ZP1 and Infertility: Although ZP1 remains by far the less studied component of the mammalian ZP, our characterisation of the hZP1 I390fs404X mutant protein (Fig. 1) suggests that infertile patients carrying the corresponding mutation lack the ZP due to an impairment of hZP1 secretion that in turn causes absence of filament cross-linking, rather than interference with hZP3 secretion as previously hypothesised39.