A 6-month-old girl presented with
hypotonia and mild psychomotor retardation. Subsequently, an atypical manifestation of a nonketotic hyperglycinaemia was diagnosed, confirmed by significantly reduced activity of the
glycine cleavage system in the liver tissue. After the patient developed
hypsarrhythmia and had a single cerebral seizure, treatment with both
sodium benzoate and
dextromethorphan was started. During the following year, the girl was free of
seizures with improvement of the EEG activity and showed retarded but continuously progressing psychomotor development. At the age of 20 months she began to walk freely but had generalized
muscular hypotonia and moderate
mental retardation. Discontinuation of
dextromethorphan medication after one year of treatment did not change the clinical and electroencephalographic status. However, after cessation of
sodium benzoate therapy, epileptic activity in the EEG and behavioural changes occurred. These changes disappeared promptly after
sodium benzoate therapy was reinstituted. Thus, this case of mild atypical nonketotic hyperglycinaemia with only moderate psychomotor retardation and without
epilepsy benefited from treatment with
sodium benzoate in terms of electroencephalographic and behavioural changes.