COL6A3 and Bethlem myopathy: Given this muscle MRI pattern strongly evocative of Bethlem myopathy and consistent with our clinical impression, and since causative variant(s) in the collagen 6 genes were not flagged by the interpretation of the whole genome sequencing data, we pursued follow-up long-read (Sanger) sequencing of COL6A1, COL6A2 and COL6A3 in a diagnostic laboratory in London.