LMNA and potassium-aggravated myotonia: This study provides evidence that (1) p.(Arg89Cys) LMNA mutation causes a myopathy featuring PAM pathology, (2) RYR1 mutations may be an additional cause of autosomal dominant PAM with an unusual phenotype of tibial myopathy, and (3) the p.(Cys30071Arg) mutation in TTN gene responsible for hereditary myopathy with early respiratory features (HMERF) is associated with cardiac involvement.