Condition: Danon Disease

Danon disease is a rare genetic disorder characterized by an X-linked dominant inheritance pattern, as a result of which males are more severely affected than females. Among boys, the key features are diseased heart muscle (cardiomyopathy), weakness of the body muscles (skeletal myopathy) and intellectual disability ranging from mild learning problems to mental retardation. In many males, the disease progresses until a heart transplant is required or death occurs in the second to third decade of life. Females are also affected, although usually more mildly, and often onset is delayed until they reach adulthood. Other features include heart arrhythmias, which can lead to a need for medications or a pacemaker, and eye disease affecting the retina; the retinal disease does not always affect vision. Danon disease is not usually evident at birth unless blood tests are done in a suspected case (i.e. a son born to a mother known to have the disease).