Recurrent deletion in glycine decarboxylase gene and nonketotic hyperglycinemia Medical genetics, Research

点击翻译按钮获取中文摘要

Mutations in glycine decarboxylase gene (GLDC) cause nonketotic hyperglycinemia (NKH), an inborn error of metabolism characterized by severe neurological disturbance. We determined the structures of GLDC and its pseudogene (psiGLDC) and studied their expression in molecular analysis of NKH. The GLDC gene spanned a least 135 kb and consisted of 25 exons. All donor and acceptor sites adhered to the canonical GT-AG rule except for the donor site of intron 21, where a variant form GC was used instead of GT. The transcription initiation site was assigned to a residue 163 bp upstream from the translation initiation triplet by primer extension analysis. The psiGLDC gene had no intron and shared 97.5% homology with the coding region of functional GLDC, suggesting that psiGLDC ia a processed pseudogene that arose from the GLDC transcript about 4 to 8 million years ago. RNA blotting analysis revealed that GLDC is expressed in human liver, kidney, brain and placenta. We then examined a patient with NKH with no detectable GLDC mRNA in his lymphoblasts. Exons 1 to 3 of the functional GLDC gene from this patient were not amplified by PCR, whereas those from control subjects were amplified. These results suggest a large homozygous deletion (at least 30 kb) in the patient. We then devise a semi-quantitative PCR to estimate the number of GLDC alleles using psiGLDC as an internal control, and confirmed the homozygosity and heterozygosity of the deletion in the patient and his parents, respectively. Structural information of GLDC and psiGLDC should facilitate the molecular analysis of NKH.