Background: Spinal muscular atrophy is a group of α-motor neuron. There are three genes for this disorder, of which SMN with two copies centromeric and telomeric is the most important one. In 95% of SMA patient’s telomeric copy of SMN is homozygously deleted and the remaining has point mutation in this gene. In most of the patient’s, exon 7 & 8 of SMN1 is deleted. Therefore, analysis of SMN1 mutation is very important for carrier detection. The aim of this study was analysis of SMN1 mutation and determination of its frequency among Iranian patients. Materials and methods: After genetic counseling and estimation of clinical symptoms of patients based on SMA consortium, molecular analysis based on PCR-RFLP has been performed.

Results: Frequency of consanguineous marriage in our study was 60%, while most of the patients were come from central and northern part of Iran. Of 243 families, 195 were categorized as type I, 30 as type II, and 18 as type III. Analysis of exon 7 deletion among families with live affected child showed that 94% of families with SMA type I, 95% in type II families and 100% in SMA type III had homozygous deletion. In prenatal diagnosis, twenty one of ninety two (22.8%) fetal samples were found to be affected and these pregnancies were terminated. Conclusion: The frequency of homozygous deletion of exon 7 of SMN1 was 94%. This is in agreement with Western Europe, China, Japan, and Kuwait.