Child Development From Infancy to Adolescence. Laura E. Levine
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.
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.
Ethical Considerations in Genetic Testing
In Chapter 2, you read about Henrietta Lacks, whose genetic information was used without her knowledge or consent. Issues of privacy and the use of results from genetic screening raise many ethical questions, particularly when children are the subjects. The AAP Committee on Bioethics (2013) recommends that genetic testing should always be motivated by the best interests of the child and should be carried out by a professional genetic counselor. Both parent and child, when appropriate, should be informed about the testing and should agree to it. The risks should be discussed with the family, including the possibility that genetic testing could uncover misattributed paternity or adoption, and a plan about disclosure or nondisclosure should be in place before testing.
There is much to be gained from genetic research and testing, but we should proceed carefully to avoid harm, especially to children. Keeping this in mind, there are several ways an individual can take a preliminary look at his or her own genetic vulnerabilities. Some are discussed in Active Learning: Assessing Genetic Risk. Remember that none of these tests are definitive and if you discover something of concern, it is best to consult with your doctor.
Active Learning: Assessing Genetic Risk
Knowing which genetic conditions affect your family members will make you aware of your own possible genetic vulnerabilities. To begin assessing your genetic risk, you can simply collect information about conditions that have affected your blood relatives that have been shown to have some genetic basis. These include cancer, diabetes, heart disease, mental illness, stroke, and learning problems.
The National Society of Genetic Counselors (n.d.) has a more complete list at http://www.aboutgeneticcounselors.com. On their home page pull down the menu for FAQs+Resources and click on Family History Resources, where you will find a list of conditions that have a genetic component. For each of the conditions, record the age at which the condition appeared in each of your relatives. The likelihood of developing these conditions increases with age, so you will need to update this information periodically. Because health issues can be a sensitive subject and some family members may be reluctant to share information, be careful about how you approach them. Another way to compile this information is to use the website set up by the U.S. Surgeon General at https://familyhistory.hhs.gov to record and save this information online.
You may have heard of commercial genetic tests that promise to help you assess your genetic risk of developing certain diseases