Distal hereditary motor neuropathy

Distal Hereditary Motor Neuropathy Distal hereditary motor neuropathy (dHMN) is a group of rare genetic disorders characterized by progressive muscle weakness and atrophy, primarily affecting the distal muscles of the limbs. This condition is part of a broader category of disorders known as hereditary motor and sensory neuropathies (HMSN), but it is distinguished by the absence of significant sensory involvement.

Classification

Distal hereditary motor neuropathy is classified into several subtypes based on genetic mutations, age of onset, and clinical features. The most common subtypes include:

• dHMN Type I: Characterized by adult onset and slow progression. It is often linked to mutations in the HSPB1 gene.
• dHMN Type II: Typically presents in childhood or adolescence with mutations in the HSPB8 gene.
• dHMN Type V: Associated with vocal cord paralysis and linked to mutations in the BSCL2 gene.

Symptoms

The primary symptoms of dHMN include:

• Progressive muscle weakness and wasting, particularly in the hands and feet.
• Difficulty with fine motor skills, such as buttoning clothes or writing.
• Foot drop, leading to a high-stepping gait.
• Muscle cramps and fasciculations.

Diagnosis

Diagnosis of dHMN involves a combination of clinical evaluation, family history, and genetic testing. Electromyography (EMG) and nerve conduction studies are used to assess the extent of motor neuron involvement.

Genetic Basis

Distal hereditary motor neuropathy is caused by mutations in various genes that are crucial for motor neuron function. Some of the genes implicated in dHMN include:

• HSPB1: Mutations in this gene are associated with dHMN Type I.
• HSPB8: Linked to dHMN Type II.
• BSCL2: Associated with dHMN Type V and Silver syndrome.

Treatment

Currently, there is no cure for distal hereditary motor neuropathy. Treatment focuses on managing symptoms and improving quality of life. This may include:

• Physical therapy to maintain muscle strength and flexibility.
• Occupational therapy to assist with daily activities.
• Orthotic devices to support weakened limbs.
• Pain management strategies for muscle cramps.

Research and Future Directions

Ongoing research aims to better understand the genetic and molecular mechanisms underlying dHMN. Advances in gene therapy and neuroprotective strategies hold promise for future treatments.

See Also

• Charcot-Marie-Tooth disease
• Spinal muscular atrophy
• Motor neuron disease

External Links

• National Organization for Rare Disorders
• [Muscular Dystrophy Association](https://www.mda.org)

NIH genetic and rare disease info

• NIH info on Distal hereditary motor neuropathy

Distal hereditary motor neuropathy is a rare disease.