Symptoms of the late infantile form of type II glycogen storage disease are mainly due to functional impairment of skeletal muscle. Cardiac muscle can be involved in the late stage of the disease.
Case report: We report the cases of two siblings seven and 12 years old with type II glycogen storage disease. The initial symptoms were hypertrophic cardiomyopathy with Wolf-Parkinson-White syndrome.
Conclusion: Hypertrophic cardiomyopathy may be the form of presentation of the late infantile form of type II glycogen storage disease. The risk of sudden death is high.