Nested PCR Amplification Secures DNA Template Quality and Quantity in Real-time mCOP-PCR Screening for SMA.

Background: Spinal Muscular Atrophy (SMA) is a common autosomal recessive disorder caused by SMN1 gene deletion. SMA has been considered an incurable disease. However, a newly-developed antisense oligonucleotide drug, nusinersen, brings about a good outcome to SMA patients in the clinical trials. Now, a screening for SMA is required for early diagnosis and early treatment so as to give a better clinical outcome to the patients. We have invented a new technology, mCOP-PCR, for SMA screening using dried blood spot (DBS) on the filter paper. One of the problems encountered in SMA screening is poor quality and quantity of DNA extracted from DBS.

Methods: DNA was extracted from DBS of six individuals. Fresh blood DNA of each individual had already been genotyped using PCR/RFLP. The fragments including the sequence of SMN1/SMN2 exon 7 were pre-amplified with conventional PCR. To determine which pre-amplified product is a better template for the real-time mCOP-PCR, we did pre-amplification with a single PCR or pre-amplification with a nested PCR.

Results: The real-time mCOP-PCR using pre-amplified products with a single PCR brought about ambiguous results in some SMN1-carrying individuals. However, the results of real-time mCOP-PCR following pre-amplification with a nested PCR were completely matched with those of PCR-RFLP.

Conclusion: In our study on the real-time mCOP-PCR screening system for SMA, a nested PCR secured the DNA template quality and quantity, leading to unambiguous results of SMA screening.