Large-scale SNP Scoring from Unamplified Genomic DNA

Discoveries from the Human Genome Project (HGP) continue to spur changes in medical technology that will lead to new diagnostic procedures in the clinical lab. As more single nucleotide polymorphisms (SNPs) are discovered and correlated to human diseases, demands for genetic tests will increase. The enormity of the number of SNPs makes developing inexpensive and reliable high-throughput methods for SNP scoring imperative. High-throughput screening (HTS) means, at a minimum, a production rate of thousands of assays per day. Ideally, the technology will be easy, inexpensive and amenable to automation. The Invader assay offers a simple diagnostic platform to detect single nucleotide changes with high specificity and sensitivity from unamplified, genomic DNA. The Invader assay uses a structure-specific 5' nuclease (or flap endonuclease) to cleave sequence-specific structures in each of two cascading reactions. The cleavage structure forms when two synthetic oligonucleotide probes hybridise in tandem to a target. One of the probes cycles on and off the target and is cut by the nuclease only when the appropriate structure forms. These cleaved probes then participate in a second Invader reaction involving a dye-labelled fluorescence resonance energy transfer (FRET) probe. Cleavage of this FRET probe generates a signal, which can be readily analysed by fluorescence microtitre plate readers. The two cascading reactions amplify the signal significantly; each original target molecule can lead to more than 10(6) cleaved signal probes in one hour. This signal amplification permits identification of single base changes directly from genomic DNA without prior target amplification. The sequences of the oligonucleotide components of the secondary reaction are independent of the target of interest and permit the development of universal secondary reaction components useful to identify any target.