PC deficiency may be categorized into 3 phenotypic subgroups. Patients from North America ('group A') have lactic acidemia and psychomotor retardation, whereas those from France and the United Kingdom ('group B') have a more complex biochemical phenotype with increased serum lactate, ammonia, citrulline, and lysine, as well as an intracellular redox disturbance in which the cytosolic compartment is more reduced and the mitochondrial compartment is more oxidized. Patients in group B have decreased survival compared to group A, and usually do not survive beyond 3 months of age. Group C is relatively benign. [From OMIM]