These two proteins bound together as a dimer, and loss of IFT20 or TTC21A was found to cause male infertility and MMAF phenotypes (Liu et al., 2019; Zhang et al., 2016a), and thus, we hypothesized that CEP78 regulates human and mice phenotypes by interacting with IFT20 and TTC21A. Here, TTC21A is linked to male infertility.