Chromosomal localization, structure, single-nucleotide polymorphisms, and expression of the human H-protein gene of the glycine cleavage system (GCSH), a candidate gene for nonketotic hyperglycinemia

dNonketotic hyperglycinemia (NKH) is an inborn error of metabolism caused b y deficiency in the glycine cleavage system (GCS); this system consists of four individual constituents, P-, T-, H-, and L-proteins. Several mutations have been identified in P- and T-protein genes, but not in the H-protein g ene (GCSH), despite the presence of case reports of H-protein deficiency. T o facilitate the mutational and functional analyses of GCSH, we isolated an d characterized a human pi-derived artificial chromosome (PAC) clone encodi ng GCSH. CCSH spanned 13.5kb and consisted of five exons. Using the PAC clo ne as a probe, we mapped GCSH to chromosome 16q24 by fluorescence in situ h ybridization. The transcription initiation site was determined by the oligo nucleotide-cap method, and potential binding sites for several transcriptio nal factors were found in the 5 ' upstream region. Direct sequencing analys is revealed five single-nucleotide polymorphisms. The expression profiles o f P-, T-, and H-protein mRNAs were studied by dot-blot analysis, using tota l RNA from various human tissues. GCSH was expressed in all 29 tissues exam ined, while T-protein mRNA was detected in 27 of the 29 tissues. In contras t, the P-protein gene was expressed in a limited number of tissues, such as liver, kidney, brain, pituitary gland, and thyroid gland, suggesting disti nct transcriptional regulation of each GCS constituent.