Detection of mutations by flow cytometric melting point analysis of PCR products

Exploring the possibilities offered by flow cytometric microbead analyses for the detection of genetic alterations, an assay based on the dependence of the melting point of double-stranded DNA molecules on their length has been developed, making use of PCR products carrying biotin and fluorescent moiety on their two ends. The samples of different length PCR products immobilized on streptavidine coated microbeads are heat-treated in the presence of formamide at temperatures between the melting point of the longer and that of the shorter PCR product, when the mean fluorescence intensity of the beads carrying the shorter molecules decreases as a result of denaturation, as opposed to the sample containing the longer product. The efficacy and sensitivity of the method is demonstrated in the case of the assessment of the degree of triplet expansion in Huntington's disease. Its utility for the detection of point mutations in heterozygous clinical samples is shown in the case of the BRCA1 gene. The assay is simple and may be offered for the purposes of clinical diagnostics of a number of genetic conditions. These include screening of samples for triplet expansions and SNPs predisposing for particular pathological or pharmacogenomic conditions. In general, the method described herein is offered for the diagnosis of any pathological condition where the length of a genomic or cDNA sequence is expected to be different from that of the normal allele.