CCDC40 and primary ciliary dyskinesia: Mutations in CCDC39 (e.g. c.1072del) (Aprea et al., 2023) and CCDC40 (e.g. c.901C>T) (Liu et al., 2021) destabilize the radial spoke structure, leading to axonemal disorganization and loss of motility, as observed in primary ciliary dyskinesia (PCD).