Patient B is a 51-year-old woman, carrying a (CCTG)36CNBP uninterrupted allele, whose clinical signs reflect progressive proximal leg weakness and muscle pain, iperCKemia (>200 U/L), no clinical or EMG myotonia, insulin resistance, and hypovitaminosis D. Her father died of respiratory insufficiency at 69 years old and was reported to be affected by a not defined muscular dystrophy. The gene discussed is INS; the disease is Myotonia.