Design: observational, case–control studyInclusion criteria: confirmed CFExclusion criteria: liver cirrhosis, cor pulmonale or an exacerbation of their respiratory symptoms (increased respiratory symptoms, weight loss, fever or reduction in FEV1 of >10% than the usual value) or elevated CRP (>15.5 μg·mL−1). The gene discussed is CRP; the disease is cirrhosis of liver.