distal spinal muscular atrophy type 2 distal spinal muscular atrophy type 2 distal spinal muscular atrophy type 2 (dsma2), also known as jerash type distal hereditary motor neuropathy (hmnj), is a very rare childhood-onset genetic disorder characterised by progressive muscle wasting affecting lower and subsequently upper limbs. the disorder has been described in arab inhabitants of jerash region in jordan as well as in a chinese family. this article is about a genetic disorder linked to a defect in the sigmar1 gene. for other conditions with similar name, see spinal muscular atrophies. distal spinal muscular atrophy type 2other namesautosomal recessive distal spinal muscular atrophy type 2this condition is inherited in an autosomal recessive mannerspecialtyneurology the condition is linked to a genetic mutation in the sigmar1 gene on chromosome 19 (locus 19p13.3) and is likely inherited in an autosomal recessive manner.