This video excerpt from NOVA uncovers the genetic mystery that nearly killed Alexis, now 14, and introduces the debate surrounding genetic testing at birth. After diagnosing Alexis and her twin brother Noah with cerebral palsy at a young age, doctors later discovered that the twins shared a rare genetic mutation that led to a condition that mimics cerebral palsy. The twins improved after receiving treatment, but then Alexis took a turn for the worse. Thanks to whole genome sequencing, doctors discovered a second problem linked to the mutation and gave her a different treatment that saved her life. While Alexis’s father believes that sequencing her genome at birth would have prevented years of anxiety and suffering for Alexis and her family, this practice does raise ethical questions.
Thousands of diseases, many quite rare, are caused by a mutation in a single gene or in just a few genes. Genetic tests can be used to look for mutations in specific genes in an individual or in family members. Finding a mutation can confirm a diagnosis or suggest that a person is predisposed to the disease. However, most diseases are caused by many genes interacting over time with our lifestyle, such as the foods we eat and how much we exercise, and our environment, including the air we breathe and the neighborhoods we live in.
A limited type of genetic disorder testing occurs during newborn screening. Each year in the United States, 4 million newborns have blood samples tested for health abnormalities. Screening, which requires just a few drops of blood, can identify genetic disorders such as cystic fibrosis and sickle cell anemia among more than 60 overall disorders that are tested for. However, even with early detection and early medical intervention, children with certain disorders will still experience symptoms.
A more rigorous form of genetic screening may be done as early as birth and throughout a person’s lifetime. Whole genome sequencing refers to the techniques that scientists use to determine the order of the chemical base pairs of a living thing throughout its entire genome. Understanding the complete sequence, including the location, structure, and function of genes, can sometimes help unlock some of the mysteries of inherited diseases. The condition shared by Alexis and her brother, Noah, who appear in this video, is a very rare disorder. Because most inherited diseases are not caused by one or two mutations, whole genome sequencing should not be thought of as something that will identify disorders in every individual.
Despite major advances in technology, identifying mutations is still extremely challenging. Many of the genes of greatest interest to researchers are enormous, containing thousands of bases. Mutations can occur anywhere, and searching through long stretches of DNA is difficult. In addition, a single gene can have many mutations, some more threatening than others. Thus, a positive test does not guarantee that disease is imminent, while a negative test, since it evaluates only the more common mutations, cannot completely rule it out.
Whole genome sequencing offers hope for some people, including those who either have or may be predisposed to a serious medical condition that has a strong genetic basis. But there are limitations that should be understood. Genetic markers may indicate definitive results, but most offer only probability that a particular disease or disorder will develop. One person with a given gene may develop disease symptoms, while another person with the same gene remains healthy. In most cases, environmental and lifestyle factors will play a key part in determining whether the disease or disorder develops.
Moreover, many health professionals and ethicists see an opportunity for abuse in using sequencing, screening, and other emerging tools of biotechnology, especially with the highly personal nature of test results. After all, genetic information could be shared with insurers or other commercial interests intent on exploiting the information for either their gain or your loss. In addition, when parents screen infants or children, they do so without their consent. Parents and physicians learn about the child’s genome before the child has had a chance to determine what he or she would—and would not—like to know. This information might shape the way the parent and others view the child, and it could even shape the way the child views him- or herself, including what the child is capable of doing—and not doing—with his or her life.
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