Overexpression of PMP22 via “gene dosage” is the widely proposed mechanism of myelin sheath defects and subsequent axonal loss and muscle atrophy in CMT1A, supported by findings of increased PMP22 protein [6,7] and messenger RNA in CMT1A patients in sural nerve biopsies [8]. Here, PMP22 is linked to Charcot-Marie-Tooth disease type 1A.