Imagine it is the year 2015 and you go to your doctor’s office for a checkup. As part of the routine examination, the technician obtains a scraping from the inside of your cheek that contains some cells. The DNA from this material will be sent for testing and the results will be used to counsel you for illnesses that you may be prone to develop as you age. You may be told that you are susceptible to cancer of the colon or lung; perhaps you are at higher risk to develop Alzheimer’s disease? Maybe you could be at higher risk to develop a mental illness. How would you feel about this information if you were an adolescent?
Gregor Mendel, an Austrian monk is considered to be the father of genetics. In 1865 he published results of his experiments on garden peas that formulated a basis for fundamental principles of heredity. In 1909, Johannsen developed the term gene to denote the basic unit of heredity. Avery showed in 1944 that genes were made of DNA. And Watson and Crick in the middle of the Twentieth Century uncovered the chemical basis of heredity with their understanding of the double helical nature or physical structure of DNA.
Every normal human has forty-six chromosomes in each cell that are composed of DNA. Chromosomes 1 through 22 are paired with one chromosome from each parent thus accounting for forty-four chromosomes. Females have two X chromosomes with one from each parent, and males have an X chromosome from the mother and a Y chromosome from the father. These account for forty-six chromosomes and approximately thirty thousand genes are located on these chromosomes.
In 1990 the Human Genome Project was initiated in order to map, identity and sequence the entire human genome-that is all genes in the human body. By the early part of the Twenty-first Century, the human genome had been mapped so that the physical structure of all thirty thousand genes had been identified. Over the coming years, researchers will be able to locate and map the genes that cause a number of diseases. At this time we know, for example, that the following are a few of the disease genes that have been mapped:
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Huntington disease gene on chromosome 4
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Juvenile diabetes gene on chromosome 11
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Alzheimer disease gene on chromosome 14
Mapping and sequencing the human genome will allow researchers to confirm the genetic basis of a disease. For example, in individuals afflicted with Parkinson’s disease, there is an accumulation of an abnormal protein in their brain cells. Researchers have determined that there is a mutation in a gene with individuals who have Parkinson’s disease. The mutated gene allows for the production of this abnormal protein in some, but not all, patients with Parkinson’s disease.
How does this apply to a teen? The gene that allows for the presence of the abnormal protein in Parkinson’s disease will be present at conception—long before a patient becomes ill from the disease. Even though adolescents will not have symptoms from Parkinson’s disease, the abnormal gene can be detected. This would allow for the diagnosis of the disease well before symptoms occur. If any preventive measures are available, then these could be instituted while the patient is not having symptoms.
Some adolescents may not wish to learn about their genetic information. Suppose you have a gene that predicts future coronary artery disease. Some clinicians might prescribe medications to lower cholesterol, ask the adolescent to engage in athletics and maintain a healthy diet and lifestyle. On the other hand, some adolescents may not wish to make lifestyle changes.
If genetic testing indicated that a teen is susceptible to colon cancer as an adult, and this information is not confidential, then insurance companies or even employers may discriminate against the individual. Suppose your life partner insisted on you having comprehensive genetic testing prior to marriage. Would that create issues for you? What if your genome and your partner’s genome created a significant health risk for any offspring? Would that affect your relationship?
Screening for genetic disease does occur at this time. For example, even prior to conception, partners may be screened for the carrier state of Tay-Sachs disease. Since this disease is transmitted as an autosomal recessive disorder, both parents need to be carriers before a child could be affected with the disease. Up to one of out thirty Ashkenazi Jews carry the abnormal gene that leads to Tay Sachs disease. It has been mapped to a location on chromosome 15q. Every normal human has two #15 chromosomes. A carrier of Tay Sachs will not have any symptoms of the disease because he or she has two #15 chromosomes where one has a normal gene and the other has the abnormal gene causing Tay Sachs. An individual with the disease has inherited the abnormal gene from both parents.
During a pregnancy, some women undergo amniocentesis where some amniotic fluid is removed and chromosomes are tested. Trisomy 21, Down syndrome, may be diagnosed in this way. Screening for abnormal genes in an unborn child could become possible, and this could result in ethical dilemmas. Suppose that the unborn child is found to have a gene that would result in the development of neurofibromatosis as he or she grows up? Should the parents consider terminating the pregnancy? Would parents seek to have a child who is the least risk for developing illness? Is it ethical or appropriate to terminate a pregnancy on the basis of the unborn child’s genome?
Each individual’s genome will allow, at some time in the future, the determination of risk for certain illnesses. A baby’s genome could be analyzed and all of the risks for genetic disease could be laid out for his or her parents. On the one hand, this would allow for any preventive measures and this may include medications, lifestyle changes or other measures that could be initiated before diseases occurred. On the other hand, this genetic information, in the wrong hands, could lead to discrimination or oppression against affected individuals.
A more chilling issue can occur if a genetic disease can be detected by studying a teen’s genome. However, if diagnosis can be done well before symptoms, but there is no treatment available to prevent or cure the ailment, then frightening consequences may ensue. In this situation, no information may be better than having information but no cure or prevention. Huntington’s disease, a progressive degenerative neurological problem that leads to death over a decade or two in affected individuals, can be predicted now by blood testing. There is no preventive or curative therapy. Some teens who have a close family history of the disease refuse to have the blood test. Since Huntington Disease has autosomal dominant transmission, half of the offspring of an individual with the defective gene will be positive. This indicates that at some time, usually after age thirty, they will begin the slow downward spiral of this disease. It may be important, however, for an individual to know prior to conceiving a child whether he or she has the gene and will be affected with the disease or could transmit it to offspring.
It is very likely that the adolescents in 2015 will be able to have some testing of their genome to predict genetic disease. The more difficult questions are whether the testing should be performed, who should have access to the information, what can be done once the information is obtained and how will this affect the life of the teenager.
Related topics:
Autism, cystic fibrosis, Down syndrome, Klinefelter’s syndrome, manic-depressive disorder, neurofibromatosis, pregnancy termination, schizophrenia, sickle cell anemia, Turner syndrome
