Hereditary infantile motor axonal neuropathy mimicking SMA: A case report

Spinal muscular atrophy (SMA) is a group of allelic autosomal recessive genetic disorders characterized by progressive motor neuron loss, symmetrical weakness, and skeletal muscle atrophy. It is traditionally classified as a pure lower motor neuron disorder, for which currently definitive diagnosis is possible by molecular genetic testing. The problem arises when an infant presents clinically like SMA but is negative for survival motor neuron gene. A 3-month-old infant presented with paucity of limb movement and weak cry. Clinical presentation was suggestive of spinal muscular atrophy type I but genetic test for exon 7 deletion on survival motor neuron gene on chromosome 5 was negative. Detailed investigation revealed this a case of infantile motor axonal neuropathy. Two years follow-up has revealed partial recovery in limb movements and of bulbar function. There is paucity in neurology literature of such cases and the importance of genetic studies is hence emphasized.