GJB1 and Charcot-Marie-Tooth disease: Despite the genetic heterogeneity underlying CMT, to date up to 90% of all genetically confirmed cases across different cohorts are reportedly due to mutations in only 4 genes—PMP22 duplication/deletion and mutations in PMP22, GJB1, MFN2, and MPZ—while up to 40% of patients remain genetically undiagnosed.3, –, 5 This is not surprising if one considers that, until recently, molecular diagnosis of CMT has relied on multiplex ligation-dependent probe amplification (MLPA) for chr17p12 and conventional Sanger sequencing of these major causative genes.