Distal hereditary motor neuropathy type 1

Distal hereditary motor neuropathy type 1 (dHMN1), also known as distal spinal muscular atrophy type 1 or spinal muscular atrophy, distal, autosomal recessive 1, is a rare inherited neuromuscular disorder characterized by progressive weakness and wasting (atrophy) of muscles in the distal parts of the limbs, particularly the hands and feet. Unlike other motor neuron diseases, dHMN1 predominantly affects the lower motor neurons without significant sensory nerve involvement, distinguishing it from hereditary motor and sensory neuropathies (such as Charcot-Marie-Tooth disease). The condition falls under the broader category of spinal muscular atrophies (ICD-10: G12.2). The disease primarily affects the peripheral nervous system, specifically the motor neurons that control voluntary muscle movement. Key clinical features include progressive distal muscle weakness beginning in the lower limbs, foot deformities such as pes cavus (high-arched feet), difficulty walking, and eventual involvement of the hands and forearms. Muscle wasting tends to progress slowly over years, and deep tendon reflexes may be reduced or absent in affected areas. Sensation typically remains intact, which is an important distinguishing feature. There is currently no cure or disease-modifying treatment for dHMN1. Management is supportive and symptomatic, focusing on physical therapy to maintain mobility and muscle strength, occupational therapy for hand function, orthotic devices such as ankle-foot orthoses to assist with walking, and surgical interventions for skeletal deformities when necessary. Genetic counseling is recommended for affected families. The prognosis varies, but the condition is generally slowly progressive and life expectancy is usually not significantly reduced.

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