Description Denon disease is a condition characterized by weakening of the heart muscle (cardiomyopathy); weakening of the muscles used for movement, called skeletal muscles, (myopathy); and intellectual disability. Males with Danon disease usually develop the condition earlier than females and are more severely affected. Signs and symptoms begin in childhood or adolescence in most affected males and in early adulthood in most affected females. Affected males, on average, live to age 19, while affected females live to an average age of 34. Cardiomyopathy is the most common symptom of Danon disease and occurs in all males with the condition. Most affected men have hypertrophic cardiomyopathy, which is a thickening of the heart muscle that may make it harder for the heart to pump blood. Other affected males have dilated cardiomyopathy, which is a condition that weakens and enlarges the heart, preventing it from pumping blood efficiently. Some affected men with hypertrophic cardiomyop...