Genetic polymorphism of MUC7: Allele frequencies and association with asthma

MUC7 encodes a small salivary mucin, previously called MG2, a glycoprotein with a putative role in facilitating the clearance of oral bacteria. The ce ntral domain of this glycoprotein was previously shown to comprise five or six tandemly repeated units of 23 amino-acids which carry most of the O-lin ked glycans. The polymorphism of these two allelic forms (MUC7*5 or MUC7*6) has been confirmed in this study in which we have analysed a large cohort of subjects (n = 375) of various ethnic origins. We have also identified a novel rare allele with eight tandem repeats (MUC7*8). MOC7*6 was the most c ommon allele (0.78-0.95) in all the populations tested. The tandem repeat a rrays of 22 MUC7*5 alleles and 34 dMUC7*6 alleles were sequenced. No sequen ce differences were detected in any of the MUC7*6 alleles. Twenty-one MUC7* 5 alleles sequenced lacked the 4th tandem repeat (structure TR12356), while one showed the structure TR12127. The structure of the MUC7*8 allele was T R12343456. Because of the known role of MUC7 in bacterial binding, and thus its potential involvement in susceptibility to chest disease we also teste d MUC7 in our previously described series of Northern European atopic indiv iduals with and without associated asthma. The MUC7*5 allele was rarer in t he atopic asthmatics than in the atopic non-asthmatics (P = 0.014, OR for n o asthma in atopic individuals 3.13, Cl 1.01 - 6.10), and the difference in frequency between all asthmatics and all non-asthmatics was statistically significant (P = 0.009) while there was no difference between atopy and non -atopy (P = 0.199). In this study we also report the electrophoretic analys is of the MUC7 glycoprotein in saliva from individuals of different MUC7 ge notype.