OBSOLETE: Distal spinal muscular atrophy

Distal spinal muscular atrophy (dSMA), also known as distal hereditary motor neuronopathy (dHMN), refers to a heterogeneous group of genetic disorders characterized by degeneration of motor neurons in the spinal cord, predominantly affecting the distal muscles of the limbs. The Orphanet entry 206713 is classified as OBSOLETE, meaning this particular grouping has been retired and its constituent conditions have been reclassified into more specific disease entities. Distal spinal muscular atrophies primarily affect the peripheral nervous system, leading to progressive weakness and wasting (atrophy) of muscles in the hands, feet, and lower legs. Unlike classical proximal spinal muscular atrophy (SMA), the distal forms spare the proximal muscles in early stages. Symptoms typically include difficulty walking, foot drop, hand weakness, and reduced deep tendon reflexes. Sensory function is generally preserved, which distinguishes these conditions from Charcot-Marie-Tooth disease, though clinical overlap can occur. Multiple genetic subtypes have been identified, each with distinct causative genes and inheritance patterns, including autosomal dominant and autosomal recessive forms. Because this Orphanet entry is obsolete, patients and clinicians should refer to the specific subtypes of distal hereditary motor neuronopathy for accurate genetic counseling and management information. Treatment remains largely supportive, including physical therapy, orthotic devices, and occupational therapy to maintain function and mobility. No disease-modifying therapies are currently approved for most dSMA subtypes.

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