PACIFIC – By studying the genomes of more than 5000 Samoans, researchers from the University of Pittsburgh have uncovered a single gene that boosts a person’s obesity risk by upwards of 40 per cent.

Remarkably, this gene –which appears in a quarter of all Samoans – may have arisen in the population as they colonised the South Pacific.

The University of Pittsburgh researchers, led by Stephen McGarvey, made the discovery while scanning the genomes of thousands of Samoans.

Samoa and other Polynesian island nations have some of the highest obesity rates in the world, a fact that prompted the scientists to conduct a genetic investigation.

Around a quarter of all Samoans involved in the study had the genetic variant, which was associated with 30 to 40 per cent increased odds of being obese compared to those who don’t have the gene.

At the same time, this gene is virtually non-existent in European and African populations and occurs at very low frequencies among East Asians.

“Although we have found a genetic variant with a reasonable biological mechanism, this genetic variant is just one part of the many reasons for the high levels of BMI and obesity among Samoans,” noted McGarvey in a press statement.

Other factors include diet and physical activity. A global shift to calorie-rich processed foods and more sedentary lifestyles has contributed significantly to the elevated rates of obesity among Samoans. But as this new study points out, their genetics have also been working against them.

The gene appears to work by causing cells to store more fat and release less energy.

As Alice Klein pointed out in New Scientist, it’s as “if cells are trying to conserve as much fuel as possible.”

There may be a very good reason why this gene appears at elevated levels among Samoans. It has to do with their history of colonising the South Pacific Islands.

Starting around 3500 years ago, ancestors of Samoans began the arduous task of settling the 24 major island groups of Polynesia. This colonization process – one of the most extreme examples in all of human history – took possibly thousands of years to complete.

“They had to endure voyages between islands and subsequently survive on those islands,” study co-author Ryan Minster told New Scientist.

As Darwin pointed out many years ago, evolution requires long timescales.

But in some instances, when environmental conditions are particularly severe and attritional, selectional processes accelerate the process—an evolutionary phenomenon dubbed “punctuated equilibrium” can occur.

The problem is that Samoans no longer require this gene. This would explain why upwards of 80 per cent of men and women in Samoa are now overweight.

“Samoans weren’t obese 200 years ago,” McGarvey said. “The gene hasn’t changed that rapidly, it’s the nutritional environment that changed that rapidly.”

Auckland University professor Peter Shepherd said the gene, known as CREB R.F, acts like a master switch for other genes.

“What it does is it stores a little bit of extra fat into fat tissue every time the people who have the gene eat food, and so in times gone by that ability to store a bit of extra fat would have been a really good protection against times of starvation and the way the gene has been inherited suggests that that’s the reason it’s accumulated in certain people.”

More research is needed, but the findings were valuable, professor Shepherd said.

“This is the first study to find any gene linked to obesity and diabetes in the Samoan population, so it’s a really important finding because it gives us for the first time a starting point from which we can develop targeted intervention strategies.”

Otago University geneticist Tony Merriman said 45 per cent of Samoans have the gene, but elsewhere it’s rare.

“So it’s telling us that there’s something unique about weight control and obesity in Samoans and this may be translatable to Pacific people and Maori living in New Zealand.”

Professor Merriman said studies were already under way in this country to see if the gene was present in Maori and Pacific people.

The US researchers stressed Samoan people should not believe they’re fated to be obese, that it’s the environment, not them, that has changed.

Auckland doctor Robyn Toomath who founded the Fight The Obesity Epidemic agrees with the researchers.

“The people who are genetically susceptible are very, very sensitive to an adverse physical environment. So this is why obesity rates are so much higher when the genetic susceptibilities haven’t changed for centuries.”

Auckland-based Pacific health researcher Ofa Dewes said Samoans wanted more information about obesity.

“They are saying, ‘Well I’m doing all this and I have family but why are only some of us you know prone to overweight and obesity or even type two diabetes and others are not?’.”

Researchers say answers are coming. - PNC sources