A rare genetic myotonic syndrome characterised by childhood onset of progressive and severe myotonia (with generalised muscular hypertrophy and progressive impairment of gait) short stature, skeletal abnormalities (including pectus carinatum, short, wedge-shaped thoracolumbar vertebrae, kyphoscoliosis, genu valgum, irregular femoral epiphyses) and mild to moderate intellectual deficiency. Facial dysmorphism and joint limitation are not associated. There have been no further descriptions in the literature since 1984. [from SNOMEDCT_US]