Charcot-Marie-Tooth Neuropathy Type 1 (CMT1) is an autosomal dominant demyelinating peripheral neuropathy characterized by distal muscle weakness and atrophy, along with slowed nerve conduction velocity. The disease typically has a slow progression, does not affect life expectancy, and manifests between the ages of 5 and 25. Approximately 70-80% of all CMT1 patients are CMT1A cases, which result from a duplication of the PMP22 gene region.
Hereditary Neuropathy with Liability to Pressure Palsies (HNPP), on the other hand, is an autosomal dominant disorder that presents with recurrent focal pressure neuropathies, such as carpal tunnel syndrome and peroneal palsy, usually appearing in individuals in their 20s to 30s.
The PMP22 gene, responsible for both conditions, is located on the short arm of chromosome 17 (17p11.2) and consists of 5 exons. While nearly all CMT1A patients exhibit a duplication of the PMP22 gene, approximately 80% of HNPP patients have a deletion of the PMP22 gene.