Duplications of PMP22 result in Charcot-Marie-Tooth type 1A (CMT1A), which is a condition characterized by distal muscle weakness and atrophy, sensory loss, and slow nerve conduction velocity. Age of onset is variable. Duplications of PMP22 account for the majority of (70-80%) cases of CMT. This condition is inherited in an autosomal dominant manner. This test does not test other genes that are associated with CMT. If this diagnosis is suspected and a duplication is not found, there are other laboratories that perform testing on additional genes associated with CMT.
Deletions of PMP22 result in Hereditary Neuropathy with Liability to Pressure Palsies (HNPP), which is a condition characterized by repeated focal neuropathies such as carpal tunnel syndrome and peroneal palsy with foot drop. Symptoms usually begin sometime during the second and third decade of life. 80% of cases are due to a deletion of PMP22, while the remaining 20% are due to a sequence variant. This condition is inherited in an autosomal dominant manner. This MLPA test detects deletions/duplications of PMP22 but no sequence variants.