Lessons from studying monogenic disease for common disease.

The prevailing paradigm for common disease emphasizes the role of common variants predisposing to various rampant health problems, and these genetic risk profiles interact with environmental and life style risk factors triggering the disease process and modifying its progress. However, most of what we know about the molecular background of common diseases is in fact based on what we have learned from rare familial forms of these traits. Further, often the mutations identified in even more rare monogenic diseases sharing some trait components with common diseases have exposed critical new pathways involved in the molecular pathogenesis of common health problems. In this review, we aim to exemplify some of the lessons learned from rare Mendelian forms of diseases that have significantly contributed to our understanding of the genetic background of common diseases and their trait components.