COL6A3 and Bethlem myopathy: Mutations in any of the three collagen 6A genes COL6A1, COL6A2 and COL6A3 result in Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) or phenotypes intermediate between UCMD and BM, characterised by a combination of distal laxity, proximal muscle weakness and joint contractures [5,6].