Glycine encephalopathy

4 cases of nonketotic hyperglycinemia (glycine encephalopathy), one with autopsy, are presented and the literature on 61 cases is reviewed. Major clinical signs include early hypotonia, lethargy and erratic and massive myoclonias with respiratory distrubances, starting during the first days of life after a symptom-free interval. Early death is common. Survivors are severely retarded and exhibit various types of seizures including infantile spasms. The EEG pattern consists initially of periodical paroxysmal bursts on an almost flat tracing, evolving later into a hypsarrhythmic pattern. Spongiosis of the myelinated pathways is the main pathological finding. Elevated CSF glycine seems to be the essential determinant of the neurological disturbances and it is, therefore, suggested that the term glycine encephalopathy be used instead of non-ketotic hyperglycinemia. A classification of disorders associated with hyperglycinemia is proposed.