Non-ketotic hyperglycinaemia in a family with an unusual phenotype.

A 10-year-old girl, one of three affected sisters, with non-ketotic hyperglycinaemia is described. In contrast to other reported cases, the course of the disorder was comparatively mild in this family. The only clinical signs were mental retardation and abnormalities in the EEG; blood glycine levels were 2-3 times normal. In the propositus, the formation of 14CO2 from glycine-1-14C and of FH414CH2OH from glycine-2-14C were impaired, shown by the decreased 14CO2 content of expired air and diminished labelling of carbon 3 of serine. However, the biochemical defect was no less than that seen in patients with much more severe clinical effects.