Lung disease modifier genes in cystic fibrosis.

Cystic fibrosis (CF) is recognized as a single gene disorder. However, a considerable diversity in its clinical phenotype has been documented since the description of the disease. Identification of additional gene alleles, so called "modifier genes" that directly influence the phenotype of CF disease became a challenge in the late '90ies, not only for the insight it provides into the CF pathophysiology, but also for the development of new potential therapeutic targets. One of the most studied phenotype has been the lung disease severity as lung dysfunction is the major cause of morbidity and mortality in CF. This review details the results of two main genetic approaches that have mainly been explored so far: (1) an "a priori" approach, i.e. the candidate gene approach; (2) a "without a priori" approach, analyzing the whole genome by linkage and genome-wide association studies (GWAS), or the whole exome by exome sequencing.