Evidence of defective threonine metabolism in non-ketotic hyperglycinaemia

Response to sodium benzoate treatment in non-ketotic hyperglycinaemia

Therapy with benzoic acid in a case of classic neonatal non-ketotic hyperglycinaemia (NKH) was successful in stopping seizures but not in promoting mental development. Serum glycine levels were normalizable even by administering low doses of 53 mg sodium benzoate/kg body mass (BM) per day. Despite giving a higher dosage (240 mg/kg BM per day) normalization of glycine concentration in cerebrospinal fluid (CSF) was not achieved. However, seizures ceased. Restriction of protein intake (< or = 2 g/kg BM per day) seemed to be profitable. CSF glycine concentrations below 100 mumol/L may be sufficient to prevent seizures in older infants who have adapted to neuronal glycine exposure. No toxicity of sodium benzoate treatment was detected when administering doses of up to 470 mg/kg BM per day but side effects such as itching and hyperactivity were obvious.

A treatment of non-ketotic hyperglycinaemia

The treatment comprising a special diet (without glycine, serine, and with a reduced amount of threonine), strychnine nitrate and ursodesoxycholic acid (UDCA) led to normoglycinaemia in this form of severe non-ketotic glycine encephalopathy. Diet and treatment were well tolerated but without significant effect upon psychomotor development. This treatment should be more effective if administered before irreversible brain damage occurs, particularly in moderate and chronic forms of NKH.

Threonine dehydratase deficiency: a probable cause of non-ketotic hyperglycinaemia

A patient with classical symptoms of non-ketotic hyperglycinaemia (NKH) is presented. Threonine dehydratase was undetectable in a liver autopsy specimen, which was obtained within 1 h of death and immediately frozen at -70 degrees C. Activities of four marker enzymes were normal. This represents the first documentation of an inborn error of threonine metabolism and a new explanation of NKH.