Phosphoglycerate kinase (PGK) deficiency is a rare x-linked disorder characterized by hemolytic anemia, seizures, muscle fatigue, and progressive neurological dysfunction. The disease is caused by the deficiency of PGK, an enzyme required for ATP formation through the glycolytic pathway. PGK is an enzyme that is ubiquitous to all cells of the human body, but red blood cells, muscles, and nerve cells are most severely affected by the absence of PGK due to their reliance upon the glycolytic pathway. Mutations of the PGK gene are highly variable and result in diverse phenotypes, ranging from mild hemolytic anemia only to severe mental retardation and early death in childhood. The more severe phenotypes show progressive neurologic deterioration between infancy and adolescence.