Skewed X-chromosome inactivation drives the proportion ofDNAAF6-defective airway motile cilia and variable expressivity in primary ciliary dyskinesia

Abstract

BackgroundPrimary ciliary dyskinesia (PCD) is a rare airway disorder caused by defective motile cilia. Only male patients have been reported with pathogenic mutations in X-linkedDNAAF6, which result in the absence of ciliary dynein arms, whereas their heterozygous mothers are supposedly healthy. Our objective was to assess the possible clinical and ciliary consequences of X-chromosome inactivation (XCI) in these mothers.MethodsXCI patterns of six mothers of male patients withDNAAF6-related PCD were determined by DNA-methylation studies and compared with their clinical phenotype (6/6 mothers), as well as their ciliary phenotype (4/6 mothers), as assessed by immunofluorescence and high-speed videomicroscopy analyses. The mutated X chromosome was tracked to assess the percentage of cells with a normal inactivatedDNAAF6allele.ResultsThe mothers’ phenotypes ranged from absence of symptoms to mild/moderate or severe airway phenotypes, closely reflecting their XCI pattern. Analyses of the symptomatic mothers’ airway ciliated cells revealed the coexistence of normal cells and cells with immotile cilia lacking dynein arms, whose ratio closely mirrored their XCI pattern.ConclusionThis study highlights the importance of searching for heterozygous pathogenicDNAAF6mutations in all female relatives of male PCD patients with aDNAAF6defect, as well as in females consulting for mild chronic respiratory symptoms. Our results also demonstrate that about one-third—ranging from 20% to 50%—normal ciliated airway cells sufficed to avoid severe PCD, a result paving the way for gene therapy.