title: Genotyping of single-nucleotide polymorphisms by primer extension reaction in a dry-reagent dipstick format.
abstract: The primer extension (PEXT) reaction is the most widely used approach to genotyping of single-nucleotide polymorphisms (SNPs). Current methods for analysis of PEXT reaction products are based on electrophoresis, fluorescence resonance energy transfer, fluorescence polarization, pyrosequencing, mass spectrometry, microarrays, and spectrally encoded microspheres. We report the first dry-reagent dipstick method that enables rapid visual detection of PEXT products without instrumentation. The method is applied to the analysis of six SNPs in the mannose-binding lectin gene (MBL2). The genomic region that spans each SNP of interest is amplified by PCR. Two primer extension reactions are performed with allele-specific primers (for one or the other variant nucleotide), which contain an oligo(dA) segment at the 5'-end. Biotin-dUTP is incorporated in the extended strand. The product is applied to the strip followed by immersion in the appropriate buffer. As the DNA moves along the strip by capillary action, it hybridizes with oligo(dT)-functionalized gold nanoparticles, such that only extended products are captured by immobilized streptavidin at the test zone, generating a red line. A second red line is formed at the control zone of the strip by hybridization of the nanoparticles with immobilized oligo(dA). The dipstick test is complete within 10 min. We analyzed six SNPs of the mannose-binding lectin gene (MBL2) using genomic DNA from 27 patients, representing a total of 74 variant nucleotide positions. Patient genotypes showed 100% concordance with direct DNA sequencing data. The described PEXT-dipstick assay is rapid and highly accurate; it does not require specialized instrumentation or highly trained technical personnel. It is appropriate for a diagnostic laboratory where a few selected SNP markers are examined per patient with a low cost per assay.
authors.affiliation: Laboratory of Analytical Chemistry, Department of Chemistry, Athens University, Athens 15771, Greece.
authors.forename: Ioannis K
authors.initials: IK
authors.lastname: Litos
authors.forename: Penelope C
authors.initials: PC
authors.lastname: Ioannou
authors.forename: Theodore K
authors.initials: TK
authors.lastname: Christopoulos
authors.forename: Joanne
authors.initials: J
authors.lastname: Traeger-Synodinos
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Kanavakis
mesh_terms: D017931:DNA Primers / Q000737:chemistry; D005838:Genotype; D006801:Humans; D037601:Mannose-Binding Lectin / Q000235:genetics; D009693:Nucleic Acid Hybridization / Q000379:methods*; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA / Q000379:methods*
chemical_list: D017931:DNA Primers; C445619:MBL2 protein, human; D037601:Mannose-Binding Lectin