Surprise, You Are Adopted
Genetic testing for cancer may result in unforeseen revelations.
Direct-to-consumer genetic testing (DTCGT) can offer information about ancestry; risk for developing some diseases including cancer, heart disease, malignancy, and Alzheimer’s disease; and physical traits. Different companies offer different options and combinations. But there are unintended risks that can come along with genetic testing.
Oncology nurses may have questions from patients and families about the significance of ancestry testing and how it is done. Although individuals may think ancestry testing is fun and entertaining, they may not realize there are hidden risks. For those undergoing the ancestry testing, there is a risk that an individual may learn that they are not related to persons they initially believed to be their biological family. The emotional consequences can be significant.
Conversely, individuals could learn they have other close relatives that they were unaware of or had been separated from, and may not want to know such information or be prepared to learn about it. Credentialed genetics professionals routinely discuss this possibility in pretest counseling so individuals realize it is a possibility.
Many are intrigued by DTCGT because they hope to better understand their ancestral roots which is often referred to as genetic genealogy. Three types of genetic ancestry testing are commonly used for genetic genealogy1:
- Y chromosome testing: The Y chromosome is passed exclusively from father to son, and can be used to explore ancestry in the direct male line so it can only be done on males. Females who are interested in this type of genetic testing sometimes get a male relative to have the test done to add this information to the ancestry assessment.
- Mitochondrial DNA: Mitochondrial DNA testing is helpful for understanding female lineage. Although most DNA is contained in chromosomes within the cell nucleus, the mitochondria also have a small amount of DNA. Males and females have mitochondrial DNA, which is passed from their mothers, so this type of testing can be used by either males or females to provide information about maternal lineage.
- Single-nucleotide polymorphisms (SNPs): SNPs are genetic variations that represent a difference in a single nucleotide in the DNA. Each SNP represents a difference in a single nucleotide which is a building block in a strand of DNA. SNPs occur regularly in every human’s DNA with an estimated 10 million SNPs in the human genome.1 In many cases SNPs play no role in gene function but some are found in a regulatory region of a gene where they may play a more direct role in disease by affecting the gene’s function. SNPs can be compared across a person’s entire genome. The results are compared with those of others who have taken the tests to provide an estimate of a person's ethnic background. Genealogists use this type of test because Y chromosome and mitochondrial DNA test results, which represent only single ancestral lines, do not capture the overall ethnic background of an individual.
Most DTCGT that offer testing for predisposition to developing disease and ancestry testing only look at some SNPs. It is not sequencing of an entire gene and not sequencing of the entire human genome. For example, 23andMe offers genetic testing for the 3 founder mutations in the BRCA1/2 genes found in approximately one in 40 persons of Ashkenazi Jewish ancestry.2 It does not offer complete sequencing of the entire BRCA1/2 genes for the more than 1,000 known mutations or any of the other genes associated with an increased risk for developing breast and/or ovarian and other cancers for which genetic testing is readily available. SNPs can be analyzed to assess predisposition and in various combinations are also utilized to evaluate ancestry. By combining information from the Y chromosome testing when available, mitochondrial DNA, and selected SNPs it is possible to estimate ancestral roots and sometimes identify close relatives. The more cases in the database, the greater the chance of identifying another relative. Persons doing DTCGT need to understand that their data is being utilized for this purpose as well as other research purposes.
There can be surprises with genetic testing. The focus of pretest counseling with a genetics professional is to provide enough information that the patient can make an informed decision and to explain the possible range of results. DTCGT is not comprehensive genetic testing so a negative test result on an SNP for developing cancer is noninformative. Individuals need to realize they could have a test result that suggests they are at high risk for developing a disease, such as Alzheimer’s, and that there is no prevention strategy for the disease, which could result in worry.
Those doing ancestry testing could also learn about misattributed paternity or maternity or that they have another close relative which can be emotionally disturbing. In the case of misattributed paternity or maternity, an individual might also learn they are at increased risk for developing other health conditions such as malignancy which can be very distressing. In cases of adoption or the potential misattributed parents, credentialed genetics professionals alert patients to the possibility and potential management strategies. In cases of adoption, genetic counselors discuss notifying the agency in the case of a positive test result so other family members potentially at risk have the option of testing. With DTCGT, this potential ethical issue is usually not discussed. In the case of comprehensive cancer genetic testing, credentialed genetics professionals emphasize that results have implications for an entire family, as well as the importance of sharing results. This can be challenging and stressful for some families. It is much more difficult when an individual unexpectedly learns that their family is not who they thought it was.
When patients and friends express an interest in DTCGT oncology nurses have an opportunity to educate on the science behind DTCGT as well as what individual might learn or not learn from DTCGT.
1. United States National Library of Medicine. Your Guide to Understanding Genetic Testing. 2018; ghr.nlm.nih.gov/primer. Accessed April 17, 2018.
2. Wiesman C, Rose E, Grant A, Zimilover A, Klugman S, Schreiber-Agus N. Experiences from a pilot program bringing BRCA1/2 genetic screening to the US Ashkenazi Jewish population. Genet Med. 2016;19:529-536. doi: 10.1038/gim.2016.154.