molecular analysis of the smn1 and naip genes in patients with spinal muscular atrophy

proximal spinal muscular atrophy (sma) is one of the most common autosomal recessive disorders. sma has an estimated incidence of 1 in 10,000 live births. the clinical picture of sma is quite variable and childhood sma has been classified into 3 types. type i, werdnig-hoffmann disease, is the most acute and severe, with an onset before the age of 6 months and death usually occurring before the age of 2. type ii has an onset before the age of 18 months, and death after 2 years. type iii, kugelberg- welander disease, is the mild form of sma, with an onset after 18 months of age. peripheral blood samples from the patients were obtained after informed consent and the genomic. analysis of smn1 exons 7 and 8 deletions: pcr products of exon 8 from smn1 and smn2 were readily distinguishable by the presence of the recognition site for ddei, for exon 7, a mismatched downstream oligonucleotide primer, directly adjacent to the variant site that contains the restriction site to create drai site in the pcr product of smn2 exon 7. analysis of naip exons 5 and 6 deletions: for detection of naip gene, exons 5 and 6 were amplified. the telomeric naip can be distinguished from its centromeric pseudogene counterpart by pcr analysis for the presence or absence of exon 5, which exists only within the functional telomeric gene. deletion of the smn in the absence of naip is sufficient to give the sma phenotype. it observs a strong correlation between telomeric naip deletion and the severity of sma. the rate of consanguineous marriages by the sma family is about 97%, which is very high compared with other diseases. it suggests a low frequency of affected smn allele among the non-consanguineous marriages in our population however, there is no data regarding the real incidence of smn deletion in iran. thus, the gene-dosage test would be useful in such cases. the available molecular genetic tests seem to be extremely useful for sma diagnosis in iran.