Child Development From Infancy to Adolescence. Laura E. Levine
determining your genetic ancestry. For these tests, you purchase a testing kit online, provide the company with a saliva sample or a swab from the inside of your cheek, and receive a report that outlines your individual genetic risks (often expressed as “high,” “low,” or “average”) for a variety of possible disorders or characteristics, as well as some strategies that can help reduce the risk. However, currently the Centers for Disease Control recommend that you only take these tests on the advice of a doctor and in a medical setting. Out of 1,000 such tests, only 12 have been approved by the U.S. Food and Drug Administration (FDA) and only one, 23andme, has been approved as a self-administered home test (Hatfield, 2016; USFDA, 2017c). Home testing for children is strongly discouraged by the AAP Committee on Bioethics (2013). You can see why the use of such tests by well-meaning parents who do not have the expertise to fully understand them could lead to negative outcomes for the children.
Treatment of Genetic Disorders
Given the toll that genetic disorders take on individuals, we continue to search for ways to treat these conditions. Scientists are working on ways to use our new knowledge about genes to prevent and treat human disorders, but gene therapy, the treatment of genetic disorders through the implantation or disabling of specific genes, is still in its infancy for humans. In 2017, the first three gene therapies were approved by the U.S. Food and Drug Administration for use in the United States (Goldschmidt & Scutti, 2017).
Gene therapy: Treatment of genetic disorders through implanting or disabling specific genes.
T/F #6
Doctors are now able to treat many genetic disorders with gene therapy that involves changing the defective genes. False
Research on gene therapy took a great leap forward with the creation of the CRISPR program that allows for direct gene editing (Ledford, 2016). Scientists can now cut out sections of genes and turn off certain genes. This technology brings great hope that genetic disorders will become treatable or preventable through editing of the genes associated with them at some point in the future (Broad Institute, 2017). For example, using mice, CRISPR has been used to edit the genes associated with a disease called Duchenne muscular dystrophy (Bengtsson et al., 2017). With humans, a different approach is being tested to treat this disorder. UC Davis Health (2013) is currently studying a national sample of boys with this disease to assess the effectiveness of a drug designed to bridge over the defective gene to make it unreadable. These new approaches offer hope that genetic diseases can be prevented or treated.
Although we may not yet be able to change the genes themselves, we can sometimes control the effects of gene-based disorders through environmental interventions. For example, a child who has the disorder phenylketonuria (PKU) cannot produce an enzyme required for the digestion of phenylalanine, a common protein in foods such as beef, poultry, fish, eggs, milk, and wheat products (de Baulny, Abadie, Feillet, & de Parscau, 2007). When phenylalanine is only partially digested because of the missing enzyme, harmful substances are produced that can damage the child’s brain and central nervous system, resulting in intellectual disability (U.S. Library of Medicine, 2017b). The brain is particularly vulnerable to these damaging toxic effects in the early years when it is growing so rapidly. By eliminating phenylalanine from the diet of an infant through the use of a special formula, the harmful effects are avoided (Schuett, 2008). A low-phenylalanine diet then must be maintained throughout life to prevent the appearance of symptoms later in development (NHGRI, 2014). That diet primarily includes fruits, vegetables, and low-protein grain products. Although there are no comparable ways to negate the effects of gene-linked behavioral disorders such as attention deficit/hyperactivity disorder, depression, autism, or schizophrenia, there are many types of intervention that help mute the negative effects of these disorders and earlier intervention is often linked with a better outcome.
Check Your Understanding
Knowledge Questions
1 When do single-gene disorders occur?
2 What causes chromosome disorders such as Down syndrome?
3 What is amniocentesis?
4 What are some risks and benefits of genetic testing?
Critical Thinking
To learn more about Down syndrome, research with individuals with the disorder is important. What special ethical considerations would need to be taken to carry out research with this population? (Think also about the ethical issues regarding research that you read about in Chapter 2.)
Behavioral Genetics
>> LQ 3.4 How do researchers study the relationship between genetic inheritance and individual traits and behavior?
With some understanding of how genes function, we now look at the question of how children’s behavior and development are related to the genes they inherit. Whereas molecular genetics begins with identification of genes and examines how they are related to outcomes such as human behavior, disease, and other characteristics, behavioral genetics begins at the level of traits and behaviors and uses several techniques to try to determine how heritable these characteristics are. If high levels of heritability are found, indicating a significant role of genes, researchers can then look for the particular genes that are involved. With the development of genome-wide association tests, described earlier as a way to look at the whole human genome, researchers can now look widely at which genes may be related to human characteristics. We should keep in mind that genetic inheritance of behavior and traits may involve not just a specific gene, but also the interaction of that gene with other genes and with the environment, so results taken from behavioral genetics and molecular genetics may indicate different levels of heritability (Thapar & Harold, 2014).
Heritability: A measure of the extent to which genes determine a particular behavior or characteristic.
Historically researchers have used several approaches to try to separate the relative influence of genes and environment on the expression of that behavior. You might think that simply noting how similar children are to their parents could tell us whether a behavior is determined by genetics, but genetic influences and environmental setting are often intertwined in complex ways. For example, imagine walking into the home of a new friend and discovering this friend is a very talented pianist. You then find out both parents in this family perform with a local choir and their youngest child is a gifted violinist. What would you conclude about the source of this musical talent? Did the children in this family inherit genes for their musical ability, or did they learn about music from the experiences their parents provided for them? In this situation, there is no way to know which has happened. It’s likely both genes and environment have had an influence, but scientifically it is impossible to sort out which factor had what effect.
TRUE/FALSE VIDEO
T/F #7
Mike is a talented pianist. Because both of his parents are musicians, genes must have determined that Mike would also have musical talent. False
In theory we might solve this problem by taking children from musical families and placing them in families that are not musical to see what happens. If musical ability is produced by genes, these children will still develop this talent. If it is produced by environmental influences, they will not necessarily be musical after growing up in a nonmusical family. Obviously it is unethical to do anything like this with human beings, so psychologists have had to look for natural situations that might provide the same information. We describe three types of studies that take advantage of such natural situations: (1) studies of adopted children, (2) comparisons of identical and fraternal twins, and (3) studies of identical twins adopted