**2. Pathogenesis**

Spinal muscular atrophy is known to be genetic disorder that is inherited as an autosomal recessive disorder but some dominant or X-linked traits are reported. The pathological basis of SMA is abnormality of the large anterior horn cells in the spinal cord caused by deletion or mutation of the Survival Motor Neuron-1 (SMN1) gene located at chromosome region 5q.1 Absence of all or part of the SMN has been detected in 98% of patients with SMA18 and results in reduction of the full length protein necessary for proper function of the anterior horn cells.10,13 The decreased level of the SMN protein results in selective death of spinal motor neurons,31 with the severity of the disease being inversely proportional to the amount of the SMN in the anterior horn cells.1The severity of SMA ranges from total paralysis and need for ventilatory support to relatively mild muscle weakness.1, 32
