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Distal hereditary motor neuropathy, type II

Distal hereditary motor neuropathy, type II

Reviewed August 2009

What is distal hereditary motor neuropathy, type II?

Distal hereditary motor neuropathy, type II is a progressive disorder that affects nerve cells in the spinal cord. It results in muscle weakness and affects movement, primarily in the legs.

Onset of distal hereditary motor neuropathy, type II ranges from the teenage years through mid-adulthood. The initial symptoms of the disorder are cramps or weakness in the muscles of the big toe and later, the entire foot. Over a period of approximately 5 to 10 years, affected individuals experience a gradual loss of muscle tissue (atrophy) in the lower legs. They begin to have trouble walking and running, and eventually may have complete paralysis of the lower legs. The thigh muscles may also be affected, although generally this occurs later and is less severe.

Some individuals with distal hereditary motor neuropathy, type II have weakening of the muscles in the hands and forearms. This weakening is less pronounced than in the lower limbs and does not usually result in paralysis.

How common is distal hereditary motor neuropathy, type II?

The prevalence of distal hereditary motor neuropathy, type II is unknown. At least 25 affected families have been identified worldwide.

What genes are related to distal hereditary motor neuropathy, type II?

Mutations in the HSPB1 and HSPB8 genes cause distal hereditary motor neuropathy, type II. These genes provide instructions for making proteins called heat shock protein beta-1 and heat shock protein beta-8. Heat shock proteins help protect cells under adverse conditions such as infection, inflammation, exposure to toxins, elevated temperature, injury, and disease. They block signals that lead to programmed cell death. In addition, they appear to be involved in activities such as cell movement (motility), stabilizing the cell's structural framework (the cytoskeleton), folding and stabilizing newly produced proteins, and repairing damaged proteins. Heat shock proteins also appear to play a role in the tensing of muscle fibers (muscle contraction).

Heat shock protein beta-1 and heat shock protein beta-8 are found in cells throughout the body and are abundant in nerve cells. In nerve cells, heat shock protein beta-1 helps to organize a network of molecular threads called neurofilaments that maintain the diameter of specialized extensions called axons. Maintaining proper axon diameter is essential for the efficient transmission of nerve impulses. The function of heat shock protein beta-8 is not well understood, but studies have shown that it interacts with heat shock protein beta-1.

The HSPB1 and HSPB8 gene mutations that cause distal hereditary motor neuropathy, type II change single protein building blocks (amino acids) in the protein sequence. If either protein is altered, they may be more likely to cluster together and form clumps (aggregates). Aggregates of heat shock proteins may block the transport of substances that are essential for the proper function of nerve axons. The disruption of other cell functions in which these proteins are involved may also contribute to the signs and symptoms of distal hereditary motor neuropathy, type II.

Read more about the HSPB1 and HSPB8 genes.

How do people inherit distal hereditary motor neuropathy, type II?

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

Where can I find information about diagnosis or management of distal hereditary motor neuropathy, type II?

These resources address the diagnosis or management of distal hereditary motor neuropathy, type II, and may include treatment providers.

You might also find information on the diagnosis or management of distal hereditary motor neuropathy, type II, in Educational resources and Patient support.

General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.

To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.

Where can I find additional information about distal hereditary motor neuropathy, type II?

You may find the following resources about distal hereditary motor neuropathy, type II, helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for distal hereditary motor neuropathy, type II?

  • distal hereditary motor neuronopathy, type II

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines and How are genetic conditions and genes named? in the Handbook.

What if I still have specific questions about distal hereditary motor neuropathy, type II?

Where can I find general information about genetic conditions?

What glossary definitions help with understanding distal hereditary motor neuropathy, type II?

acids ; atrophy ; autosomal ; autosomal dominant ; axons ; big toe ; cell ; contraction ; cytoskeleton ; diameter ; distal ; gene ; hereditary ; infection ; inflammation ; inherited ; injury ; motor ; neuropathy ; prevalence ; protein ; protein sequence ; shock ; teenage ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

See also Understanding Medical Terminology.

References (6 links)

 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

 
Reviewed: August 2009
Published: December 22, 2014