Nonketotic hyperglycinemia: treatment with diazepam--a competitor for glycine receptors.

Two female infants with nonketotic hyperglycinemia (NKH) were treated with diazepam for the control of seizures. The first infant had seizures, lethargy, and respiratory distress in the first 24 hours of life. The diagnosis of NKH was made at 3 weeks of age and she was then placed on a regimen of strychnine and a low-protein diet. Strychnine therapy was discontinued after three months of treatment because there was no improvement in the seizure control or in the patient's condition. At 5 months of age the patient was referred to our clinic for further work-up. The second infant had seizures, hypotonia, and respiratory distress shortly after birth. She was treated with phenobarbital and diphenylhydantoin, which had no effect on her seizures. The baby was referred to our clinic at 8 months of age and diagnostic studies revealed NKH. All previous medications were stopped and both infants were placed on diazepam, a competitor for glycine receptors in the CNS. Choline and folic acid were added for one-carbon unit transfer and sodium benzoate to bind excessive glycine. Both infants responded to this treatment with cessation of seizures; they became more responsive and alert, and their EEGs showed remarkable improvement despite the persistence of elevated glycine levels in plasma, CSF, and urine. Diazepam as a competitor for the receptors of glycine may prove helpful in controlling the intractable seizures associated with NKH.