Required for assembly of dynein regulatory complex (DRC) and inner dynein arm (IDA) complexes, which are responsible for ciliary beat regulation, thereby playing a central role in motility in cilia and flagella. Probably acts together with CCDC39 to form a molecular ruler that determines the 96 nanometer (nm) repeat length and arrangements of components in cilia and flagella. Not required for outer dynein arm complexes assembly. Required for axonemal recruitment of CCDC39. Localizes to cytoplasm and motile cilium. Specifically expressed in the embryonic node and midline. Defects are the cause of the lnks phenotype, a phenotype related to primary ciliary dyskinesia (PCD). PCD is characterized by recurrent respiratory infections, situs inversus and ciliary immotility and hydrocephalus. The length of the cilia projecting from the nodal pit cells in mutants is drastically reduced. Belongs to the CCDC40 family. Truncated N-terminus.