CLCN1 and Myotonia: For example, the Arrested development of righting (Adr) mouse model of myotonia congenita develops myotonia due to homozygous loss-of-function mutation in the Clcn1 gene and features a predominance of oxidative fibers in most muscles18, while a chemically-induced experimental myotonia shifted fiber type from glycolytic to oxidative in rats19.