A rare, genetic neuromuscular disease characterized by permanent myotonia, mask-like facies (with blepharospasm, narrow palpebral fissures, small mouth with pursed lips and puckered chin) , and chondrodysplasia (variably manifesting with short stature, pectus carinatum, kyphoscoliosis, bowing of long bones, epiphyseal, metaphyseal, and hip dysplasia).