MUC7 haplotype analysis: results from a longitudinal birth cohort support protective effect of the MUC7*5 allele on respiratory function.

The mucin MUC7 is a glycoprotein that plays a role in bacterial clearance and has candidacidal activity. There are two common allelic forms with 5 or 6 tandem repeats (TR) of a 23 amino acid motif within the highly glycosylated (mucin) domain. The MUC7*5 allele has previously been shown to be less prevalent in patients with asthma, suggesting a protective role in respiratory function. Here we report the characterisation of other frequent genetic variation within and in the vicinity of the gene MUC7. A total of 26 polymorphisms were identified of which 5 are located in transcribed regions. A subset of 8 polymorphisms was selected to represent the major haplotypes, and allelic association was studied in individuals of Northern European ancestry, including known asthmatics. There was low haplotype diversity and strong association between each of the loci, and the MUC7*5 allele-carrying haplotype remained the one most strongly associated with asthma. Five of these polymorphisms have also been tested in the 1946 longitudinal birth cohort, for whom developmental, environmental and respiratory health data are available. We show that the haplotype carrying MUC7*5 is associated with higher FEV1 at 53 years, reduced age-related decline of FEV1, and also reduced incidence of wheeze.