A recurrent ZP1 variant is responsible for oocyte maturation defect with degenerated oocytes in infertile females

Abstract

A female factor is present in approximately 70% of couple infertility, often due to ovulatory disorders. In oocyte maturation defect (OMD), affected patients have a primary infertility with normal menstrual cycles but produce no oocyte, degenerated (atretic) or abnormal oocytes blocked at different stages of maturation. Four genes have so far been associated with OMD: PATL2, TUBB8, WEE2, and ZP1. In our initial study, 6 out of 23 OMD subjects were shown to carry the same PATL2 homozygous loss of function variant and one patient had a TUBB8 truncating variant. Here, we included four additional OMD patients and reanalyzed all 27 subjects. In addition to the seven patients with a previously identified defect, five carried the same deleterious homozygous ZP1 variant (c.1097G>A; p.Arg366Gln). All the oocytes from ZP1-associated patients appeared shriveled and dark indicating that the abnormal ZP1 protein induced oocyte death and degeneration. Overall ZP1-associated patients had degenerated or absent oocytes contrary to PATL2-associated subjects who had immature oocytes blocked mainly at the germinal vesicle stage. In this cohort of North African OMD patients, whole exome sequencing permitted to diagnose 44% of the patients studied and to identify a new frequent ZP1 variant.