PMP22 and Charcot-Marie-Tooth disease: The most common genetic form of CMT is CMT1A, accounting for around half of all CMT patients and 70% of CMT1 patients in Western Europe.3 CMT1A is most commonly caused by a 1.5 Mb tandem duplication on chromosome 17p11.2-p12 that includes the peripheral myelin protein 22 gene (PMP22, here referred as PMP22d),4,5 a protein critical to the synthesis of myelin layers ensheathing the peripheral axons.