Tiny gene change affects brain size, IQ

2012-04-16 07:44

Paris - An international team of scientists said on Sunday the largest brain study of its kind had found a gene linked to intelligence, a small piece in the puzzle as to why some people are smarter than others.

A variant of this gene "can tilt the scales in favour of a higher intelligence", study leader Paul Thompson told AFP, stressing though that genetic blessings were not the only factor in brainpower.

Searching for a genetic explanation for brain disease, the scientists stumbled upon a minute variant in a gene called HMGA2 among people who had larger brains and scored higher on standardised IQ tests.

Thompson dubbed it "an intelligence gene" and said it was likely that many more such genes were yet to be discovered.

The variant occurs on HMGA2 where there is just a single change in the permutation of the four "letters" of the genetic code.

DNA, the blueprint for life, comprises four basic chemicals called A (for adenine), C (cytosine), T (thymine) and G (guanine), strung together in different combinations along a double helix.

In this case, the researchers found that people with a double "C" and no "T" in a specific section of the HMGA2 gene had bigger brains on average.

"It is a strange result, you wouldn't think that something as simple as one small change in the genetic code could explain differences in intelligence worldwide," said Thompson, a neurologist at the University of California at Los Angeles.

Study of brain scans

The discovery came in a study of brain scans and DNA samples from more than 20 000 people from North America, Europe and Australia, of European ancestry.

People who received two Cs from their parents, a quarter of the population, scored on average 1.3 points higher than the next group -half of the population with only one C in this section of the gene.

The last quarter of people, with no Cs, scored another 1.3 points lower.

"The effect is small," said Thompson, but "would be noticeable on a [IQ] test ... [it] may mean you get a couple more questions correct.

"It wouldn't be an enormous change. Even so, it would help our brain resist cognitive decline later in life."

It is generally accepted that genes, a good education and environmental factors combine to determine our intelligence.

"If people wanted to change their genetic destiny they could either increase their exercise or improve their diet and education," said Thompson. "Most other ways we know of improving brain function more than outweigh this gene."

He added there were ethical safeguards and laws in place to guard against the abuse of genetic information.

The research, published in Nature Genetics, was conducted by more than 200 scientists from 100 institutions worldwide, working together on a project called Enigma.

Thompson said other studies have implicated some genes in IQ, but this was the first to link a common gene to brain size.

Small genetic changes

The team found that every T in place of a C represented a 0.6% smaller brain - equal to more than a year's worth of brain loss through the normal ageing process.

Asked to comment on the research, Tom Hartley, a psychologist at Britain's University of York said he was "a little wary of thinking in terms of a gene for intelligence.

"There are undoubtedly a lot of things that have to work properly in order to get a good score on an IQ test, if any of these go wrong the score will be worse".

But he said it was "fascinating" to find that such small genetic changes could affect the size of critical structures such as the hippocampus, the brain's memory centre.

"Given the importance of the hippocampus in disorders such as Alzheimer's disease these could turn out to be very significant findings," said Hartley.

John Williams, head of neuroscience and mental health at the Wellcome Trust, a British charitable foundation which backs biomedical research, said the findings paved the way for further research into "structural changes" which occur in disorders such as dementia, autism and schizophrenia.

  • SarcasticAgnostic - 2012-04-16 10:35

    How long before the atheists claim "double C" for themselves?

      zaatheist - 2012-04-16 11:20

      Actually we don't need to. Obviously T stands for theist.

      zaatheist - 2012-04-16 11:20

      Actually we don't need to. Obviously T stands for theist.

      SarcasticAgnostic - 2012-04-16 11:52

      Not exactly what I was expecting, but I'll let that count. 3h 36min. Took you long enough, now go prove it.

      zaatheist - 2012-04-16 12:07

      Prove what?

      zaatheist - 2012-04-16 13:05

      Ok. It took me a while to get it. Atheists scored an average of 1.95 IQ points higher than Agnostics, 3.82 points higher than Liberal persuasions, and 5.89 IQ points higher than Dogmatic persuasions. - and

      SarcasticAgnostic - 2012-04-16 20:37

      Firstly, i'm going to ignore the atheist site (off-hand) for being biased. Secondly, Helmuth Nyborg, the guy who did the study in 2008 has this in his track record (Wikipedia Helmuth Nyborg): "His research has been widely criticized, and in 2007, after having been accused of scientific misconduct, he received a warning from Aarhus University for producing research of unacceptably low quality. In 2007 he retired." and if the sentence following directly after that("Nyborg's case is frequently cited as an example of how political correctness impedes science") does not impede your support, keep reading: "A recent article proposing that migration from third world countries to Denmark would cause a dysgenic effect on the country's average IQ over time, has led to Nyborg being indicted to the Danish Council for Scientific Misconduct a second time, accused of committing scientific fraud by using statistic models of population growth known to be erroneous and for not properly attributing the source of the model." In my opinion the racist accusation later in his career sounds like media sensationalism. If this sounds like an ad-homenim attack, you are rather perceptive, it is.

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