Primary ciliary dyskinesia caused by a large homozygous deletion including exons 1–4 of DRC1 in Japanese patients with recurrent sinopulmonary infection

BACKGROUND: Diffuse panbronchiolitis (DPB) is a sinopulmonary disease mainly affecting Asian populations. Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disorder impairing ciliary structure and function. These two disorders are not easily distinguished by clinical signs and symptoms. METHODS: In 105 Japanese patients with recurrent sinopulmonary infection, initially diagnosed with DPB, and 37 patients with recurrent airway infection diagnosed in adulthood, the deletion allele of DRC1 or CCDC164, recently recognized as a pathogenic PCD gene variant, was searched using a multiplexed PCR‐based method, and the deletion breakpoints and other variants around the gene were determined by Sanger sequencing and targeted resequencing. RESULTS: A large homozygous deletion in DRC1 was identified in three of the 142 patients. Furthermore, heterozygous carriers of the deletion with the same breakpoint were found with the allele frequency of 0.002 in the healthy Japanese population, indicating that this loss‐of‐function variant may be acting as a common mutation causing PCD in Japanese. CONCLUSION: PCD caused by the DRC1 defect is not readily identified by either high‐speed video‐microscopy or ciliary ultrastructure analysis, posing significant difficulties in reaching a correct diagnosis without the aid of genetic tests. Careful investigation of the causes of sinopulmonary diseases is warranted in Asian populations.