Mucin Variable Number Tandem Repeat Polymorphisms and Severity of Cystic Fibrosis Lung Disease: Significant Association with <em>MUC5AC</em>

Variability in cystic fibrosis (CF) lung disease is partially due to non-CFTR genetic modifiers. Mucin genes are very polymorphic, and mucins play a key role in the pathogenesis of CF lung disease; therefore, mucin genes are strong candidates as genetic modifiers. DNA from CF patients recruited for extremes of lung phenotype was analyzed by Southern blot or PCR to define variable number tandem repeat (VNTR) length polymorphisms for MUC1, MUC2, MUC5AC, and MUC7. VNTR length polymorphisms were tested for association with lung disease severity and for linkage disequilibrium (LD) with flanking single nucleotide polymorphisms (SNPs). No strong associations were found for MUC1, MUC2, or MUC7. A significant association was found between the overall distribution of MUC5AC VNTR length and CF lung disease severity (p = 0.025; n = 468 patients); plus, there was robust association of the specific 6.4 kb HinfI VNTR fragment with severity of lung disease (p = 6.2×10−4 after Bonferroni correction). There was strong LD between MUC5AC VNTR length modes and flanking SNPs. The severity-associated 6.4 kb VNTR allele of MUC5AC was confirmed to be genetically distinct from the 6.3 kb allele, as it showed significantly stronger association with nearby SNPs. These data provide detailed respiratory mucin gene VNTR allele distributions in CF patients. Our data also show a novel link between the MUC5AC 6.4 kb VNTR allele and severity of CF lung disease. The LD pattern with surrounding SNPs suggests that the 6.4 kb allele contains, or is linked to, important functional genetic variation.囊性纤维化（cystic fibrosis, CF）肺疾病的异质性部分源于非囊性纤维化跨膜传导调节因子（cystic fibrosis transmembrane conductance regulator, CFTR）遗传修饰因子。黏蛋白基因具有高度多态性，且黏蛋白在CF肺疾病的发病机制中发挥关键作用，因此黏蛋白基因是极具潜力的遗传修饰因子候选者。本研究对因肺表型极端差异入组的CF患者的DNA样本，采用Southern印迹（Southern blot）或聚合酶链反应（polymerase chain reaction, PCR）进行分析，以明确MUC1、MUC2、MUC5AC及MUC7的可变数目串联重复序列（variable number tandem repeat, VNTR）长度多态性。我们检测了VNTR长度多态性与肺疾病严重程度的关联，以及其与侧翼单核苷酸多态性（single nucleotide polymorphism, SNP）的连锁不平衡（linkage disequilibrium, LD）。未发现MUC1、MUC2或MUC7存在显著关联。MUC5AC VNTR长度的总体分布与CF肺疾病严重程度存在显著关联（p=0.025；n=468例患者）；此外，特定6.4 kb HinfI酶切VNTR片段与肺疾病严重程度存在强关联（经Bonferroni校正后p=6.2×10⁻⁴）。MUC5AC VNTR长度模态与侧翼SNPs之间存在强连锁不平衡。与疾病严重程度相关的MUC5AC 6.4 kb VNTR等位基因被证实与6.3 kb等位基因存在遗传差异，因其与邻近SNPs的关联强度显著更高。本研究明确了CF患者呼吸道黏蛋白基因VNTR等位基因的详细分布特征。此外，本研究还揭示了MUC5AC 6.4 kb VNTR等位基因与CF肺疾病严重程度之间的全新关联。其与周围SNPs的连锁不平衡模式提示，6.4 kb等位基因包含或连锁于具有重要功能的遗传变异。