Gastrointestinal manifestations in cystic fibrosis.

CFTR, or cystic fibrosis transmembrane conductance regulator, the gene product that is defective in cystic fibrosis, is present in the apical membrane of the epithelial cells from the stomach to the colon. In the foregut, the clinical manifestations are not directly related to the primary defect of the CFTR chloride channel. The most troublesome complaints and symptoms originate from the oesophagus as peptic oesophagitis or oesophageal varices. In the small intestinal wall, the clinical expression of CF depends largely on the decreased secretion of fluid and chloride ions, the increased permeability of the paracellular space between adjacent enterocytes and the sticky mucous cover over the enterocytes. As a rule, the brush border enzyme activities are normal and there is some enhanced active transport as shown for glucose and alanine. The results of continuous enteral feeding of CF patients clearly show that the small intestinal mucosa, in the daily situation, is not functioning at maximal capacity. Although CFTR expression in the colon is lower, the large intestine may be the site of several serious complications such as rectal prolapse, meconium ileus equivalent, intussusception, volvulus and silent appendicitis. In recent years colonic strictures, after the use of high-dose pancreatic enzymes, are being increasingly reported; the condition has recently been called CF fibrosing colonopathy. The CF gastrointestinal content itself differs mainly from the normal condition by the lower acidity in the foregut and the accretion of mucins and proteins, eventually resulting in intestinal obstruction, in the ileum and colon. Better understanding of the CF gastrointestinal phenotype may contribute to improvement of the overall wellbeing of these patients.