Nonketotic hyperglycinemia (OMIM no. 605899) is an autosomal recessively inherited glycine encephalopathy, caused by a deficiency in the mitochondrial glycine cleavage system. Here we report 2 neonates who were admitted to the hospital with complaints of respiratory failure and myoclonic seizures with an elevated cerebrospinal fluid/plasma glycine ratio and diagnosed as nonketotic hyperglycinemia. We report these cases as 2 novel homozygous mutations; a missense mutation c.593A>T (p.D198 V) in the glycine decarboxylase gene and a splicing mutation c.339G>A (Q113Q) in the aminomethyltransferase gene were detected. We would like to emphasize the genetic difference of our region in inherited metabolic diseases once again.