Genetics of tracking of body mass index from birth to late middle age: evidence from twin and family studies.

The persistence of obesity from early childhood to late middle age is well known. We reviewed the results from existing genetic studies on tracking of BMI to discover how much genetic and environmental factors contribute to this tracking of obesity. In total, we found 5 genetic longitudinal studies on childhood obesity and 8 on obesity in adulthood. One was an adoption study, 3 were family studies, and 9 were twin studies. All were based on Caucasian populations, and one included genetic level information (the FTO gene). Strong genetic continuity in BMI was found from early childhood to onset of adulthood. Although new genetic factors started to affect BMI during the growth period, genetic correlations remained high. Evidence of the effect of common environment on the tracking of BMI during childhood was also found. The heritability estimates reported in twin studies ranged from 0.57 to 0.86 for the trend of BMI from early adulthood to late middle age. The three family studies gave lower estimates. Important unresolved questions are the genetics of BMI change in old age, the genetics of body composition change, the genetic architecture of tracking of obesity in ethnic groups other than Caucasians, and the interplay between genes and environment underlying the development and tracking of obesity.