Fifty-three patients of unknown genetic diagnosis were selected from 265 unrelated individuals with demyelinating CMT in whom 175 have PMP22 duplication, 26 have a mutation in the gap junction protein beta 1 (GJB1) gene and 11 have a mutation in the myelin protein zero (MPZ) gene. The gene discussed is PMP22; the disease is Charcot-Marie-Tooth disease.