Hyperammonemia

This urea-cycle disorder results from a failure of conversion of ammonia to urea. Subsequently, ammonia and glutamine are elevated, and urea nitrogen is decreased in the blood. The disease is associated with several enzyme deficiencies, mainly of ornithine transcarbamy-lase. Except for the ornithine transcarbamylase deficiency, which is X-linked inherited, all the other enzyme deficiencies are transmitted in autosomal recessive pattern.

Hyperammonemia presents shortly after birth with lethargy, vomiting, alkalosis, temperature abnormalities and, if not treated, death ensues from cerebral edema. Partial enzyme deficiencies are prone to cause episodic encephalopathies that can be precipitated by high protein intake, infection, and treatment with valproate.

The pathology consists of edema, variable neuronal losses in the cerebral cortex and deep gray structures, and the presence of Alzheimer type 2 glia. Cerebellar heterotopias, suggesting intrauterine damage, have been reported.

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