Hereditary neuropathy with liability to pressure palsy (HNPP) is a disorder that affects peripheral nerves. This condition causes recurrent episodes of numbness, tingling, and/or loss of muscle function (palsy). An episode can last from several minutes to several months, but recovery is usually complete. Repeated incidents, however, can cause permanent muscle weakness or loss of sensation. The most common problem sites involve nerves in wrists, elbows, and knees. Symptoms usually begin during adolescence or early adulthood but may develop anytime from childhood to late adulthood. Symptoms vary in severity; many people never realize they have the disorder, while some people experience prolonged disability. This condition is caused by the loss of one copy of the PMP22 gene or alterations within the gene. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.