The potential for understanding human genetics increased greatly when the Human Genome Project successfully identified and mapped all the genes on human chromosomes in 2003. Genetic techniques can be used to study individual genes to learn more about specific disorders. For example, some kinds of disorders that have been classified based on what symptoms they caused have been reclassified based on what the genetic abnormality is.
Genetic tests are used to diagnose certain disorders (for example, hemochromatosis and chromosomal disorders such as Down syndrome and Turner syndrome). Genetics is also increasing the ability to predict what disorders a person is likely to develop. For example, women with certain abnormalities in the BRCA genes are prone to breast and ovarian cancers. These predictions may allow disease prevention and screening to be tailored much more to each person.
Advances in techniques that assess people's genetic characteristics and increased understanding of human genetics have improved diagnosis of genetic disorders before birth. In some cases, genetic disorders that are diagnosed before birth can be treated, which prevents future complications. For example, corticosteroids given to the mother before birth may decrease the severity of a type of genetic hormone deficiency. Genetic screening can be used to counsel parents about the risks of passing on a genetic disorder to their offspring (see see Genetic Screening). Screening can also be used to detect fetal abnormalities (see see Prenatal Diagnostic Testing).
Increased understanding of human genetics has the potential to predict how people, depending on their precise genetic makeup, will respond to certain drugs (see Genetic Makeup and Response to Drugs). For example, specific genes can predict how much warfarin, a blood thinner, a person is likely to require. This prediction is important because taking too much warfarin can cause serious bleeding and taking too little makes the drug ineffective, which is also risky. Gene analysis can also predict whether a person will have intolerable or only minor side effects when taking irinotecan, an anticancer drug. People likely to have intolerable side effects can be treated with a different drug. Gene analysis can also determine how quickly people metabolize and thus respond to codeine, an analgesic. People who metabolize codeine rapidly can accumulate high levels of a metabolic byproduct of codeine that impairs their unconscious drive to breathe. This effect of rapid metabolization resulted in the death of some children who were given codeine after tonsillectomy and adenoidectomy were done to treat obstructive sleep apnea.
The genetics of diseased tissue (such as cancers) can also help drug manufacturers identify more precise treatment targets when developing drugs (such as anticancer drugs). For example, the anticancer drug trastuzumab can target specific cancer cells in breast cancers that involve the breast cancer gene HER2/neu.
Last full review/revision August 2013 by David N. Finegold, MD