Benign autosomal dominant myopathy, also called Bethlem myopathy, is a rare form of slowly progressive muscular dystrophy. This means that over time muscle fibers do not function correctly, and the muscle weakens. Fewer than 100 cases have been reported. This condition is autosomal dominant, meaning that is it passed from parent to child, and if one parent has it there is a 50% chance their child will have it as well. Benign autosomal dominant myopathy typically presents during the first few years of life, around age 5. There is no specific treatment for this condition, but it is benign, and thus many people with this condition only experience mild muscle weakness, and even at old age, patients are only minimally impaired.