Analysis Of Deletion Mutation In SMN I Gene For Spinal Muscular Atrophy In A Tertiary Care Centre, Kolkata

Abstract

The loss of lower motor neurons in the ventral horns of the spinal cord is the hallmark of spinal muscular atrophy (SMA), the second most prevalent autosomal recessive disorder in children. Some genes cause SMA. Among them, the mutation in the SMN1 gene is the most common, especially exon 7 and exon 8. SMN gene has at least one homologous but inverted copy in the chromosome. From newborns to adults, mutations in the SMN1 gene can impact people in a wide spectrum of severity. Types I, II, III, and IV are the four variations of SMA. The SMN2 gene can be found in each cell of certain individuals with SMA types II and III in three or more copies. The condition is less severe because of these numerous copies of the SMN2 gene. In our tertiary center, we have tried to find out the pattern of deletion and type in the patients. We investigated them depending on their clinical manifestation by PCR of exon 7 and exon 8 followed by RFLP with restriction enzymes DraI & DdeI respectively, for molecular diagnosis. Through molecular study, we have confirmed forty patients with deletions in the SMN1 gene. Among them twenty-five cases showed both deletions of exon 7 and exon 8, thirteen cases were detected with exon 7 deletion, and only two cases with deletion of exon 8.The patients with confirmed deletions were divided into three groups: 16 patients with type III, 19 patients with type II, and 5 patients with type I, based on the clinical symptoms and age of onset. It was commonly observed that the majority of the patient who showed both deletions had a severe phenotype, even if there was some overlap between the deletions detected and the type and severity of SMA.