Few things are more devastating than finding out your new baby has a genetic disease. DNA testing has become more popular prior to pregnancy since testing is more available and affordable. The decision to test isn't always an easy one, since it raises questions about what to do if one or both parents to be carry a lethal gene.
Deciding to Test
Couples with a known family history of a particular disease, or who are from certain ethnic backgrounds, are most likely to request DNA carrier testing. For example, people of Ashkenazi Jewish descent may want to test to see if they carry genes found commonly in this population, such as the Tay-Sachs gene or the gene for Canavan disease.
Process
DNA testing is done by having blood drawn and sent to a specialized lab. DNA is found inside chromosomes located in every cell of the human body. People normally have 46 chromosomes in each cell, 23 from each parent. Each chromosome is made up of genes. Every gene found in DNA is a code that controls a certain action within the cell. There are between 50,000 and 100,000 genes, each made up of thousands of chemical bases that make up the code the gene follows, the National Health Museum explains. Gene mutations occur when a single chemical base is out of order or missing. Sections of a gene can also be missing altogether. Some mutations cause serious disease, while others have less effect. Results typically arrive in two to three weeks.
Deciphering Results
DNA testing is complicated. Your doctor or genetic counselor may go over the results with you to be sure you understand them. Genetic disorders are inherited in several ways; they may be dominant or recessive. Dominant genes means only one copy of the gene needs to be present for a person to have the disease. Huntington's disease is an example of a dominant disease; you either have the gene or you don't. If you have it, you will have the disease.
Most diseases are recessive, meaning that both parents need to pass on a copy of the gene. If you both have it, there's a one in four chance your child will have the disease. The odds, in this case, are one in four for each pregnancy, so if you have a child with the disease, it doesn't mean your next three children will be free of it.
Advantages
DNA testing can provide relief as you know you don't carry certain genes, or that only one of you carries a recessive gene. While knowing that you carry a certain gene can bring some hard choices, it can also help you plan ahead. Couples with a high risk for certain genetic diseases may decide not to have biological children, or may decide to do pre-implantation genetic diagnosis testing, or PGD, done on embryos during an in vitro fertilization cycle.
Testing can also be done during pregnancy on the fetus through chorionic villus sampling, where a small piece of the placenta is tested, or amniocentesis, which takes fetal cells from the amniotic fluid around the fetus.
Limitations
DNA testing also has limitations. For instance, the cystic fibrosis gene is carried by as many as 1 in 29 Caucasian couples, the Cystic Fibrosis foundation states. The problem is, there are over 1,000 different CF gene mutations, and the disease they pass on ranges from very mild to severe. DNA testing also won't diagnose all possible genetic diseases, although close to 1,000 diseases can be tested, the Human Genome Project states. Spontaneous gene mutations can also arise; children can be born with genetic mutations that their parents don't have.
