Collagen XII myopathy with rectus femoris atrophy and collagen XII retention in fibroblasts

: Mutation in the collagen XII gene ( COL12A1 ) was recently reported to induce Bethlem myopathy. We describe a family affected by collagen XII‐related myopathy in 3 generations. Methods : Systematic interview, clinical examination, skin biopsies, and MRI of muscle were used. Results : The phenotype was characterized by neonatal hypotonia, contractures, and delayed motor development followed by resolution of contractures and a motor performance limited by reduced endurance. DNA analyses revealed a novel donor splice‐site mutation in COL12A1 (c.8100 + 2T>C), which segregated with clinical affection and abnormal collagen XII retention in fibroblasts. MRI disclosed a selective wasting of the rectus femoris muscle. Discussion: COL12A1 mutations should be considered in patients with a mild Bethlem phenotype who present with selective wasting of the rectus femoris, absence of the outside‐in phenomenon on MRI, and abnormal collagen XII retention in fibroblasts. Muscle Nerve 57 : 1026–1030, 2018