Diagnostic testing is used to identify or confirm the diagnosis of a disease or condition in a person or a family. Diagnostic testing gives a "yes" or "no" answer in most cases. It is sometimes helpful in determining the course of a disease and the choice of treatment. Examples of diagnostic testing include chromosome studies, direct DNA studies, and biochemical genetic testing.
Predictive genetic testing determines the chances that a healthy individual with or without a family history of a certain disease might develop that disease. There is predictive testing available for some adult-onset conditions (those diseases which manifest themselves in adulthood), such as some types of cancer, cardiovascular disease, and some single gene disorders.
Presymptomatic genetic testing is used to determine whether persons who have a family history of a disease, but no current symptoms, have the gene alterations associated with the disease.
Carrier testing is performed to determine whether a person carries one copy of an altered gene for a particular disease. The disease may be autosomal recessive, which means that the disease is present in an individual only if two copies of the altered gene are inherited. Couples who both carry the same autosomal recessive gene have a one in four, or 25 percent, chance with each pregnancy to have a child with that disease.
A recessive disease may also be X-linked recessive, which means that the altered gene is located on the X chromosome. Since females have two X chromosomes, and males have one X and one Y chromosome, females can be carriers of a gene on the X but are not affected (provided the other X has the normal copy of the gene). On the other hand, males are usually affected with the disease if they have the altered gene on their X chromosome (because they do not possess the normal copy of the gene on the Y chromosome). Therefore, "carrier testing" for X-linked conditions is usually done in females.
Prenatal diagnosis is used to diagnose a genetic disease or condition in the developing fetus and includes maternal serum screening, ultrasound (sonograms), amniocentesis, chorionic villus sampling (CVS), and percutaneous umbilical blood sampling (PUBS).
Preimplantation studies are used following in vitro fertilization to diagnose a genetic disease or condition in an embryo before it is implanted into the mother's uterus.
Newborn screening is performed in newborns by state public health programs to detect certain genetic diseases for which early diagnosis and treatment are available.