Washington: It`s believed that the bigger brains are smarter ones. Now scientists have found two genes that not only affect the brain size and intelligence, but also your risk of developing cognitive disorders like Alzheimer`s.
The study, the world`s largest brain research conducted by an international team of over 200 scientists, measured the size of the brain and its memory centers in thousands of MRI images from 21,151 healthy people, while simultaneously screening their DNA.
They found two genetic variants -- one that appears to be associated with overall brain size and another that was linked to the volume of the hippocampus, or memory centre, which typically shrinks in people with dementia.
"We found fairly unequivocal proof supporting a genetic link to brain function and intelligence. For the first time, we have watertight evidence of how these genes affect the brain," lead researcher Paul Thompson, a neurologist at the University of California at Los Angeles was quoted as saying by LiveScience.
The researchers involved in the Enhancing Neuro Imaging Genetics through Meta-Analysis (ENIGMA) Consortium scoured the data for single genes that influence disease risk as well as for genes linked to brain-tissue atrophy and brain size.
Brains shrink naturally with age, but size is important in a number of mental ailments. Decreased brain volume marks disorders including Alzheimer`s disease, depression and schizophrenia, the researchers reported in the journal Nature Genetics.
For example, the hippocampus is the part of the brain linked to memory formation and organisation, and the team found a gene sequence called rs7294919 on chromosome 12 that is linked to variations in hippocampus volume.
Every instance of a genetic variant called a T-allele in this region was linked to lower hippocampus volume equivalent to 3.9 years of ageing, the researchers said.
Another notable genetic sequence located within the HMGA2 gene on chromosome 12 was found to have association with the intracranial volume -- the space inside the skull that marks the outer limit as to how big your brain can get.
At this spot, every C-allele variant was linked to not only lower intracranial volume, but also to lower IQ scores on the Multidimensional Aptitude Battery -- a measure of intelligence.
"This is a really exciting discovery: that a single letter change leads to a bigger brain," said Thompson.
Going forward, Thompson said, researchers could start to figure out how to mediate these genes` influences on the brain. The genes influence brains across a wide subset of people from North America, Europe and Australia means that drug therapies targeting these genes could have broad applications, the researchers said.
The team now plans to tackle the genes that influence the brain`s wiring, in hope to unravel the secrets of connectivity-related disorders such as autism.