ABSTRACT
In this study we examined the deletion of SMN and NAIP genes in 60 Tunisian families There were 35 patients with type I SMA. 18 with type II SMA, 6 with type Ill SMA and 1 with type IV SMA .The age of onset was before 6 months for type I, between 6 months and 2 years for type II. between 2 years and 17 years for type III and 30 years for type IV. Exon 7 of SMN 1 gene was homozygously deleted in 95% [57/60] of SMA patients. There was a higher frequency of homozygous absence of SMN I in type I and type 11 [100% and 94% respectively] than in type III [66,7%]. SMN 1 exon 8 was undetectable in 88%[53/60] of patients .The case type II patient with homozygous deletion of SMN I exon 7 and not exon 8 was tested for the presence of a hybrid SMN gene. This patient showed in the second PCR a SMN I exon 8 product by restriction site assay indicating that a gene conversion event had occurred. All parents' individuals retained one copy of their SMN I gene. Exon 5 of NAIP gene was homozygously deleted in 58% [35/60] of patients [77% in type I [27/35], 27, 7% in type 11 [5/18], 50% [3/6] in type III [Table 1]. No patient had a deletion in NAIP gene without a deletion in the SMN1 gene. Homozygous deletion of NAIP exon 5 was detected in 1 parent. Our results show that the incidence of NAIP deletion is higher in the more severe SMA cases