For ten-year-old leukaemia patient Jason Saunders, the usual chemotherapy was not going to work. Given the standard drug treatment, there was a strong chance that toxic metabolites would build up in his body and make him sick, requiring a break in his therapy that would allow the cancer to return.
This is because Jason is one of the 10% of Caucasians with a genetic variation that reduces his ability to metabolize thiopurines, the drugs most commonly used to treat acute lymphoblastic leukaemia. Rather than having two high-activity copies of the TPMT gene that produces the enzyme responsible for metabolizing these drugs, Jason has only one.
Our current understanding of pharmacogenetic principles involves enzymes responsible fordrug biotransformation. Individuals are classified as being “fast,” “rapid,” or “extensive” metabolizers at one end and “slow” or “poor” metabolizers at the other end of the continuum. This may or may not also include an “intermediate” metabolizer group, depending on the particular enzyme. With regard to biotransformation, children are more complex than adults; fetuses and newborns may be phenotypically “slow” or “poor” metabolizers for certain drug-metabolizing pathways because of their stage of development and may acquire a phenotype consistent with their genotype at some point later in the developmental process as they mature.
Pharmacogenomics is the study of how genes affect a person’s response to drugs. This field combines pharmacology (the science of drugs) and genomics (the study of genes and their functions) to develop effective, safe medications that can be prescribed based on a person’s genetic makeup.
Many drugs that are currently available are “one size fits all,” but they don’t work the same way for everyone. It can be difficult to predict who will benefit from a medication, who will not respond at all, and who will experience negative side effects (called adverse drug reactions). Adverse drug reactions are a significant cause of hospitalizations and deaths in the United States.
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