IDENTIFICATION OF APOLIPOPROTEIN-E POLYMORPHISMS USING TEMPERATURE CYCLED PRIMER OLIGO BASE EXTENSION AND MASS-SPECTROMETRY

The isothermal Primer Oligo Base Extension (PROBE) reaction combined w ith matrix-assisted laser desorption/ionization time-of-flight mass sp ectrometry for diagnostic product detection as recently introduced by our group is modified to incorporate temperature cycling during the pr imer extension step, resulting in enhanced levels of diagnostic produc t generation. Utilizing temperature cycled PROBE, the identities of tw o apolipoprotein E polymorphisms (codons 112 and 158) for differentiat ion of epsilon 2/epsilon 3, epsilon 3/epsilon 3, epsilon 3/epsilon 4, and epsilon 4/epsilon 4 genotypes were simultaneously determined. Prim ers specific for each site are extended by a series of bases unique to the identity of that variable site, producing low mass diagnostic pro ducts (M-r < 9000) highly amenable to detection by mass spectrometry. The temperature cycled PROBE method has yielded unambiguous and correc t diagnoses for all samples tested thus far. The increased amount of d iagnostic product generated per primer by the cycling method makes pos sible faster spectrum acquisition due to the increased signal intensit y, critical for future automated measurement of such samples.