What is Hereditary Neuropathy With Liability To Pressure Palsies HNPP

Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) is a rare genetic peripheral nerve disorder characterized by recurrent episodes of numbness, tingling, and muscle weakness following minor physical pressure or trauma. It is caused by a deletion in the PMP22 gene, which leads to structural vulnerability in the protective covering of peripheral nerves.

What causes Hereditary Neuropathy with Liability to Pressure Palsies (HNPP)?

Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) is inherited in an autosomal dominant pattern. It is primarily caused by a deletion of a 1.5-megabase region on chromosome 17p12, which includes the PMP22 gene. This gene is vital for the production of myelin, the insulating sheath around nerves. When this gene is missing, nerves become excessively sensitive to compression, stretching, or repetitive movement, leading to "pressure palsies."

Who is affected by HNPP?

While exact prevalence is difficult to determine, Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) is estimated to affect approximately 2 to 5 in 100,000 individuals. Onset typically occurs in late adolescence or early adulthood, though symptoms can appear at any age. The condition affects both males and females equally, with no significant geographic clustering. At DiseaseMaps.org, 89 members are currently sharing their experiences with this condition, highlighting the importance of community support for those navigating this diagnosis.

What are the primary clinical features of HNPP?

The clinical presentation of Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) can vary significantly even within the same family. Common features include:

• Sudden, painless loss of sensation or muscle weakness in the distribution of a single peripheral nerve.


• Common sites of involvement include the peroneal nerve (causing foot drop) and the ulnar nerve (causing hand weakness).


• Episodes may last from a few minutes to several months.


• Most patients experience partial or full recovery between episodes, though recurring nerve damage can eventually lead to permanent deficits.

How is HNPP differentiated from other neuropathies?

Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) is distinct from Charcot-Marie-Tooth disease (CMT). While both involve the PMP22 gene, CMT is typically caused by a duplication of the gene, whereas Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) is caused by a deletion. Electromyography (EMG) and nerve conduction studies are critical for diagnosis, as they reveal characteristic generalized slowing of nerve conduction velocities even in nerves not currently showing symptoms.

Next steps

• Consult a neurologist or neuromuscular specialist for electrodiagnostic testing and genetic confirmation.


• Practice "nerve hygiene" by avoiding prolonged crossing of legs, leaning on elbows, or repetitive forceful movements.


• Join a community like DiseaseMaps.org to connect with others managing this condition.


• Work with a physical therapist to maintain muscle strength and range of motion.

Medical disclaimer: This information is for educational purposes only and should not replace professional medical advice, diagnosis, or treatment.

References

• NIH Genetic and Rare Diseases Information Center (GARD): HNPP Overview


• Orphanet: Hereditary Neuropathy with Liability to Pressure Palsies


• OMIM (Online Mendelian Inheritance in Man): #162500


• Neuropathy Commons (Harvard Medical School)