The presence of CF up/down-regulated genes in a network provides clues not only on how expression is affected by CFTR dysfunction, but also the opposite, e.g., how systemic alterations in circulating estrogen over the course of the female menstrual cycle, might bring about differential gene expression profiles, which help to explain subtle differences in lung function in male and female CF patients [40,55]. Here, CFTR is linked to cystic fibrosis.