RESUMO
During a multicentric study conducted in Southern Italy, we studied five sets of cystic fibrosis siblings bearing a strongly discordant liver phenotype, three with genotype DeltaF508/R553X, one with genotype DeltaF508/unknown, and one with genotype unknown/unknown. The siblings of each set were raised in the same family environment, and there were no interpair differences in nutritional state or in therapy compliance. All siblings had pancreatic insufficiency and moderate respiratory expression. One sibling of each of the five sets was free of liver involvement, and the other had severe liver expression. Other causes of liver disease (viral, metabolic, and genetic other than cystic fibrosis) were ruled out. Therefore, environmental factors, nutritional state, and therapy compliance are not involved in the liver expression of cystic fibrosis in the five unrelated sibships. This suggests that modifier genes, inherited independently of the cystic fibrosis transmembrane regulator gene, could modulate the liver expression in cystic fibrosis patients.