Homozygous mutations in the SLC6A9 gene that encodes GLYT1 cause glycine encephalopathy, also known as nonketotic hyperglycinemia (NKH), which is a severe neurological disease caused by abnormally high levels of glycine in the cerebrospinal fluid (CSF) and characterized by respiratory failure, progressive hypotonia, and startle-like reflexes (24, 25). The gene discussed is SLC6A9; the disease is glycine encephalopathy.