The gene variant most strongly associated with childhood obesity and adult morbid obesity in the study is located near the PTER gene, the function of which is not known. This variant is estimated to account for up to a third of all childhood obesity, and a fifth of all cases of adult obesity.

The second variant associated with child and adult obesity is found in the NPC1 gene. Previous studies in mice have suggested that this gene has a role in controlling appetite, as mice with a non-functioning NPC1 gene suffer late-onset weight loss and have poor food intake. This gene variant accounts for around 10 per cent of all childhood obesity and about 14 per cent of adult morbid obesity cases.

The final variant is found near the MAF gene, which controls the production of the hormones insulin and glucagon, as well as chains of amino acids called glucagon-like peptides. These hormones and peptides are known to play key roles in people’s metabolisms by metabolising glucose and carbohydrates in the body. In addition, glucagon and glucagon-like peptides appear to have a strong effect on people’s ability to feel ‘full’ or satiated after eating. This variant accounts for about 6 per cent of early-onset obesity in children, and 16 per cent of adult morbid obesity.

Further research is needed to determine whether the gene variants are acting independently, but if they are, then together these three new variations may account for up to half of all cases of severe adult and child obesity.

more than three quarters of the difference between children’s waistlines, with lifestyle factors such as diet and exercise playing a much smaller role.

Lead author of the study, Dr. Jane Wardle:

Weight gain in a child is unlikely to be the fault of the parents and is more likely to be due to the child’s genetic susceptibility.

The study was conducted using a twin study and drew the following conclusions:

The researchers found that, overall, the twins’ heights and weights were greater than the 1990 averages, though BMI was similar. Waist circumferences were substantially higher than in populations in 1990, particularly in girls. They also found that identical twins were more likely than non-identical twins to have similar BMI and waist circumference measurements, suggesting a genetic component to these characteristics.

Using the modelling method, the researchers conclude that variation in BMI scores is 77 per cent heritable, while variation in waist circumference is 76 per cent heritable. They also found that the “shared-environment” had little effect on BMI and waist circumference (10 per cent each).

One problem that I find with these studies is that it shows correlation but not causation, but the researchers discuss such criticisms:

• Firstly, the common finding that the shared environment has little effect. In studies of obesity, this is surprising considering the fact that many models suggest that the environment is “the root cause of obesity”. They say that this finding suggests caution when assuming that if all parents followed “current child-feeding recommendations, the obesity problem would be solved”.
• Secondly, twin studies assume that identical and non-identical twins share the same environment (in the uterus and in the family). There is discussion in the scientific literature about whether this is an accurate assumption, however the researchers here say that the effect is small and “it would not materially change the conclusion”.
• Thirdly, such studies do not identify genes responsible for traits or behaviours. No major genes that cause obesity have been identified and obesity is likely to be due to the influences of many different genes, affecting appetite as well as how fat is stored. 

Until such time as the boffins find a “fat” gene can we understand the cause of obesity an, hopefully, from that finding the best ways to combat it. What this study also means is that parents who are overweight and obese must not abandon their and their children’s efforts to lead an active and healthy lifestyle. It just means they have to work a little harder at it.