Am Fam Physician. 2006 Feb 1;73(3):540-541.
I have a patient with a family history of attention-deficit/hyperactivity disorder (ADHD) and drug addiction. She is concerned that her young children will be affected by these conditions later in life. She searched the Internet and found that she could order an at-home genetic test without consulting a physician. She asked my opinion about these tests.
What is the evidence regarding predictive genetic testing? Do these tests have clinical value? Who regulates them? Can patients order genetic tests without consulting a physician? What are the implications for the patient’s family members?
Many common disorders, including ADHD, are complex. They are caused by a combination of multiple genetic variations and environmental factors. Drug and alcohol addiction also have genetic components. For instance, children who have a parent or parents who are alcoholics have an increased risk of becoming alcoholics themselves, even if they are adopted into families that do not use alcohol or drugs.1,2 Additionally, concordance for alcohol or drug abuse is higher in identical twins than in fraternal twins and is higher in biologic siblings than in adoptive siblings.3
Current genetic tests for complex diseases are not diagnostic. They instead provide important information about susceptibility and can be key in prevention. For example, genetic testing to detect a factor V Leiden gene mutation, which is known to increase the risk of blood clots, alerts physicians when to be more vigilant for signs and symptoms of blood clots, and guides management if a clot occurs.
Although many studies have suggested that ADHD and drug and alcohol addiction are associated with certain genes, no predictive genetic variations have been identified for these conditions.4–7 However, genetic testing can help prevent iatrogenic complications. Tests are available to detect important genes that help metabolize many prescription drugs (e.g., common antidepressants and antipsychotics, beta blockers, some chemotherapy drugs). Variations in these genes can cause abnormal or no metabolization, creating a potential for undertreatment or overtreatment with these drugs.
Gene variations that affect a patient’s susceptibility to certain diseases are identified almost daily. This knowledge offers the clinical opportunity to change prevention algorithms from population-based averages to individual risk stratifications. For example, a common variant recently was discovered in factor H that increases the risk of age-related macular degeneration, the leading cause of blindness among older patients.8 This discovery not only provides the opportunity for earlier screening and intervention, but it may lead to new treatments because the gene’s biologic activity is amenable to both lifestyle changes and available drug therapies.
Although the complexity and sophistication of genetic testing is increasing, regulatory oversight is a problem. Advertising for genetic tests is regulated by the Federal Trade Commission (FTC). The FTC may take formal action against the creators of fraudulent advertisements; however, the enormity of the Internet makes these advertisements difficult to regulate. On the other hand, the U.S. Food and Drug Administration (FDA) regulates diagnostic testing kits. Unfortunately, many genetic tests are not kits but rather freestanding tests developed by laboratories and offered directly to patients. The FDA calls these tests “home brews” and regulates only their components, which need only to conform to general standards (e.g., good manufacturing practices).9,10
Because of this current lack of regulatory oversight, consumers should be wary of direct-to-consumer advertising. Direct-to-consumer marketing of genetic tests may: (1) oversimplify complex information, (2) mislead patients by not disclosing all of the risks and limitations of a test, and (3) claim validity or clinical utility when it has not been established. Even if a predictive genetic test has been validated and its results offer a change in clinical intervention, patients whose tests show genetic mutations may feel as though they have been diagnosed with a disease or that disease is eminent. Without adequate interpretation and counseling by a physician, the test may cause unneeded anxiety. Furthermore, a physician is needed to apply genetic test results to the patient’s entire life span as well as to his or her family members.
The American College of Medical Genetics has issued a policy statement11 that discourages the use of genetic testing unless it is provided by a qualified health care professional.
REFERENCESshow all references
1. Kumpfer KL. Outcome measures of interventions in the study of children of substance-abusing parents. Pediatrics. 1999;103(pt 2):1128–44....
2. Schuckit MA, Goodwin DA, Winokur G. A study of alcoholism in half siblings. Am J Psychiatry. 1972;128:1132–6.
3. Rhee SH, Hewitt JK, Young SE, Corley RP, Crowley TJ, Stallings MC. Genetic and environmental influences on substance initiation, use, and problem use in adolescents. Arch Gen Psychiatry. 2003;60:1256–64.
4. Somerville MJ, Mervis CB, Young EJ, Seo EJ, del Campo M, Bamforth S. Severe expressive-language delay related to duplication of the Williams-Beuren locus. N Engl J Med. 2005;353:1694–701.
5. Thapar A, O’Donovan M, Owen MJ. The genetics of attention deficit hyperactivity disorder. Hum Mol Genet. 2005;14:275–82.
6. Scholz H, Franz M, Heberlein U. The hangover gene defines a stress pathway required for ethanol tolerance development. Nature. 2005;436:845–7.
7. Luo X, Kranzler HR, Zuo L, Wang S, Blumberg HP, Gelernter J. CHRM2 gene predisposes to alcohol dependence, drug dependence and affective disorders: results from an extended case-control structured association study. Hum Mol Genet. 2005;14:2421–34.
8. Edwards AO, Ritter R III, Abel KJ, Manning A, Panhuysen C, Farrer LA. Complement factor H polymorphism and age-related macular degeneration. Science. 2005;308:421–4.
9. Javitt GH, Stanley E, Hudson K. Direct-to-consumer genetic tests, government oversight, and the first amendment: what the government can (and can’t) do to protect the public’s health. Okla L Rev. 2004;57:251–301.
10. Burke W, Zimmerman RL. Ensuring the appropriate use of genetic tests. Nat Rev Genet. 2004;5:955–9.
11. American College of Medicine Genetics Board of Directors. ACMG statement on direct-to-consumer genetic testing. Genet Med. 2004;6:60
Case scenarios are written to express typical situations that family physicians may encounter; authors remain anonymous. The Commentary in this issue was written by Phyllis Frosst, Ph.D., and Daniel J. Wattendorf, M.D., Bethesda, Maryland.
Please send scenarios to Caroline Wellbery, MD, at firstname.lastname@example.org. Materials are edited to retain confidentiality.
Copyright © 2006 by the American Academy of Family Physicians.
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