PMP22 and Charcot-Marie-Tooth disease type 1A: Charcot-Marie-Tooth neuropathy type 1A (CMT1A) is also most often associated with a tandem 1.5 Mb duplication of PMP22 [5]. PMP22 is a 40 kb gene that consists of six exons, of which two alternatively transcribed exons (1a and 1b) comprise the first exon of the gene [6, 7].