Distal spinal muscular atrophy type 3

Distal spinal muscular atrophy type 3 (DSMA3), also known as distal hereditary motor neuronopathy type III or HMN III, is a rare genetic neuromuscular disorder characterized by progressive weakness and wasting (atrophy) of muscles in the distal parts of the limbs, particularly the hands and feet. It belongs to the group of distal spinal muscular atrophies, which are caused by degeneration of the lower motor neurons in the spinal cord without sensory nerve involvement, distinguishing them from hereditary motor and sensory neuropathies (Charcot-Marie-Tooth disease). The disease primarily affects the peripheral nervous system and skeletal muscles. Key clinical features include slowly progressive weakness and atrophy of the distal muscles of the lower limbs, often beginning in childhood or adolescence, with later involvement of the hands and forearms. Patients may experience difficulty with fine motor tasks, foot drop, and gait abnormalities. Unlike some forms of Charcot-Marie-Tooth disease, sensory function is typically preserved, and nerve conduction studies show normal sensory responses with reduced motor amplitudes or evidence of denervation on electromyography. There is currently no cure or disease-modifying treatment for DSMA3. Management is supportive and symptomatic, including 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 if they develop. The disease generally follows a slowly progressive course, and many affected individuals maintain ambulation into adulthood, though functional limitations may increase over time.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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