Pharmacogenetics and Pharmacogenomics

Of the approximately 3 billion nucleotides in each of the two sets of chromosomes in human cells, the vast majority are identical from person to person. On average, though, the genomes of individuals differ from one another by about 1 million nucleotides. This is largely what accounts for the enormous diversity of humans. A nucleotide in a gene from one person that is different from the nucleotide found at the same position of the gene in most other people is called a single nucleotide polymorphism, or SNP (pronounced "snip").

Almost 1.5 million human SNPs have been identified and catalogued as part of the human genome sequencing project. Many of these polymorphisms are within the protein-coding or control regions of genes and may contribute to particular diseases, to a predisposition to a disease, or to adverse drug reactions. By comparing the SNP patterns of many different people, geneticists can infer whether a particular SNP (and therefore the gene it is in) is correlated with a disease or adverse drug reaction. Once a correlation is found, doctors can determine if their patients have the SNP in their genomes, to test for the likelihood of contracting the disease or experiencing the adverse reaction.