MPZ and Charcot-Marie-Tooth disease type 1B: In a quite recent sleep study on 61 patients with CMT1 (dominant HMSN), 34 suffered from HMSN-1A, 10 from HMSN-1B (OMIM #118200) caused by heterozygous mutation in the gene encoding myelin protein zero (MPZ) located on chromosome 1, and 17 had HMSN-X1 (OMIM #302800) caused by hemizygous or heterozygous mutation in the GJB1 (Gap Junction Beta 1) gene located on chromosome X. All patients had subjective reduced nocturnal sleep quality, daytime hypersomnolence, and significant fatigue.