Degradation of glycine is brought about by the glycine cleavage system, which is composed of four mitochondrial protein components: P protein (a pyridoxal phosphate-dependent glycine decarboxylase), H protein (a lipoic acid-containing protein), T protein (a tetrahydrofolate-requiring enzyme), and L protein (a lipoamide dehydrogenase). GCSH is the H protein, which transfers the methylamine group of glycine from the P protein to the T protein. Defects in GCSH gene are a cause of nonketotic hyperglycinemia (NKH). Two transcript variants, one protein-coding and the other probably not protein-coding,have been found for GCSH gene. Also, several transcribed and non-transcribed pseudogenes of GCSH gene exist throughout the genome.