Tm. Hsu et al., Genotyping single-nucleotide polymorphisms by the invader assay with dual-color fluorescence polarization detection, CLIN CHEM, 47(8), 2001, pp. 1373-1377
Background: The PCR-Invader assay is a robust, homogeneous assay that has b
een shown to be highly sensitive and specific in genotyping single-nucleoti
de polymorphism (SNP) markers. In this study, we introduce two changes to i
mprove the assay: (a) we streamline the PCR-Invader method by assaying both
alleles for each SNP in one reaction; and (b) we reduce the cost of the me
thod by adopting fluorescence polarization (FP) as the detection method.
Methods: PCR product was incubated with Invader oligonucleotide and two pri
mary probes at 93 degreesC for 5 min. Signal probes corresponding to the cl
eaved flaps of the primary probes [labeled with fluorescein and 6-carboxyte
tramethy1rhodamine (TAMRA) dye] and Cleavase((R)) VIII enzyme (a flap endon
uclease) were then added to the mixture. This reaction mixture was incubate
d at 63 degreesC for 5 min. FP measurements were made with a fluorescence p
late reader.
Results: Eighty-eight individuals were genotyped across a panel of 10 SNPs,
using PCR product as template, for a total of 880 genotypes. An average "n
o call" rate of 3.2% was observed after first round of experiments. PCR pro
ducts were remade in those samples that failed to produce any genotype in t
he first round, and all gave clear-cut genotypes. When the genotypes determ
ined by the PCR-Invader assay and template-directed dye-terminator incorpor
ation assay with FP were compared, they were in 100% concordance for all SN
P markers and experiments.
Conclusions: The improvements introduced in this study make PCR-Invader ass
ay simpler and more cost-effective, and therefore more suitable for high-th
rough-put genotyping. (C) 2001 American Association for Clinical Chemistry.