Effect of sodium benzoate in the treatment of atypical nonketotic hyperglycinaemia

A 6-month-old girl presented with hypotonia and mild psychomotor retardatio n. 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 hypsarrhyt hmia 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 b ut continuously progressing psychomotor development. At the age of 20 month s she began to walk freely but had generalized muscular hypotonia and moder ate mental retardation. Discontinuation of dextromethorphan medication afte r one year of treatment did not change the clinical and electroencephalogra phic status. However, after cessation of sodium benzoate therapy, epileptic activity in the EEG and behavioural changes occurred. These changes disapp eared promptly after sodium benzoate therapy was reinstituted. Thus, this c ase of mild atypical nonketotic hyperglycinaemia with only moderate psychom otor retardation and without epilepsy benefited from treatment with sodium benzoate in terms of electroencephalographic and behavioural changes.