Published by the Students of Johns Hopkins since 1896
January 28, 2022

Scientists confirm that brain size affects intelligence

By MICHAEL YAMAKAWA | April 27, 2012

The genetic link between brain size and intelligence has proven controversial. Studies have demonstrated weak to moderate relationships between brain size and IQ and have not provided definitive conclusions about the effects of genetic makeup on the construction of the brain. The high cost of brain imaging has impeded scientists' abilities to gather sufficient data, leading to underpowered brain studies.
Project ENIGMA (Enhancing Neuro Imaging Genetics through Meta-Analysis) was initiated three years ago by Paul Thompson, a professor of neurology at the David Geffen School of Medicine at UCLA. For the past three years, ENIGMA, the world's largest ever ongoing brain study, has led to the discovery of new genes that are responsible for differences in brain size and intelligence.
ENIGMA offers watertight evidence of the correlations between the genes of humans and the size of their brains, especially within the hippocampal and intercranial regions. The study was published in Nature Genetics.
The cognoscenti of neurology from all over the world, including Australia and the Netherlands, worked together to recruit brain-imaging labs around the world to share brain scans and genomic data and to derive definitive explanations from a very large pool of information. 21,151 individuals were included in this study, which allowed scientists to categorize them according to brain size and analyze their genetic makeup. Unlike previous studies, ENIGMA has allowed contributors to make conclusions with great statistical significance.
Scientists discovered that in humans with smaller brains there is a link between shifts in genetic code and the diminishing of memory centers of the brain. This was consistent between subjects from different continents.
They also discovered that a variant of a gene called HMGA2 could impact both the size of the brain and intelligence. Shockingly, people with a single mutation in HMGA2 - a "T" (thymine) is changed to a "C" (cytosine) in the genetic code - demonstrated superior performance in IQ testing. A single letter!
It is not doubtful that this project will pave the way for new discoveries with great implications in medicine and neurology. By definitively identifying genes that are linked to the diminishing of certain regions of the brain, scientists can discover avenues for the development of drugs that can reduce their adverse effects. If the underlying puzzle of the wiring of the brain is solved, preventive measures may be devised to minimize adverse affects as well.
The publication of this particular study delves into the identification of common variants that seem to affect brain volume in people of different origins. ENIGMA can also allow scientists to look into the relationship between brain size and susceptibility to certain diseases such as Alzheimer's or schizophrenia, by screening the patient's genes for a genetic culprit that may be causing the deterioration of the brain.
ENIGMA can provide scientists with new opportunities that previous, much smaller studies have failed to offer because the collaboration has led to a vast range of subjects. This massive project may have provided fertile grounds for scientists to finally determine how the brain is wired.

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