Nonketotic Hyperglycinemia

Nonketotic hyperglycinemia, an autosomal recessive disorder, results from failure of glycine degradation caused by mutations in three proteins (P, H, T) of a mitochondrial enzyme complex. Protein P, most commonly involved, is coded by a gene on chromosome 9. Failure of degradation leads to elevated concentrations of glycine in the blood, CSF, and urine.

The disease affects neonates and rapidly progresses to coma and death. Survivors present with psychomotor retardation and seizures. The brain shows spongy degeneration of the white matter, especially prominent in the cerebellum. Malformations with cerebellar hypoplasia, agenesis of the corpus callosum, and cortical dysplasias have been reported in some cases.

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