Glycogen Storage Disease, Type IXd is a disorder characterized by exercise-induced muscle stiffness and pain as well as myoglobinuria. Affected individuals are intolerant to exercise and suffer from muscle weakness and atrophy. Biochemical studies of patients reveal elevated levels of serum creatine kinase while muscle biopsies exhibit increased subsarcolemmal vacuolar glycogen accumulation, mitochondrial paracrystalline inclusions and decreased muscle-specific phosphorylase kinase activity.
GSD9D is a rare condition with only a handful of cases reported thus far. Symptoms usually present in adolescence or adulthood and are induced by intense exercise. The disorder is relatively mild and has a good prognosis, with some patients remaining asymptomatic even till late adulthood.
Diagnosis is confirmed based on clinical findings, laboratory investigations of blood and urine, muscle biopsies and genetic testing of the PHKA1 gene. Patients may benefit from physical therapy and can work with a metabolic nutritionist to optimize blood glucose concentrations. They are also advised to refrain from vigorous exercise and certain medications that can cause rhabdomyolysis such as succinylcholine and statins.