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Obesity genetics goes 'pear-shaped'

18 October 2010
Appeared in BioNews 580

Scientists from the GIANT (Genetic Investigation of Anthropometric Traits) consortium have identified new genetic markers linked to body shape and obesity. In the first study, the researchers identified 13 new genetic markers linked to body shape. They found that waist-hip ratio (WHR) was strongly correlated to a person's genetic makeup.

Individuals usually have a pear-shape body type, where fat tends to be stored on the thighs, or an apple-shape, where fat is stored around the stomach region. The former body type is traditionally seen as a female trait and the latter a male trait and the researchers found a 'marked sexual dimorphism' in seven of these loci, which may account for these differences. Having a distinctive apple-shape body type is linked to an increased risk of type 2 diabetes and heart disease, although these genetic markers are thought to only explain one percent of the variation in waist-hip ratios.

Dr Cecilia Lindgren, a key researcher on the study from Oxford University, said: 'By finding genes that have an important role in influencing whether we are apple-shaped or pear-shaped, and the ways in which that differs between men and women, we hope to home in on the crucial underlying biological processes'.

In the second study, researchers screened 124,000 individuals for 2.8 million SNPs (single nucleotide polymorphism), looking for an association with body mass index (BMI). They identified 42 potential candidate SNPs, which they then looked at in a further 126,000 individuals. BMI is used as a measure of standard body weight, and is based on a person's height and weight. Adults with a BMI of 25-29.9 are classed as overweight, and are defined as obese if they have a BMI of 30 or more.

They identified 14 loci previously linked to obesity, and also 18 new markers associated with increased BMI, with some of these mapping to regions thought to play an important role in the regulation of body weight. However, these genetic markers are believed to only account for 1.45 percent of the variation in BMI.

Putting the research into perspective, Dr Ruth Loos from the Medical Research Council (MRC) in Cambridge, who led the work, told the Telegraph: 'we should not forget that, while the genetic contribution to obesity is substantial, a large part of obesity susceptibility remains down to our lifestyle'.

The research was published across two papers in Nature Genetics.

SOURCES & REFERENCES
An apple or a pear? It's in your genes
The Telegraph |  10 October 2010
Association analyses of 249,796 individuals reveal 18 new loci associated with body mass index
Nature Genetics |  10 October 2010
Meta-analysis identifies 13 new loci associated with waist-hip ratio and reveals sexual dimorphism in the genetic basis of fat distribution
Nature Genetics |  10 October 2010
New insights into the genetics of body shape
Wellcome Trust |  11 October 2010
'Pear-shaped' genes uncovered
BBC News |  10 October 2010
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