Glycine Cleavage System in Ketotic Hyperglycinemia

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Abstract
Glycine cleavage activity was compared in the livers, from 3 infants with ketotic hyperglycinemia (2 cases of propionic acidemia and 1 case of methylmalonic acidemia) and 3 controls. In one case of propionic acidemia, glycine cleavage activity (5.2 nmol/mg protein per h) was normal in the liver obtained at biopsy when the patient was well controlled by the treatment with low protein diet (0.8 g/kg per day) and the level of serum glycine was lowered to normal. In the 2 other cases of ketotic hyperglycinemia, glycine cleavage activity was significantly reduced in the liver obtained at autopsy when the patients died in the state of metabolic acidosis. Its activity in the liver of one case of propionic acidemia (0.7 nmol/mg protein per h) was 6-26% of that in controls (2.7-10.8 nmol/mg protein per h), and 2-7% in a case of methylmalonic acidemia (0.2 nmol/mg protein per h). Analyzing of the individual components of the glycine cleavage system, a marked decrease in the activity of H-protein was revealed in the livers of the both patients; it (0.2 nmol/mg protein per h) was only 3-4% of that in controls (4.9-6.3 nmol/mg protein per h). These findings suggest that the reduction of the glycine cleavage system in the liver of ketotic hyperglycinemia occurs secondarily as speculated previously and is caused mainly by a decrease of H-protein activity.