A genetic variant in people who lack a specific blood group has been identified as a cause of obesity thanks to new research.

An international study, led by the University of Exeter, has revealed that some people expend less energy when resting because of a genetic variant that disables the SMIM1 gene. This means they are predisposed to be overweight or obese.

The SMIM1 gene was identified a decade ago when researchers were looking for the gene encoding a specific blood group, known as Vel.

People who lack both copies of the gene are Vel-negative, something which affects one in 5,000 people.

The latest research shows that these people are more likely to have obesity, a finding which could pave the way for new treatments. In addition, scientists found that this group of people also have high levels of fat in the blood, signs of fat tissue dysfunction and increased liver enzymes – all measures linked to obesity – along with lower levels of thyroid hormones.

The research team are now planning to test a drug used for thyroid dysfunction to tackle obesity in people who lack both copies of SMIM1.

Lead author Mattia Frontini, Associate Professor of Cell Biology at the University of Exeter Medical School, said: “Obesity rates have nearly tripled in the past 50 years, and by 2030, more than one billion individuals worldwide are projected to be obese. The associated diseases and complications create significant economic burden on healthcare systems.

“Obesity is due to an imbalance between energy intake and expenditure, often a complex interplay of lifestyle, environmental, and genetic factors.

“In a small minority of people, obesity is caused by genetic variants. When this is the case, new treatments can sometimes be found to benefit these people – and we’re now hoping to run a clinical trial to find out whether widely-available drug for thyroid supplementation may be beneficial in treating obesity in people who lack SMIM1.

“Our findings highlight the need to investigate the genetic cause of obesity, to select the most appropriate and effective treatment, but also to reduce the social stigma associated to it.”

The research team studied data from 500,000 people and identified 104 people with the variant that triggers a loss of function in the SMIM1 gene. They also examined fresh blood samples from both Vel-negative and Vel-positive individuals.

From this, they determined that the SMIM1 variant could be a significant factor which contributes to obesity for approximately 300,000 people globally.

They also found that having the variant equated to an average extra 4.6kg in females and 2.4kg in males.

Co-author Jill Storry, Adjunct Professor at Lund University, Sweden, said: “SMIM1 was only discovered a decade ago, as a long-sought blood group protein on red blood cells, but its other function has remained unknown until now. It’s very exciting to find that it has a more general role in human metabolism.”

Co-author Professor Ole Pedersen, at University of Copenhagen, said: “The whole team is very much looking forward to seeing how this new knowledge can be translated into practical solutions for people with this genetic make-up.”

First author Dr Luca Stefanucci, at the University of Cambridge, added: “With the increased availability of genetic data, and more information on SMIM1 mechanism, we would like to see that when individuals lacking SMIM1 are identified, they receive information and support.”

Read more in Med.

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