Late-Onset Nonketotic Hyperglycinemia With a Heterozygous Novel Point Mutation of the GLDC Gene

BACKGROUND: Atypical nonketotic hyperglycinemia is characterized by heterogeneous phenotypes that often include nonspecific behavioral problems, cognitive deficits, and developmental delays. PATIENT: We describe a girl with late-onset nonketotic hyperglycinemia presenting at 5 years of age with hypotonia, chorea, ataxia, and alterations in consciousness in the setting of febrile illness. RESULTS: Serum amino acid analysis was mildly elevated; however, urine amino acid analysis was instrumental in demonstrating marked hyperglycinuria. Mutation testing showed a heterozygous novel sequence change/point mutation in the glycine decarboxylase gene. CONCLUSIONS: This patient illustrates the importance of obtaining urine amino acids in individuals whose clinical manifestations are suspicious for any form of nonketotic hyperglycinemia, because this testing may provide more prominent evidence of elevations in glycine. She also illustrates the potential for a heterozygous mutation to result in manifestations of an atypical form of nonketotic hyperglycinemia.