DNA tests for IQ are coming, but it might not be smart to take one

Abstracted from MIT Technology Review, Antonio Regalado April 2, 2018

A year ago, no gene had ever been tied to performance on an IQ test. Since then, more than 500 have, thanks to gene studies involving more than 200,000 test takers. Results from an experiment correlating one million people’s DNA with their academic success are due at any time.

The discoveries mean we can now read the DNA of a young child and get a notion of how intelligent he or she will be, says Plomin, an American based at King’s College London, where he leads a long-term study of 13,000 pairs of British twins.

Robert Plomin, a behavioral geneticist, says that’s exactly what’s coming. Plomin outlined the DNA IQ test scenario in January in a paper titled “The New Genetics of Intelligence,” making a case that parents will use direct-to-consumer tests to predict kids’ mental abilities and make schooling choices, a concept he calls precision education.

As of now, the predictions are not highly accurate. The DNA variations that have been linked to test scores explain less than 10 percent of the intelligence differences between the people of European ancestry who’ve been studied.

Even so, MIT Technology Review found that aspects of Plomin’s testing scenario are already happening. At least three online services, including GenePlaza and DNA Land, have started offering to quantify anyone’s genetic IQ from a spit sample. Others are holding back. The largest company offering direct-to-consumer DNA health reports, 23andMe, says it’s not telling people their brain rating out of concern the information would be poorly received.

Nonethelss measure of intelligence are  highly heritable. Comparisons of twins, both identical and fraternal, separated at birth or raised together, had shown that genetics must account for more than half of intelligence—a huge effect for genes. The rest is due to your schools, your diet, and other environmental factors.

The search for a gene did not go well at first. Plomin failed to discover any links when he looked at the genomes of 7,900 children in 2010. He later became involved in a misadventure involving a Chinese sequencing company, BGI, to which he supplied the DNA of more than a thousand American geniuses. The project got derailed after news reports accused the Chinese of hatching a plot to breed “genius babies.”  The gene hunt finally paid off in May 2017. A Dutch-led study of the genetic makeup of 78,308 people who’d taken tests (including 2,825 of Plomin’s twins) zeroed in on variations in 22 genes linked to IQ scores. By this March, the tally had rapidly risen to 199,000 people and 500 genes. Plomin says a forthcoming report will establish links to 1,000 genes.

Each genetic variable found so far has only a tiny effect, either weakly increasing IQ on average or weakly decreasing it. The trick to turning the discoveries into a personal DNA IQ test? Simply add up all the pluses and minuses you find in a specific person’s genome.  These  “polygenic scores becoming a very big deal  because they work for any trait, including heart disease, diabetes, and schizophrenia—in all, more than 200 traits so far.

Several scientists told MIT Technology Review they don’t believe genetic IQ tests can tell individuals anything useful and aren’t sure why Plomin is saying they will. “We will never be able to look into someone’s DNA and say your IQ will be 120,” says Danielle Posthuma, who led the big 2017 IQ study. “I don’t think it makes much sense to use it that way. I would just give people an IQ test.” Posthuma says her main interest is in discovering how the brain works at a basic level, where finding genes associated with intelligence can help.

Plomin, however, points out that IQ tests with colored blocks barely work for little kids, failing to accurately capture how they will do on tests later in life. Your DNA, on the other hand, is there from the day you are born and doesn’t change. Early in life, Plomin says, DNA may already provide a better intelligence prediction than any test does.

Still, the issue is accuracy—or lack of it. Right now, the polygenic scores capture only a fraction of the genetic determinants of intelligence and none of the environmental ones. That means the predictions remain fuzzy.
Plotted one against the other, the result looks more like a slightly elongated cloud of dots than a straight line. That is, the DNA predictions and the test scores tended to line up, though not perfectly. Some with low DNA scores had gotten great test results as teens. Others had bombed despite the promise in their genes.

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