PMFBP1 and spermatogenic failure 16: Defects in SUN5 and PMFBP1 are the most common etiologies of human acephalic spermatozoa syndrome, as identified by different investigators and demonstrated in a mouse model (Zhu et al., 2016, 2018; Elkhatib et al., 2017; Shang et al., 2017; Sha et al., 2018b, 2019; Liu et al., 2020; Lu et al., 2021; Zhang et al., 2021).