Birth defects of the muscles can occur alone or as part of a syndrome.
The pectoralis major muscle (the major muscle in the chest, sometimes called the "pecs" in adults) can be partly developed or missing altogether. This defect can occur alone or with various hand, breast, or nipple abnormalities, as in Poland syndrome. The cause of most of these types of muscle disorders is unknown.
One or more layers of the abdominal muscles may be missing at birth, as in prune-belly syndrome. In this disorder, the missing layers of abdominal muscles cause the abdominal wall to have a wrinkled appearance, the testes do not descend into the scrotum (cryptorchidism) in boys, and/or urinary tract defects develop. The cause of prune-belly syndrome is not clear.
Before birth, doctors are sometimes able to diagnose these defects during an ultrasound.
After birth, doctors can identify the defects during a physical examination.
