Spinal muscular atrophy – determination of copy number of exon 7 and 8 in the SMN1 gene

Examination of SMN1 and SMN2 genes associated with spinal muscular atrophy (SMA) by MLPA method. This concerns an autosomal recessive disease that is most often associated with homozygous deletion of exon 7 in the SMN1 gene (almost 95% of all patients with SMA).

Spinal muscular atrophy (SMA) is a neuromuscular inherited disease. The cause of SMA in more than 95% of patients is a mutation in the SMN gene, with homozygous biallelic deletion of exon 7 in the SMN1 gene. The remaining patients include compound heterozygotes with a deletion in combination with a small intragenic mutation of the SMN1 gene and patients with an SMA phenotype not caused by a mutation in the SMN1 gene. It manifests as progressive muscle weakness and atrophy. The number of copies of the SMN2 gene does not affect the development of the disease. On the contrary, patients with multiple copies of the SMN2 gene have been shown to have milder manifestations of the disease. It is the second most common fatal AR childhood disease after cystic fibrosis, with an incidence of 1:6,000–10,000 live births and a heterozygous frequency of 1:40 to 1:60. The deletion of exons 7 and 8 in the SMN1 gene is detected by Multiplex Ligation-dependent Probe Amplification (MLPA). This method is not intended to detect point mutations.