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Specific IQ genes still elusive, latest hunt finds

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LOS ANGELES (AP) — Scientists who hunt for “intelligence genes”

used to think there were fewer than half a dozen of

them.

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In recent years, they determined there may be at least 1,000 – each

with just a tiny effect on the differences in people’s IQ. A study

released Tuesday found new evidence that many genes play a role in

intelligence, but scientists still couldn’t pinpoint the specific

genes involved.

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“It’s been kind of a shock to the system that it hasn’t worked,”

said psychologist Eric Turkheimer at the University of Virginia,

who had no role in the study. “We can’t find the effects of any

individual genes that are large enough to seem worth worrying

about.”

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Previous work involving twins and adopted children has found that

genes have a significant influence on differences in IQ scores,

producing about half the difference between adults in general. The

influence of genes on IQ appears to grow from childhood to

adulthood.

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Scientists have come to realize that, as with height, differences

in intelligence come not from a few genes, but rather the overall

effect of many genes, each with only tiny influence. That makes

them hard to tease out.

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The new DNA study, reported online Tuesday in the journal Molecular

Psychiatry, came to similar conclusions. Many genes work together

to shape intelligence much like the different instruments of an

orchestra that play in sync. Unless there’s a soloist playing, it’s

often difficult to decipher the contributions of individual

instruments.

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As important as genes are in determining intelligence, they don’t

act alone and the role of one’s upbringing and experiences cannot

be ignored.

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So why do researchers care so much about the relationship between

genes and intelligence?

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Our memory, reasoning skills and thinking abilities tend to decline

as we age, some faster than others. Understanding the genetics of

intelligence may someday help researchers gain a better handle on

mind-robbing diseases such as Alzheimer’s.

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The new work was done by I.J. Deary of the University of Edinburgh

in Scotland and colleagues in several countries.

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The team wanted to find out “whether genetic differences that we

could test on people’s DNA could explain some of the reasons that

people have different intelligence test scores,” Deary said in an

email.

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Researchers didn’t ID any genes affecting IQ. But they estimated

that they found a genetic influence that accounts for at least 40

percent to 50 percent of the differences on intelligence test

scores in the 3,511 unrelated adults in their study who were tested

on knowledge and problem-solving skills.

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They focused on more than 500,000 places in the participants’ DNA,

looking for evidence that IQ-influencing genes lay close to those

places. They concluded that the overall effect was coming from many

scattered genetic differences, each of only small

influence.

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The latest work adds to evidence that even the most powerful of

these has only weak influence. Deary said that future studies will

probably need to involve millions of people to detect the genetic

effects.

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Robert Plomin of the Institute of Psychiatry in London, who’s

looked for intelligence-related genes for 15 years but didn’t

participate in the new study, isn’t surprised by the latest

findings.

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“We’ve got a century of twin and adoption studies,” such as those

comparing twins reared in different families, that support the

notion that about half of IQ differences come from DNA, he

said.

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Plomin said this doesn’t mean half of a person’s intelligence is

due to genes nor does such a genetic influence imply that a

person’s intelligence is fixed.

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Turkheimer, the Virginia psychologist, thinks other types of

research such as brain scans might have better luck in

understanding what intelligence is.

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Those methods are better than “pinning your hopes on adding

together a bunch” of small effects from individual genes, he

said.

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John Olsen, of Orange, Calif., who was adopted at birth, attributes

his brainpower to his genes. As a kid, he always wondered where his

inquisitiveness came from. School bored him and there were no

lively debates at the dinner table growing up.

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“I was a bit of a challenge,” he recalled. “I was very curious and

like a lot of intelligent people always asked, `Why?'”

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In his late 20s, Olsen took a genius test and scored high enough to

get accepted into Mensa, the high IQ group. A telephone call from a

long-lost aunt several years ago led to a reunion with his

biological mother.

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Olsen soon discovered his mother had the same curiosity and liked

to ask probing questions. He also learned his maternal grandmother

was fond of one-line comebacks and “was wickedly smart till the day

she died.”

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Online: Journal:Ā 

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Ritter reported from New York.

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