MTM1 and myopathy: Centronuclear/myotubular myopathy may be caused by homozygous or compound heterozygous pathogenic variants in the gene BIN1, heterozygous pathogenic variants in the gene DNM2, or hemizygous pathogenic variants in MTM1. Muscle biopsy in these conditions reveals small, rounded myofibers with increased percentages of centrally located nuclei.