Also termed pharmacogenetics – this is the science underpinning the relationship between a person's genetic makeup and how they utilise or tolerate medication. Genes affect drug absorption, distribution, METABOLISM and excretion. Thus, the variations in GENES and the PROTEIN products whose manufacture they control could be utilised to provide safer and more effective drugs. For example, nearly one-third of patients fail to respond to the cholesterol-reducing group of drugs, the STATINS. Around half do not respond to the tricyclic ANTIDEPRESSANT DRUGS and most of this variability depends on the individual's genetic makeup – their genome. Additionally some patients respond to a standard dose of a medication with an unusual and unwanted ill-effect, for example a dramatically severe skin reaction to the anticonvulsant carbamazepine. Such a reaction, which does not occur in the large majority of patients has been traditionally termed IDIOSYNCRASY. However, it is now known that Chinese persons who react abnormally to carbamazepine are likely to carry in their HLA SYSTEM the ALLELE HLA-B*15:02 while Europeans more commonly carry HLA-A*31:01. Ultimately, as knowledge of pharmacogenomics evolves, it is hoped that particular medications or their dose could be specifically designed to best fit a patient's genetic make-up.