Gene modifiers in pediatrics: application to cystic fibrosis.

Human disease is a result of interactions between each person's genetic program and the environment. Individual genes responsible for many pediatric diseases have been discovered, but there is still considerable variability in phenotype within a given disorder. While some of the variability is undoubtedly caused by environmental factors, genes other than the primary disease gene likely modify phenotypes. These gene modifiers alter the effects of the primary disease gene and therefore result in phenotypic variability. Studying gene modifiers will therefore likely lead to a better understanding of pathophysiology and to development of new treatments. Statistical and genetic methods used to identify gene modifiers range from simple association studies to complex family studies, each with its own strengths. The search for gene modifiers in cystic fibrosis (CF), a common mendelian disorder, provides a good example of an application of the latest approaches. Potential modifiers of CF are chosen to reflect the known pathophysiology of CF, including genes involved in the host response to infection and CF complications such as intestinal obstruction, diabetes, and liver disease. A region on chromosome 19 that modifies intestinal obstruction in CF has been identified based on a region of synteny in the mouse; however, the specific gene has not been completely characterized. While a number of other putative gene modifiers have been investigated in CF, none are clearly substantiated. To date, only a few gene modifiers in pediatric disease have been conclusively identified, but we believe that future research will open the doors for new knowledge and treatment.