LRRC6 Mutation Causes Primary Ciliary Dyskinesia with Dynein Arm Defects

Despite recent progress in defining the ciliome, the genetic basis for many cases of primary ciliary dyskinesia (PCD) remains elusive. We evaluated five children from two unrelated, consanguineous Palestinian families who had PCD with typical clinical features, reduced nasal nitric oxide concentrations, and absent dynein arms. Linkage analyses revealed a single common homozygous region on chromosome 8 and one candidate was conserved in organisms with motile cilia. Sequencing revealed a single novel mutation in LRRC6 (Leucine-rich repeat containing protein 6) that fit the model of autosomal recessive genetic transmission, leading to a change of a highly conserved amino acid from aspartic acid to histidine (Asp146His). LRRC6 was localized to the cytoplasm and was up-regulated during ciliogenesis in human airway epithelial cells in a Foxj1-dependent fashion. Nasal epithelial cells isolated from affected individuals and shRNA-mediated silencing in human airway epithelial cells, showed reduced LRRC6 expression, absent dynein arms, and slowed cilia beat frequency. Dynein arm proteins were either absent or mislocalized to the cytoplasm in airway epithelial cells from a primary ciliary dyskinesia subject. These findings suggest that LRRC6 plays a role in dynein arm assembly or trafficking and when mutated leads to primary ciliary dyskinesia with laterality defects.

尽管目前在纤毛组（ciliome）的界定方面已取得一定进展，但诸多原发性纤毛运动障碍（primary ciliary dyskinesia, PCD）病例的遗传基础仍未明确。本研究对来自两个无亲缘关系、近亲婚配的巴勒斯坦家庭的5名儿童进行了评估，这些患儿均患有符合典型临床特征的原发性纤毛运动障碍，表现为鼻腔一氧化氮浓度降低、动力蛋白臂缺失。连锁分析显示，8号染色体上存在一个共同的纯合区域，且其中一个候选基因在具有运动纤毛的生物中保守存在。测序结果发现LRRC6（富含亮氨酸重复序列蛋白6，Leucine-rich repeat containing protein 6）存在一种全新突变，该突变符合常染色体隐性遗传模式，会将高度保守的天冬氨酸替换为组氨酸（Asp146His）。LRRC6定位于细胞质中，且在人类气道上皮细胞的纤毛发生过程中，以依赖于Foxj1的方式被上调。从患者体内分离的鼻腔上皮细胞，以及经短发夹RNA（shRNA）介导沉默LRRC6的人类气道上皮细胞，均呈现出LRRC6表达降低、动力蛋白臂缺失以及纤毛摆动频率减慢的表型。原发性纤毛运动障碍患者的气道上皮细胞中，动力蛋白臂蛋白要么缺失，要么错误定位于细胞质内。上述研究结果表明，LRRC6参与动力蛋白臂的组装或转运过程，当其发生突变时，可引发伴随左右侧发育异常的原发性纤毛运动障碍。