From a technical perspective, genetic screening is a more narrow term which refers to the detection of genes that may predispose individuals, or their descendants, to certain diseases. It is performed on populations (or individuals from populations) that are at risk for certain diseases. Genetic testing is similar in that it focuses on detecting genes that may predispose individuals to certain diseases. However, it differs in that it is generally performed on individuals who do not necessarily belong to high risk populations. Since this distinction is negligible for most people, we will use the broader term, genetic testing, to encompass both categories.
Genetic testing is done by analyzing chromosomes, DNA, or gene products (proteins) for abnormalities. It can be either predictive or diagnostic. Predictive tests can tell a person (or the parents of a preborn baby) if they or their child have inherited the gene(s) to be susceptible to disease later in life. Diagnostic tests can diagnose the presence of a genetic disease in someone who may be showing symptoms. It is important to emphasize here that the majority of genetic tests do not actually tell an individual if they have a disease – rather, they tell them what level of risk they have (their susceptibility) to develop a specific disease.
As of 2001, there were at least 300 tests available for genetic disorders. In 2004, the number is closer to 900.
From preimplantation testing in embryos to adult testing, there are a variety of genetic tests that encompass every period of life. We will examine six categories – beginning with those at the earliest stages of life and proceeding to the adult years. Within each category we will examine the testing uses and procedures, as well as some ethical implications for the testing.
Prenatal Testing
Testing Uses and Procedures
This type of testing is done to determine if an embryo or fetus is at risk for a variety of recognizable genetic anomalies.
One type of prenatal testing is preimplantation genetic diagnosis which utilizes in vitro fertilization (IVF) and then tests for specific genetic diseases before the embryos are implanted into the mother’s uterus. For more information, see Preimplantation Genetic Diagnosis
Prenatal testing can also be done after the embryo has implanted in the uterine wall with either IVF babies or natural conception. This testing falls under two broad categories: invasive and non-invasive procedures. Invasive procedures have a higher risk of miscarriage than non-invasive procedures.
Invasive Procedures:
- Amniocentesis – with this test, a needle is inserted through the mother’s abdomen and into the amniotic sac to collect a small sample of amniotic fluid. This fluid can then be tested for biochemical, chromosomal, or genetic abnormalities. This is typically done at 14-20 weeks.
- Chorionic villus sampling (CVS) – a catheter is inserted through the mother’s cervix or abdomen in order to obtain a sample of placental tissue which can then be tested for chromosomal or genetic abnormalities. This is typically done at 10-12 weeks.
Non-invasive Procedures:
- Maternal serum screening – this tests the mother’s blood during pregnancy in order to look for any markers in the mother’s blood that might indicate the presence of birth defects or chromosomal abnormalities. The baby is not exposed to any risks associated with the performance of this test.
Ethical Implications
Examining the intent of the prenatal testing should be the most important consideration for parents considering it. If the baby is found to have a genetic disorder, the parents can legally choose to end the life of their preborn child through abortion. Unfortunately, this is often what happens when a preborn baby’s test indicates a genetic abnormality. If the parents reject abortion as an option, genetic testing could help them better prepare for the birth of an affected child. However, if the parents are not considering an abortion, they may choose to forego the testing altogether.
Newborn Testing
Testing Uses and Procedures
As the name suggests, this procedure tests newborns’ blood or tissue samples for genetic diseases. This type of screening has been in place for PKU (phenylketonuria) as early as the 1960s. If diagnosed early, the mental retardation that PKU causes can be prevented or minimized by putting the child on a special diet. There are also tests for sickle cell anemia, Tay-Sachs disease, hypothyroidism, galactosemia, and medium chain acyl CoA dehydrogenase deficiency.
Ethical Implications
Unlike prenatal testing, the window for terminating the pregnancy has ended with newborn screening. Instead of focusing on ending the life of a preborn baby, newborn screening can focus on detecting diseases that can be remedied or their effects decreased early in the child’s life (through special diets, medications, etc.).
Carrier Testing
Testing Uses and Procedures
Carrier testing determines if an individual has a genetic abnormality that could be passed on to their children. A “carrier” is someone who only carries one copy of an altered gene. It is normally done for autosomal (non-sex cells) or sex-linked recessive disorders. An autosomal recessive genetic disease must have two copies of the altered gene – one from the mother and one from the father – in order for the disease to be expressed in the individual. If two people who are carry the recessive gene produce children, their children may have the disease. Examples of recessive genetic diseases include sickle cell anemia, Tay-Sachs disease, and cystic fibrosis.
Carrier testing can also be done for sex-linked genetic diseases. Hemophilia is an example of a disease that is normally inherited by sons from their mothers. Girls do not generally have the disease – they are usually only carriers for the mutated gene.
Carrier testing is normally done before pregnancy in order to determine if an individual’s future children might be affected by a particular disease.
Ethical Implications
Carrier testing can be used by couples who know they have a family history of genetic disease. The knowledge they gain from the testing can help determine their course of action in starting a family. The desire to have a child of their own may override the risk of bringing a baby into the world with the susceptibility for a genetic disease. Or, they may choose to look into other options such as traditional and/or embryo adoption.
Predictive testing
Testing Uses and Procedures
Sometimes called pre-symptomatic testing, this type of testing has traditionally been used to determine if a patient was at risk for a rare genetic disorder. For example, a person could be tested to see if they will develop Huntington’s disease later in life. In more recent years, especially with the completion of the Human Genome Project, specific gene alterations have been identified to help detect a predisposition for particular diseases in individuals. Some these include cardiovascular disease, breast, ovarian, and colon cancer, and neurofibromatosis.
Ethical Implications
Decisions to utilize this type of testing should be made at a personal level. The nature of the disease, and the foreknowledge that the individual wants to have about their potential health risks in future years, will help determine if this testing is right for them. The information, in some cases, can be helpful for individuals who can take preventative measures to reduce the likelihood that they will develop the disease.
Additionally, there are questions of privacy and discrimination that must be addressed. For instance, who will have access to this information and how will it be used? Could it be used to discriminate regarding employment or health care?
Susceptibility Testing
Testing Uses and Procedures
This can be used to identify individuals who, due to a genetic predisposition, may display increased susceptibility to certain toxic substances found in the workplace, and thus be at risk for adverse reactions and future disabilities because of these substances.
Ethical Implications
This information, like predictive testing, could also be used by employers to discriminate against employees who are more susceptible to disease – ranging from losing a promotion to being fired. In a more positive way, this information could also be beneficial to individuals who are willing to change jobs in order to avoid these health risks.
Forensic testing
Testing Uses and Procedures
Forensic testing is used to ascertain a genetic link between criminal suspects and investigations. It can also be used to determine family relationships – such as paternity. As this form of testing continues to increase in popularity, our news headlines are becoming more and more populated with stories of suspects who have been convicted or acquitted based on DNA tests.
Ethical Implications
There are issues of confidentiality, standards, and quality control with this type of testing. With confidentiality, the question is, who has access to the information gained from testing? This is especially important if the information obtained from criminal investigations is stored in national police databases. In terms of standards and quality control, there are issues concerning the methodology used.
Dawn Vargo is a research assistant in the Public Policy Division of Focus on the Family.
