ADOPTION STUDY OF ENVIRONMENTAL MODIFICATIONS OF THE GENETIC INFLUENCES ON OBESITY

BACKGROUND: Adult body mass index (BMI weight (kg)/height(2) (m(2))) u sually shows familial correlations below 0.3, which are almost entirel y due to genetic influences. The considerable remaining non-familial i ndividual variation may be due to non-shared environmental influences which, however, may interact with or modify the genetic influence. OBJ ECTIVE: To investigate whether the genetic influence on adult BMI is m odified by various obesity-related environmental conditions during chi ldhood and adulthood. DESIGN: Adoption study, in which the genetic inf luence is assessed by the correlations in adult BMI between adoptees a nd their biological fathers, mothers and full siblings. These correlat ions were compared between groups of families characterized by differe nces in rearing or adult environment of the adoptees and/or their biol ogical relatives. SUBJECTS: Height, current weight and greatest weight ever, were obtained in 3651 subjects, who were adopted by non-related families in Copenhagen between 1924 and 1947. Groups representing thi n, medium weight, overweight and obese proband adoptees were selected by current BMI (n = 540) and by maximum BMI (n = 524). The members of the biological and adoptive families of the proband adoptees were iden tified and their BMI was computed from height and weight obtained by m ailed questionnaires. MAIN VARIABLES: Indicators related to the rearin g environment of the adoptees were age of the adoptee at transfer to t he adoptive family, region of residence, presence of adoptive siblings and, for the adoptive parents, year of birth, age at time of adoption , occupational rating, smoking habits and BMI. Indicators of the envir onment of both the adoptee and the biological relatives were: year of birth; occupational rating and smoking habits, and, of the environment of the biological parents, age and parity at birth of the adoptee. RE SULTS: The correlations in BMI between adoptees and the biological fat hers, mothers and siblings were 0.11, 0.15 and 0.26 for adoptees selec ted by current BMI, and 0.13, 0.16, and 0.27 for adoptees selected by maximum BMI, respectively (all P < 0.001), demonstrating the previousl y reported genetic influence, None of the environmental indicators sho wed consistent and significant effects on these six correlations. The same negative results were obtained in analysis of environmental indic ators applied to the two adoptive parents together or to the adoptee a nd the biological relatives together. CONCLUSION: The genetic influenc e on BMI was unaffected by several different environmental conditions otherwise associated with obesity.