Neuronopathy, distal hereditary motor, type 2B(HMN2B; DHMN2B; HMND3)

MedGen UID:: 382017
•Concept ID:: C2608087
•: Disease or Syndrome

Synonyms:	Distal Hereditary Motor Neuronopathy, Type IIB; HMN IIB; NEURONOPATHY, DISTAL HEREDITARY MOTOR, AUTOSOMAL DOMINANT 3; NEURONOPATHY, DISTAL HEREDITARY MOTOR, HARDING TYPE IIB; NEUROPATHY, DISTAL HEREDITARY MOTOR, HARDING TYPE IIB

Gene (location): Gene(s) directly associated with this condition or phenotype.	HSPB1 (7q11.23)

Monarch Initiative:	MONDO:0012080
OMIM®:	608634

Definition

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.

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.

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. [from MedlinePlus Genetics]

Additional description

From OMIM
Autosomal dominant distal hereditary motor neuronopathy-3 (HMND3) is a slowly progressive adult-onset motor neuron disorder without sensory involvement. Weakness and atrophy of distal lower limb muscles begins in the third to sixth decade and progresses to the upper limbs 5 to 10 years later (Houlden et al., 2008). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal dominant distal HMN, see HMND1 (182960). http://www.omim.org/entry/608634

Clinical features

From HPO

Hyporeflexia of lower limbs

MedGen UID:: 371881
•Concept ID:: C1834696
•: Finding

Reduced intensity of muscle tendon reflexes in the lower limbs. Reflexes are elicited by stretching the tendon of a muscle, e.g., by tapping.

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Distal lower limb muscle weakness

MedGen UID:: 324514
•Concept ID:: C1836450
•: Finding

Reduced strength of the distal musculature of the legs.

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Areflexia of lower limbs

MedGen UID:: 347285
•Concept ID:: C1856694
•: Finding

Inability to elicit tendon reflexes in the lower limbs.

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Peripheral neuropathy

MedGen UID:: 18386
•Concept ID:: C0031117
•: Disease or Syndrome

Peripheral neuropathy is a general term for any disorder of the peripheral nervous system. The main clinical features used to classify peripheral neuropathy are distribution, type (mainly demyelinating versus mainly axonal), duration, and course.

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Paralysis

MedGen UID:: 105510
•Concept ID:: C0522224
•: Finding

Paralysis of voluntary muscles means loss of contraction due to interruption of one or more motor pathways from the brain to the muscle fibers. Although the word paralysis is often used interchangeably to mean either complete or partial loss of muscle strength, it is preferable to use paralysis or plegia for complete or severe loss of muscle strength, and paresis for partial or slight loss. Motor paralysis results from deficits of the upper motor neurons (corticospinal, corticobulbar, or subcorticospinal). Motor paralysis is often accompanied by an impairment in the facility of movement.

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Gait disturbance