 Polymorphisms in one or both mannan-binding lectin alleles that result in lower circulating levels of the protein are associated with a threefold higher risk of end-stage lung disease, as well as an increased burden of chronic bacterial infections.Up to 1 in 25 individuals of Northern European ancestry is considered a genetic carrier.The disease appears only when two of these carriers have children, as each pregnancy between them will have a 25% chance of producing a child with the disease.