One problem with studying direct genetic effects on obesity is that, so far, there aren't any. (geneticliteracyproject.org)
Such studies are needed to resolve conflicting results regarding the importance of genetic effects for ADHD in adults. (cambridge.org)
A recent study of 25,000 twin families found that additive genetic effects account for 25 % of variance, with the rest due to environmental factors. (massgenomics.org)