The Sequenome assay uses the unique combination of a single-base primer extension assay incorporating one of four modified nucleotides. The four modified nucleotides each have a unique mass that allows them to be distinguished from one another using mass spectrometry. Each SNP is determined analyzing the primer extension product from a PCR amplicon that surrounds the SNP of interest. The development of each assay involves designing flanking PCR primers and an internal extension assay using web-based software provided by Sequenome. The assays can be designed to analyze up to 30 SNPs in a single reaction, providing a customizable, efficient and high-throughput assay for SNPs of interest.