%0 Journal Article %T The common FTO variant rs9939609 is not associated with BMI in a longitudinal study on a cohort of Swedish men born 1920-1924 %A Josefin A Jacobsson %A Ulf Ris¨¦rus %A Tomas Axelsson %A Lars Lannfelt %A Helgi B Schi£¿th %A Robert Fredriksson %J BMC Medical Genetics %D 2009 %I BioMed Central %R 10.1186/1471-2350-10-131 %X The FTO rs9936609 was genotyped using an Illumina golden gate assay. BMI was calculated using standard methods and body fat was estimated by measuring skinfold thickness using a Harpenden caliper. Physical activity was assessed using a four question medical questionnaire.FTO rs9939609 was genotyped in 1153 elderly Swedish men taking part of a population-based cohort study, the ULSAM cohort. The risk of obesity and differences in BMI according to genotype at the ages of 50, 60, 70, 77 and 82 were investigated. We found no increased risk of obesity and no association with BMI at any age with the FTO rs9939609 variant. We found however interaction between physical activity at the age of 50 years and genotype on BMI levels (p = 0.039) and there was a clear trend towards larger BMI differences between the TT and AA carriers as well as between AT and AA carriers in the less physically active subjects.Here we found that the well established obesity risk allele for a common variant in FTO does not associate with increased BMI levels in a Swedish population of adult men which reached adulthood before the appearance of today's obesogenic enviroment. There is an interaction between physical activity and the effect of the FTO genotype on BMI levels suggesting that lack of physical activity is a requirement for an association of FTO gene variants to obesity.Today, about one in three adult can be classified as obese based on objectively measured weight and height. The increase started after the World War II, escalated in the seventies and the obesity rates have roughly tripled in the past 20 years. In Sweden one in hundred is considered morbidly obese today compared to one in thousand in the early 1970s [1-4].This worldwide rapid increase in the prevalence of obesity is much due to environmental factors, such as a sedentary lifestyle and develops from an imbalance between energy ingested and expended [5]. It is however also widely accepted that obesity is under strong genetic con %U http://www.biomedcentral.com/1471-2350/10/131