PMP22 and hereditary neuropathy with liability to pressure palsies: Moreover, PMP22 small mutations are also related to hereditary neuropathy with pressure palsies (HNPP), an inherited peripheral neuropathy caused by a deletion of PMP22 or pathogenic variant of PMP22. PMP22 small insertion mutations are rare and only 6 cases have been reported according to the Human Gene Mutation Database (HGMD) (http://www.hgmd.cf.ac.uk).