CCDC39 and primary ciliary dyskinesia: CCDC39 and CCDC40 have been identified in PCD patients (Becker-Heck et al., 2011; Merveille et al., 2011), and their encoded proteins form a molecular ruler to ensure establishment of 96-nm repeats, which are essential for anchoring the dynein regulatory complex (DRC) to connect the outer doublets and IDA proteins (Oda et al., 2014).