Determination of SMN2 Copy Numbers in Iranian Spinal Muscular Atrophy Patients Using Multiplex Ligation-Dependent Probe Amplification

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by homozygous deletion of the survival motor neuron gene 1 (SMN1) in more than 90% of patients. According to the age of onset and severity of the disease, SMA is classified into three groups: type I (severe), type II (intermediate) and type III (mild). As reported, the SMN2 gene, centromeric copy gene, showed correlation with severity of the disease. To determine genotypephenotype correlation, we studied 45 Iranian patients (15 SMA I, 10 SMA II, and 20 SMA III) using multiplex ligationdependent probe lification (MLPA) assay.14 out of 15 SMA I patients (93.3%) carried two copies of SMN2, while the remaining 6.7% carried three copies. Among the type II and type III, 30% of the type II and 10% of the type III SMA patients carried two copies of the gene, while 70% of the type II and 90% of the type III carried three or four copies of SMN2, respectively. This study showed that SMN2 copy number can effect on survival duration in SMA type I and ambulation conservation or loss in type III. Thus, investigation of SMN2 copy number could be an appropriate predictor for SMA disease types.