and -Mutant Cilia Lack the Central Pair-associated Protein SPEF2, Aiding Primary Ciliary Dyskinesia Diagnostics.

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous chronic destructive airway disease. PCD is traditionally diagnosed by nasal nitric oxide measurement, analysis of ciliary beating, transmission electron microscopy (TEM), and/or genetic testing. In most genetic PCD variants, laterality defects can occur. However, it is difficult to establish a diagnosis in individuals with PCD and central pair (CP) defects, and alternative strategies are required because of very subtle ciliary beating abnormalities, a normal ciliary ultrastructure, and normal situs composition. Mutations in are known to cause CP defects, but the genetic analysis of variants is confounded by the pseudogene , which is almost identical in terms of intron/exon structure. We have previously shown that several types of PCD can be diagnosed via immunofluorescence (IF) microscopy analyses. Here, using IF microscopy, we demonstrated that in individuals with PCD and CP defects, the CP-associated protein SPEF2 is absent in -mutant cells, revealing its dependence on functional HYDIN. Next, we performed IF analyses of SPEF2 in respiratory cells from 189 individuals with suspected PCD and . Forty-one of the 189 individuals had undetectable SPEF2 and were subjected to a genetic analysis, which revealed one novel loss-of-function mutation in and three reported and 13 novel mutations in 15 individuals. The remaining 25 individuals are good candidates for new, as-yet uncharacterized PCD variants that affect the CP apparatus. mutations have been associated with male infertility but have not previously been identified to cause PCD. We identified a mutation of that is causative for PCD with a CP defect. We conclude that SPEF2 IF analyses can facilitate the detection of CP defects and evaluation of the pathogenicity of variants, thus aiding the molecular diagnosis of CP defects.