Genetic Tests Can Unearth Family Secrets, Such as Incest

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Nancy Spinner, director of the Clinical CytoGenetics Laboratory at The Children's Hospital of Philadelphia, said the lab's administrative team flags test results where large regions of genetic material inherited from each parent appear the same. She said that among 4,500 cases completed since 2008, the lab found "two clear cases of incest, but after we agonized and discussed it with the physician, they were both known. One father was incarcerated; in the other case, it was known to the family. We will see what happens with a third case we have, which is in the lab right now. It's not even completed yet."

Like Jorde, Spinner cautioned that mothers and fathers can share large amounts of DNA without their relationship being incestuous. "You can have people who are pretty related, but it doesn't mean it's incest per se. Some populations get so inbred, you can have double-first-cousin marriages." Therefore, it's crucial to first review the findings "and make sure you're comfortable that this could really be incest."

Jorde and Spinner noted that more consumers are paying commercial enterprises like "23 and Me" for what Jorde called "recreational genetic testing" to learn about disease risks, ancestry and traits like baldness. Those findings are based on the same kinds of genetic analyses that the university labs use, and "from that information you could certainly deduce parentage," Jorde said.

He recently co-authored a study with data "where you can see if people are third cousins or fourth cousins" that he said could be useful in missing persons cases, or cases where an entire family has disappeared and the only relatives whose DNA is available for comparison might be first or second cousins.

Genetic Testing Shows Fantastic Potential, But Merits Prudence

"The bottom line is we want to be sure that the science is considered carefully and that we contribute to making good, sound scientific judgments and the many legal and ethical issues are considered appropriately," Jorde said.

The American Society of Reproductive Medicine already has been dealing with issues of consanguinity that could arise if children of sperm donors or egg donors met and unknowingly mated with their half-siblings. ASRM guidelines advised limiting pregnancies per sperm or oocyte donor to 25 within a population of 800,000.

Beaudet's publication in The Lancet was accompanied by a graphic depiction of DNA from a 3-year-old boy with multiple medical problems, in which identical genetic regions from his mother and father were depicted as vivid green blocks on his chromosomes.

Asked what he thought the first time he saw such results, Beaudet said: "It is very striking. I've thought, looking at these lab results, these images, it would be fantastic if we could get Mendel and Darwin and other famous geneticists to be able to see what we see today.

"But socially," he said, "it's a disastrous image."

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