PMP22 and Roussy-Lévy syndrome: Pathogenic variants in the <i>PMP22</i> gene can lead to hereditary peripheral demyelinating neuropathies of varying severity, including hereditary neuropathy with liability to pressure palsies (HNPP), Charcot-Marie-Tooth disease types 1A and 1E (CMT1A, CMT1E), Roussy-Lévy syndrome, and Dejerine-Sottas disease (DSS).