To alleviate the limitations discussed above, we developed a novel PCR-based application – coamplification at lower denaturation temperature (COLD)-PCR [24], that preferentially enriches minority alleles from mixtures of wild-type and mutation-containing sequences, irrespective of mutation type and location within the amplicon. COLD-PCR amplification yields amplicons containing enriched proportions of mutant (or variant) alleles, thus permitting the discrete detection and identification of minority alleles by downstream applications.
As PCR is typically an integral step in most genetic analyses, COLD-PCR can be used in place of PCR as a fundamental platform to improve the sensitivity of downstream or combinatorial technologies, including techniques such as Sanger sequencing, pyrosequencing, next-generation sequencing, mutation scanning and mutation genotyping. COLD-PCR is one of relatively few methods that are capable of simultaneously enriching both known and unknown mutations [23]; as such, COLD-PCR is highly advantageous owing to its ability to enrich nearly all low-abundance mutations, regardless of whether they are known or unknown mutations [24,25].
The unique attribute of COLD-PCR is that the selective enrichment of low-abundance mutations (or variants) within a target amplicon is achieved by exploiting a small, but critical and reproducible, difference in amplicon melting temperature (Tm). A single nucleotide variation or mismatch at any position along a double-stranded DNA sequence changes the amplicon Tm. The Tm for amplicons up to 200 bp in length may vary by approximately 0.2–1.5°C and is dependent on the sequence composition [26]. Just below the Tm there is a critical denaturation temperature (Tc) wherein PCR efficiency drops abruptly as a result of the limited number of denatured amplicons. This difference in PCR efficiency, at specifically defined denaturation temperatures, can be used to selectively enrich minority (or low-abundance mutant) alleles throughout the course of PCR.