Hereditary motor and sensory neuropathies (HMSN) is a name sometimes given to a group of different

neuropathies Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...

which are all characterized by their impact upon both afferent and

efferent Efferent may refer to: Anatomical structures Meaning 'conveying away from a center': *Efferent arterioles, conveying blood away from the Bowman's capsule in the kidney *Efferent nerve fiber, carries nerve impulses away from the central nervous sy ...

neural In Biology, biology, the nervous system is the Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sensory information by transmitting action potential, signals to and from different parts of its ...

communication. HMSN are characterised by atypical neural development and degradation of

neural tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain ...

. The two common forms of HMSN are either hypertrophic demyelinated nerves or complete atrophy of neural tissue. Hypertrophic condition causes neural stiffness and a

demyelination A demyelinating disease is any disease of the nervous system in which the myelin sheath of neurons is damaged. This damage impairs the conduction of signals in the affected nerves. In turn, the reduction in conduction ability causes deficiency i ...

of nerves in the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain ...

, and atrophy causes the breakdown of

axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...

s and

neural cell A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. No ...

bodies. In these disorders, a patient experiences progressive

muscle atrophy Muscle atrophy is the loss of skeletal muscle mass. It can be caused by immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system. Muscle atrophy leads to muscle weakness ...

and sensory neuropathy of the extremities. The term "hereditary motor and sensory neuropathy" was used mostly historically to denote the more common forms

Charcot–Marie–Tooth disease Charcot–Marie–Tooth disease (CMT) is a hereditary motor and sensory neuropathy of the peripheral nervous system characterized by progressive loss of muscle tissue and touch sensation across various parts of the body. This disease is the mos ...

(CMT). With the identification of a wide number of genetically and phenotypically distinct forms of CMT, the term HMSN is now used less frequently.

Symptoms and signs

Neuropathy disorders usually have onset in childhood or young adulthood. Motor symptoms seem to be more predominant than sensory symptoms. Symptoms of these disorders include: fatigue, pain, lack of balance, lack of feeling, lack of reflexes, and lack of sight and hearing, which result from muscle atrophy. Patients can also have high arched feet, hammer toes, foot drop, foot deformities, and scoliosis. These symptoms are a result of severe muscular weakness and atrophy. In patients with demyelinating neuropathy, symptoms are due to slow nerve conduction velocities; however people with axonal degradation have average-to-normal nerve conduction velocities.

Causes

All hereditary motor and sensory neuropathies are inherited. Chromosomes 17 and 1 seem to be the most common chromosomes with mutations. The disease can be inherited in an autosomal dominant, autosomal recessive or X-linked manner.

Diagnosis

Patients with hereditary motor and sensory neuropathies are diagnosed through a physical evaluation that looks for muscle atrophy, weakness, and sensory responses.American Association of Neuromuscular & Electrodiagnostic Medicine. (2013). Hereditary Motor Sensory Neuropathy. http://www.aanem.org/Education/Patient-Resources/Disorders/Hereditary-Motor-Sensory-Neuropathy.aspx Accessed on 11/10/13. In addition to this, electromyography and motor nerve conduction tests can help clinicians decide what type of motor and sensory neuropathy it is and how severe the disease is. Final confirmation can come through

genetic testing Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...

Classification

Charcot–Marie–Tooth disease was first described in 1886 by

Jean-Martin Charcot Jean-Martin Charcot (; 29 November 1825 – 16 August 1893) was a French neurology, neurologist and professor of anatomical pathology. He worked on hypnosis and hysteria, in particular with his hysteria patient Louise Augustine Gleizes. Charcot ...

Pierre Marie Pierre Marie (9 September 1853 – 13 April 1940) was a French neurologist and political journalist close to the SFIO. Medical Career After finishing medical school, he served as an interne (1878), working as an assistant to neurologist Jean- ...

, and independently

Howard Henry Tooth Howard Henry Tooth (1856–1925) was a British neurologist and one of the discoverers of Charcot–Marie–Tooth disease. Early life and education Dr. Tooth was born on 22 April 1856 to Frederick Tooth of Hove, Sussex, England. He attended Ru ...

. In the 1950s, further classification occurred and separated patients into two distinct groups. Group one was characterized by slow nerve conduction velocities and demyelinating neuropathy. Group two was characterized by mostly normal nerve conduction velocities and degeneration of axons. In 1968, HMSN were classified again into seven groups:

Treatment

There is currently no known pharmacological treatment to hereditary motor and sensory neuropathy. However, the majority of people with these diseases are able to walk and be self-sufficient. Some methods of relief for the disease include physical therapy, stretching, braces, and sometimes orthopedic surgery. Since foot disorders are common with neuropathy, precautions must be taken to strengthen these muscles and use preventative care and physical therapy to prevent injury and deformities.

Prognosis

Hereditary motor and sensory neuropathy are relatively common and are often inherited with other neuromuscular conditions, and these comorbidities cause an accelerated progression of the disease. Most forms of HMSN affect males earlier and more severely than females, but others show no predilection to either sex. HMSN affects all ethnic groups, with the most common forms having no racial predilection, but other recessively inherited forms tending to impact specific ethnic groups. Onset of HMSN is most common in early childhood, with clinical effects occurring before the age of 10, but some symptoms are lifelong and progress slowly. Therefore, these symptoms do not appear until later in life.

References

External links

{{PNS diseases of the nervous system Neurological disorders Sensory systems Neurogenetic disorders nl:Hereditaire motorische en sensorische neuropathieën