Pathogenic homozygous PLCZ1 mutation reduces sperm protein levels with a simulated reduction of PIP2 binding: a case report

Mammalian oocyte activation is driven by intracellular calcium (Ca²⁺) oscillations induced by sperm-specific phospholipase C zeta (PLCζ). Sperm PLCζ deficiency is linked to male infertility caused by oocyte activation deficiency. Using whole exome sequencing, we report finding a previously reported loss-of-activity pathogenic mutation of PLCZ1 from two unrelated males in a separate ethnicity, homozygous in both cases. We examined sperm PLCζ using immunoblotting and immunofluorescence to compare levels with fertile control sperm. We also utilised bioinformatics tools to characterise the effect of this variant. The variant caused a guanine (G)-to-adenine (A) change at position 1,154 (c.1154G > A), resulting in an arginine (R)-to-glutamine (Q) change at amino acid 385 (p.Arg385Gln; R385Q), disrupting the local protein fold in the Y domain of the active site in a highly deleterious and pathogenic manner. A previous study identified this mutation as heterozygous, while we identified this variant as homozygous in an ethnically distinct population from this previous study. Sperm PLCζ was significantly reduced compared to controls. The R385Q change indicated a reduction in PIP2 interaction with PLCζ following docking analyses. Pathogenic PLCζ mutation may be common in men with repeated fertilisation failure. Raw ejaculate analysis, rather than density gradient washed sperm, could provide a more accurate assessment of PLCζ levels, especially in men with low sperm count or ejaculate volume. Such pathogenic cases may underlie higher proportions of sperm exhibiting abnormal PLCζ localisation and could stand to aid a larger number of patients seeking fertility treatment.