A widely carried gene variant that causes weight gain and is linked to obesity, may also be associated with the loss of brain tissue, according to researchers at the University of California, Los Angeles. The gene variant is carried by roughly half of people of European descent in the United States and one-quarter of U.S. Hispanics, 15 percent of African Americans, and 15 percent of Asian Americans. The researchers call their findings “worrying and mysterious.” The so-called fat mass and obesity associated gene, which causes people to gain from three to seven pounds on average is now said to put more than a third of the U.S. population at risk for a variety of diseases, such as Alzheimer’s.

In a study published in the early online edition of the journal Proceedings of the National Academy of Sciences, the UCLA researchers report that they used magnetic resonance imaging to generate three-dimensional maps of brain volume differences in 206 healthy elderly subjects drawn from 58 sites in the United States as part of the Alzheimer's Disease Neuroimaging Initiative, a large, five-year study aimed at better understanding factors that help the brain resist disease as it ages.

They found that there was consistently less tissue in the brains of those subjects that carry the so-called FTO allele compared with non-carriers. Individuals with the bad version of the FTO gene had an average of 8 percent less tissue in the frontal lobes, the command center of the brain, and 12 percent less in the occipital lobes, areas in the back of the brain responsible for vision and perception. The researchers say the brain differences could not be directly attributed to other obesity-related factors such as cholesterol levels, diabetes or high blood pressure.

“The results are curious. If you have the bad FTO gene, your weight affects your brain adversely in terms of tissue loss,” says senior study author Paul Thompson, a UCLA professor of neurology. “If you don't carry FTO, higher body weight doesn't translate into brain deficits. In fact, it has nothing to do with it. This is a very mysterious, widespread gene.”

People who carry this specific DNA sequence are heavier on average, and their waist circumference is half an inch bigger.

“This is a shocking finding. Any loss of brain tissue puts you at greater risk for functional decline,” he says. “The risk gene divides the world into two camps―those who have the FTO allele and those who don't.”
Thompson says the findings will help develop and fine tune drugs to combat neurodegeneration and brain aging. He also said carriers of the risk gene can exercise and eat healthily to resist both obesity and brain decline.

“A healthy lifestyle will counteract the risk of brain loss, whether you carry the gene or not,” says Thompson. “So it's vital to boost your brain health by being physically active and eating a balanced diet.”