COL6A1 and Ullrich congenital muscular dystrophy: Deficiency of collagen type VI (Col VI) caused by mutations of COL6 genes (COL6A1, COL6A2, and COL6A3) gives rise to three main muscle disorders: Bethlem myopathy (BM), Ullrich congenital muscular dystrophy (UCMD), and myosclerosis myopathy.