Essential Role of BRCA2 in Ovarian Development and Function

Comparative genome-wide association study on body weight in Chinese native ducks using four models

The Jinling White duck represents a newly developed breed characterized by a rapid growth rate and a superior meat quality, offering significant economic value and research potential; however, the genetic basis underlying their body weight traits remains less understood. Here, we performed whole-genome resequencing for 201 diverse Jinling White male ducks and conducted population genomic analyses, suggesting a rich genetic diversity within the Jinling White duck population. Equipped with our genomic resources, we applied genome-wide association analysis for body weight on birth (BWB), body weight on 1 wk (BW1), body weight on 3 wk (BW3), body weight on 5 wk (BW5) and body weight on 7 wk (BW7) using 4 statistical models. Comparative studies indicated that factored spectrally transformed linear mixed models (FaST-LMM) demonstrated the most superior efficiency, yielding more results with the minimal false positives. We discovered that PUS7, FBXO11, FOXN2, MSH6, and SLC4A4 were associated with BWB. RAG2, and TMEFF2 were candidate genes for BW1, and STARD13, Klotho, ZAR1L are likely candidates for BW3 and BW5. PLXNC1, ATP1A1, CD58, FRYL, OCIAD1, and OCIAD2 were linked to BW7. These findings provide a genetic reference for the selection and breeding of Jinling White ducks, while also deepened our understanding of Growth and development phenotypic in ducks.

Pediatric acute promyelocytic leukemia and Fanconi anemia: Case report and literature review

Acute promyelocytic leukemia (APL) represents 5%-10% of childhood acute myeloid leukemia (AML) and is the most curable subtype of AML. Fanconi anemia (FA) is one of the most common inherited bone marrow failure syndromes caused by biallelic pathogenic variants (PV) in specific DNA-repair genes. Biallelic PVs in FANCD1/BRCA2 (FA-D1) account for 3% of FA and are associated with early-onset leukemia and a high risk of solid tumors. We report a 4 year-old boy from non-consanguineous parents diagnosed with standard risk APL. This child had café-au-lait spots and an extra thumb remnant. Genomic sequencing revealed two PV in FANCD1/BRCA2 confirming a diagnosis of FA-D1. Chromosomal breakage studies were compatible with FA. Each parent carried one variant and had no personal history of cancer. Morphological then molecular remissions were achieved with all-trans retinoic acid and Arsenic trioxide. This patient underwent haploidentical stem cell transplant. In addition to our patient, a literature search revealed four additional patients with APL/FA, with a total of three patients with FA-D1. This raises the possibility of an association between such rare disorders. Practical management of APL in the setting of FA-D1 is discussed with an overview of current evidence and knowledge gaps.

Research progress on the fanconi anemia signaling pathway in non-obstructive azoospermia

Non-obstructive azoospermia (NOA) is a disease characterized by spermatogenesis failure and comprises phenotypes such as hypospermatogenesis, mature arrest, and Sertoli cell-only syndrome. Studies have shown that FA cross-linked anemia (FA) pathway is closely related to the occurrence of NOA. There are FA gene mutations in male NOA patients, which cause significant damage to male germ cells. The FA pathway is activated in the presence of DNA interstrand cross-links; the key step in activating this pathway is the mono-ubiquitination of the FANCD2-FANCI complex, and the activation of the FA pathway can repair DNA damage such as DNA double-strand breaks. Therefore, we believe that the FA pathway affects germ cells during DNA damage repair, resulting in minimal or even disappearance of mature sperm in males. This review summarizes the regulatory mechanisms of FA-related genes in male azoospermia, with the aim of providing a theoretical reference for clinical research and exploration of related genes.

Biallelic FANCA variants detected in sisters with isolated premature ovarian insufficiency

Premature ovarian insufficiency is a common form of female infertility affecting up to 4% of women and characterised by amenorrhea with elevated gonadotropin before the age of 40. Oocytes require controlled DNA breakage and repair for homologous recombination and the maintenance of oocyte integrity. Biallelic disruption of the DNA damage repair gene, Fanconi anemia complementation group A (FANCA), is a common cause of Fanconi anaemia, a syndrome characterised by bone marrow failure, cancer predisposition, physical anomalies and POI. There is ongoing dispute about the role of heterozygous FANCA variants in POI pathogenesis, with insufficient evidence supporting causation. Here, we have identified biallelic FANCA variants in French sisters presenting with POI, including a novel missense variant of uncertain significance and a likely pathogenic deletion that initially evaded detection. Functional studies indicated no discernible effect on DNA damage sensitivity in patient lymphoblasts. These novel FANCA variants add evidence that heterozygous loss of one allele is insufficient to cause DNA damage sensitivity and POI. We propose that intragenic deletions, that are relatively common in FANCA, may be missed without careful analysis, and could explain the presumed causation of heterozygous variants. Accurate variant curation is critical to optimise patient care and outcomes.

Primordial germ cell DNA demethylation and development require DNA translesion synthesis

Mutations in DNA damage response (DDR) factors are associated with human infertility, which affects up to 15% of the population. The DDR is required during germ cell development and meiosis. One pathway implicated in human fertility is DNA translesion synthesis (TLS), which allows replication impediments to be bypassed. We find that TLS is essential for pre-meiotic germ cell development in the embryo. Loss of the central TLS component, REV1, significantly inhibits the induction of human PGC-like cells (hPGCLCs). This is recapitulated in mice, where deficiencies in TLS initiation (Rev1-/- or PcnaK164R/K164R) or extension (Rev7 -/-) result in a > 150-fold reduction in the number of primordial germ cells (PGCs) and complete sterility. In contrast, the absence of TLS does not impact the growth, function, or homeostasis of somatic tissues. Surprisingly, we find a complete failure in both activation of the germ cell transcriptional program and in DNA demethylation, a critical step in germline epigenetic reprogramming. Our findings show that for normal fertility, DNA repair is required not only for meiotic recombination but for progression through the earliest stages of germ cell development in mammals.

Novel compound heterozygous variants in FANCI cause premature ovarian insufficiency

Premature ovarian insufficiency (POI) is a common reproductive aging disorder due to a dramatic decline of ovarian function before 40 years of age. Accumulating evidence reveals that genetic defects, particularly those related to DNA damage response, are a crucial contributing factor to POI. We have demonstrated that the functional Fanconi anemia (FA) pathway maintains the rapid proliferation of primordial germ cells to establish a sufficient reproductive reserve by counteracting replication stress, but the clinical implications of this function in human ovarian function remain to be established. Here, we screened the FANCI gene, which encodes a key component for FA pathway activation, in our whole-exome sequencing database of 1030 patients with idiopathic POI, and identified two pairs of novel compound heterozygous variants, c.[97C > T];[1865C > T] and c.[158-2A > G];[c.959A > G], in two POI patients, respectively. The missense variants did not alter FANCI protein expression and nuclear localization, apart from the variant c.158-2A > G causing abnormal splicing and leading to a truncated mutant p.(S54Pfs*5). Furthermore, the four variants all diminished FANCD2 ubiquitination levels and increased DNA damage under replication stress, suggesting that the FANCI variants impaired FA pathway activation and replication stress response. This study first links replication stress response defects with the pathogenesis of human POI, providing a new insight into the essential roles of the FA genes in ovarian function.

Positive and negative regulators of RAD51/DMC1 in homologous recombination and DNA replication

RAD51 recombinase plays a central role in homologous recombination (HR) by forming a nucleoprotein filament on single-stranded DNA (ssDNA) to catalyze homology search and strand exchange between the ssDNA and a homologous double-stranded DNA (dsDNA). The catalytic activity of RAD51 assembled on ssDNA is critical for the DNA-homology-mediated repair of DNA double-strand breaks in somatic and meiotic cells and restarting stalled replication forks during DNA replication. The RAD51-ssDNA complex also plays a structural role in protecting the regressed/reversed replication fork. Two types of regulators control RAD51 filament formation, stability, and dynamics, namely positive regulators, including mediators, and negative regulators, so-called remodelers. The appropriate balance of action by the two regulators assures genome stability. This review describes the roles of positive and negative RAD51 regulators in HR and DNA replication and its meiosis-specific homolog DMC1 in meiotic recombination. We also provide future study directions for a comprehensive understanding of RAD51/DMC1-mediated regulation in maintaining and inheriting genome integrity.

Genome Instability and DNA Repair in Somatic and Reproductive Aging

Genetic material is constantly subjected to genotoxic insults and is critically dependent on DNA repair. Genome maintenance mechanisms differ in somatic and germ cells as the soma only requires maintenance during an individual's lifespan, while the germline indefinitely perpetuates its genetic information. DNA lesions are recognized and repaired by mechanistically highly diverse repair machineries. The DNA damage response impinges on a vast array of homeostatic processes and can ultimately result in cell fate changes such as apoptosis or cellular senescence. DNA damage causally contributes to the aging process and aging-associated diseases, most prominently cancer. By causing mutations, DNA damage in germ cells can lead to genetic diseases and impact the evolutionary trajectory of a species. The mechanisms ensuring tight control of germline DNA repair could be highly instructive in defining strategies for improved somatic DNA repair. They may provide future interventions to maintain health and prevent disease during aging.

Research progress of the Fanconi anemia pathway and premature ovarian insufficiency†

The Fanconi anemia pathway is a key pathway involved in the repair of deoxyribonucleic acidinterstrand crosslinking damage, which chiefly includes the following four modules: lesion recognition, Fanconi anemia core complex recruitment, FANCD2-FANCI complex monoubiquitination, and downstream events (nucleolytic incision, translesion synthesis, and homologous recombination). Mutations or deletions of multiple Fanconi anemia genes in this pathway can damage the interstrand crosslinking repair pathway and disrupt primordial germ cell development and oocyte meiosis, thereby leading to abnormal follicular development. Premature ovarian insufficiency is a gynecological clinical syndrome characterized by amenorrhea and decreased fertility due to decreased oocyte pool, accelerated follicle atresia, and loss of ovarian function in women <40 years old. Furthermore, in recent years, several studies have detected mutations in the Fanconi anemia gene in patients with premature ovarian insufficiency. In addition, some patients with Fanconi anemia exhibit symptoms of premature ovarian insufficiency and infertility. The Fanconi anemia pathway and premature ovarian insufficiency are closely associated.

BRCA2-HSF2BP oligomeric ring disassembly by BRME1 promotes homologous recombination

In meiotic homologous recombination (HR), BRCA2 facilitates loading of the recombinases RAD51 and DMC1 at the sites of double-strand breaks (DSBs). The HSF2BP-BRME1 complex interacts with BRCA2. Its absence causes a severe reduction in recombinase loading at meiotic DSB. We previously showed that, in somatic cancer cells ectopically producing HSF2BP, DNA damage can trigger HSF2BP-dependent degradation of BRCA2, which prevents HR. Here, we report that, upon binding to BRCA2, HSF2BP forms octameric rings that are able to interlock into a large ring-shaped 24-mer. Addition of BRME1 leads to dissociation of both of these ring structures and cancels the disruptive effect of HSF2BP on cancer cell resistance to DNA damage. It also prevents BRCA2 degradation during interstrand DNA crosslink repair in Xenopus egg extracts. We propose that, during meiosis, the control of HSF2BPBRCA2 oligomerization by BRME1 ensures timely assembly of the ring complex that concentrates BRCA2 and controls its turnover, thus promoting HR.

DNA damage and repair: underlying mechanisms leading to microcephaly

DNA-damaging agents and endogenous DNA damage constantly harm genome integrity. Under genotoxic stress conditions, the DNA damage response (DDR) machinery is crucial in repairing lesions and preventing mutations in the basic structure of the DNA. Different repair pathways are implicated in the resolution of such lesions. For instance, the non-homologous DNA end joining and homologous recombination pathways are central cellular mechanisms by which eukaryotic cells maintain genome integrity. However, defects in these pathways are often associated with neurological disorders, indicating the pivotal role of DDR in normal brain development. Moreover, the brain is the most sensitive organ affected by DNA-damaging agents compared to other tissues during the prenatal period. The accumulation of lesions is believed to induce cell death, reduce proliferation and premature differentiation of neural stem and progenitor cells, and reduce brain size (microcephaly). Microcephaly is mainly caused by genetic mutations, especially genes encoding proteins involved in centrosomes and DNA repair pathways. However, it can also be induced by exposure to ionizing radiation and intrauterine infections such as the Zika virus. This review explains mammalian cortical development and the major DNA repair pathways that may lead to microcephaly when impaired. Next, we discuss the mechanisms and possible exposures leading to DNA damage and p53 hyperactivation culminating in microcephaly.

Loss of function of FIGNL1, a DNA damage response gene, causes human ovarian dysgenesis

Ovarian dysgenesis (OD), an XX disorder of sex development, presents with primary amenorrhea, hypergonadotrophic hypogonadism, and infertility. In an Ashkenazi Jewish patient with OD, whole exome sequencing identified compound heterozygous frameshifts in FIGNL1, a DNA damage response (DDR) gene: c.189del and c.1519_1523del. Chromosomal breakage was significantly increased in patient cells, both spontaneously, and following mitomycin C exposure. Transfection of DYK-tagged FIGNL1 constructs in HEK293 cells showed no detectable protein in FIGNL1c.189del and truncation with reduced expression in FIGNL1c.1519_1523del (64% of wild-type [WT], P = .003). FIGNL1 forms nuclear foci increased by phleomycin treatment (20.6 ± 1.6 vs 14.8 ± 2.4, P = .02). However, mutant constructs showed reduced DYK-FIGNL1 foci formation in non-treated cells (0.8 ± 0.9 and 5.6 ± 1.5 vs 14.8 ± 2.4 in DYK-FIGNL1WT, P < .001) and no increase with phleomycin treatment. In conclusion, FIGNL1 loss of function is a newly characterized OD gene, highlighting the DDR pathway's role in ovarian development and maintenance and suggesting chromosomal breakage as an assessment tool in XX-DSD patients.

DNA double-strand break genetic variants in patients with premature ovarian insufficiency

Premature ovarian insufficiency (POI) is a clinically heterogeneous disease that may seriously affect the physical and mental health of women of reproductive age. POI primarily manifests as ovarian function decline and endocrine disorders in women prior to age 40 and is an established cause of female infertility. It is crucial to elucidate the causative factors of POI, not only to expand the understanding of ovarian physiology, but also to provide genetic counselling and fertility guidance to affected patients. Factors leading to POI are multifaceted with genetic factors accounting for 7% to 30%. In recent years, an increasing number of DNA damage-repair-related genes have been linked with the occurrence of POI. Among them, DNA double-strand breaks (DSBs), one of the most damaging to DNA, and its main repair methods including homologous recombination (HR) and non-homologous end joining (NHEJ) are of particular interest. Numerous genes are known to be involved in the regulation of programmed DSB formation and damage repair. The abnormal expression of several genes have been shown to trigger defects in the overall repair pathway and induce POI and other diseases. This review summarises the DSB-related genes that may contribute to the development of POI and their potential regulatory mechanisms, which will help to further establish role of DSB in the pathogenesis of POI and provide theoretical guidance for the study of the pathogenesis and clinical treatment of this disease.

The reduction of oocytes and disruption of the meiotic prophase I in Fanconi Anemia E deficient mice

Fance is an important factor participating in the repair of DNA interstrand cross-links and its defect causes severe follicle depletion in female mice. To explore the underlying mechanisms, we investigated the effects of Fance on ovarian development in embryonic and newborn mice. We found that the number of oocytes was significantly decreased in Fance-/- mice as early as 13.5 days post coitum (dpc). The continuous decrease of oocytes in Fance-/- mice compared with the Fance+/+ mice led to the primordial follicles being almost exhausted at 2 days postpartum (dpp). The mitotic-meiotic transition occurred normally, but the meiotic progression was arrested in pachytene in Fance-/- oocytes. We detected the expressions of RAD51 (homologous recombination repair factor), 53BP1 (non-homologous end-joining repair factor), and γH2AX by immunostaining analysis and chromosome spreads. The expressions of 53BP1 were increased and RAD51 decreased significantly in Fance-/- oocytes compared with Fance+/+ oocytes. Also, the meiotic crossover indicated by MLH1 foci was significantly increased in Fance-/- oocytes. Oocyte proliferation and apoptosis were comparable between Fance-/- and Fance+/+ mice (P>0.05). The aberrant high expression at 17.5dpc and low expressions at 1dpp and 2dpp indicated the expression pattern of pluripotent marker OCT4 was disordered in Fance-/- oocytes. These findings elucidate that Fance mutation leads to a progressive reduction of oocytes and disrupts the progression of meiotic prophase I but not the initiation. And our study reveals that the potential mechanisms involve DNA damage repair, meiotic crossover, and pluripotency of oocytes.

In silico analysis of a novel pathogenic variant c.7G > A in C14orf39 gene identified by WES in a Pakistani family with azoospermia

Infertility is a multifactorial disorder that affects approximately 12% of couples of childbearing ages worldwide. Few studies have been conducted to understand the genetic causes of infertility in depth. The synaptonemal complex (SC), which is essential for the progression of meiosis, is a conserved tripartite structure that binds homologous chromosomes together and is thus required for fertility. This study investigated genetic causes of infertility in a Pakistani consanguineous family containing two patients suffering from non-obstructive azoospermia (NOA). We performed whole-exome sequencing, followed by Sanger sequencing, and identified a novel pathogenic variant (c.7G > A [p.D3N]) in the SC coding gene C14orf39, which was recessively co-segregated with NOA. In silico analysis revealed that charges on wild-type residues were lost, which may result in loss of interactions with other molecules and residues, and a reduction in protein stability occurred, which was caused by the p.D3N mutation. The novel variant generated the mutant protein C14ORF39^D3N, and homozygous mutations in C14orf39 resulted in NOA. The transcriptome profile of C14ORF39 shows that it is specifically expressed in early brain development, which suggests that research in this area is required to study other functions of C14ORF39 in addition to its role in the germline. This research highlights the conserved role of C14orf39/SIX6OS1 in assembly of the SC and its indispensable role in facilitating genetic diagnosis in patients with infertility, which may enable the development of future treatments.

Heterozygous FMN2 missense variant found in a family case of premature ovarian insufficiency

Background

Premature ovarian insufficiency (POI) plagues 1% of women under 40, while quite a few remain an unknown cause. The development of sequencing has helped find pathogenic genes and reveal the relationship between DNA repair and ovarian reserve. Through the exome sequencing, our study targets screening out the possible POI pathogenic gene and variants in a Chinese family and 20 sporadic POI patients, preliminarily exploring the functional impact and finding out potential linkages between the gene and POI.

Results

The whole exome sequencing suggested a novel FMN2 heterozygous variant c.1949C > T (p.Ser650Leu) carried by all three patients in a Chinese family and another c.1967G > A(p.Arg656His) variant in a sporadic case. Since no FMN2 missense mutation is reported for causing human POI, we preliminarily assessed p.Ser650Leu variant via cross-species alignment and 3D modeling and found it possibly deleterious. A series of functional evidence was consistent with our hypothesis. We proved the expression of FMN2 in different stages of oocytes and observed a statistical difference of chromosomal breakages between the POI patient carrying p.Arg656His variant and the health control (p = 0.0013). Western Blot also suggested a decrease in FMN2 and P21 in the mutant type and an associated increase in H2AX. The p.Arg656His variant with an extremely low frequency also indicated that the gene FMN2 might play an essential role in the genetic etiology of POI. To the best of our knowledge, this is the first POI report on missense variants of FMN2.

Conclusion

This finding indicates a novel gene possibly related to POI and sheds lights on the study of FMN2.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13048-022-00960-y.

Causal and Candidate Gene Variants in a Large Cohort of Women With Primary Ovarian Insufficiency

CONTEXT

A genetic etiology likely accounts for the majority of unexplained primary ovarian insufficiency (POI).

OBJECTIVE

We hypothesized that heterozygous rare variants and variants in enhanced categories are associated with POI.

DESIGN

The study was an observational study.

SETTING

Subjects were recruited at academic institutions.

PATIENTS

Subjects from Boston (n = 98), the National Institutes of Health and Washington University (n = 98), Pittsburgh (n = 20), Italy (n = 43), and France (n = 32) were diagnosed with POI (amenorrhea with an elevated follicle-stimulating hormone level). Controls were recruited for health in old age or were from the 1000 Genomes Project (total n = 233).

INTERVENTION

We performed whole exome sequencing (WES), and data were analyzed using a rare variant scoring method and a Bayes factor-based framework for identifying genes harboring pathogenic variants. We performed functional studies on identified genes that were not previously implicated in POI in a D. melanogaster model.

MAIN OUTCOME

Genes with rare pathogenic variants and gene sets with increased burden of deleterious variants were identified.

RESULTS

Candidate heterozygous variants were identified in known genes and genes with functional evidence. Gene sets with increased burden of deleterious alleles included the categories transcription and translation, DNA damage and repair, meiosis and cell division. Variants were found in novel genes from the enhanced categories. Functional evidence supported 7 new risk genes for POI (USP36, VCP, WDR33, PIWIL3, NPM2, LLGL1, and BOD1L1).

CONCLUSIONS

Candidate causative variants were identified through WES in women with POI. Aggregating clinical data and genetic risk with a categorical approach may expand the genetic architecture of heterozygous rare gene variants causing risk for POI.

Recurring pathogenic variants in the BRCA2 gene in the Ethiopian Jewish population. Founder mutations?

Mutations in the BRCA1 and BRCA2 genes increase the risk for various cancers including breast, ovarian, prostate, pancreas and melanoma. Identifying BRCA1/2 mutation carriers enables risk assessment, surveillance, early detection and risk reduction. In certain Israeli sub-populations recurring and founder mutations have been identified and for these, testing for founder mutations is simple, efficient and cost-effective. Founder mutations in the Jewish Ethiopian population have not been described. We report here the identification of a recurring BRCA2 mutation in the Ethiopian Jewish population; c.5159C>A; p.Ser1720Ter, which has only been described once before in this population. In addition, in another family of the same origin we found the BRCA2 c.7579delG; p.Val2527Ter mutation that has been previously described in two different Jewish Ethiopian families. In Israel genetic testing is performed in a sequential stepwise manner, first testing a panel of predominant mutations and if negative further testing by gene sequencing is offered. Recently it has been decided to expand the founder mutation panel to include mutations which have been found in two or more separate families. This new panel will include the BRCA2 c.7579delG; p.Val2527Ter mutation, and we recommend that the BRCA2 c.5159C>A; p.Ser1720Ter mutation should also be added to the new predominant mutation panel.

Genetics of ovarian insufficiency and defects of folliculogenesis

Primary ovarian insufficiency (POI) is determined by exhaustion of follicles in the ovaries, which leads to infertility before the age of 40 years. It is characterized by a strong familial and heterogeneous genetic background. Therefore, we will mainly discuss the genetic basis of POI in this review. We identified 107 genes related to POI etiology in mammals described by several independent groups. Thirty-four of these genes (AARS2, AIRE, ANTXR1, ATM, BMPR1B, CLPP, CYP17A1, CYP19A1, DCAF17, EIF2B, ERAL1, FANCA, FANCC, FMR1, FOXL2, GALT, GNAS, HARS2, HSD17B4, LARS2, LMNA, MGME1, NBN, PMM2, POLG, PREPL, RCBTB1, RECQL2/3/4, STAR, TWNK, and XRCC4/9) have been linked to syndromic POI and are mainly implicated in metabolism function and meiosis/DNA repair. In addition, the majority of genes associated with nonsyndromic POI, widely expanded by high-throughput techniques over the last decade, have been implicated in ovarian development and meiosis/DNA repair pathways (ATG7, ATG9, ANKRD31, BMP8B, BMP15, BMPR1A, BMPR1B, BMPR2, BNC1, BRCA2, CPEB1, C14ORF39, DAZL, DIAPH2, DMC1, ERCC6, FANCL, FANCM, FIGLA, FSHR, GATA4, GDF9, GJA4, HELQ, HSF2BP, HFM1, INSL3, LHCGR, LHX8, MCM8, MCM9, MEIOB, MSH4, MSH5, NANOS3, NOBOX, NOTCH2, NR5A1, NUP107, PGRMC1, POLR3H, PRDM1, PRDM9, PSMC3IP, SOHLH1, SOHLH2, SPIDR, STAG3, SYCE1, TP63, UBR2, WDR62, and XRCC2), whereas a few are related to metabolic functions (EIF4ENIF1, KHDRBS1, MRPS22, POLR2C). Some genes, such as STRA8, FOXO3A, KIT, KITL, WNT4, and FANCE, have been shown to cause ovarian insufficiency in rodents, but mutations in these genes have yet to be elucidated in women affected by POI. Lastly, some genes have been rarely implicated in its etiology (AMH, AMHR2, ERRC2, ESR1, INHA, LMN4, POF1B, POU5F1, REC8, SMC1B). Considering the heterogeneous genetic and familial background of this disorder, we hope that an overview of literature data would reinforce that genetic screening of those patients is worthwhile and helpful for better genetic counseling and patient management.

lncRNA DDGC participates in premature ovarian insufficiency through regulating RAD51 and WT1

The list of long non-coding RNAs (lncRNAs) that participate in the function of ovarian granulosa cells (GCs) is rapidly expanding, but the mechanisms through which lncRNAs regulate GC function are not yet fully understood. Here, we recognized a minimally expressed lncRNA RP4-545C24.1 (which we named DDGC) in GCs from patients with biochemical premature ovarian insufficiency (bPOI). We further explored the role of lncRNA DDGC in GC function and its contribution to the development of bPOI. Mechanistically, silencing DDGC downregulated RAD51 by competitively binding with miR-589-5p, and this resulted in significant inhibition of DNA damage repair capacity. In addition, decreased expression of DDGC promoted ubiquitin-mediated degradation of Wilms tumor 1 (WT1) protein through interactions with heat shock protein 90 (HSP90), which led to aberrant differentiation of GCs. Moreover, DDGC was able to ameliorate the etoposide-induced DNA damage and apoptosis in vivo. Taken together, these findings provide new insights into the contribution of lncRNAs in POI pathogenesis.

Female Oncofertility: Current Understandings, Therapeutic Approaches, Controversies, and Future Perspectives

Recent advances in early detection and oncological therapies have ameliorated the survival rate of young cancer patients. Yet, ovarian impairment induced by chemotherapy and radiotherapy is still a challenging issue. This review, based on clinical and lab-based studies, summarizes the evidence of gonadotoxicity of chemoradiotherapy, the recent approaches, ongoing controversies, and future perspectives of fertility preservation (FP) in female patients who have experienced chemo- or radio-therapy. Existing data indicate that chemotherapeutic agents induce DNA alterations and massive follicle activation via the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. Meanwhile, the radiation causes ionizing damage, leading to germ cell loss. In addition to the well-established methods, numerous therapeutic approaches have been suggested, including minimizing the follicle loss in cryopreserved ovarian grafts after transplantation, in vitro activation or in vitro growing of follicles, artificial ovarian development, or fertoprotective adjuvant to prevent ovarian damage from chemotherapy. Some reports have revealed positive outcomes from these therapies, whereas others have demonstrated conflictions. Future perspectives are improving the live birth rate of FP, especially in patients with adverse ovarian reserve, eliminating the risk of malignancy reintroducing, and increasing society’s awareness of FP importance.

Catastrophic chemotherapy toxicity leading to diagnosis of Fanconi anaemia due to FANCD1/BRCA2 during adulthood: description of an emerging phenotype

Fanconi anaemia due to biallelic loss of BRCA2 (Fanconi anaemia subtype D1) is traditionally diagnosed during childhood with cancer rates historically reported as 97% by 5.2 years. This report describes an adult woman with a history of primary ovarian failure, who was diagnosed with gastrointestinal adenocarcinoma and BRCA2-associated Fanconi anaemia at 23 years of age, only after she suffered severe chemotherapy toxicity. The diagnostic challenges include atypical presentation, initial false-negative chromosome fragility testing and variant classification. It highlights gastrointestinal adenocarcinoma as a consideration for adults with biallelic BRCA2 pathogenic variants with implications for surveillance. After over 4 years, the patient has no evidence of gastrointestinal cancer recurrence although the tumour was initially considered only borderline resectable. The use of platinum-based chemotherapy, to which heterozygous BRCA2 carriers are known to respond, may have had a beneficial anticancer effect, but caution is advised given its extreme immediate toxicity at standard dosing. Fanconi anaemia should be considered as a cause for women with primary ovarian failure of unknown cause and referral to cancer genetic services recommended when there is a family history of cancer in the hereditary breast/ovarian cancer spectrum.

BRCA2 binding through a cryptic repeated motif to HSF2BP oligomers does not impact meiotic recombination

BRCA2 and its interactors are required for meiotic homologous recombination (HR) and fertility. Loss of HSF2BP, a BRCA2 interactor, disrupts HR during spermatogenesis. We test the model postulating that HSF2BP localizes BRCA2 to meiotic HR sites, by solving the crystal structure of the BRCA2 fragment in complex with dimeric armadillo domain (ARM) of HSF2BP and disrupting this interaction in a mouse model. This reveals a repeated 23 amino acid motif in BRCA2, each binding the same conserved surface of one ARM domain. In the complex, two BRCA2 fragments hold together two ARM dimers, through a large interface responsible for the nanomolar affinity - the strongest interaction involving BRCA2 measured so far. Deleting exon 12, encoding the first repeat, from mBrca2 disrupts BRCA2 binding to HSF2BP, but does not phenocopy HSF2BP loss. Thus, results herein suggest that the high-affinity oligomerization-inducing BRCA2-HSF2BP interaction is not required for RAD51 and DMC1 recombinase localization in meiotic HR.

A kaleidoscopic view of ovarian genes associated with premature ovarian insufficiency and senescence

Ovarian infertility and subfertility presenting with premature ovarian insufficiency (POI) and diminished ovarian reserve are major issues facing the developed world due to the trend of delaying childbirth. Ovarian senescence and POI represent a continuum of physiological/pathophysiological changes in ovarian follicle functions. Based on advances in whole exome sequencing, evaluation of gene copy variants, together with family-based and genome-wide association studies, we discussed genes responsible for POI and ovarian senescence. We used a gene-centric approach to sort out literature deposited in the Ovarian Kaleidoscope database (http://okdb.appliedbioinfo.net) by sub-categorizing candidate genes as ligand-receptor signaling, meiosis and DNA repair, transcriptional factors, RNA metabolism, enzymes, and others. We discussed individual gene mutations found in POI patients and verification of gene functions in gene-deleted model organisms. Decreased expression of some of the POI genes could be responsible for ovarian senescence, especially those essential for DNA repair, meiosis and mitochondrial functions. We propose to set up a candidate gene panel for targeted sequencing in POI patients together with studies on mitochondria-associated genes in middle-aged subfertile patients.

Onco-fertility and personalized testing for potential for loss of ovarian reserve in patients undergoing chemotherapy: proposed next steps for development of genetic testing to predict changes in ovarian reserve

Women of reproductive age undergoing chemotherapy face the risk of irreversible ovarian insufficiency. Current methods of ovarian reserve testing do not accurately predict future reproductive potential for patients undergoing chemotherapy. Genetic markers that more accurately predict the reproductive potential of each patient undergoing chemotherapy would be critical tools that would be useful for evidence-based fertility preservation counselling. To assess the possible approaches to take to develop personalized genetic testing for these patients, we review current literature regarding mechanisms of ovarian damage due to chemotherapy and genetic variants associated with both the damage mechanisms and primary ovarian insufficiency. The medical literature point to a number of genetic variants associated with mechanisms of ovarian damage and primary ovarian insufficiency. Those variants that appear at a higher frequency, with known pathways, may be considered as potential genetic markers for predictive ovarian reserve testing. We propose developing personalized testing of the potential for loss of ovarian function for patients with cancer, prior to chemotherapy treatment. There are advantages of using genetic markers complementary to the current ovarian reserve markers of AMH, antral follicle count and day 3 FSH as predictors of preservation of fertility after chemotherapy. Genetic markers will help identify upstream pathways leading to high risk of ovarian failure not detected by present clinical markers. Their predictive value is mechanism-based and will encourage research towards understanding the multiple pathways contributing to ovarian failure after chemotherapy.

Monepantel antitumor activity is mediated through inhibition of major cell cycle and tumor growth signaling pathways

In women, epithelial ovarian cancer is the leading cause of gynaecological malignancy-related deaths. Development of resistance to standard platinum and taxane based chemotherapy and recurrence of the disease necessitate development of novel drugs to halt disease progression. An established concept is to target molecular and signaling pathways that substantially contribute to development of drug resistance and disease progression. We have previously shown that, monepantel (MPL) a novel small molecule acetonitrile derivative is highly effective in suppressing growth, proliferation and colony formation of ovarian cancer cells. These effects are achieved through inhibition of the mTOR/p70S6K pathway in cancer cells. The present study was conducted to find in vivo corroboration and explore the effect of MPL om other growth stimulating putative signaling pathways. Here, female nude mice with subcutaneous OVCAR-3 xenografts were treated with 25 and 50 mg/kg doses of MPL administered (IP) three times weekly for 2 weeks. At the doses employed, MPL was modestly effective at suppressing tumor growth, but highly effective in inhibiting, mTOR, P70S6K and 4EBP1. There were also modest reductions in tumor cyclin D1 and retinoblastoma protein expression. Furthermore, it was found that MPL treatment causes down-regulation of IGF-1R, and c-MYC thus unveiling new dimensions to the growing antitumor actions of this potential anticancer drug. MPL treatment led to reduced tumor volume and weights without causing any detectable side effects. Coupled with the recent human safety data published on this molecule, expanded future trials are highly anticipated.

Fanconi Anemia Gene Variants in Patients with Gonadal Dysfunction

Fanconi anemia (FA) is a multisystem disease, characterized by the triad of physical abnormalities, bone marrow failure, and increased risk for malignancy. In the past few years, data has accumulated regarding fertility issues in FA patients, mostly due to gonadal dysfunction, which is prevalent in FA patients reaching puberty. It seems that attenuated FA phenotype lacking the classical manifestations often is presented with POI or azoospermia. Searching the literature, we summarized data regarding FA patients presenting as suffering from sub/infertility due to gonadal dysfunction, with or without other FA symptoms. We present a summary of the patients having biallelic pathogenic variants in FA genes FANCA, FANCM, BRCA2, and XRCC2 that presented with gonadal dysfunction with or without other phenotypic features of FA. Some were in mosaic, while some are considered hypomorphic, enabling residual protein function. There are also a few descriptions of POI associated with monoallelic pathogenic variants in FANCA, BRCA2, and FANCL. We conclude that the diagnosis of FA in gonadal dysfunction patients is of utmost importance due to its actionability. Follow-up strategies in FA patients are designed to discover early stages of leukemias and solid tumors and thus save lives. The feasibility of next-generation sequencing (NGS) can now ease this diagnostic procedure. An open question is the justification of performing NGS for all isolated azoospermia/POI patients.

BRCA1 and BRCA2 Tumor Suppressor Function in Meiosis

Meiosis is a specialized cell cycle that results in the production of haploid gametes for sexual reproduction. During meiosis, homologous chromosomes are connected by chiasmata, the physical manifestation of crossovers. Crossovers are formed by the repair of intentionally induced double strand breaks by homologous recombination and facilitate chromosome alignment on the meiotic spindle and proper chromosome segregation. While it is well established that the tumor suppressors BRCA1 and BRCA2 function in DNA repair and homologous recombination in somatic cells, the functions of BRCA1 and BRCA2 in meiosis have received less attention. Recent studies in both mice and the nematode Caenorhabditis elegans have provided insight into the roles of these tumor suppressors in a number of meiotic processes, revealing both conserved and organism-specific functions. BRCA1 forms an E3 ubiquitin ligase as a heterodimer with BARD1 and appears to have regulatory roles in a number of key meiotic processes. BRCA2 is a very large protein that plays an intimate role in homologous recombination. As women with no indication of cancer but carrying BRCA mutations show decreased ovarian reserve and accumulated oocyte DNA damage, studies in these systems may provide insight into why BRCA mutations impact reproductive success in addition to their established roles in cancer.

Haploinsufficiency in non-homologous end joining factor 1 induces ovarian dysfunction in humans and mice

BACKGROUND

Premature ovarian insufficiency (POI) is a common disease in women that leads to a reduced reproductive lifespan. The aetiology of POI is genetically heterogeneous, with certain double-strand break (DSB) repair genes being implicated in POI. Although non-homologous end joining (NHEJ) is an efficient DSB repair pathway, the functional relationship between this pathway and POI remains unknown.

METHODS AND RESULTS

We conducted whole-exome sequencing in a Chinese family and identified a rare heterozygous loss-of-function variant in non-homologous end joining factor 1 (NHEJ1): c.532C>T (p.R178*), which co-segregated with POI and irregular menstruation. The amount of NHEJ1 protein in the proband was half of the normal level, indicating a link between NHEJ1 haploinsufficiency and POI. Furthermore, another rare heterozygous NHEJ1 variant c.500A>G (p.Y167C) was identified in one of 100 sporadic POI cases. Both variants were predicted to be deleterious by multiple in silico tools. In vitro assays showed that knock-down of NHEJ1 in human KGN ovarian cells impaired DNA repair capacity. We also generated a knock-in mouse model with a heterozygous Nhej1 variant equivalent to NHEJ1 p.R178* in familial patients. Compared with wild-type mice, heterozygous Nhej1-mutated female mice required a longer time to first birth, and displayed reduced numbers of primordial and growing follicles. Moreover, these mice exhibited higher sensitivity to DSB-inducing drugs. All these phenotypes are analogous to the progressive loss of ovarian function observed in POI.

CONCLUSIONS

Our observations in both humans and mice suggest that NHEJ1 haploinsufficiency is associated with non-syndromic POI, providing novel insights into genetic counselling and clinical prevention of POI.

Meiotic Recombination Defects and Premature Ovarian Insufficiency

Premature ovarian insufficiency (POI) is the depletion of ovarian function before 40 years of age due to insufficient oocyte formation or accelerated follicle atresia. Approximately 1–5% of women below 40 years old are affected by POI. The etiology of POI is heterogeneous, including genetic disorders, autoimmune diseases, infection, iatrogenic factors, and environmental toxins. Genetic factors account for 20–25% of patients. However, more than half of the patients were idiopathic. With the widespread application of next-generation sequencing (NGS), the genetic spectrum of POI has been expanded, especially the latest identification in meiosis and DNA repair-related genes. During meiotic prophase I, the key processes include DNA double-strand break (DSB) formation and subsequent homologous recombination (HR), which are essential for chromosome segregation at the first meiotic division and genome diversity of oocytes. Many animal models with defective meiotic recombination present with meiotic arrest, DSB accumulation, and oocyte apoptosis, which are similar to human POI phenotype. In the article, based on different stages of meiotic recombination, including DSB formation, DSB end processing, single-strand invasion, intermediate processing, recombination, and resolution and essential proteins involved in synaptonemal complex (SC), cohesion complex, and fanconi anemia (FA) pathway, we reviewed the individual gene mutations identified in POI patients and the potential candidate genes for POI pathogenesis, which will shed new light on the genetic architecture of POI and facilitate risk prediction, ovarian protection, and early intervention for POI women.

Predictable increase in female reproductive window: A simple model connecting age of reproduction, menopause, and longevity

With the ever-increasing lifespan along with societal changes, women can marry and procreate later than in previous centuries. However, pathogenic genetic variants segregating in the population can lead to female subfertility or infertility well before the average age of normal menopause, leading to counter-selection of such deleterious alleles. In reviewing this field, we speculate that a logical consequence would be the later occurrence of menopause and the extension of women's reproductive lifespan. We illustrate this point with a simple model that applies to other variants that contribute to female infertility, including epigenetic variation. We also consider the effect of medical interventions and lifestyle.

Homozygous mutations in C14orf39/SIX6OS1 cause non-obstructive azoospermia and premature ovarian insufficiency in humans

Human infertility is a multifactorial disease that affects 8%-12% of reproductive-aged couples worldwide. However, the genetic causes of human infertility are still poorly understood. Synaptonemal complex (SC) is a conserved tripartite structure that holds homologous chromosomes together and plays an indispensable role in the meiotic progression. Here, we identified three homozygous mutations in the SC coding gene C14orf39/SIX6OS1 in infertile individuals from different ethnic populations by whole-exome sequencing (WES). These mutations include a frameshift mutation (c.204_205del [p.His68Glnfs∗2]) from a consanguineous Pakistani family with two males suffering from non-obstructive azoospermia (NOA) and one female diagnosed with premature ovarian insufficiency (POI) as well as a nonsense mutation (c.958G>T [p.Glu320∗]) and a splicing mutation (c.1180-3C>G) in two unrelated Chinese men (individual P3907 and individual P6032, respectively) with meiotic arrest. Mutations in C14orf39 resulted in truncated proteins that retained SYCE1 binding but exhibited impaired polycomplex formation between C14ORF39 and SYCE1. Further cytological analyses of meiosis in germ cells revealed that the affected familial males with the C14orf39 frameshift mutation displayed complete asynapsis between homologous chromosomes, while the affected Chinese men carrying the nonsense or splicing mutation showed incomplete synapsis. The phenotypes of NOA and POI in affected individuals were well recapitulated by Six6os1 mutant mice carrying an analogous mutation. Collectively, our findings in humans and mice highlight the conserved role of C14ORF39/SIX6OS1 in SC assembly and indicate that the homozygous mutations in C14orf39/SIX6OS1 described here are responsible for infertility of these affected individuals, thus expanding our understanding of the genetic basis of human infertility.

Meiosis interrupted: the genetics of female infertility via meiotic failure

Idiopathic or 'unexplained' infertility represents as many as 30% of infertility cases worldwide. Conception, implantation, and term delivery of developmentally healthy infants require chromosomally normal (euploid) eggs and sperm. The crux of euploid egg production is error-free meiosis. Pathologic genetic variants dysregulate meiotic processes that occur during prophase I, meiotic resumption, chromosome segregation, and in cell cycle regulation. This dysregulation can result in chromosomally abnormal (aneuploid) eggs. In turn, egg aneuploidy leads to a broad range of clinical infertility phenotypes, including primary ovarian insufficiency and early menopause, egg fertilization failure and embryonic developmental arrest, or recurrent pregnancy loss. Therefore, maternal genetic variants are emerging as infertility biomarkers, which could allow informed reproductive decision-making. Here, we select and deeply examine human genetic variants that likely cause dysregulation of critical meiotic processes in 14 female infertility-associated genes: SYCP3, SYCE1, TRIP13, PSMC3IP, DMC1, MCM8, MCM9, STAG3, PATL2, TUBB8, CEP120, AURKB, AURKC, andWEE2. We discuss the function of each gene in meiosis, explore genotype-phenotype relationships, and delineate the frequencies of infertility-associated variants.

IDDB: a comprehensive resource featuring genes, variants and characteristics associated with infertility

Infertility is a complex multifactorial disease that affects up to 10% of couples across the world. However, many mechanisms of infertility remain unclear due to the lack of studies based on systematic knowledge, leading to ineffective treatment and/or transmission of genetic defects to offspring. Here, we developed an infertility disease database to provide a comprehensive resource featuring various factors involved in infertility. Features in the current IDDB version were manually curated as follows: (i) a total of 307 infertility-associated genes in human and 1348 genes associated with reproductive disorder in 9 model organisms; (ii) a total of 202 chromosomal abnormalities leading to human infertility, including aneuploidies and structural variants; and (iii) a total of 2078 pathogenic variants from infertility patients’ samples across 60 different diseases causing infertility. Additionally, the characteristics of clinically diagnosed infertility patients (i.e. causative variants, laboratory indexes and clinical manifestations) were collected. To the best of our knowledge, the IDDB is the first infertility database serving as a systematic resource for biologists to decipher infertility mechanisms and for clinicians to achieve better diagnosis/treatment of patients from disease phenotype to genetic factors. The IDDB is freely available at http://mdl.shsmu.edu.cn/IDDB/.

A TOP6BL mutation abolishes meiotic DNA double-strand break formation and causes human infertility

Meiosis is pivotal for sexual reproduction and fertility. Meiotic programmed DNA double-strand breaks (DSBs) initiate homologous recombination, ensuring faithful chromosome segregation and generation of gametes. However, few studies have focused on meiotic DSB formation in human reproduction. Here, we report four infertile siblings born to a consanguineous marriage, with three brothers suffering from non-obstructive azoospermia and one sister suffering from unexplained infertility with normal menstrual cycles and normal ovary sizes with follicular activity. An autosomal recessive mutation in TOP6BL was found co-segregating with infertility in this family. Investigation of one male patient revealed failure in programmed meiotic DSB formation and meiotic arrest prior to pachytene stage of prophase I. Mouse models carrying similar mutations to that in patients recapitulated the spermatogenic abnormalities of the patient. Pathogenicity of the mutation in the female patient was supported by observations in mice that meiotic programmed DSBs failed to form in mutant oocytes and oocyte maturation failure due to absence of meiotic recombination. Our study thus illustrates the phenotypical characteristics and the genotype-phenotype correlations of meiotic DSB formation failure in humans.

Preimplantation genetic testing for carriers of BRCA1/2 pathogenic variants

The detection of germline BRCA1/2 pathogenic variant has relevant implications for the patients and their family members. Family planning, prophylactic surgery and the possibility of preimplantation genetic testing for monogenic disorders (PGT-M) to avoid transmittance of pathogenic variants to the offspring are relevant topics in this setting. PGT-M is valuable option for BRCA carriers, but it remains a controversial and underdiscussed topic. Although the advances in PGT technologies have improved pregnancy rate, there are still several important challenges associated with its use. The purpose of this review is to report the current evidence on PGT-M for BRCA1/2 carriers, ethical concerns and controversy associated with its use, reproductive implications of BRCA pathogenic variants, underlying areas in which an educational effort would be beneficial as well as possibilities for future research efforts in the field.

MicroRNA-127-5p impairs function of granulosa cells via HMGB2 gene in premature ovarian insufficiency

Distinct microRNA (miRNA) profiles have been reported in premature ovarian insufficiency (POI), but their functional relevance in POI is not yet clearly stated. In this study, aberrant expressions of miR-127-5p and high mobility group box 2 (HMGB2) were observed by microarrays in granulosa cells (GCs) from biochemical POI (bPOI) women and further confirmed by a quantitative reverse-transcription polymerase chain reaction. Immortalized human granulosa cell line and mouse primary ovarian GCs were used for functional validation. Orthotopic mouse model was established to examine the role of miR-127-5p in vivo. Finally, the expression of miR-127-5p was measured in the plasma of bPOI women. The receiver operating characteristic curve analysis was performed to determine the indicative role of miR-127-5p for ovarian reserve. Results showed the upregulation of miR-127-5p was identified in GCs from bPOI patients. It inhibited GCs proliferation and impaired DNA damage repair capacity through targeting HMGB2, which was significantly downregulated in GCs from the same cohort of cases. miR-127-5p was confirmed to attenuate DNA repair capability via HMGB2 in mouse ovary in vivo. Intriguingly, the upexpression of miR-127-5p was also detected in plasma of bPOI individuals, suggesting that miR-127-5p could be a promising indicator for bPOI. Taken together, our results discovered the deleterious effects of miR-127-5p on GCs function and its predictive value in POI process. The target gene HMGB2 could be considered as a new candidate for POI. This study highlights the importance of DNA repair capacity for ovarian function and sheds light on the epigenetic mechanism in the pathogenicity of POI.

Genetics of Primary Ovarian Insufficiency

The diagnosis of primary ovarian insufficiency (POI) has untold effects on women and a better understanding alongside potential treatments are paramount to improve quality of life of these women. Various causes have been linked to the development of POI with genetics playing a key role. A better understanding of the genetics of POI could lead to earlier diagnosis and broaden fertility options. This chapter discusses previously known and more recently discovered genes that have been implicated in the development of POI. It explores the varying phenotypic expressions of some genes in different populations and areas for further research in the genetics of POI.

A heterozygous hypomorphic mutation of Fanca causes impaired follicle development and subfertility in female mice

Reduced fertility is a common clinical feature of the individuals with Fanconi anemia (FA), a rare autosomal recessive disorder due to deficiency in FA pathway during DNA repair. Our previous study reported that the heterozygous pathogenic variants in FANCA (Fanconi anemia complementation group A) induced premature ovarian insufficiency (POI). However, the genotype-phenotype correlation in POI caused by FANCA variants remains considerably uncertain. Herein, a heterozygous non-frameshift Fanca-mutated mouse strain (Fanca^+/hypo) carrying a 9-bp deletion (c.3581del9, p.QEA1194-1196del) was generated. The mutant mice exhibited slightly decreased Fanca protein level in ovaries, suggesting the non-frameshift deletion mutant is hypomorphic. Female fertility test showed decreased number of litters, litter sizes and prolonged litter interval time in the female Fanca^+/hypo mice compared to wild-type mice. Follicle counting revealed a consistent decreasing pattern of follicle numbers in Fanca^+/hypo females compared to that in wild-type mice with aging. Furthermore, embryonic fibroblasts of Fanca^+/hypo mice were hyper-responsive to Mitomycin C in vitro, demonstrating a partial loss of function of this hypomorphic Fanca mutant in DNA repair. Collectively, our experimental observations suggest that the hypomorphic Fanca allele is sufficient to reduce female fertility in mice, providing new insights into the genetic counseling of FANCA variants in subfertile women.

Helicase-inactivating BRIP1 mutation yields Fanconi anemia with microcephaly and other congenital abnormalities

Fanconi anemia is a genetically and phenotypically heterogeneous disorder characterized by congenital anomalies, bone marrow failure, cancer, and sensitivity of chromosomes to DNA cross-linking agents. One of the 22 genes responsible for Fanconi anemia is BRIP1, in which biallelic truncating mutations lead to Fanconi anemia group J and monoallelic truncating mutations predispose to certain cancers. However, of the more than 1000 reported missense mutations in BRIP1, very few have been functionally characterized. We evaluated the functional consequence of BRIP1 p.R848H (c.2543G > A), which was homozygous in two cousins with low birth weight, microcephaly, upper limb abnormalities, and imperforate anus and for whom chromosome breakage analysis of patient cells revealed increased mitomycin C sensitivity. BRIP1 p.R848H alters a highly conserved residue in the catalytic DNA helicase domain. We show that BRIP1 p.R848H leads to a defect in helicase activity. Heterozygosity at this missense has been reported in multiple cancer patients but, in the absence of functional studies, classified as of unknown significance. Our results support that this mutation is pathogenic for Fanconi anemia in homozygotes and for increased cancer susceptibility in heterozygous carriers.

Genetics of human female infertility†

About 10% of women of reproductive age are unable to conceive or carry a pregnancy to term. Female factors alone account for at least 35% of all infertility cases and comprise a wide range of causes affecting ovarian development, maturation of oocytes, and fertilization competence, as well as the potential of a fertilized egg for preimplantation development, implantation, and fetal growth. Genetic abnormalities leading to infertility in females comprise large chromosome abnormalities, submicroscopic chromosome deletion and duplications, and DNA sequence variations in the genes that control numerous biological processes implicated in oogenesis, maintenance of ovarian reserve, hormonal signaling, and anatomical and functional development of female reproductive organs. Despite the great number of genes implicated in reproductive physiology by the study of animal models, only a subset of these genes is associated with human infertility. In this review, we mainly focus on genetic alterations identified in humans and summarize recent knowledge on the molecular pathways of oocyte development and maturation, the crucial role of maternal-effect factors during embryogenesis, and genetic conditions associated with ovarian dysgenesis, primary ovarian insufficiency, early embryonic lethality, and infertility.

MEIOK21: a new component of meiotic recombination bridges required for spermatogenesis

Repair of DNA double-strand breaks (DSBs) with homologous chromosomes is a hallmark of meiosis that is mediated by recombination ‘bridges’ between homolog axes. This process requires cooperation of DMC1 and RAD51 to promote homology search and strand exchange. The mechanism(s) regulating DMC1/RAD51-ssDNA nucleoprotein filament and the components of ‘bridges’ remain to be investigated. Here we show that MEIOK21 is a newly identified component of meiotic recombination bridges and is required for efficient formation of DMC1/RAD51 foci. MEIOK21 dynamically localizes on chromosomes from on-axis foci to ‘hanging foci’, then to ‘bridges’, and finally to ‘fused foci’ between homolog axes. Its chromosome localization depends on DSBs. Knockout of Meiok21 decreases the numbers of HSF2BP and DMC1/RAD51 foci, disrupting DSB repair, synapsis and crossover recombination and finally causing male infertility. Therefore, MEIOK21 is a novel recombination factor and probably mediates DMC1/RAD51 recruitment to ssDNA or their stability on chromosomes through physical interaction with HSF2BP.

Novel variants in women with premature ovarian function decline identified via whole-exome sequencing

PURPOSE

To investigate the potential etiologies of premature ovarian insufficiency (POI) and diminished ovarian reserve (DOR).

METHODS

Fourteen women with sporadic POI and 6 women with DOR were enrolled. We used whole-exome sequencing (WES) and bioinformatics analysis to identify variants in a subset of 599 selected POI candidate genes. The identified genes were subjected to gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment and protein-protein interaction (PPI) network analyses to uncover key genes and pathways.

RESULTS

Among the 20 patients, 79 heterozygous variants were detected in 49 genes, which were classified as "likely pathogenic" or "variants of uncertain significance" according to the guidelines of the American College of Medical Genetics and Genomics. Most patients (17/20) carried two or more variants. Monoacylglycerol O-acyltransferase 1 mutations were found in six patients, and cytochrome P450 family 26 subfamily B member 1 and Bardet-Biedl syndrome 9 mutations were each found in four patients. Some variants were shared between DOR and POI. Enrichment analyses showed that the identified genes participate in key ovarian processes, such as follicular development, gonadal development, meiosis, Fanconi anemia, homologous recombination, and transforming growth factor β signaling. A PPI network revealed interactions between these proteins.

CONCLUSION

Premature ovarian function decline may be polygenic, and overlap exists between the genetic backgrounds of DOR and POI. WES and in silico analyses may be a useful clinical tool for etiological diagnosis and risk prediction for high-risk women in the future.

Homozygous hypomorphic BRCA2 variant in primary ovarian insufficiency without cancer or Fanconi anaemia trait

BACKGROUND

Primary ovarian insufficiency (POI) affects 1% of women under 40 years and is a public health problem. The genetic causes of POI are highly heterogeneous with isolated or syndromic forms. Recently, variants in genes involved in DNA repair have been shown to cause POI. Notably, syndromic POI with Fanconi anaemia (FA) traits related to biallelic BRCA2 truncated variants has been reported. Here, we report a novel phenotype of isolated POI with a BRCA2 variant in a consanguineous Turkish family.

METHODS

Exome sequencing (ES) was performed in the patient. We also performed functional studies, including a homologous recombination (HR) test, cell proliferation, radiation-induced RAD51 foci formation assays and chromosome breakage studies in primary and lymphoblastoid immortalised cells. The expression of BRCA2 in human foetal ovaries was studied.

RESULTS

ES identified a homozygous missense c.8524C>T/p.R2842C-BRCA2 variant. BRCA2 defects induce cancer predisposition and FA. Remarkably, neither the patient nor her family exhibited somatic pathologies. The patient's cells showed intermediate levels of chromosomal breaks, cell proliferation and radiation-induced RAD51 foci formation compared with controls and FA cells. R2842C-BRCA2 only partially complemented HR efficiency compared with wild type-BRCA2. BRCA2 is expressed in human foetal ovaries in pachytene stage oocytes, when meiotic HR occurs.

CONCLUSION

We describe the functional assessment of a homozygous hypomorphic BRCA2 variant in a patient with POI without cancer or FA trait. Our findings extend the phenotype of BRCA2 biallelic alterations to fully isolated POI. This study has a major impact on the management and genetic counselling of patients with POI.

A Novel Phenotype Combining Primary Ovarian Insufficiency Growth Retardation and Pilomatricomas With MCM8 Mutation

CONTEXT

Primary Ovarian insufficiency (POI) affects 1% of women aged <40 years and leads most often to definitive infertility with adverse health outcomes. Very recently, genes involved in deoxyribonucleic acid (DNA) repair have been shown to cause POI.

OBJECTIVE

To identify the cause of a familial POI in a consanguineous Turkish family.

DESIGN

Exome sequencing was performed in the proposita and her mother. Chromosomal breaks were studied in lymphoblastoid cell lines treated with mitomycin (MMC).

SETTING AND PATIENTS

The proposita presented intrauterine and postnatal growth retardation, multiple pilomatricomas in childhood, and primary amenorrhea. She was treated with growth hormone (GH) from age 14 to 18 years.

RESULTS

We identified a novel nonsense variant in exon 9 of the minichromosome maintenance complex component 8 gene (MCM8) NM_001281522.1: c0.925C > T/p.R309* yielding either a truncated protein or nonsense-mediated messenger ribonucleic acid decay.The variant was homozygous in the daughter and heterozygous in the mother. MMC induced DNA breaks and aberrant metaphases in the patient's lymphoblastoid cells. The mother's cells had intermediate but significantly higher chromosomal breaks compared with a control.

CONCLUSION

We describe a novel phenotype of syndromic POI related to a novel truncating MCM8 variant. We show for the first time that spontaneous tumors (pilomatricomas) are associated with an MCM8 genetic defect, making the screening of this gene necessary before starting GH therapy in patients with POI with short stature, especially in a familial or consanguineous context. Appropriate familial monitoring in the long term is necessary, and fertility preservation should be considered in heterozygous siblings to avoid rapid follicular atresia.