Testing Your Genes
Minor differences in genes can have an effect on disease risk, and nearly all conditions and diseases have a genetic component. Some disorders, such as sickle cell anemia and cystic fibrosis, are caused by mutations (changes in the code) in a single gene. Some of the disease-related gene mutations are recessive (it takes two copies of the mutated gene to produce the disorder), while others are dominant (only one copy of the gene results in the disease). Some are sex-linked and are found only in males.
Some mutations have been passed down in specific families, some are more prevalent in individuals of certain ethnic descent, and others occur de novo (without warning). Still others are related to a change in the number of chromosomes or the presence of broken chromosomes. The most difficult to assess are the complex or multifactorial disorders such as heart disease, diabetes, and obesity, which do not have a single genetic cause—they are likely associated with the effects of multiple genes in combination with lifestyle and environmental factors.
Genetic counseling and testing can identify familial patterns and changes in chromosomes, genes, or proteins that are associated with inherited disorders. The results of a genetic test can confirm or rule out a suspected genetic condition or help determine risk. More than a thousand genetic tests are currently in use, and more are being developed. Genetic tests are used for a variety of reasons:
- Carrier testing tells people whether they "carry" a genetic mutation that can cause a disease. Carriers usually show no signs of the disorder; however, they can pass on the genetic mutation to their children, who may develop the disorder or become carriers themselves.
- Predictive and pre-symptomatic genetic testing may help provide information about a person's risk of developing a disease such as Huntington's disease or breast cancer.
- Preimplantation genetic diagnosis (PGD) is done in conjunction with in vitro fertilization to determine whether embryos for implantation carry genes that could cause disease.
- Prenatal testing is performed during pregnancy by chorionic villous sampling or amniocentesis to help identify fetuses that have certain genetic or chromosomal abnormalities.
- Newborn screening is used to test babies one or two days after birth to find out whether they have certain diseases known to cause problems with health and development.
- Pharmacogenomic testing gives genetic information about how certain medicines are processed in a person's body so that a doctor can choose medications that will work best with a person's genetic makeup.
- Nutrigenomics provides genetic information regarding an individual's requirement for nutrients so that they can function optimally.
- Research genetic testing helps scientists learn more about how genes contribute to health and disease, as well as develop gene-based treatments.