Colorimetric Assay for Exon 7 SMN1/SMN2 Single Nucleotide Polymorphism Using Gold Nanoprobes.

Introduction: Proximal spinal muscular atrophy (SMA) is one of the most significant neurodegenerative diseases amongst the autosomal-recessive genetic disorders which is caused by the absence of protein survival of motor neuron (SMN). A critical nucleotide difference in SMN2 compared to SMN1 gene leads to an inefficient protein. Hence, homozygous lack of SMN1 provides a progressive disease. Due to the high prevalence, up to now, several molecular diagnostic methods have been used which most of them are lengthy, expensive, and laborious.

Methods: In the present study, we exploited a gold nanoprobe-based method for semi-quantitative SMN1 gene dosage analysis compared to SMN2. The assay was done under hybridization process between Au nanoprobes and different ratios of SMN1/SMN2 amplicons.

Results: UV-vis spectra indicated that after the salt addition, nanoprobes aggregated gradually and their peak shifted to longer wavelengths except in the stable target-nanoprobes hybridization. The results revealed that the homozygous genotype of SMN2 gene is distinguished from the heterozygous genotypes of SMN genes by the naked eye, whereas different ratio of heterozygous genotypes (SMN1/SMN2) are differentiated better from each other using peak analysis ratios.

Conclusion: The presented strategy is an alternative simple method for discrimination of homozygous deletion of SMN1 in less than 30 min. However, further evaluation of the assay using clinical samples is recommended prior to real-world use.