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People become particularly concerned about genetics when they are about to start a family. In each pregnancy, any couple statistically has a 3% chance of having a child with a genetically based disorder (CDC, 2017b). Based on these low odds, there is usually no reason for genetic counseling. However, in some cases individual risk is higher, and individuals may want to seek out a genetic counselor to help them assess the type and amount of risk. See Table 3.2 for additional information about couples who might consider having genetic counseling because they are at increased risk of conceiving a child with a genetic disorder or birth defect.

Table 3.2

Source: March of Dimes (2017). Used with permission.

Genetic counseling and testing can occur before or during a pregnancy. Counselors ask about the couple’s own medical histories and their families’ history of diseases and genetic disorders and may recommend certain tests. There are tests that can identify whether an individual is a carrier of one recessive gene for a disorder. As you learned in Active Learning: Understanding the Inheritance of Tay-Sachs Disease, a child will only have the disease if both partners carry the recessive gene, so if one partner is found to have the gene, the other would need to be tested as well if they wanted to determine the risk for their future children. If both partners have the gene, the child will have a 25% chance of having the disease. There are over 100 diseases that can be tested for through either a blood or saliva sample (American Congress of Obstetricians and Gynecologists [ACOG], 2017a). We have already discussed two of the most common genetic disorders, sickle-cell anemia and Tay-Sachs disease. Another common genetic disorder is thalassemia, a blood disorder associated with reduced production of hemoglobin, which is most common among people of Middle Eastern, African, Asian, or Mediterranean descent (especially Greek or Italian). However, many people do not even know all the ethnic groups that make up their ancestry, and these disorders can occur in any ethnic group, so a screening for many different genetic disorders can be performed regardless of ethnic background.

You notice that we talk above about someone’s ancestry rather than their race and there is a particular reason to do that when we are talking about genetic inheritance. Although race has long been used to categorize people into different groups, genetic research is now making it clear that most people do not fit easily into one racial category. For example, 23andMe, a company that tests individual genomes that you’ll read more about in Active Learning: Assessing Genetic Risk, studied the genomes of over 150,000 people across the United States. They found that on average people who identify as African American have a genetic ancestry that is 73% African, 24% European, and .8% Native American, with the percentage of African genetic ancestry for those who identify as African American ranging from 0% to 100% (Bryc, Durand, Macpherson, Reich, & Mountain, 2015). Racial identity is more a social construct than a genetic reality. For that reason, we must be careful not to draw the conclusion that differences between people with different racial identities are due to genetic inheritance. In genetic research it is more important to look at where a person’s ancestors came from than the race they identify with when assessing risk for genetic disorders. With all that said, racial identity still has a great impact on children’s experiences as they grow up.

During pregnancy there are two types of tests that can identify some possible genetic abnormalities in the developing fetus: screening tests and diagnostic tests. One type of screening test examines small amounts of DNA from the placenta that are found in the mother’s blood allowing for nonintrusive screening of fetal genes for chromosome disorders such as Down syndrome (ACOG, 2016). Other screening tests of the mother’s blood, such as the alpha-fetoprotein test and the quadruple screen, can uncover abnormalities in hormone levels that signal a possible defect in the neural tube, the structure from which the brain and spinal cord develop. If there is a positive finding from these screening tests, it should be followed up with diagnostic tests for the disorder (Chitayat, Langlois, & Wilson, 2011).

Diagnostic tests can confirm or disconfirm findings concerning chromosome disorders and some single-gene disorders, such as sickle-cell disease. Because all the structures that support the pregnancy (including the placenta, the amniotic sac, and the chorion) are the result of the conception, the cells they contain have the same genetic makeup as the embryo, and that is why they can be tested for genetic problems. As shown in Figure 3.6, in amniocentesis, a long, thin needle is inserted through the mother’s abdomen and into the amniotic sac, which surrounds the fetus. Fluid withdrawn from the sac contains fetal cells (such as skin cells the fetus routinely sheds) that can be analyzed for genetic abnormalities. In chorionic villus sampling or CVS, cells are obtained from microscopic projections called villi found on the chorion, the outside layer of the embryonic sac. These cells can be obtained either through the abdomen or through the vagina and cervix, and the sample is then analyzed (Jorde et al., 2006). CVS is performed at 10 to 11 weeks of gestation, while amniocentesis cannot be performed until 15 to 17 weeks. The risk of miscarriage resulting from the procedure itself is slightly higher for CVS than for amniocentesis, so the parents must weigh this risk against information they receive about possible genetic problems earlier in the pregnancy (Jorde et al., 2006).

Amniocentesis: A test to look for genetic abnormalities prenatally, in which a physician uses a long, thin needle to extract amniotic fluid, which is then tested.

Chorionic villus sampling (CVS): A test to look for genetic abnormalities prenatally, in which a small tube is inserted either through the vagina and cervix or through a needle inserted in the abdomen, and a sample of cells from the chorion is retrieved for testing.

Description

Figure 3.6 Genetic testing.

Source: Dorling Kindersley/Getty Images.

Genetic testing can also be done once the baby is born. The American Academy of Pediatrics [AAP] Committee on Bioethics (2013) recommends that all parents be offered the option of having genetic screening for their newborns, but the parents should be informed of the benefits, the very low risks, and what would happen if genetic abnormalities are found. All parents must have the right to turn down this option after they have information about it. In the United States, about 4 million infants are screened each year for genetic conditions leading to critical early treatment that reduces the long-term effects of the disorders. Conditions under which older children may receive genetic screening and the ethical issues involved are described in the next section.