Distal hereditary motor neuropathy, Jerash type

Distal hereditary motor neuropathy, Jerash type (also known as dHMN Jerash type or DSMA2) is a rare inherited neuromuscular disorder first described in families from the Jerash region of Jordan. It belongs to the group of distal hereditary motor neuropathies (dHMN), which are characterized by progressive weakness and wasting (atrophy) of muscles in the distal parts of the limbs — particularly the hands and feet. Unlike some other motor neuropathies, the Jerash type is distinguished by the presence of upper motor neuron signs, including pyramidal tract involvement with brisk reflexes and extensor plantar responses (Babinski sign), in addition to the lower motor neuron features of distal muscle weakness and atrophy. The disease typically presents in childhood or adolescence with progressive difficulty walking due to weakness and wasting of the lower leg muscles, often leading to foot drop and a steppage gait. Over time, the hands may also become affected, causing difficulty with fine motor tasks. Sensory function is generally preserved, distinguishing this condition from other hereditary neuropathies such as Charcot-Marie-Tooth disease. The combination of lower motor neuron signs (muscle wasting, weakness) with upper motor neuron signs (spasticity, hyperreflexia) can sometimes lead to diagnostic confusion with juvenile amyotrophic lateral sclerosis, though the Jerash type follows a much slower and more benign course. The condition is caused by mutations in the SIGMAR1 gene (also known as the sigma non-opioid intracellular receptor 1 gene) on chromosome 9p13. It follows an autosomal recessive inheritance pattern. There is currently no cure or disease-modifying treatment available. Management is supportive and symptomatic, including physical therapy, occupational therapy, orthotic devices (such as ankle-foot orthoses) to assist with mobility, and regular monitoring by a multidisciplinary team including neurologists and rehabilitation specialists.

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