DrMKZ

Homocystinuria is a rare autosomal recessive disease caused by deficiency of cystathionine beta synthase. This results in an accumulation of homocysteine which is then oxidized to homocystine.

Features

• often patients have fine, fair hair
• musculoskeletal: may be similar to Marfan’s – arachnodactyly etc
• neurological patients may have learning difficulties, seizures
• ocular: downwards (inferonasal) dislocation of lens
• increased risk of arterial and venous thromboembolism
• also malar flush, livedo reticularis

Diagnosis is made by the cyanide-nitroprusside test, which is also positive in cystinuria

Treatment is vitamin B6 (pyridoxine) supplements

Example of question

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Galactosaemia

Galactosaemia is a rare autosomal recessive condition caused by the absence of galactose-1-phosphate uridyl transferase. This results in intracellular accumulation of galactose-1-phosphate

Features

• jaundice
• failure to thrive
• hepatomegaly
• cataracts
• hypoglycaemia after exposure to galactose
• Fanconi syndrome

Diagnosis

• urine reducing substances

Management is with a galactose free diet

The following conditions are inherited in a X-linked recessive fashion:

Androgen insensitivity syndrome
Becker muscular dystrophy
Colour blindness
Duchenne muscular dystrophy
Fabry’s disease
G6PD deficiency
Haemophilia A,B
Hunter’s disease
Lesch-Nyhan syndrome
Nephrogenic diabetes insipidus
Ocular albinism
Retinitis pigmentosa
Wiskott-Aldrich syndrome

The following diseases have varying patterns of inheritance, with the majority being in an X-linked recessive fashion:

Chronic granulomatous disease (in > 70%)