We investigated the manifestations of CMT4C disease in a genetically homogeneous group of patients homozygous for the recently identified Gypsy founder mutation p.Arg1109X in SH3TC2. We observed a surprising degree of variation in age at onset, rate of progression, extent and severity of motor and sensory involvement, scoliosis, and cranial nerve involvement, suggesting that the phenotypic spectrum of CMT4C disease is much broader than the classical diagnostic criteria. Phenotype similarity in first degree relatives and increasing heterogeneity in more distantly related subjects point to the involvement of genetic modifiers, possibly variants in the genes encoding protein partners interacting with SH3TC2.