Genetic testing is the testing of a person's DNA. Genetic testing is done for many reasons, including to establish paternity, diagnose disease, determine sex, or determine tissue type. Scientists perform genetic testing on adults, children, fetuses, and, more recently, embryos in the very early stages of development.
In general, genetic testing looks for mutations in DNA. A mutation is a change in the number, arrangement, or molecular sequence of a gene. We all have mutations. That is how our DNA is distinguishable from others. Only some mutations cause disease. The most common reason for genetic testing is to diagnose disease. There are many diseases such as Huntington's, Tay-Sachs, and sickle cell anemia where the cause is only genetic. If a person has certain mutations in specific genes, they have the disease. There are other diseases and conditions, such as diabetes, heart disease, cancer, and obesity, that have a genetic contribution, but whether one develops those diseases also depends on environmental factors. That means that a person who is predisposed to a genetic disorder may be able to change environmental factors to delay the onset or reduce the severity of the disease, or eliminate the disease altogether.
Increasingly, genetic testing is used for carrier screening. A carrier is person who carries a mutation for a disease but does not suffer from that disease. Some genetic diseases, like cystic fibrosis and sickle cell anemia are autosomal recessive disorders. Because humans reproduce sexually, we have two copies of every gene, one from our mother and one from our father. To suffer from an autosomal recessive disorder one must have mutations that cause disease in both copies of a gene. If one copy of the gene is normal, a person does not suffer from the disease, but is called a carrier. A carrier can pass this mutation onto his or her children. If two carriers of the same mutation have children together, there is a 1 in 4 chance their child will inherit mutations from both parents and suffer from the disease. Carrier screening has implications for a whole family since it is recommended that other family members also get tested to see who has the mutation and who does not.
The Human Genome Project (HGP) is an effort to sequence the entire human genome, approximately 3 billion base pairs or 30,000 genes. In 2001, HGP geneticists announced that they had rough draft of the human genome. That is, they had the sequence of bases in the DNA that make up all the chromosomes in the human genome. But this sequence is a code that researchers must decipher. A sequence in our DNA may be a gene that codes for a crucial protein required for proper human metabolism, or it may just be nonsense. It will be a long and painstaking process to decipher the code. As each gene is deciphered and its job is uncovered, scientists will be able to pinpoint the causes of many diseases and begin to develop cures. Once a disease-causing mutation is discovered, scientists can then offer a genetic test to identify patients who are carriers or who suffer from a genetic disorder.
Genetic testing simply provides information. In and of itself, genetic testing is not unethical, unless human life is put at risk or destroyed to obtain that information. The reason for the testing and what is done with the information provided are where the ethical dilemmas arise. As a result of the HGP, we will soon be able to get a complete genetic profile. We will be able to look into our future and find out if we may suffer from Alzheimer's, or heart disease, or diabetes. Whether this information will be used for good or ill is a major question. Genetic testing is neither all bad nor all good. This technology is still young, and as Catholics we must understand genetic testing so we can make moral judgments and shape public policy on what is ethical and what is not.