PGK1 and Parkinsonism: Parkinsonism in patients with PGK-1 deficiency has been postulated to occur due to insufficient ATP regeneration in the substantia nigra as a result of low levels of PGK activity.2 In heterozygous carriers, the mutant allele of PGK-1 on the X chromosome is randomly inactivated during early embryonic stages due to lyonization, resulting in a “mosaic” or “patchy” pattern of enzymatic activity.