A SNP (pronouced "s-nip"), or a single nucleotide polymorphism, is the position on the human genome in which a single nucleotide is different in certain individuals. It transmits according to Mendelian law and, thus, can be used to localize an area containing disease-associated genes. An SNP, when located within the gene, may be the causative mutation. It can be used to estimate the risk of developing certain diseases and prognostic markers or predict the response to drug treatment and its side effects (Pharmacogenomics).

SNPs in the public database mostly come from alignments of genomic or EST sequences obtained during large-scale sequencing. After validation, only half of these SNPs were confirmed as polymorphic in Caucasian populations. In addition, a complete SNP database does not exist, even for Caucasians. Most SNP databases aim to identify the SNP for the whole genome. However, the set of SNPs for each gene is not complete. It is well accepted that information concerning the SNP in one population cannot be used for others because of the difference in allele frequency. Some SNPs may be specific for a certain population. In addition, groups of SNPs that are associated with each other (linkage disequilibrium (LD) block) are not the same in different populations. The LD block determines how many SNPs should be investigated to complete the study of one gene. The correlation between diseases, which are prevalent in Thailand, and an SNP that shows a high frequency or is specific to Thai populations, is also of interest in investigations. In order to facilitate post genomic research activities in Thailand, SNPs, allele frequency and LD blocks in the Thai population will be determined, and a Thailand SNP database will be created.