There are well over 100 different genes that cause the collection of diseases collectively known as CMT.
The most common is a duplication on chromosome 17, called PMP22 and this causes CMT type 1a, which accounts for approximately 50% of all cases. The next most common is type 1x, followed by 2a and 1b. These make up 40% of the rest, with the final 10% making up all the other types.