Susceptibility loci for adiposity phenotypes on 8p, 9p, and 16q in American Samoa and Samoa.

Obesity is a complex phenotype affected by genetic and environmental influences such as sociocultural factors and individual behaviors. Previously, we performed two separate genome-wide investigations for adiposity-related traits (BMI, percentage body fat (%BF), abdominal circumference (ABDCIR), and serum leptin and serum adiponectin levels) in families from American Samoa and in families from Samoa. The two polities have a common evolutionary history but have lately been influenced by variations in economic development, leading to differences in income and wealth and in dietary and physical activity patterns. We now present a genome-wide linkage scan of the combined samples from the two polities. We adjust for environmental covariates, including polity of residence, education, cigarette smoking, and farm work, and use variance component methods to calculate univariate and bivariate multipoint lod scores. We identified a region on 9p22 with genome-wide significant linkage for the bivariate phenotypes ABDCIR-%BF (1-d.f. lod 3.30) and BMI-%BF (1-d.f. lod 3.31) and two regions with genome-wide suggestive linkage on 8p12 and 16q23 for adiponectin (lod 2.74) and the bivariate phenotype leptin-ABDCIR (1-d.f. lod 3.17), respectively. These three regions have previously been reported to be linked to adiposity-related phenotypes in independent studies. However, the differences in results between this study and our previous polity-specific studies suggest that environmental effects are of different importance in the samples. These results strongly encourage further genetic studies of adiposity-related phenotypes where extended sets of carefully measured environmental factors are taken into account.

Farming and adiposity in Samoan adults.

Samoans are experiencing some of the highest prevalences of obesity and associated health conditions in the world. Sustainable interventions are needed to prevent further increases in obesity. This study describes the cross-sectional association between farm work and adiposity among 754 adults residing in American Samoa in 2002 and 957 adults residing in Samoa in 2003. Adiposity was measured by body mass index (BMI) and percent body fat (% BF), based on bioelectrical impedance. Regression models adjusted for the effects of age, education, occupation (in women), and material lifestyle (MLS), and the clustering within households due to the family design of the parent study. After controlling for these variables, participation in farm work was associated with a significantly lower BMI and % BF in men of all ages residing in American Samoa, women >or=45 years residing in American Samoa, and women 18-44 years residing in Samoa, and a significantly lower BMI in men 18-44 years residing in Samoa. These results suggest that farm work plays an important role in regulating body size and fatness of adult Samoans and may be ideal for interventions in the Samoan archipelago.