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DTC Genetic Testing for Diabetes, Breast Cancer, Heart Disease and Paternity

By: Karen Norrgard, Ph.D. (Write Science Right) © 2008 Nature Education 
Citation: Norrgard, K. (2008) DTC genetic testing for diabetes, breast cancer, heart disease and paternity. Nature Education 1(1):86
Just because testing can be done without the advice of a doctor, does that mean it should be? This controversy lies at the heart of the field of direct-to-consumer (DTC) genetic testing.
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There are many interesting things our DNA can tell us. Scientists have developed several different ways of querying our DNA for information. For example, they can look at the arrangement of our DNA in chromosomes (a karyotype). They can look for patterns in tiny portions of our genome called short tandem repeats (STRs), which can reveal our paternity and our ancestry. They can test for specific changes within a gene, or perform more comprehensive DNA sequencing of particular genes to look for changes that may cause disease. They can also scan our entire genome for single base changes and try to estimate what effect, if any, these changes will have on our health. As exciting as this new technology is, it must be noted that the technical ease with which any of these tests can be performed is inversely proportional to the power of the test result information. This, in turn, raises an important question: Just because testing can be done without the involvement of a health care provider, does that mean it should be done? This controversy lies at the heart of the burgeoning field of direct-to-consumer (DTC) genetic testing.

The Whys and Hows of DTC Genetic Testing

DTC genetic testing is a method of marketing genetic tests to consumers without the direct involvement of a health care provider, and it is gaining in popularity for a variety of reasons. Some consumers of DTC testing view it as another method of gathering medical information about themselves. Moreover, fears of genetic discrimination make DTC testing an attractive alternative to undergoing testing in a doctor's office, because it allows individuals to keep their test results out of their medical records. In the United States, it is hoped that passage of the Genetic Information Nondiscrimination Act (GINA) in May 2008 will reduce consumer fears in this area, but only time will tell whether the measure is successful. In any case, the bottom line is that consumers are increasingly participating in their own health care decisions, and many want to know about the information stored in their DNA.

Shown is a photograph of a gloved hand holding a sample swab. The swab resembles a cotton-tipped ear cleaner, but has a 10-inch wooden handle. On the handle is a protective plastic snap cover that is open, but is intended to enclose the cotton tip after a bio sample is taken with the tip.
A typical swab used for collecting biological samples containing DNA.
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Proponents of DTC genetic testing argue that this practice offers numerous benefits, including increased consumer access to testing, greater consumer autonomy and empowerment, and enhanced privacy of the information obtained. On the other hand, critics of DTC testing point out that consumers may undergo testing without adequate context or counseling, may receive tests from laboratories of dubious quality, and may be misled by unproven claims of benefit. The following vignettes highlight some such benefits and risks associated with different types of DTC genetic testing.

DTC Testing and Family Planning

Imagine that a couple that has not been able to start a family on their own has just gone through one unsuccessful round of in vitro fertilization (IVF). They want to know about any genetic factors, such as balanced chromosomal translocations, that might be contributing to their infertility. Before they undergo another expensive round of IVF, they seek DTC testing for chromosomal rearrangements. In this type of testing, the couple would receive a kit from the testing company that would include a voucher for blood collection at a local lab facility. The couple would then submit their samples for karyotype analysis. A karyotype looks for numbers of chromosomes, large additions to or deletions from chromosomes, and rearrangements of the chromosomal material.

The only type of chromosomal abnormality that an individual might not be aware of until adulthood would be a balanced translocation. This is a situation in which an individual has a complete complement of chromosomes, and therefore is healthy, but his or her chromosomal material is rearranged in such a way that during meiosis most gametic cells end up with missing or extra chromosomal material. An embryo resulting from this type of gamete would likely be miscarried early in development. This couple must be aware, however, that finding a normal karyotype for both parents does not mean their next round of IVF will be successful. In order for DTC testing to be beneficial to this couple, they will need counseling from a knowledgeable source to discuss the results they receive. This is vitally important, because the couple will be making family planning decisions based on their understanding of these results.

DTC Paternity Testing

Say that a man who was recently contacted by a woman claiming to be his daughter wants to know if the claim is true. He seeks DTC paternity testing to find out. The test kit contains supplies, and it provides the man with instructions on how to collect a sample of cells from the inside of his cheek. The samples are then sent to a lab, where genetic paternity testing is performed by analyzing regions of repetitive DNA known as short tandem repeats (STRs). STRs vary in size, but the size of each STR is inherited. Thus, the lab performing the analysis will compare at least nine STRs from different locations in the man's genome with the same STRs in the potential daughter's genome. If at least two STR sizes (called alleles) do not match between the alleged father and daughter, the man is excluded as the biological father. On the other hand, if the alleged father and daughter have a matching allele for each STR analyzed, a mathematical calculation is performed to determine the likelihood of paternity. The formula takes into account the fact that a certain proportion of individuals in the general population also carry these STR alleles. Therefore, a determination of paternity is always given as a likelihood, with most laboratories performing enough testing to determine a likelihood of paternity of greater than 99.99%. Conversely, an exclusion of paternity is definite, with a likelihood of 100%.

Paternity testing kits can be ordered online and are now even available in some pharmacies. For testing accuracy, the samples must be collected carefully to avoid contamination. Additionally, it is important to understand that this type of paternity testing is not legally admissible and would not be accepted by any court. This is not because this type of testing is inaccurate; it is simply due to the chain-of-custody requirements for the DNA samples. Thus, if the daughter plans to claim inheritance rights or the father wants to dispute child support obligations, this duo should not rely on DTC testing; rather, they must utilize a third party to collect and maintain the samples before they are shipped to the lab for analysis. If the man and his potential daughter are simply curious, however, this type of DTC paternity test will tell them whether they are related.

DTC Testing for Cancer Susceptibility

Now, imagine that a young mother has just lost her good friend to breast cancer. Her friend was in her forties and left behind young children. The woman is devastated by this loss, and she is determined to do everything she can to reduce her risk of breast cancer. She therefore decides to seek DTC testing for mutations in the breast cancer susceptibility genes, BRCA1 and BRCA2. But is this testing right for her?

Ideally, this woman would first meet with her doctor to discuss whether she is a good candidate for this type of test. Physicians in the United States and other countries are given guidelines to help determine who would best be served by such testing. The reasons for this are many. One important reason is that BRCA1 and BRCA2 gene mutations are associated with very few cases of breast cancer. Most breast cancer does not have a predictable genetic basis. Also, the results of genetic testing for BRCA1 and BRCA2 mutations are not easily interpreted. Sometimes, it is unclear whether a change identified in the gene is associated with cancer or is simply due to normal human variation. Additionally, the absence of a detectable BRCA1 or BRCA2 mutation does not mean that a woman is safe from breast cancer; thus, such results could give a woman a false sense of security. The fact is, the causes of breast cancer are many and are due to a combination of family history, genetic factors, environmental factors, and gene-environment interactions.

If this woman has no family history of breast or ovarian cancer and does not have any other risk factors, her physician would advise her that she is not a good candidate for breast cancer genetic testing. However, because of her personal experience involving her friend, the woman's perception of her own risk is likely to be inflated. In cases such as this one, circumventing the medical system and seeking DTC testing for BRCA1 and BRCA2 mutations may allow an individual some relief from anxiety. However, it is vitally important that any woman seeking DTC genetic testing for breast cancer susceptibility gets adequate genetic counseling before and after testing. These women must also understand the limitations of the testing, including the possibility of receiving results that add no helpful information. It is critical to remember that many women will be making important medical decisions based on these results, including the possibility of prophylactic mastectomy.

Genome-wide Scans to Check for Disease Risk

Say that a young man who knows that his eating and exercise habits are not ideal is curious to find out whether he might be susceptible to heart disease or diabetes. He therefore seeks a genome-wide assessment survey to obtain information about his genetic predisposition to these conditions. He hopes the information will help him to make better lifestyle choices. The test kit contains instructions on how to collect a saliva sample for analysis. The lab will analyze the DNA in the saliva for individual base changes (called single nucleotide polymorphisms, or SNPs) and make a statistical estimation of the man's risk for certain conditions based on studies that compare the presence of particular SNPs to the presence of these conditions in a large population.

With this type of testing, it is important to remember that genes are certainly not the only determinant of health; other factors can play an equal or greater role in determining the development of a particular disease or condition. Additionally, the scientific understanding of how genetics may affect disease risk and other aspects of a person's health is changing and will continue to change as more research is performed. However, these results could certainly inspire this young man to adopt better lifestyle choices, and they may also serve to educate him about genetics. At the very least, this type of testing should stimulate a dialog between the man and his doctor about genes and their role in health.

Risks of DTC Genetic Testing: Lack of Oversight and Inadequate Interpretation and Counseling

Unquestionably, there are advantages to allowing consumers to access genetic tests directly. For example, DTC testing helps raise awareness of genetics in general and the interaction between genes and environment in particular, and it challenges physicians to be better educated. However, real and potential harms do exist. For one, there is currently very little federal oversight of DTC genetic testing. Although all U.S. laboratories that offer test results to the public are required to be certified and employ certain basic practices per the Clinical Laboratory Improvement Amendments of 1988 (CLIA), these regulations do not address the clinical validity of the tests that a lab offers. In other words, even if a lab is certified, there is no guarantee that the test results that the lab provides are relevant to existing or future diseases or conditions.

Moreover, the only oversight by the U.S. Food and Drug Administration (FDA) on testing for genetic diseases comes in the regulation of test kits that are marketed and sold to labs for use in testing procedures. Compounding this issue is the fact that most laboratories do not use such kits to perform genetic tests (only very few are available); instead, they rely on methods developed in-house (so-called home brews) that are not currently reviewed by the FDA.

It is also critical to note that some tests offered by DTC companies, such as those for addiction, fetal gender, and general nutrition, are not widely accepted in the scientific community. In addition, even if a test is credible and the lab proficient, receiving test results without adequate interpretation and counseling can cause more harm than good. There simply are no standards governing how much information and what type of information DTC companies must provide to consumers before and after testing, leaving each company to make these decisions for itself.

Given these and other concerns, about half of the states in the U.S. currently ban the use of DTC genetic testing altogether, with several more states allowing consumers only limited use of it, such as by requiring a physician to request the testing on behalf of a patient. DTC companies have found ways around these rules, however, such as having medical doctors on their staff order testing for consumers.

Several countries have published guidelines to warn consumers of the risks associated with DTC genetic testing. Similarly, the American Society of Human Genetics (ASHG) statement on DTC testing expresses the following concerns:

"[I]n the current environment, consumers are at risk of harm from DTC testing if testing is performed by laboratories that are not of high quality, if tests lack adequate analytic or clinical validity, if claims made about tests are false or misleading, and if inadequate information and counseling are provided to permit the consumer to make an informed decision about whether testing is appropriate and about what actions to take on the basis of test results."

It is possible that with enhancements to DTC testing, such as truth-in-advertising requirements for vendors, development of evidence-based reviews of tests, professional guidelines for the administration and interpretation of tests, and incentives for laboratories to use FDA-approved test kits rather than home brews, the medical community may one day look more favorably upon DTC genetic testing. Of course, only time will tell.

References and Recommended Reading

Genetics and Public Policy Center. "Survey of Direct-to-Consumer Testing Statutes and Regulations." (2007). Accessed August 26, 2008

Hudson, K., et al. ASHG statement on direct-to-consumer genetic testing in the United States. American Journal of Human Genetics 81, 635–637 (2007)

Human Genetics Commission. "Genes Direct: Ensuring the Effective Oversight of Genetic Tests Supplied Directly to the Public." (2003). [PDF]

Williamson, R., et. al., DNA testing for all, Nature 418, 585–586 (2002) doi: 10.1038/418585a (link to article)


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