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 (PubMed:21131974). 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 (By similarity). Not required for outer dynein arm complexes assembly. Required for axonemal recruitment of CCDC39 (PubMed:21131974). Localizes to cytoplasm and motile cilium. The disease is caused by variants affecting the gene represented in this entry. The disease is characterized by primary ciliary dyskinesia with inner dynein arm (IDA) defects and axonemal dizorganisation: defects in CCDC39 and CCDC40 constitute the major cause of this phenotype. Belongs to the CCDC40 family. Extended N-terminus. The length of things - Issue 170 of June 2015