A defect in the P-protein component of the glycine cleavage system has been the most frequent abnormality found in patients with glycine encephalopathy (NKH).
Screening a DNA bank from 50 patients with enzymatic confirmation of their diagnosis of nonketotic hyperglycinemia gave allele frequencies of 5% for R515S of P-protein (glycine decarboxylase) and 7% for R320H of T-protein (aminomethyltransferase).
Molecular analysis of NKH has identified two prevalent mutations to date; the S564I mutation in a gene encoding the P-protein, a component of the GCS, in a Finnish population, and the H42R mutation in a gene encoding the T-protein in the Israeli-Arab population.
Furthermore, this mutation was present in 70% (14 of 20) of P protein gene alleles in Finnish patients with NKH, whereas it was not found in 20 alleles of non-Finnish patients.
We studied the structure of the mutant P-protein mRNA expressed in the liver of a patient with nonketotic hyperglycinemia (NKH) deficient of P-protein.