Hyperglycinuria and hyperglycinemia in two siblings with mild developmental delays
D. M. Frazier, G. K. Summer and H. R. Chamberlin
Two preschool-age siblings with similar histories of encephalopathy were
examined for developmental retardation and found to have elevated levels of
urinary and blood glycine. Their inability to convert glycine into serine
in the absence of elevated blood and urinary ketone levels was suggestive
of a defect in the glycine-cleavage enzyme system (or serine hydroxymethyl
transferase). These patients differ significantly from the majority of
reported cases of nonketotic hyperglycinemia in that they did not manifest
life-threatening neonatal illness, severe mental retardation, or
neurological deficits. However, during an oral glycine load, alterations in
the electroencephalographic pattern occurred that suggested a relationship
between elevated blood glycine levels and pathological involvement of the
central nervous system. The ratio of CSF-blood glycine was found to be in
the range expected for nonketotic hyperglycinemia.
