Mutations in the COL6A1, COL6A2, and COL6A3 genes result in either the absence or malformation of the microfibrils, causing a spectrum of muscle disorders: Bethlem myopathy (BM, MIM 158810), Ullrich congenital muscular dystrophy (UCMD, MIM 254090), and myosclerosis myopathy (MM, MIM 255600). The gene discussed is COL6A3; the disease is Ullrich congenital muscular dystrophy.