Nonketotic hyperglycinemia: two patients with primary defects of P-protein and T-protein, respectively, in the glycine cleavage system.

The glycine cleavage system was investigated in the livers and brains of two patients with typical nonketotic hyperglycinemia who died in the neonatal period. The overall activity of the glycine cleavage system was found to be extremely low in both the liver and brain of each patient. In one patient, the disturbance of the glycine cleavage system was due to absence of activity of the P-protein. Immunochemical analysis indicated that this resulted from an absence of the enzyme protein. In the other patient, the activity of the T-protein was undetectable in the brain and was extremely low in the liver. Clinically classic nonketotic hyperglycinemia resulted from molecular defects in two different protein components of the glycine cleavage system.