Hereditary neuropathy with liability to pressure palsy

Symptoms and symptom onset vary; some individuals are diagnosed in childhood, others in adulthood, some report minor problems, whilst others experience severe discomfort and disability. In many cases, symptoms are mild enough to go unnoticed. The time period between episodes is known to vary between individuals. HNPP has not been found to alter the lifespan, although in some cases a decline in quality of life is noticed. Some sufferers (10–15%) report various pains growing in severity with progression of the disease. ==Causes==

HNPP is typically caused by autosomal dominant deletion of PMP22 (peripheral myelin protein 22 at locus 17p11.2). PMP22 displays haploinsufficiency, such that the normal copy of the gene's activity is insufficient to compensate for loss of function of the affected copy. PMP22 point mutations, such as the frameshift mutation Gly94fsX222 (c.281_282insG), can cause clinical overlap between PNPP and Charcot–Marie–Tooth disease type 1A. Missense, nonsense, and splice site mutations have been described. It is involved in maintaining the myelin sheath that surrounds peripheral nerves to facilitate conductivity. ==Diagnosis==

Diagnosis of HNPP is established via genetic testing. The diagnosis should be suspected in individuals who display the clinical syndrome, display abnormal nerve conduction study findings, and have known family history of HNPP. ==Treatment==

There is no current treatment, however management of HNPP can be done via: • Physical therapist • Occupational therapist • Ankle/foot orthosis • Wrist splint • Avoid repetitive movements ==Epidemiology==

HNPP is a rare disorder. Partly because it is so rare and partly because many people who have it only experience mild symptoms, it is difficult to tell what percentage of people have it. One range of estimates is from one in 50,000 up to about one in 33,333. In a study of newborns in Korea who all got a genetic test for the disorder, around one in 1,698 of the newborns had it. ==History==

Inherited peripheral nervous system disorders were first described by Charcot, Marie and Tooth (1886). De Jong (1947) first described HNPP in a Dutch family. Dyck and Lambert (1968) showed nerve conduction studies, and Chance et al. (1993) detected the chromosome deletion in most of the individuals with the HNPP condition. ==See also==