CFTR and exocrine pancreatic insufficiency: and our experience, many factors can impair L-T4 absorption at gastrointestinal level, and in particular several diseases like Helicobacter pylori infection, celiac disease, inflammatory bowel diseases (IBDs), etc. In this context, CF must be mentioned since the mutations of CFTR gene correlate to pancreatic insufficiency, reduced biliary salt production, abnormal intestinal transit, and chronic intestinal inflammation, that ultimately concur to malabsorption in variable degrees, depending on disease severity.