Great question. The heritability of T2D is typically estimated to be around 40%-60% and the risk of developing T2D ~40% for individuals who have one parent with T2D and ~70% if both parents are affected. T2D affects ~14.3% of the U.S. adult population and the prevalence is projected to at least double over the next two decades. T2D is what we call a 'complex disease trait'- risk of T2D comes from a host of genetic and environmental factors, and to make things even harder, those genetic factors can interact with one another and can interact with the environment as well. So a genetic risk factor in one environmental condition may not have the same effect in another environmental (or genetic) context. Not only that, but it looks like T2D might not just be the result of one system failing... it can result from a number of different pathways being disrupted- all of this makes T2D a poster child for the hard to study diseases. Here is a link to an amazing paper on T2D that likens overall risk to a palette of major pathophysiological processes that contribute to diabetes risk and progression. It really impacted the way I think about the disease and strategies for researching genetic risk factors.