SMN1 and NAIP genes deletions in different types of spinal muscular atrophy in Khuzestan province, Iran

Background: Spinal muscular atrophy (SMA) is the second most common lethal autosomal recessive disease. It is a neuromuscular disorder caused by degenerative of lower motor neurons and occasionally bulbar neurons leading to progressive limb paralysis and muscular atrophy. The SMN1 gene is recognized as a SMA causing gene while NAIP has been characterized as a modifying factor for the clinical severity and age at disease onset in SMA patients (SMA subtypes). The relationship between NAIP deletion and type of SMA remains to be clarified; we investigated this gene alteration in all types of SMA patients. Methods: Molecular analysis was performed on fifty patients with a clinical diagnosis of SMA in Khuzestan province. In addition to common PCR-RFLP analysis for exon 7 and 8 of SMN1 gene, as an internal control we analysed NAIP deletion with PCR of exon 5 of this gene in a multiplex PCR with exon 13 of it. Results: Homozygous-deletion frequency rate for the telomeric copy of SMN (SMN1) exon 7 in all types (type I, II, Ш) of SMA was approximately 90% and the frequency of deletion in exon 7 and 8 together in all types estimated about 70%. Moreover NAIP gene was deleted in about 60% of these patients and this shows deletion in 91% of type I SMA patients. The correlation between NAIP-deletion and SMN1 mutation showed a high frequency rate. Conclusion: In this study, high frequency of NAIP gene deletion in all type of disease shows the importance role of it in disease pathogenesis. High frequency of NAIP deletion in SMA type I, also shows the importance of the gene in type and severity of disease so it may be a modifier factor in severity of disease.