Nonketotic hyperglycinemia: report of a case and review of the clinical, chemical, and pathological changes.

A female infant with neonatal hypotonia and lethargy was found to have nonketotic hyperglycinemia. She died at the age of 5 days. Autopsy revealed slightly retarded myelination and severe spongy change in the well-myelinated areas of the brain. Analysis of this and the other 26 reported cases suggests that patients with nonketotic hyperglycinemia develop severe mental retardation, not seen in ketotic hyperglycinemia. Elevated glycine levels in the brain and cerebrospinal fluid appear to differentiate these two forms of hyperglycinemia better than the presence of ketosis or leukopenia, and high glycine levels apparently occur in the same areas as the spongy change. While both forms show defective glycine cleavage in the liver, defective glycine cleavage in the brain has been reported only in nonketotic hyperglycinemia.