Distal hereditary motor neuropathy type 7

Distal hereditary motor neuropathy type 7 (dHMN7), also known as HMN7 or distal spinal muscular atrophy type 7, is a rare inherited neuromuscular disorder characterized by progressive weakness and wasting (atrophy) of muscles in the distal extremities, with a distinctive involvement of the vocal cords. The disease is caused by mutations in the SLC5A7 gene (encoding the high-affinity choline transporter) or, in some families, has been linked to chromosome 2q14. It primarily affects the lower motor neurons in the spinal cord, leading to progressive distal muscle weakness predominantly in the hands and feet, along with vocal cord paralysis that can cause breathing difficulties and a hoarse or weak voice. Unlike many other forms of hereditary motor neuropathy, the vocal cord involvement is a hallmark feature that distinguishes dHMN7 from related conditions. The disease typically presents in young adulthood, though the age of onset can vary. Early symptoms often include difficulty with fine motor tasks in the hands, foot drop, and voice changes due to vocal cord paresis. Over time, muscle weakness may progress proximally but tends to remain most severe in the distal limbs. Sensory function is generally preserved, which distinguishes this condition from hereditary motor and sensory neuropathies (Charcot-Marie-Tooth disease). Electromyography (EMG) and nerve conduction studies typically show evidence of chronic denervation with preserved sensory nerve conduction. There is currently no cure or disease-modifying treatment for dHMN7. Management is supportive and multidisciplinary, focusing on physical therapy and occupational therapy to maintain mobility and function, orthotic devices for foot drop, and speech therapy or surgical interventions (such as vocal cord medialization) for vocal cord paralysis. Respiratory monitoring may be necessary in cases where vocal cord dysfunction compromises the airway. Genetic counseling is recommended for affected individuals and their families.

Common questions about Distal hereditary motor neuropathy type 7