Largest brain study reveals size really does matter

Researchers from the Queensland Institute of Medical Research (QIMR) have contributed to the world’s largest study of the human brain, which has discovered genes that affect brain size and may play a role in intelligence and memory function.

QIMR’s Dr Margie Wright said that by combining brain scans and genetic data from 21,000 people from around the world, it was found that brain size can not only have some effect on people’s thought patterns and behaviour, but also intelligence

“By working with research organisations from all corners of the globe, we created the world’s largest database of brain imaging results and found one gene that showed a strong correlation with overall brain size and another that influenced the size of the brain’s hippocampus, which is involved with memory,” Dr Wright said.

“The gene involved with the hippocampus influences the rate at which this section of the brain shrinks with age. We found that about 10% of people carry a genetic variant that slightly increases the rate of atrophy in this section of the brain.

“While no direct connection was found, people with dementia often show pronounced shrinkage in the hippocampus, so further investigation to see if there are genetic links to dementia would be beneficial. The hippocampus is also reduced in schizophrenia, major depression and mesial temporal lobe epilepsy.

“In a separate study here at QIMR, we also found that those with larger brains scored slightly higher on a standardised IQ test. That is, performance in the group of people in the study with the variant that influences brain size was increased by about one IQ point, which is equivalent to answering one to two more questions correctly.”

The variant that influences brain size was found to be very common across the population, with 50% of people having the variant.

Dr Wright said this study was a wonderful opportunity to collaborate on brain research and although this study does not offer any direct treatment solutions, it is a stepping stone for further work into the genetics of the brain and brain disorders.

“The effects of the two genes on brain size are very small and the links to cognitive function are subtle,” Dr Wright said.

“However as we can lose up to 10% of our brain volume in later life these results are quite significant in people with the genetic variant that increases shrinkage. They may be more vulnerable to environmental factors, such as a poor diet, excessive alcohol consumption, or little exercise.”

The study was an international collaboration including more than 200 scientists from 100 institutions worldwide from the Enhancing Neuro Imaging Genetics through Meta-Analysis (ENIGMA) Consortium. The senior co-authors of the study included Margie Wright and Nick Martin from the Queensland Institute of Medical Research, Paul Thompson, from The University of California, Los Angeles and Barbara Franke, from Radboud University Nijmegen Medical Center in the Netherlands. Sarah Medland, also from QIMR, was first co-author.

The paper was published in Nature Genetics. The paper is available online: http://www.nature.com/ng