Amyotrophic lateral sclerosis 21 (ALS21) is a rare form of ALS characterized by muscle weakness in the throat, lower legs and forearms, usually beginning in adulthood. Distal refers to the fact that the muscles involved are those not close to the center of the body. Initial symptoms usually involve muscle weakness in the ankles, and possibly the hands, wrists, and shoulders. The muscles weakness may occur only one side of the body at first, but eventually may affect both sides. The affected individual may eventually have trouble walking or lifting his or her fingers. Other symptoms include a weak, breathy, or nasal voice and difficulty swallowing due to a weakness of muscles in the vocal cords and throat. It has been noted in at least some affected individuals that the vocal cord weakness may progress to respiratory failure.
ALS21 is caused by different changes or mutations in the matrin-3 gene (MATR3) on chromosome 5q31. It is inherited or passed through families in an autosomal dominant manner which means the individual only needs one copy of the affected gene from his or her parents to have this condition. Each child of an affected individual has a 50% chance of inheriting the changed gene and therefore the condition. A genetic counselor can provide a better understanding of the underlying genetics and recurrence risks. If you or a family member has been diagnosed with ALS21 talk with your doctor about the latest treatment options.