Strong evidence indicates that CMTX is caused by loss of function of Cx32 (Shy et al., 2007; Sargiannidou et al., 2009): a CMTX phenotype is present in Cx32-null mice (Scherer et al., 1998); and this can be rescued by re-expression of Cx32 targeted only to Schwann cells (Scherer et al., 2005; Sargiannidou et al., 2015). Here, GJB1 is linked to X-linked Charcot-Marie-Tooth disease.