By Caroline Lieber, M.S., CGC, Director, Human Genetics Program, Sarah Lawrence College
and Wendy R. Uhlmann, M.S., CGC, Coodinator, Medical Genetics Clinic, University of Michigan
Every day genetic counseling presents people with many difficult choices: whether to be tested, who should have access to the results, and who has a voice in these decisions. Here are the stories of a few families who have grappled with the complex implications of genetic information.
Weighing a Parent's Right Against a Child's
A 35-year-old woman, the mother of a 10-year-old son and an 8-year-old daughter, came to the genetics clinic for counseling. Her father had been diagnosed in his late forties with Huntington's disease, a devastating progressive neurological condition which shortens life span and has no cure. Now that she was nearing the typical age of onset for the disease, she wanted to find out whether she was facing the same fate.
The genetic counselor explained the relevant testing guidelines, and they talked about how the results could affect the woman's life decisions. A month later, the woman completed the necessary evaluations, and proceeded with testing. Unfortunately, her test results came back positive. Since that meant that each of her children had a 50 percent chance of inheriting the disease, she requested that they too be tested. As a parent, she felt she had a right to this information and wanted relief from the emotional burden of not knowing what lay ahead for her kids. In the event that either one or both of them had the Huntington's disease gene mutation, she wanted to be able to allocate her limited financial resources accordingly.
Since Huntington's disease mainly affects adults and childhood cases are rare, the testing guidelines specify that individuals should make their own decisions about testing and be at least eighteen years of age. Therefore, the genetic counselor declined the mother's request, also emphasizing that genetic testing of children is only performed when there is a medical benefit to the child.
How Does Genetic Information Affect a Family?
A three-year-old boy was referred to the genetics clinic by his pediatrician. The boy was delayed in his development and hyperactive, and his speech ability was extremely limited. His parents had no idea why. The geneticists who examined the child established that he had the physical features of Fragile X syndrome and recommended genetic testing. Results confirmed that he had Fragile X syndrome, which is the most common inherited cause of mental retardation. Fragile X syndrome results from a gene mutation on the X chromosome and more often affects males, as they just have a single X chromosome.
Since males receive their X chromosomes from their mothers, the boy's mother was informed that she was a carrier. This meant that not only was she at high risk of having another child with Fragile X syndrome, but that other relatives were at increased risk of being carriers or being affected as well. The boy's parents were relieved to have an explanation for their son's behavior at last, and armed with this new knowledge they were better able to put appropriate therapies in place.
Genetic information often affects an entire extended family. The woman had three sisters, all of whom were at risk of being carriers and one of whom was pregnant. Feeling strongly that her siblings should be in a position to make informed decisions, she told them her son's diagnosis. The question, "Why didn't I know?" reverberated up the family tree. Some family members appreciated this information while others were angry. The pregnant sister initially wanted nothing to do with the information, but later decided to be tested. It turned out that her fetus was positive for Fragile X syndrome. The sister continued the pregnancy, but was able to prepare psychologically for the birth of a boy with special needs. While genetic testing had made it possible to diagnose the 3-year-old boy, the results had significant implications for other family members as well.
When Current Technology Falls Short
Since Shelley and David were planning to start a family, they decided to request genetic testing for cystic fibrosis (CF). David's 24-year-old sister had CF, which is a serious lung disease usually diagnosed in the first few years of life. While some individuals are mildly affected, most have a shortened life span.
Cystic fibrosis is an autosomal recessive condition, which means that when both parents carry a gene mutation for the disease, each of their children has a 25 percent risk of being affected. One of the most commonly inherited genetic conditions, CF affects one in 3,300 people, usually Caucasians. One in 29 individuals is a carrier. Because the incidence is so high, it became standard in 2001 to offer cystic fibrosis screening to prospective parents regardless of family history. Unfortunately, screening isn't straightforward. While the most common CF gene mutation was identified back in 1989, geneticists have since discovered over 900 mutations. Most of these are rare and family-specific. Laboratories only test for the most common mutations, which means that only about 85 percent of carriers are detected by current methods.
Shelley had no family history of cystic fibrosis, so she was surprised when test results showed her to be a CF carrier. Also surprising was the fact that David, whose family history gave him a 66 percent chance of being a carrier, tested negative. At this point, a blood sample was obtained from his sister, who turned out to have only one identifiable CF mutation. A second, unidentifiable CF mutation had to be present to cause her illness.
Was David a carrier of his sister's unidentifiable CF mutation? If so, he and Shelley would have a 25 percent risk of having a child with cystic fibrosis. Because the second mutation was unknown, the severity of the disease could not be predicted. Testing David's parents did not resolve his carrier status either. After weighing all these factors, the couple came to the difficult decision to achieve a pregnancy using donor sperm.
When a Genetics Evaluation Saves a Life
Tall and thin for sixteen, Tad was a high school basketball star. He wore contact lenses during games to correct his nearsightedness. Tad's sister Denise, also a basketball player, recently died of an aortic aneurysm during a college game.
At the recommendation of their physician, Tad's devastated parents arranged for a genetic evaluation of their son. Based on Tad's physical examination and the family history, he was diagnosed with Marfan syndrome, a genetic abnormality that often escapes medical diagnosis. Characteristics include nearsightedness and other eye problems, and skeletal features that include disproportionately long arms, legs, fingers, and toes. The major health concern involves the heart: people with Marfan have an increased risk that their aorta will enlarge and eventually rupture. Enlargement is progressive and more likely to occur if the heart needs to work hard over a long period of time, as is the case during competitive sports.
Approximately one quarter of Marfan cases are the result of a spontaneous mutation. The remainder are inherited. Marfan syndrome is an autosomal dominant condition, meaning that every child of a carrier of the gene mutation has a 50 percent chance of having the condition. The fact that both Tad and his sister were affected meant that at least one parent was a carrier. It also meant that other members of Tad's family were at significant risk and needed to be genetically evaluated. Counselors recommended that Tad and other affected family members have annual checkups that include evaluations of their hearts, eyes, and skeletal systems.
Although Tad's echocardiogram appeared to be within the normal limits, the physician recommended that he quit basketball. The cardiovascular stress was extremely dangerous, and a blow to his chest could be fatal. The physician also prescribed beta-blocker medication to slow Tad's heartbeat and lessen the risk of aortic enlargement. Understandably, the diagnosis upset and angered Tad, much of whose identity had centered around his basketball prowess. Eager to engage him in a new activity, his parents introduced him to golf, and within a few months, the teenager was developing confidence in his newfound skills. Tad continued to work with the genetics team to address his concerns and feelings of "Why me?"