Cystic fibrosis is a common lethal autosomal recessive disease affecting whites with an incidence of about 1 in 2500. The median lifespan is approximately 30 years. Chronic obstruction and infection of the respiratory tract, pancreatic insufficiency, elevated sweat electrolyte concentration, and male infertility characterise this disease. Clinical manifestations are attributed to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene,¹ which encodes an epithelial chloride channel.² Certain phenotypes of cystic fibrosis, such as pancreatic insufficiency, are highly associated with the CFTR genotype. Pulmonary symptoms are highly variable, even among patients from the same family.³ Other genetic factors, as well as environmental factors, thus affect the cystic fibrosis disease phenotype.

In association studies, evidence has been found that mannose binding lectin (MBL) protein affects cystic fibrosis disease.^4,5 MBL protein is an important mediator component of the innate immune defense system, which functions as an opsonin and complement activator. It is part of a family of proteins called collectins, because they contain collagen-like regions and lectin domains. Through the lectin domain, they bind to carbohydrate structures presented by a wide range of pathogenic bacteria, viruses, fungi, and parasites. Mannose binding lectin protein is synthesised in the liver by hepatocytes and secreted in the blood, and circulates as dimers or hexamers composed of subunits containing three identical polypeptides.^6,7

The MBL2 gene is located on chromosome 10q11.2–q21. Three single polymorphic MBL2 alleles are known, which are either caused by a nucleotide substitution in codon 52 (arginine with cysteine, allele D), codon 54 (glycine with aspartic acid, allele B) or codon 57 (glycine with glutamic acid, allele C).^8–10 These amino acid changes are thought to affect the tertiary structure of the MBL protein collagenous region. Heterozygosity or homozygosity for these mutations results in little …