Does this dog look like a Saint Bernard? The questionable business of home DNA tests

A home DNA test said Teddy is a Saint Bernard and pit bull mix. Critics say such tests — for humans and pooches — aren't always reliable. (David Lazarus)

A DNA test found that I’m 72.3% of Ashkenazi Jewish descent, thanks to ancestors from Ukraine. I expected as much.

It also determined that I’m 11.3% Scandinavian, 7.8% Spanish or Portuguese, and 3.1% Italian.

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This is unexpected, both to me and my parents, who insist there are no secret Swedes or Spaniards in our family tree. I gesture a lot when I speak, so who knows about the Italian thing.

Another DNA test found that my family’s dog, Teddy, is part pit bull, which comes as no surprise. Many rescue pooches have pit bull roots.

The test also says Teddy is to a great extent of Saint Bernard stock, which maybe you can see if you really squint, but which, to my mind, is a bit of a stretch. Rottweiler maybe, or mastiff — he’s a big, strong dog — but Saint Bernard?

These results raise questions many people ask (or should ask) when they approach the multibillion-dollar business of home DNA tests, which are readily available online:

Are they accurate?

Are they worth the money?

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What good is the information?

I spoke with a number of geneticists, and the consensus was that you should approach home DNA tests with a degree of skepticism.

It’s not that the test results are routinely wrong. It’s more that they may not be entirely right.

And because each testing company has its own proprietary database and algorithms, results can vary from company to company and test to test.

“I’d say these tests are reliable up to a certain point,” said Sheldon Krimsky, a professor of urban and environmental policy and planning at Tufts University and author of a number of books on genetics and bioethics.

“For the ancestry tests, it’s best to think of it more as a recreational activity,” he told me. “It will probably satisfy you because it will provide results you generally expected.”

Kind of like a horoscope. You readily embrace it when it sounds good, and you easily dismiss it when it doesn’t.

Potentially more troublesome is relying on home DNA tests for medical information, such as indications of a genetic propensity for cancer or diabetes.

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As with the ancestry results, maybe some of the findings will be spot on. But do you really want to start planning for a future with Lou Gehrig’s disease based on a $100 test kit purchased through Amazon?

“I’d always get a second opinion,” Krimsky said.

A recent study in the journal Genetics in Medicine found that as many as 40% of findings in home DNA tests that indicated a risk of disease turned out to be false positives — that is, they were wrong.

And some test results that showed an “increased risk” of a specific ailment couldn’t be replicated in more advanced clinical labs, where testing showed no heightened risk of sickness.

The study’s authors concluded that “while having access to raw genotyping data can be informative and empowering for patients, this type of information can also be inaccurate and misinterpreted.”

Nevertheless, consumers are fascinated by the prospect of peeking under the genetic hood. It’s like riding along on that microscopic sub in “Fantastic Voyage.”

The industry received a boost after recent reports that investigators tracked down a man suspected of being the Golden State Killer through a rare genetic mutation found in a DNA database.

The number of people who submitted DNA samples to testing firms more than doubled last year, according to the MIT Technology Review. Aggressive marketing by industry leaders such as Ancestry.com and 23andMe has prompted over 12 million people to give home testing a try.

It’s easy to do. You swab the inside of your cheek, seal it in a tube and send it to the company. Within weeks, your results are available online.

“People come to 23andMe for a variety of reasons — a desire to learn more about their genetic heritage, connect with family members, or learn how their DNA can impact health and wellness,” said Andy Kill, a company spokesman.

It’s a refrain I heard repeatedly from test providers, how they’re making the world a better place by creating a genetically informed public.

Only one company, Ancestry.com, said it was “confident in the science and the results that we give to customers.” But it insisted that I attribute that to “an Ancestry official,” rather than someone who could stand behind such a bold statement by giving their name.

On-the-record comments were more in line with what I heard from David Nicholson, co-founder of Living DNA, who said that “DNA testing offers new insights that have not previously been possible.”

Marcy Darnovsky, executive director of the Center for Genetics and Society, a Berkeley nonprofit organization, said such claims should be taken with a grain of salt.

“In fact,” she said, “there are so many grains needed, you’re going to have a really big shaker.”

Darnovsky said frequent stories of people receiving dubious results — one testing company reportedly couldn’t tell that DNA from a Labrador retriever wasn’t human — should prompt potential test takers to think twice.

She also noted that most testing firms make additional money by sharing user data with drug companies and others, although the test-kit providers insist that their business partners can’t identify individual people.

“I wouldn’t take one of these tests,” Darnovsky said.

Neither would Wayne Grody, director of the UCLA Molecular Diagnostic Laboratories and Clinical Genomics Center.

He told me an ancestry check might be fun as long as it isn’t taken too seriously. But no one should make medical choices based on a relatively inexpensive home DNA test.

“The science just isn’t that good,” Grody said, noting that a full sequencing of one’s genome can run thousands of dollars and involve multiple analysts.

On the critter front, Angela Hughes, a veterinary geneticist, said breed-identification results tend to be more reliable, although 1 in 10 findings about a dog’s past could be wrong.

“The less of a mix the dog is, the more accurate the results will be,” she said.

If there’s a takeaway from all this, it’s: Go into home DNA testing with your eyes open.

Think of it as a form of entertainment, like getting your fortune told. Don’t use it as the basis for major decisions, at least not without getting confirmation via a more comprehensive exam.

Remember: Sweden has one of the world’s best reputations, according to the Reputation Institute, and I’m 11.3% Scandinavian.

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So I know what I’m talking about.

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