Over 100 mutations spanning the SELENON (SEPN1) gene [32] have been associated with the autosomal recessive congenital Rigid Spine Muscular Dystrophy 1 (RSMD1; OMIM: 602771), with a prevalence of <1:1,000,000 (orpha.net) and a subset of cases of Myopathy, Congenital, With Fiber-Type Disproportion (CFTD; OMIM: 255310), jointly named SELENON (SEPN1)-myopathies [[33], [34], [35], [36]](www.LOVD.nl/SEPN1) due to the clinical overlap. Here, SELENON is linked to myopathy.