Myotonic muscular dystrophy, also known as MMD or Steinert’s disease, is the most common form of MD in adults. It occurs in 1/30,000 people. It occurs in males and females, with symptoms typically beginning any time from early childhood through adulthood.
One symptom of the disorder is myotonia, a condition in which muscles have trouble relaxing after use (prolonged spasm). The spasms are not painful. Other symptoms may include muscle weakness, slurred speech, difficulties swallowing, constipation, or abnormal heart beat (arrhythmia). MMD may also be associated with low immune system, cataracts, thyroid disorders, or diabetes.
Many men with MMD experience infertility and early onset of frontal baldness, while, women with MMD may have difficulties with childbirth due to weak muscles of the uterus. It is unusual for people with this form of MD to lose the ability to walk. However, braces or other assistive devices may become necessary. Although, about 50% of those with myotonic dystrophy have less than average intelligence, severe mental impairment is rare. Others will have average, or occasionally above average, intelligence.