The obesity-related gene FTO also plays a role in loss of brain tissue, according to a US study published in the Proceedings of the National Academy of Sciences last week.
As reported in BioNews, UK researchers three years ago found people carrying two copies of a common variant of FTO are on average three kilograms heavier than people who carry normal versions of the gene, and have a 70 per cent increased risk of obesity. At least one copy of the variant is carried by nearly half of all Western Europeans.
Since then, scientists worldwide have worked to discover how this gene functions. The new research comes from neurologist Professor Paul Thompson and his team at the University of California, Los Angeles. They generated three-dimensional maps of the brains of 206 healthy elderly people, who had had MRI scans as part of the Alzheimer's Disease Neuroimaging Initiative - a five-year study aimed at better understanding the factors that help aging brains resist disease.
The team found that people carrying the obesity-related variation of the FTO gene had brain volume deficits compared to people with the normal version of the gene. In fact, people with the variant had eight per cent lower brain volume in the frontal lobes, sometimes known as the 'command centre' of the brain, and 12 per cent lower volume in the occipital lobes - areas responsible for vision and perception.
The brain deficits were also present in subjects with higher body mass index (BMI) measurements, but the study showed that the differences were not attributable to cholesterol levels, high blood pressure or diabetes - factors which could otherwise cause damage to the brain.
Loss of brain tissue depletes a person's compensatory brain reserves, putting them at higher risk from Alzheimer's and other neurodegenerative disorders, as well as stroke.
Professor Thompson said: 'this is a shocking finding. Any loss of brain tissue puts you at greater risk for functional decline'. He continued that it is important that carriers of the gene variant should: 'exercise and eat healthily to resist both obesity and brain decline'. This is especially true since previous research found that the predisposition to obesity can be overcome by exercise and a low-fat diet.
'The present finding has important implications for obesity research and for combating the progression of neurodegeneration' said Professor Thompson. 'The gene discovery will help to develop and fine tune the anti-dementia drugs being developed to combat brain ageing'.
A spokesperson from the Alzheimer's Society said: 'We've known for some time that there's a link between obesity in mid life and the development of Alzheimer's disease. However, this study suggests that healthy people who carry a specific DNA sequence associated with obesity could be at a greater risk of developing dementia. This is a relatively small study but the findings support the need for more research. One million people will develop dementia in the next 10 years, but dementia research is desperately under-funded, however with the right investment, it can be defeated'.