Genetic variation can cause susceptibility to common diseases. Given constant environmental conditions, the influence of genetic factors can be examined. The ideal situation for measuring the impact of environmental factors on disease phenotypes are constant genetic factors. In both cases, it is necessary to assign quantitative parameters for genetic factors, environmental factors, and disease phenotypes.

The disease phenotype can be classified according to qualitative and quantitative attributes and their progression over time. Environmental factors are more difficult to measure experimentally. Genetic factors are most easily accessible through measures of genomic and transcriptomic variation. Technical progress has allowed genome-wide studies to be performed in large numbers with allows to address both genetic heterogeneity and the small effect sizes of the individual genetic factors. In the presentation, I will give examples from metabolic and neurodegenerative diseases for study designs aimed to achieve a better understanding of the interplay between genes, environment and disease etiology and for strategies to improve our ability for risk prediction of both genetic and environmental factors.