23
Q

What is co-dominant inheritance?

A

Two different versions (alleles) of a gene are expressed, and each version makes a slightly different protein

24
Q

What is mitochondrial inheritance inherited from?

A

Inherited exclusively from mother

25
Q

What can only contribute mitochondria to developing embryo?

A

only the egg contributes mitochondria to the developing embryo

26
Q

Which parent can only pass on mitochondrial mutations to their children?

A

only females can pass on mitochondrial mutations to their children

27
Q

What is the criteria for screening inborn errors for metabolism?

A
  • Condition should be an important health problem
  • Natural history of the condition should be understood
  • Should be a recognisable latent or early symptomatic stage
  • Should be a test that is easy to perform and interpret, acceptable, accurate, reliable, sensitive and specific
  • Should be an accepted treatment recognised for the disease
  • Treatment should be more effective if started early
  • Should be a policy on who should be treated
  • Diagnosis and treatment should be cost-effective
  • Case-finding should be a continuous process
28
Q

Who criteria for good screening test for inborn errors for metabolism?

A
  • Condition screened for should be an important one
  • There should be an acceptable treatment for patients with the disease
  • Facilities for diagnosis and treatment should be available
  • There should be a recognised latent or early symptomatic stage
  • There should be a suitable test or examination which has few false positives -specificity - and few false negatives - sensitivity
  • Test or examination should be acceptable to the population
  • Cost, including diagnosis and subsequent treatment, should be economically balanced in relation to expenditure on medical care as a whole
  • Screening programme shouldn’t have too many false postives/negatives
29
Q

What is the national programme for newborn blood spot screening?

A
  • PKU
  • Congenital hypothyroidism
  • Cystic fibrosis
  • MCADD
  • Haemoglobinopathies
  • Maple syrup urine disease (MSUD)
  • Homocystinuria (pyridoxine unresponsive) (HCU)
  • Isovaleric acidaemia (IVA)
  • Glutaric aciduria type 1 (GA1)
30
Q

Steps involved in prick heel of baby

A
  1. Samples should be taken on day 5 (day of birth is day 0)
  2. All four circles on card need to be completely filled with a single drop of blood which soaks through to the back of the Guthrie card
    - Can get very different results if not done properly
31
Q

Presentation of IEM from neonate to adult

A
  • Neonatal presentation often acute

- Often caused by defects in energy metabolism

32
Q

Presentation of IEM in adults(Wilson’s)

A

Build up of copper

33
Q

Presentation of IEM in adult(Haemochromatosis)

A

Men will present before women as women lose blood monthly whereas in men, iron will begin depositing

34
Q

Neonates with IEM

A

Most are born at term with normal birthweight and no abnormal features

35
Q

What are clues of IEM in neonates?

A
  • Consanguinity
  • FH of similar illness in sibs or unexplained deaths
  • Infant who was well at birth but starts to deteriorate for no obvious reason
36
Q

Classic presentation of IEM

A
  • Symptoms - can be very non-specific
    • Poor feeding, Lethargy, Vomiting, Hypotonia, Fits
  • Specific symptoms
    - Abnormal smell (sweet, musty, cabbage-like)
    - Cataracts
    - Due to galactosaemia
    - Hyperventilation due to metabolic acidosis
    - Hyponatraemia and ambiguous genitalia
    - Neurological dysfunction with respiratory alkalosis
37
Q

Biochemical abnormalities of IEMs

A
  • Hypoglycaemia
  • Hyperammonaemia
  • Unexplained metabolic acidosis / ketoacidosis
  • Lactic acidosis
38
Q

What are the routine laboratory investigations of IEMS?

A
  • Blood gas analysis
  • Blood glucose
  • Plasma ammonia
39
Q

What are specialist investigations of IEMS?

A
  • Plasma amino acids
    - Looking at phenylketonuria
  • Urinary organic acids + orotic acid
  • Blood acyl carnitines
  • Blood lactate and pyruvate
    • Mitochondrial disorders
  • Urinary glycosaminoglycans
  • Plasma very long chain fatty acids
    • Peroxisomal disorders
40
Q

What are confirmatory investigations for IEMs?

A
  • Enzymology
    • Red cell galactose-1-phosphate uridyl transferase
      - Lysosomal enzyme screening (if suspicious of lysosomal disorder)
  • Biopsy (muscle, liver)
  • Fibroblast studies
  • Complementation studies
  • Mutation analysis – whole genome sequencing

Clinical Genetics (4 decks)

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