CLCN1 and Myotonia: Another important limitation for the improvement of genotype-phenotype correlations has been the lack of a sufficient number of individuals carrying each mutation (23), in particular in the case of novel mutations [such as the very recent study that described seven novel CLCN1 mutations (68)], which makes the situation even more complex, not without mentioning all those cases that show myotonia or a myotonia-like phenotype but in which the mutation has not been found.