Danon disease is an X-linked disorder caused by deficiency of lysosomal-associated membrane protein Lamp2 and resulting in cardiomyopathy, myopathy, and mental retardation. Originally Danon disease was classificatied as a variant of glycogen storage disease II (Pompe disease). However, at present, it is considered that Danon disease is not a glycogen storage disease because the disease is caused by the primary deficiency of a lysosomal membrane protein instead of a glycolytic enzyme and detailed pathological features are different from those of Pompe disease.
