Empty follicle syndrome (EFS) is defined as the failure to aspirate oocytes from mature ovarian follicles during in vitro fertilization. Except for some cases caused by pharmacological or iatrogenic problems, the etiology of EFS remains enigmatic. In the present study, we describe a large family with a dominant inheritance pattern of female infertility characterized by recurrent EFS. Genome-wide linkage analyses and whole-exome sequencing revealed a paternally transmitted heterozygous missense mutation of c.400 G>A (p.Ala134Thr) in zona pellucida glycoprotein 3 (ZP3). The same mutation was identified in an unrelated EFS pedigree. Haplotype analysis revealed that the disease allele of these two families came from different origins. Furthermore, in a cohort of 21 cases of EFS, two were also found to have the ZP3 c.400 G>A mutation. Immunofluorescence and histological analysis indicated that the oocytes of the EFS female had degenerated and lacked the zona pellucida (ZP). ZP3 is a major component of the ZP filament. When mutant ZP3 was co-expressed with wild-type ZP3, the interaction between wild-type ZP3 and ZP2 was markedly decreased as a result of the binding of wild-type ZP3 and mutant ZP3, via dominant negative inhibition. As a result, the assembly of ZP was impeded and the communication between cumulus cells and the oocyte was prevented, resulting in oocyte degeneration. These results identified a genetic basis for EFS and oocyte degeneration and, moreover, might pave the way for genetic diagnosis of infertile females with this phenotype.During in vitro fertilization (IVF) treatment, oocyte retrieval is performed after ovarian stimulation via vaginal puncture. Cumulus-oocyte complexes (COCs), which consist of cumulus cells surrounding the centrally located oocyte, are isolated from the individual's follicular fluid. As was first described by Coulam et al. in 1986, empty follicle syndrome (EFS) is a condition in which the ovarian response to stimulation and follicular development seems normal but no oocytes are retrieved for fertilization.1 EFS can be classified as either false EFS (FEFS) or genuine EFS (GEFS). FEFS is mainly caused by pharmacological or iatrogenic problems; however, the etiology of GEFS, which is responsible for about 33% of EFS, still remains enigmatic. 2 It has been proposed that GEFS is caused by dysfunctional folliculogenesis, ovarian aging, or genetic factors including pericentric inversion of chromosome 2 and LHCGR (MIM: 152790) mutations. 3-7 A retrospective study of 12,359 individuals who underwent assisted reproductive technology (ART) revealed that the prevalence of GEFS was about 0.016%. 8 Without oocytes for fertilization, these individuals fail to achieve pregnancy after a demanding and expensive medical intervention, resulting in stress to both physicians and the individuals themselves.9

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Applications of genome editing ultimately depend on DNA repair triggered by targeted doublestrand breaks (DSBs). However, repair mechanisms in human cells remain poorly understood and vary across different cell types. Here we report that DSBs selectively induced on a mutant allele in heterozygous human embryos are repaired by gene conversion using an intact wildtype homolog as a template in up to 40% of targeted embryos. We also show that targeting of homozygous loci facilitates an interplay of non-homologous end joining (NHEJ) and gene conversion and results in embryos which carry identical indel mutations on both loci. Additionally, conversion tracks may expand bidirectionally well beyond the target region leading to an extensive loss of heterozygosity (LOH). Our study demonstrates that gene conversion and NHEJ are two major DNA DSB repair mechanisms in preimplantation human embryos. While gene conversion could be applicable for gene correction, extensive LOH presents a serious safety concern.

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ZP gene variants may account for patients with oocyte morphologic abnormalities but not for those with oocyte maturation arrest.

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Objective: To determine whether variants in the WEE2 (WEE1 homolog 2, also known as WEE1B) gene, which has been known to function in the formation of pronuclei during fertilization, contribute to fertilization failure. Design: Case-control genetic study. Setting: University hospital. Patient(s): Ninety infertile women with repeated cycles of pronucleus formation failure undergoing in vitro fertilization and/or intracytoplasmic sperm injection treatment as well as 200 fertile control women. Intervention(s): Genomic DNA was extracted from the peripheral blood. The whole exons of WEE2 were amplified by means of polymerase chain reaction and then Sanger sequencing was performed. Main Outcome Measure(s): Variants analysis of WEE2 gene. Result(s): We identified five subjects that were subjected to homozygous or compound-heterozygous variants of WEE2: case 1 (from a consanguineous family) with homozygous frameshift variant: c.293_294insCTGAGACACCAGCCCAACC (p.Pro98Pro fsX2); case 2 with homozygous missense variant: c.1576T>G (p.Tyr526Asp); and three cases with compound-heterozygous variants: case 3: c.991C>A (p.His331Asn) and c.1304_1307delCCAA (p.Thr435Met fsX31); case 4: c.341_342 del AA (p.Lys114Asn fsX20) and c.864G>C (p.Gln288His); and case 5: c.1A>G (p.0?) and c.1261G>A (p.Gly421Arg). Besides c.1576T>G (from case 2) and c.864G>C (from case 4), which have been previously reported as rare single nucleotide polymorphisms (SNPs), the other six variants were novel and predicted by software to be deleterious. The parental genotypes of case 1 and case 2 indicated that the detected homozygous variants were inherited in an autosomal recessive mode. All of the detected variants were absent from the control cohort. Conclusion(s): Novel variants found in WEE2, which is autosomal-recessive inherited, may be related to recurrent pronucleus formation failure and female infertility. (Fertil Steril Ò 2019;111:519-26. Ó2018 by American Society for Reproductive Medicine.) El resumen está disponible en Español al final del artículo.