PMP22 and Charcot-Marie-Tooth disease: However, up to 12.3% of the cases of apparently-sporadic axonal neuropathy present have disease-causing variants in genes associated with Charcot-Marie-Tooth disease (CMT).33In suspected demyelinating forms of CMT without positive family history, the frequency of duplication of theperipheral myelin protein 22(PMP22) gene ranges from 20 to 90% of the cases.34, 35