Non-ketotic hyperglycinemia: an aim of the second generation of studies on pathogenesis

Non-ketotic hyperglycinemia is caused by a molecular lesion involved in the glycine cleavage system and shows striking features representing the impaired central nervous system. For the study on molecular genetics of non-ketotic hyperglycinemia, we have isolated several cDNA clones, each encoding human glycine decarboxylase of H-protein, two of the four component enzymes of the glycine cleavage system. Although one of eight patients with this disease resulting from a lesion of glycine decarboxylase had the glycine decarboxylase gene deleted at a 5' region, they showed no common aberration detectable by glycine decarboxylase cDNA. Using the H-protein cDNA, we have demonstrated the rearranged structures, identified by one of the undetectable 5.0 and 5.5 kb SacI fragments, in the genomes of patients in whom there was an impaired expression of H-protein or glycine decarboxylase. The aberration of the 5.5 kb SacI fragment was associated with a defect of the 5.2 kb EcoRI fragment. Multiple genomic lesions are suggested for non-ketotic hyperglycinemia, and their implications in pathogenesis are discussed.