Abstract
DNA melting analysis for genotyping and mutation scanning of PCR products by use of high-resolution instruments with special "saturation" dyes has recently been reported. The comparative performance of other instruments and dyes has not been evaluated. A 110-bp fragment of the beta-globin gene including the sickle cell anemia locus (A17T) was amplified by PCR in the presence of either the saturating DNA dye, LCGreen Plus, or SYBR Green I. Amplicons of 3 different genotypes (wild-type, heterozygous, and homozygous mutants) were melted on 9 different instruments (ABI 7000 and 7900HT, Bio-Rad iCycler, Cepheid SmartCycler, Corbett Rotor-Gene 3000, Idaho Technology HR-1 and LightScanner, and the Roche LightCycler 1.2 and LightCycler 2.0) at a rate of 0.1 degrees C/s or as recommended by the manufacturer. The ability of each instrument/dye combination to genotype by melting temperature (Tm) and to scan for heterozygotes by curve shape was evaluated. Resolution varied greatly among instruments with a 15-fold difference in Tm SD (0.018 to 0.274 degrees C) and a 19-fold (LCGreen Plus) or 33-fold (SYBR Green I) difference in the signal-to-noise ratio. These factors limit the ability of most instruments to accurately genotype single-nucleotide polymorphisms by amplicon melting. Plate instruments (96-well) showed the greatest variance with spatial differences across the plates. Either SYBR Green I or LCGreen Plus could be used for genotyping by T(m), but only LCGreen Plus was useful for heterozygote scanning. However, LCGreen Plus could not be used on instruments with an argon laser because of spectral mismatch. All instruments compatible with LCGreen Plus were able to detect heterozygotes by altered melting curve shape. However, instruments specifically designed for high-resolution melting displayed the least variation, suggesting better scanning sensitivity and specificity. Different instruments and dyes vary widely in their ability to genotype homozygous variants and scan for heterozygotes by whole-amplicon melting analysis.
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