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Hereditary Neuropathy with Liability to Pressure Palsy (HNPP) is a peripheral neuropathy (disorder of the nerves).
HNPP is a nerve disorder that affects the peripheral nerves. The main effect of HNPP are pressure palsies. Pressure on the nerves can cause tingling sensations, numbness, pain, weakness, muscle atrophy, and even paralyzation of affected area.
In normal individuals these symptoms disappear quickly but in sufferers of HNPP even a short period of pressure can cause the symptoms to occur. These usually subside over an extended period of time . Palsies can last from minutes, day to weeks or even months or years.However repeated incidents can cause permanent muscle weakness.
HNPP evolves slowly with symptoms surfacing between usually in the late teens to early twenties (range 8 to 64 years).
The symptoms vary from person to person. Some report minor problems, whilst others experience severe discomfort and a moderate disability. In many cases the 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.
The nerves most commonly affected are the peroneal nerve at the fibular head (leg and feet), the ulnar nerve at the elbow (arm) and the median nerve at the wrist (palm, thumbs and fingers).
HNPP can be diagnosed by a genetic blood test. Measuring nerve conduction velocities may also give an indication of the presence of the disease.
HNPP is an autosomal dominant genetic disease. A mutation in one copy of the gene PMP-22 (Peripheral myelin protein 22, 17p11.2) that makes the peripheral myelin protein causes haploinsufficiency, where the activity of the normal gene is insufficient to compensate for the loss of function of the other gene. The lack of myelin causes the nerves to be poorly insulated and it is this that causes symptoms. On visualization the nerves have a sausage like appearance that blocks the nerve signals (hence the name 'tomaculous neuropathy' that is sometimes used for HNPP).
Both male and females are equally affected. A child has a 50% chance of inheriting the disease if one parent is a sufferer of the disease. It is estimated that it occurs in 2 to 5 in 100000 individuals.
Currently there are no effective treatments but it is a possible candidate for gene therapy. Currently simple adjustments to the individuals lifestyle are the best treatment in order to avoid excess pressure on the nerves. Avoiding repetitive injury of a nerve is important, as this makes the symptoms worse.
There are lots of common problems, mainly caused by focused pressure on the nerves :
Inherited peripheral nerve 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 slowing in families using electrophysiological studies. Chance et al. (1993) detected the chromosome deletion in most of the patients with HNPP.