Bethlem myopathy is predominantly an autosomal dominant myopathy, classified as a congenital form of limb-girdle muscular dystrophy. There are two types of Bethlem myopathy, based on which type of collagen is affected.

Bethlem myopathy 1 (BTHLM1) is caused by a mutation in one of the three genes coding for type VI collagen. These include COL6A1,