Genetic skin diseases with altered aging

Integration, homeostasis, and redundancy of function are hallmarks of important biological processes. Individual gene defects may overcome and override normal homeostatic systems and lead to dramatic, recognizable phenotypes by profoundly altering 1 or more physiological systems. Classical human geneticists interested in a monogenetic disease began at the level of altered function and struggled to determine the genomic defect of that disease. In the past 1 1/2 decades, many monogenetic defects have been identified by positional cloning, and the abnormal gene has been characterized. A challenge for current investigators is to understand how a genetic defect, identified by a DNA mutation, leads to the altered phenotype. This effort is not trivial, since there are multiple metabolic and structural consequences of a single altered gene. Further complexity results from individual genetic changes being modified by the genetic diversity of the human host. Pleiotropy refers to the phenomenon of multiple phenotypic effects of a single gene.