Increased intra- and interfamilial phenotypic variability in CMT4C has previously been attributed to the presence of cryptogenic modifiers or to the diversity of SH3TC2 protein function.5,7,8,35-37 Our own observations in the Sh3tc2−/− mouse model also suggest the presence of several vulnerability sites for potentially different pathomechanisms involved in CMT4C. This evidence concerns the gene SH3TC2 and Charcot-Marie-Tooth disease type 4C.