a-Mannosidase

This is an X-linked dominant disorder with variable course in heterozygous females. The most common presentation in males is lethargy, poor feeding and tachypnoea within a few hours of birth. The majority of these patients die within the first few weeks. Survivors have severe mental retardation, neurological impairment and a poor prognosis. Other males have a later onset and a more prolonged course, the first attack sometimes being precipitated by a high-protein feed. These patients have a higher residual OTC activity than the severely affected neonates. The variable course in females is consistent with varying degrees of inactivation of the normal X chromosome by Lyonisation.

ENZYME TESTS: Ornithine transcarbamylase in liver is assayed to diagnose this disorder.

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