Paediatric Imaging

Homocystinuria

metabolic disorder usually inherited as an autosomal recessive trait involving a congenital enzyme defect, cystathionine beta synthase. The resultant abnormal accumulation of homocysteine is converted to homocystine resulting in increased levels of homocystine in blood and urine. There are three types of homocystinuria each affecting a defect at a different step in the enzymatic pathway. Patients with type I homocystinuria often have mental retardation, are tall with long limbs, have inferior displacement of the lens and venous and arterial thromboembolic episodes. Radiographs show generalized osteoporosis with frequent pathological fractures and biconcavity of vertebral bodies, and enlarged carpal bones. They may also show arachnodactyly and scoliosis and pectus deformities. The skeletal changes and thrombotic episodes are absent in patients with type II or III homocystinuria.

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