Two novel mutations in the glycine decarboxylase gene in a boy with classic nonketotic hyperglycinemia: case report.

Nonketotic hyperglycinemia is an extremely rare autosomal recessively inherited glycine encephalopathy caused by a deficiency in the mitochondrial glycine cleavage system, which leads to severe clinical symptoms. Nonketotic hyperglycinemia is characterized by complex and diverse phenotypes, such as hypotonia, seizures, cognitive impairment, developmental delays and myoclonic jerks that may lead to apnea and even death. Here we report a 1-year-old boy with myoclonic seizures, hypotonia and coma; he had elevated plasma and cerebrospinal fluid glycine levels, and cerebrospinal fluid/plasma glycine ratio was 0.24. Two novel heterozygous mutations confirm the diagnosis of nonketotic hyperglycinemia. One is a missense mutation c.2516A>G (p.Y839C) and the other one is a splicing mutation c.2457+2T>A in the GLDC gene.