This video describes several traits that a human being can exhibit when they have chimerism (two-toned skin, hair and different colored eyes). Additional traits include being from a fraternal twin/multiples pregnancy, having two different blood types, and having transgender identity. Individuals who are left-handed or ambidextrous are thought to have a higher likelihood of having had a twin, and therefore may be chimeras. Lastly, being excluded from a standard DNA test for maternity/paternity for unexplained reasons can be an indication that chimerism is at play.

DNA tests have limitations, and DNA relationship tests are no exception. Current DNA paternity/maternity tests can fail to identify parents who have chimerism. The current, standard DNA tests (called STR-based tests) rely on 15-20 DNA markers, and if one single marker does not match between two tested individuals, they can accidentally exclude an adult with chimerism from being a biological parent. Cases of mothers with chimerism who nearly lost parental rights have been documented since 2002, and more recently, a father in 2014. If chimerism is a known cause of false negative parental DNA tests, why are relationship testing labs continuing to use the STR-based test methodology? The 2014 chimerism case demonstrated the power of using more advanced DNA tests (called microarrays) which are already utilized by ancestry testing labs. Why are paternity testing labs slower to evolve?

What should you do if you or someone you know might have chimerism? If you suspect chimerism, you might consider contacting a genetic specialist such as a genetic counselor. Chimerism specialists can evaluate relationship test results, and/or help you to design a chimerism-appropriate testing strategy. By identifying a second genome, paternity and maternity can be restored, and parental rights can be protected. If you are a clinician, a researcher, or a legal professional, you may be interested in a clinical guide.

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