(Antfer) #1
8 June 2013 | NewScientist | 15

YOUR eye colour is a product of
your DNA, but what about your
IQ? The biggest-ever search for
genes that affect intelligence,
and the first to give reproducible
results, has found 10 variations
in DNA that seem to influence
intelligence – but not by much.
Studies of families show
intelligence is 40 to 50 per cent
inherited, and otherwise depends
on environment. Since mass-
analysis of DNA variations became
possible, a number of studies have
sought the genes involved in this
inheritance, and some papers
have claimed strong associations
between particular genes and IQ.
Yet results have varied widely and
none have been replicated.
“Many of the published findings
of the last decade are wrong,” says
John Hewitt of the University of
Colorado in Boulder, who was not
involved in the new study.
So if intelligence is inherited,
where are the genes hiding? The
research may have hit problems
because each gene linked with IQ
has only a tiny effect on overall
intelligence. This means you need
data on a large number of people
to reliably distinguish such effects
from measurement error. Most
studies have involved between
100 and 2000 subjects.
Now, some 200 researchers
have assembled 54 sets of data on
more than 126,000 people who
have had their genomes analysed
for 2.5 million common, small
mutations called SNPs.
Information was also available for
how long they spent in education
and the level they reached.
Educational achievement is
only a rough proxy for intelligence,
says Philipp Koellinger of
Erasmus University in Rotterdam,
the Netherlands, an organiser of
the study. But this information is
available for the requisite large
number of people.
The team began by studying

100,000 of the people and found
three SNPs that correlated
significantly with educational
attainment. They then used data
from the other 26,000 people to
test whether the same correlations
held. They did, replicating the
first analysis.
But when the team did a
statistical analysis for the strength
of the correlations for each SNP,
they found that even the strongest
accounted for just 0.02 per cent of
the total variation in educational
attainment (Science, doi.org/mqw).
The three SNPs – and a further
seven that correlated weakly –
accounted for only 2 to 3 per cent
of all the educational variation.
Yet the 2.5 million SNPs account
for half of the heritability of other
complex traits such as height. If
intelligence is 40 to 50 per cent
heritable, the SNPs should have
accounted for at least 20 per cent

of the variation in educational
attainment. Why the discrepancy?
“Probably thousands of SNPs
are involved, each with an effect
so small we need a much bigger
sample to see it,” says Koellinger.
Either that, or intelligence is
affected to a greater degree than
other heritable traits by genetic
variations beyond these SNPs –
perhaps rarer gene mutations
or interactions between genes.
Amassing data from many
studies to detect the small effects
of SNPs makes sense for now, says
Robert Plomin of King’s College
London, who was not involved in
the study. “When whole genome
sequencing is cheap enough, we
can look for sequence variations
of every kind.” Then, the missing
genes for intelligence may finally
be found. Debora MacKenzie^ n

Finding the players in the

symphony of IQ genes

“Research has hit problems
because each gene linked
with IQ has a tiny effect
on overall intelligence”

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  • Myriad genes in concert–

Patrick Gaillardin/Picturetank

Royal Society Ferrier Lecture by
Professor John O’Keefe FRS, University College London

Tuesday 18 June 2013, 6.30pm – 7.30pm
The Royal Society, 6 – 9 Carlton House Terrace,
London, SW1Y 5AG

Admission free – doors open at 6pm

Learn how the brain performs the fundamental task
of locating ourselves in our environment. Professor
O’Keefe will describe how the hippocampal formation,
neuronal activities and ‘space cells’ underpin a sense of
place, direction and distance to create a cognitive map.

For more information visit


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how the brain represents the space

we live in and finds our way around

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