Bioethics terms

Newborn screening

Used to uncover genetic diseases in newborns so treatment can begin early. Every state mandates some form of it, and some screen for as many as 30 disorders. The first mandatory test was for PKU.

Carrier testing

Used to determine whether someone carries one copy of a mutated gene for an autosomal recessive disorder (such as PKU, cystic fibrosis, sickle cell disease, or Tay-Sachs). Carriers don't get the disease, but if two carriers have a child, that child could inherit two mutated copies and has a greatly increased chance of having the disease.

Predictive testing

Used to find out, before any symptoms appear, whether someone is likely to develop a genetic disease later in life. Often recommended for people with a family history of a disorder. Results are sometimes highly predictive (Huntington's disease: nearly 100%) but usually more uncertain (venous thrombosis: only slightly higher risk than the general population).

Diagnostic testing

Used to confirm or rule out a genetic disorder in someone who already has symptoms.

Prenatal testing

Used to determine whether a fetus has genetic abnormalities likely to cause physical or mental impairments. Performed when there is reason to suspect risk, such as maternal age 35 or older, a family history of inherited disorders, or ancestry linked to certain disorders. Common procedures are amniocentesis (amniotic fluid sample) and chorionic villus sampling (cells from the placenta).

Preimplantation genetic diagnosis (PGD)

Used to test embryos created through IVF for genetic abnormalities. Embryos with defects are screened out, and only mutation-free embryos are transferred to the uterus. One or two cells are removed from a five- to eight-cell embryo. It is costly and usually reserved for cases with a high probability of a serious disorder, such as Down syndrome or Tay-Sachs.