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 genotype-phenotype correlation, we studied 45 iranian patients (15 sma i, 10 sma ii, and 20 sma iii) using multiplex ligation-dependent probe amplification (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.