Diagnostic testing is used to identify or confirm the diagnosis of a disease or condition. 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, including chromosome studies, direct DNA studies and biochemical genetic testing.
Predictive genetic testing
Predictive genetic testing determines the chances that a healthy individual might develop a certain disease. Predictive testing is available for some adult-onset conditions--diseases which manifest themselves in adulthood--such as some types of cancer, cardiovascular disease and some single gene disorders.
Presymptomatic genetic testing
Presymptomatic genetic testing determines whether a person with a family history of a disease, with no current symptoms, have the genes associated with the disease.
Carrier testing determines if a person carries a copy of an altered gene for a particular disease. The disease may be autosomal recessive, which means an individual has the disease only if two copies of the altered gene are inherited. Couples who both carry the same autosomal recessive gene have a 25 percent chance with each pregnancy to have a child with that disease.
A recessive disease may also be X-linked recessive, which means 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 chromosome but can be unaffected, provided the other X chromosome has the normal copy of the gene.
If a man has the altered gene on their X chromosome and do not possess the normal copy of the gene on the Y chromosome, then the male is usually affected with the disease. Therefore, carrier testing for X chromosome-linked conditions is usually done in females.
Prenatal diagnosis is used to diagnose a genetic disease or condition of the developing fetus, including maternal serum screening, ultrasound (sonograms), amniocentesis, chorionic villus sampling (CVS) and percutaneous umbilical blood sampling (PUBS).
Pre-implantation studies are used after an 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 in state public health programs to detect certain genetic diseases for which early diagnosis and treatment are available.