Microdeletions in FMR2 may be a significant cause of premature ovarian failure

Screening of premature ovarian insufficiency associated genes in Hungarian patients with next generation sequencing

BACKGROUND

Premature ovarian insuffiency (POI) is one of the main cause behind infertility. The genetic analysis of POI should be part of the clinical diagnostics, as several genes have been implicated in the genetic background of it. The aim of our study was to analyse the genetic background of POI in a Hungarian cohort.

METHODS

The age of onset was between 15 and 39 years. All patients had the 46,XX karyotype and they were prescreened for the most frequent POI associated FMR1 premutation. To identify genetic alterations next-generation sequencing (NGS) of 31 genes which were previously associated to POI were carried out in 48 unrelated patients from Hungary.

RESULTS

Monogenic defect was identified in 16.7% (8 of 48) and a potential genetic risk factor was found in 29.2% (14 of 48) and susceptible oligogenic effect was described in 12.5% (6 of 48) of women with POI using the customized targeted panel sequencing. The genetic analysis identified 8 heterozygous damaging and 4 potentially damaging variants in POI-associated genes. Further 10 potential genetic risk factors were detected in seven genes, from which EIF2B and GALT were the most frequent. These variants were related to 15 genes: AIRE, ATM, DACH2, DAZL, EIF2B2, EIF2B4, FMR1, GALT, GDF9, HS6ST2, LHCGR, NOBOX, POLG, USP9X and XPNPEP2. In six cases, two or three coexisting damaging mutations and risk variants were identified.

CONCLUSIONS

POI is characterized by heterogenous phenotypic features with complex genetic background that contains increasing number of genes. Deleterious variants, which were detected in our cohort, related to gonadal development (oogenesis and folliculogenesis), meiosis and DNA repair, hormonal signaling, immune function, and metabolism which were previously associated with the POI phenotype. This is the first genetic epidemiology study targeting POI associated genes in Hungary. The frequency of variants in different POI associated genes were similar to the literature, except EIF2B and GALT. Both of these genes potential risk factor were detected which could influence the phenotype, although it is unlikely that they can be responsible for the development of the disease by themselves. Advances of sequencing technologies make it possible to aid diagnostics of POI Since individual patients show high phenotypic variance because of the complex network controlling human folliculogenesis. Comprehensive NGS screening by widening the scope to genes which were previously linked to infertility may facilitate more accurate, quicker and cheaper genetic diagnoses for POI. The investigation of patient's genotype could support clinical decision-making process and pave the way for future clinical trials and therapies.

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.

Simultaneous Screening of the FRAXA and FRAXE Loci for Rapid Detection of FMR1 CGG and/or AFF2 CCG Repeat Expansions by Triplet-Primed PCR

Moderate to hyper-expansion of trinucleotide repeats at the FRAXA and FRAXE fragile sites, with or without concurrent hypermethylation, has been associated with intellectual disability and other conditions. Unlike molecular diagnosis of FMR1 CGG repeat expansions in FRAXA, current detection of AFF2 CCG repeat expansions in FRAXE relies on low-throughput and otherwise inefficient techniques combining Southern blot analysis and PCR. A novel triplet-primed PCR assay was developed for simultaneous screening for trinucleotide repeat expansions at the FRAXA and FRAXE fragile sites, and was validated using archived clinical samples of known FMR1 and AFF2 genotypes. Population samples and FRAXE-affected samples were sequenced for the evaluation of variations in the AFF2 CCG repeat structure. The duplex assay accurately identified expansions at the FMR1 and AFF2 trinucleotide repeat loci. On Sanger sequencing of the AFF2 CCG repeat, the single-nucleotide polymorphism variant rs868914124(C) that effectively adds two CCG repeats at the 5'-end, was enriched in the Malay population and with short repeats (<11 CCGs), and was present in all six expanded AFF2 alleles of this study. All expanded AFF2 alleles contained multiple non-CCG interruptions toward the 5'-end of the repeat. A sensitive, robust, and rapid assay has been developed for the simultaneous detection of expansion mutations at the FMR1 and AFF2 trinucleotide repeat loci, simplifying screening for FRAXA- and FRAXE-associated disorders.

Assessment of FMR1 triplet repeats in patients affected with mental retardation, fragile X syndrome and primary ovarian insufficiency

The CGG repeats in the FMR1 gene expand in patients with fragile X syndrome, fragile X-associated tremour/ataxia syndrome and fragile X-associated primary ovarian failure. In this study, the CGG repeats in the FMR1 gene were studied in 449 males and 207 females using traditional polymerase chain reaction and triplet repeat primed PCR methods, also 18 CVS samples (six males and 12 females) were tested for prenatal diagnosis. Further, methylation sensitive multiplexed ligation dependent probe amplification was performed on some samples to confirm the results. Regarding the male patients, 1.1% and 9.7% had premutation (PM) and full mutation (FM) alleles, respectively. Also three (0.66%) male patients were mosaic for PM and FM alleles. Among females, 1.9% were GZ carriers and 5.8% were PM carriers. Prenatal diagnosis resulted in detection of two PM and one FM males as well as one FM carrier female. Our results were in concordance with the previously published results.

Ablation of beta subunit of protein kinase CK2 in mouse oocytes causes follicle atresia and premature ovarian failure

Premature ovarian failure (POF), a major cause of female infertility, is a complex disorder, but the molecular mechanisms underlying the disorder are only poorly understood. Here we report that protein kinase CK2 contributes to maintaining follicular survival through PI3K/AKT pathway and DNA damage response pathway. Targeted deletion of CK2β in mouse oocytes from the primordial follicle stage resulted in female infertility, which was attributed to POF incurring by massive follicle atresia. Downregulated PI3K/AKT signaling was found after CK2β deletion, indicated by reduced level of phosphorylated AKT (S473, T308, and S129) and altered AKT targets related to cell survival. Further studies discovered that CK2β-deficient oocytes showed enhanced γH2AX signals, indicative of accumulative unrepaired DSBs, which activated CHK2-dependant p53 and p63 signaling. The suppressed PI3K/AKT signaling and failed DNA damage response signaling probably contribute to large-scale oocyte loss and eventually POF. Our findings provide important new clues for elucidating the mechanisms underlying follicle atresia and POF.

Distribution of FMR1 and FMR2 Repeats in Argentinean Patients with Primary Ovarian Insufficiency

The premutation state of FMR1 (Fragile X Mental Retardation 1) has been associated with primary ovarian insufficiency (POI), and is the most common known genetic cause for 46,XX patients. Nevertheless, very few studies have analyzed its frequency in Latin American populations. Additionally, a relationship between alleles carrying a cryptic microdeletion in the 5’UTR of FMR2 and the onset of POI has only been studied in one population. Our aim was to analyze the incidence of FMR1 premutations and putative microdeletions in exon 1 of FMR2 in a cohort of Argentinean women with POI. We studied 133 patients and 84 controls. Fluorescent PCR was performed, and the FMR2 exon 1 was further sequenced in samples presenting less than 11 repeats. We found the frequency of FMR1 premutations to be 6.7% and 2.9% for familial and sporadic patients, respectively. Among controls, 1/84 women presented a premutation. In addition, although we did not find microdeletions in FMR2, we observed a change (T >C) adjacent to the repeats in two sisters with POI. Given the repetitive nature of the sequence involved, we could not ascertain whether this represents a single nucleotide polymorphism (SNP) or a deletion. Therefore, a relationship between FMR2 and POI could not be established for our population.

Premature Ovarian Insufficiency: New Perspectives on Genetic Cause and Phenotypic Spectrum

Premature ovarian insufficiency (POI) is one form of female infertility, defined by loss of ovarian activity before the age of 40 and characterized by amenorrhea (primary or secondary) with raised gonadotropins and low estradiol. POI affects up to one in 100 females, including one in 1000 before the age of 30. Substantial evidence suggests a genetic basis for POI; however, the majority of cases remain unexplained, indicating that genes likely to be associated with this condition are yet to be discovered. This review discusses the current knowledge of the genetic basis of POI. We highlight genes typically known to cause syndromic POI that can be responsible for isolated POI. The role of mouse models in understanding POI pathogenesis is discussed, and a thorough list of candidate POI genes is provided. Identifying a genetic basis for POI has multiple advantages, such as enabling the identification of presymptomatic family members who can be offered counseling and cryopreservation of eggs before depletion, enabling personalized treatment based on the cause of an individual's condition, and providing better understanding of disease mechanisms that ultimately aid the development of improved treatments.

Analysis of FMR1 gene premutation and X chromosome cytogenetic abnormalities in 100 Tunisian patients presenting premature ovarian failure

OBJECTIVE

To evaluate the prevalence of FMR1 premutations and X chromosome cytogenetic abnormalities in a large cohort of Tunisian women with premature ovarian failure (POF).

PATIENTS AND METHODS

The cohort consisted of 127 Tunisian women with POF referred by endocrinologists and gynecologists for genetic investigation in the context of idiopathic POF and altered hormonal profiles. Clinical information concerning the reproductive function in the family, previous hormonal measurements and/or possible fertility treatment were collected. Karyotype, FISH analyses, FMR1 and FMR2 testing were performed for all patients.

RESULTS

Fifteen patients (11.81%) presented structural or numerical X chromosomal abnormalities. Moreover, we detected in 12 patients (10.71%) a high level of X mosaicism. Analysis of FMR1 gene in the 100 patients without X chromosomal abnormalities showed that five percent of the patients carried a FMR1 premutation allele. On the other hand, the FMR2 screening did not reveal any deletion.

CONCLUSION

Our study confirms the major role of X chromosome abnormalities in POF and highlights the importance of karyotype analyses and FMR1 screening. These investigations provide valuable information for diagnosis and genetic counseling for these women who still have a 5% chance of spontaneous conception.

Aetiological coding sequence variants in non-syndromic premature ovarian failure: From genetic linkage analysis to next generation sequencing

Premature ovarian failure (POF) is a frequent pathology affecting 1-1.5% of women under 40 years old. Despite advances in diagnosing and treating human infertility, POF is still classified as being idiopathic in 50-80% of cases, strongly suggesting a genetic origin for the disease. Different types of autosomal and X-linked genetic anomalies can originate the phenotype in syndromic and non-syndromic POF cases. Particular interest has been focused on research into non-syndromic POF causative coding variants during the past two decades. This has been based on the assumption that amino acid substitutions might modify the intrinsic physicochemical properties of functional proteins, thereby inducing pathological phenotypes. In this case, a restricted number of mutations might originate the disease. However, like other complex pathologies, POF might result from synergistic/compensatory effects caused by several low-to-mildly drastic mutations which have frequently been classified as non-functional SNPs. Indeed, reproductive phenotypes can be considered as quantitative traits resulting from the subtle interaction of many genes. Although numerous sequencing projects have involved candidate genes, only a few coding mutations explaining a low percentage of cases have been described. Such apparent failure to identify aetiological coding sequence variations might have been due to the inherent molecular complexity of mammalian reproduction and to the difficulty of simultaneously analysing large genomic regions by Sanger sequencing. The purpose of this review is to present the molecular and cellular effects caused by non-synonymous mutations which have been formally associated, by functional tests, with the aetiology of hypergonadotropic non-syndromic POF. Considerations have also been included regarding the polygenic nature of reproduction and POF, as well as future approaches for identifying novel aetiological genes based on next generation sequencing (NGS).

Dynamics of the ovarian reserve and impact of genetic and epidemiological factors on age of menopause

The narrow standard age range of menopause, ∼50 yr, belies the complex balance of forces that govern the underlying formation and progressive loss of ovarian follicles (the "ovarian reserve" whose size determines the age of menopause). We show here the first quantitative graph of follicle numbers, distinguished from oocyte counts, across the reproductive lifespan, and review the current state of information about genetic and epidemiological risk factors in relation to possible preservation of reproductive capacity. In addition to structural X-chromosome changes, several genes involved in the process of follicle formation and/or maintenance are implicated in Mendelian inherited primary ovarian insufficiency (POI), with menopause before age 40. Furthermore, variants in a largely distinct cohort of reported genes-notably involved in pathways relevant to atresia, including DNA repair and cell death-have shown smaller but additive effects on the variation in timing of menopause in the normal range, early menopause (age <45), and POI. Epidemiological factors show effect sizes comparable to those of genetic factors, with smoking accounting for about 5% of the risk of early menopause, equivalent to the summed effect of the top 17 genetic variants. The identified genetic and epidemiological factors underline the importance of early detection of reproductive problems to enhance possible interventions.

A clinical research integration special program (CRISP) for young women with primary ovarian insufficiency

Large-scale medical sequencing provides a focal point around which to reorganize health care and health care research. Mobile health (mHealth) is also currently undergoing explosive growth and could be another innovation that will change the face of future health care. We are employing primary ovarian insufficiency (POI) as a model rare condition to explore the intersection of these potentials. As both sequencing capabilities and our ability to intepret this information improve, sequencing for medical purposes will play an increasing role in health care beyond basic research: it will help guide the delivery of care to patients. POI is a serious chronic disorder and syndrome characterized by hypergonadotrophic hypogonadism before the age of 40 years and most commonly presents with amenorrhea. It may have adverse health effects that become fully evident years after the initial diagnosis. The condition is most commonly viewed as one of infertility, however, it may also be associated with adverse long-term outcomes related to inadequate bone mineral density, increased risk of cardiovascular disease, adrenal insufficiency, hypothyroidism and, if pregnancy ensues, having a child with Fragile X Syndrome. There may also be adverse outcomes related to increased rates of anxiety and depression. POI is also a rare disease, and accordingly, presents special challenges. Too often advances in research are not effectively integrated into community care at the point of service for those with rare diseases. There is a need to connect community health providers in real time with investigators who have the requisite knowledge and expertise to help manage the rare disease and to conduct ongoing research. Here we review the pathophysiology and management of POI and propose the development of an international Clinical Research Integration Special Program (CRISP) for the condition.

Genetics of primary ovarian insufficiency: a review

Primary ovarian insufficiency is one of the main causes of female infertility owing to an abnormal ovarian reserve. Its relevance has increased in more recent years due to the fact that age of motherhood is being delayed in developed countries, with the risk of having either primary ovarian insufficiency or less chances of pregnancy when women consider the option of having their first baby. Several exogenous factors can lead to this event, such us viral infections, metabolomic dysfunction, autoimmune diseases, and environmental or iatrogenic factors, although in most cases the mechanism that leads to the disorder is unknown. Genetic factors represent the most commonly identified cause and the impact of sex chromosome abnormalities (e.g., Turner syndrome or X structural abnormalities), autosomal and X-linked mutations on the genesis of primary ovarian insufficiency has also been well described. Yet in most cases, the genetic origin remains unknown and there are multiple candidate genes. This review aims to collect all the genetic abnormalities and genes associated with syndromic and non syndromic primary ovarian insufficiency that have been published in the literature to date using the candidate-gene approach and a genome-wide analysis.

Analysis of progesterone receptor membrane component 1 mutation in Han Chinese women with premature ovarian failure

The gene PGRMC1 is highly expressed in the granulose and luteal cells of rodent and primate ovaries. Its role in anti-apoptosis and regulating cell-cycle progression suggests a role in regulating follicle growth. The hypothesis is supported by the study in mice and studies in Sweden. In this study, the coding exons of PGRMC1 were sequenced among 196 Chinese women with premature ovarian failure (POF) and 200 controls, and one novel missense mutation was identified (C.556C>T, p. Pro186Ser) in the POF group and one novel SNP (C.533C>T, p. Trh177Ile) was identified in both groups. The mutation is not considered causative because protein prediction did not indicate a deleterious effect. It is concluded that coding mutations of PGRMC1 do not seem to be a common cause of the disease in Han Chinese women. Future studies in larger cohorts from other ethnic groups are necessary to establish the role of PGRMC1 in POF.

Premature ovarian failure: a critical condition in the reproductive potential with various genetic causes

Premature ovarian failure (POF) is identified as a heterogeneous disorder leading to amenorrhea and ovarian failure before the age of 40 years. The first known symptom of the disease is having irregular menstrual periods. The phenotype appearance of POF depends significantly on the variations in hormones. Low levels of gonadal hormones (estrogens and inhibins) and increased level of gonadotropins [luteinizing hormone (LH) and Follicle stimulating hormone (FSH)] (hypergonadotropic amenorrhea) are well documented as causes of POF. There is an association between the failure of germ cell development and complete ovarian failure, and consistently decreased number of germ cells is more likely associated with partial ovarian failure resulting in secondary amenorrhea. A literature review on recent findings about POF and its association with genomic alterations in terms of genes and chromosomes. POF is a complex heterogeneous disorder. Some of POF cases are carriers of a single gene mutation inherited in an autosomal or X-linked manner while a number of patients suffer from a chromosome abnormality like Turner syndrome in mosaic form and manifest secondary amenorrhea associated with ovarian dysgenesis. Among many of the known involved genes in POF development, several are prove to be positively associated to the disease development in different populations. While there is a promising association between X chromosome anomalies and specific gene mutations with POF, genome-wide analysis could prove a powerful tool for identifying the most important candidate genes that influence POF manifestation.

Drosophila lilliputian is required for proneural gene expression in retinal development

BACKGROUND

Proper neurogenesis in the developing Drosophila retina requires the regulated expression of the basic helix-loop-helix (bHLH) proneural transcription factors Atonal (Ato) and Daughterless (Da). Factors that control the timing and spatial expression of these bHLH proneural genes in the retina are required for the proper formation and function of the adult eye and nervous system.

RESULTS

Here we report that lilliputian (lilli), the Drosophila homolog of the FMR2/AF4 family of proteins, regulates the transcription of ato and da in the developing fly retina. We find that lilli controls ato expression at multiple enhancer elements. We also find that lilli contributes to ato auto-regulation in the morphogenetic furrow by first regulating the expression of da prior to ato. We show that FMR2 regulates the ato and da homologs MATH5 and TCF12 in human cells, suggesting a conservation of this regulation from flies to humans.

CONCLUSIONS

We conclude that lilliputian is part of the genetic program that regulates the expression of proneural genes in the developing retina.

Microdeletion of Xq28 involving the AFF2 (FMR2) gene in two unrelated males with developmental delay

Fragile X E (FRAXE) is an X-linked form of intellectual disability characterized by mild to moderate cognitive impairment, speech delay, hyperactivity, and autistic behavior. The folate-sensitive fragile site FRAXE is located in Xq28 approximately 600 kb distal to the fragile X syndrome fragile site (FRAXA) and harbors an unstable GCC (CCG) triplet repeat adjacent to a CpG island in the 5' untranslated region of the AFF2 (FMR2) gene. The disorder results from amplification and methylation of the GCC repeat and resultant silencing of AFF2. Although chromosome abnormalities that disrupt AFF2 have been reported in two individuals with mild-moderate intellectual disability, microdeletions of Xq28 that delete only AFF2 have not been described as a potential cause of FRAXE-intellectual disability. We performed clinical and molecular characterization of two males with 240 and 499 kb deletions, respectively, at Xq28, both of which encompassed only one gene, AFF2. The 240 kb deletion in Patient 1 was intragenic and lead to the loss of 5' exons 2-4 of AFF2; the 499 kb deletion in Patient 2 removed the 5' exons 1-2 of AFF2 including approximately 350 kb upstream of the gene. Both individuals had developmental and speech delay, and one had mild dysmorphism. We predict disruption of AFF2 in these two patients is likely the cause of their overlapping phenotypes.

Contemporary genetic technologies and female reproduction

BACKGROUND

The Fifth Evian Annual Reproduction (EVAR) Workshop Meeting discussed knowledge regarding contemporary genetics in female reproduction.

METHODS

Specialist reproductive medicine clinicians and geneticists delivered presentations based on published literature and current research. The content of this report is based on the expert presentations and subsequent group discussions that took place during this Workshop.

RESULTS

Numerous ovarian genes with a role in infertility have been identified. Future challenges for genetic screening of patients, such as those with polycystic ovary syndrome, primary ovarian insufficiency or endometriosis, include the identification of high-throughput strategies and how to apply these findings to infertile patients. The identification of high-quality embryos in IVF using objective technologies remains a high priority in order to facilitate single-embryo transfer. Gene expression profiling of cumulus cells surrounding the oocyte, and proteomic and metabolomic approaches in embryo culture media may significantly improve non-invasive embryo quality assessment.

CONCLUSIONS

The way forward in advancing the knowledge of genes involved in reproduction was considered to be through genome-wide association studies involving large numbers of patients. Establishing international collaboration is required to enable the application of such technologies in sufficient numbers of patients.

Sequence analysis of the CDKN1B gene in patients with premature ovarian failure reveals a novel mutation potentially related to the phenotype

Earlier reports demonstrated a key role of Cdkn1b during mouse ovarian development. In this study, the sequencing analysis of the complete coding region of this gene in a panel of premature ovarian failure patients and control subjects reveals a novel mutation potentially related to the phenotype.

Genetic aspects of premature ovarian failure: a literature review

BACKGROUND

The diagnosis of premature ovarian failure (POF) is based on the finding of amenorrhea before the age of 40 years associated with follicle-stimulating hormone levels in the menopausal range. It is a heterogeneous disorder affecting approximately 1% of women <40 years, 1:10,000 women by age 20 years and 1:1,000 women by age 30 years. POF is generally characterized by low levels of gonadal hormones (estrogens and inhibins) and high levels of gonadotropins (LH and FSH) (hypergonadotropic amenorrhea).

METHODS

Review of significant articles regarding genetic causes that are associated with POF.

RESULTS

Heterogeneity of POF is reflected by a variety of possible causes, including autoimmunity, toxics, drugs, as well as genetic defects. Changes at a single autosomal locus and many X-linked loci have been implicated in women with POF. X chromosome abnormalities (e.g., Turner syndrome) represent the major cause of primary amenorrhea associated with ovarian dysgenesis. Many genes have been involved in POF development, among them BMP15, FMR1, FMR2, LHR, FSHR, INHA, FOXL2, FOXO3, ERα, SF1, ERβ and CYP19A1 genes.

CONCLUSION

Despite the description of several candidate genes, the cause of POF remains undetermined in the vast majority of cases.

Primary ovarian insufficiency

Primary ovarian insufficiency is a subclass of ovarian dysfunction in which the cause is within the ovary. In most cases, an unknown mechanism leads to premature exhaustion of the resting pool of primordial follicles. Primary ovarian insufficiency might also result from genetic defects, chemotherapy, radiotherapy, or surgery. The main symptom is absence of regular menstrual cycles, and the diagnosis is confirmed by detection of raised follicle-stimulating hormone and declined oestradiol concentrations in the serum, suggesting a primary ovarian defect. The disorder usually leads to sterility, and has a large effect on reproductive health when it arises at a young age. Fertility-preservation options can be offered to some patients with cancer and those at risk of early menopause, such as those with familial cases of primary ovarian insufficiency. Long-term deprivation of oestrogen has serious implications for female health in general; and for bone density, cardiovascular and neurological systems, wellbeing, and sexual health in particular.

Genes governing premature ovarian failure

Premature ovarian failure (POF) is unexplained amenorrhoea (>6 months), increased FSH (>20 IU/l) and LH occurring before 40 years. Several genes are reported as having significance in POF, including genes governing regulation of the hypothalamic-pituitary-ovarian axis, but their role in ovarian physiology is not known. Deletions or translocations in Xq arm have been found to be associated with POF, assuming presence of ovarian-related genes but ovary-related function of these genes is unclear. Several researchers have suggested specific loci on Xq critical region, POF1 and POF2 and genes DIA, FMR1 and FMR2. The understanding of ovarian physiology, its regulation and genes involved is important to explain the causes of POF. Some genes coordinate development of germ cell to primordial stage, e.g. GDF9, BMP15 and NGF, while others regulate development of further stages, such as FSH and LH. Mutation in these genes may lead to female infertility and are likely to be candidate genes for POF. Recently, association between blepharophimosis-ptosis-epicanthus inversus syndrome type 1 and POF has emerged as a possibility. Galactosaemia is also shown to be important in POF due to toxic effects of accumulated galactose or downstream products. Thus, understanding the role of several genes can be used for the appropriate genetic diagnosis, research and in the clinical practice of POF.

Aging of the human ovary and testis

Aging is associated with structural and functional alterations in all organs of the human body. The aging of gonads represents in this respect a special case, because these organs are not functional for the whole lifespan of an individual and their normal function is not indispensable for functions of the rest of the body. Ovarian function lasts for the reproductive life of a woman, i.e., from menarche until menopause. The testicular endocrine function, in contrast, begins already in utero, is interrupted between neonatal life and puberty, and continues thereafter along with spermatogenesis, with only slight decline, until old age. The aging processes of the ovary and testis are therefore very different. We describe in this review the structural and functional alterations in the human ovary and testis upon aging. Special emphasis will be given to clinically significant alterations, which in women concern the causes and consequences of the individual variability of fertility during the latter part of the reproductive age. The clinically important aspect of testicular aging entails the decline of androgen production in aging men.

Alterations in the expression, structure and function of progesterone receptor membrane component-1 (PGRMC1) in premature ovarian failure

Premature ovarian failure (POF) is characterized by hypergonadotropic hypogonadism and amenorrhea before the age of 40. The condition has a heterogeneous background but genetic factors are demonstrated by the occurrence of familial cases. We identified a mother and daughter with POF both of whom carry an X;autosome translocation [t(X;11)(q24;q13)]. RNA expression studies of genes flanking the X-chromosome breakpoint revealed that both patients have reduced expression levels of the gene Progesterone Receptor Membrane Component-1 (PGRMC1). Mutation screening of 67 females with idiopathic POF identified a third patient with a missense mutation (H165R) located in the cytochrome b5 domain of PGRMC1. PGRMC1 mediates the anti-apoptotic action of progesterone in ovarian cells and it acts as a positive regulator of several cytochrome P450 (CYP)-catalyzed reactions. The CYPs are critical for intracellular sterol metabolism, including biosynthesis of steroid hormones. We show that the H165R mutation associated with POF abolishes the binding of cytochrome P450 7A1 (CYP7A1) to PGRMC1. In addition, the missense mutation attenuates PGRMC1's ability to mediate the anti-apoptotic action of progesterone in ovarian cells. These findings suggest that mutant or reduced levels of PGMRC1 may cause POF through impaired activation of the microsomal cytochrome P450 and increased apoptosis of ovarian cells.

[Genetic analysis of premature ovarian failure: role of forkhead and TGF-beta genes]

Premature ovarian failure is a common pathology affecting 1% of women. Although multiple etiologies have been described the majority of cases are idiopathic. Forkhead transcription factors as FOXL2 and FOXO3A are of particular interest in the research of genetic factors related with the pathology as they are present in diverse developmental pathways and ovarian physiology. Similarly, some TGF-beta factors (i.e. BMP 15 and GDF-9) have been demonstrated to play a key role in the regulation, at ovarian level, of female reproduction. In recent years numerous studies have been performed in order to elucidate the implication of these factors in the ovarian physiopathology. The aim of this manuscript is to describe some of these advances in the context of premature ovarian failure.

Primary ovarian insufficiency: a more accurate term for premature ovarian failure

Premature ovarian failure (POF) is a disorder with a complicated clinical presentation and course that is poorly defined by its name. A more scientifically accurate term for the disorder is primary ovarian insufficiency (POI), a term that can be appropriately modified to describe the state of ovarian function. In recent years, the known aetiologies of POI have expanded, although the cause of POI in a majority of clinical cases remains undefined. The most common aetiologies should be ruled out clinically including chromosomal abnormalities, fragile X premutations and autoimmune causes. Management should be directed at symptom resolution and bone protection, but most importantly should include psychosocial support for women facing this devastating diagnosis.

Recent advances in the study of genes involved in non-syndromic premature ovarian failure

Premature ovarian failure (POF) is a common pathology leading to infertility affecting about 1% of women under 40 years old. In POF patients, the ovarian dysfunction is characterized by the lack of the ovarian response to close a negative feedback loop on the synthesis of pituitary gonadotropins. Although the majority of cases are considered as idiopathic, diverse aetiologies have been associated, including genetic factors. Up to now, the potential genetic causes of non-syndromic POF have been established mainly by genetic linkage analysis of familial cases or by the screening of mutations in candidate genes based on animal models. Here, we review recent advances in the study of candidate genes.

Argonaute-2-dependent rescue of a Drosophila model of FXTAS by FRAXE premutation repeat

Fragile X Syndrome is the most common form of hereditary mental retardation. It is caused by a large expansion of the CGG trinucleotide repeat (>200 repeats) in the 5'-untranslated region (UTR) of the FMR1 gene that leads to silencing of its transcript. Individuals with CGG repeat expansions approximately between 60 and 200 are referred to as premutation carriers. Fragile X-associated tremor and ataxia syndrome (FXTAS), an RNA-mediated neurodegenerative disease has been described in up to 50% of males carrying premutation alleles. FRAXE, the most common form of non-syndromic X-linked mental retardation, is caused by expansion of a CCG trinucleotide repeat (>200) in the 5'-UTR of the FMR2 gene. While the FRAXE premutation length repeat is observed in the general population, there has not yet been a report of a neurodegenerative phenotype associated with these alleles. In this study, we show that the CCG premutation length repeat leads to an RNA-mediated neurodegenerative phenotype in a Drosophila model. Furthermore, we show that co-expression of both the CCG and CGG-containing RNAs suppresses their independent toxicity and is dependent on the RNAi pathway. These data support the concept that RNA toxicity is the mechanism of neuronal toxicity and suggests potential reversal of RNA-mediated phenotypes with complementary RNA molecules.

L’insuffisance ovarienne prématurée

Premature ovarian failure (POF) is defined by at least four months of amenorrhea with elevated gonadotropins (usually above 40 UI/L) detected on two occasions a few weeks apart, in a woman before the age of 40. It occurs in 1 out of 10,000 in women below the age of 20, 1/1,000 below 30 and 1% in women before the age of 40. In 80% of POF cases, the etiology is unknown, except for Turner syndrome. The different etiologies identified are 1) iatrogenic following chemotherapy and/or radiotherapy, 2) autoimmune, 3) viral, 4) genetic (RFSH, FOXL2, FRAXA, BMP15, GDF9, GALT, 17 hydroxylase...). Management of these patients includes hormone replacement therapy in order to avoid an increase in cardiovascular risk and osteoporosis related to hypoestrogenism. Infertility is common, as only 3 to 10% of the patients will have natural conception. When fertility is desired, women with POF should be oriented towards oocyte donation centers. Research is currently performed in order to identify new genes involved in POF.

Lack of FMR3 expression in a male with non-syndromic mental retardation and a microdeletion immediately distal to FRAXE CCG repeat

FRAXE fragile site associated mental retardation (FRAXE MR) belongs to a group of non-syndromic X-linked mental retardation. Two genes, FMR2 and FMR3 (likely a non-coding RNA) are transcribed from the FRAXE CpG island in the opposite directions. While the contribution of the FMR2 gene to FRAXE MR has been demonstrated, the role of the FMR3 gene is not known. We have screened 441 Brazilian mentally handicapped males for CCG repeat expansions in the FMR2 gene and identified a boy with a mutation (c.-414_-357del58) immediately distal to the FRAXE CCG repeat. We have established a skin fibroblast cell line from this patient and tested expression of both FMR2 and FMR3 genes. Reverse transcriptase PCR studies on the FMR2 and FMR3 genes showed that only the FMR3 gene transcription was abolished, suggesting a possible causal relationship between the lack of FMR3 expression and mental retardation in this patient. In the literature, there have been few deletions described near the FRAXE CCG repeat, but none was followed with expression studies. This is the first study showing missing expression in the FMR3 gene with normal FMR2 transcription leading to FRAXE mutation-likely phenotype. The FMR3 gene is likely a non-coding RNA gene. So far all individuals with FRAXE CCG repeat expansions and cytogenetically detectable FRAXE fragile site have both FMR2 and FMR3 gene expression abolished. Although the function of the FMR3 gene is not known, our present study together with previous studies on FRAXE MR suggest that it may play role in the processes underpinning normal learning and memory.

Premature ovarian failure

Premature ovarian failure (POF) causing hypergonadotrophic hypogonadism occurs in 1% of women. In majority of cases the underlying cause is not identified. The known causes include: (a) Genetic aberrations, which could involve the X chromosome or autosomes. A large number of genes have been screened as candidates for causing POF; however, few clear causal mutations have been identified. (b) Autoimmune ovarian damage, as suggested by the observed association of POF with other autoimmune disorders. Anti-ovarian antibodies are reported in POF by several studies, but their specificity and pathogenic role are questionable. (c) Iatrogenic following surgical, radiotherapeutic or chemotherapeutic interventions as in malignancies. (d) Environmental factors like viral infections and toxins for whom no clear mechanism is known. The diagnosis is based on finding of amenorrhoea before age 40 associated with FSH levels in the menopausal range. Screening for associated autoimmune disorders and karyotyping, particularly in early onset disease, constitute part of the diagnostic work-up. There is no role of ovarian biopsy or ultrasound in making the diagnosis. Management essentially involves hormone replacement and infertility treatment, the only proven means for the latter being assisted conception with donated oocytes. Embryo cryopreservation, ovarian tissue cryopreservation and oocyte cryopreservation hold promise in cases where ovarian failure is foreseeable as in women undergoing cancer treatments.

Premature ovarian failure and FRAXA premutation: Positive correlation in a Brazilian survey

Fragile X syndrome (FRAXA) is the most common form of inherited mental retardation (MR). The mutational mechanism leading to the disease involves an expansion of a trinucleotide repeat located at the 5' UTR region of the gene FMR-1. Four types of alleles can be identified in the population, based on the number of repeats: normal (6-40), gray-zone (41-60), premutated (61-200), and fully mutated (>200). Despite only full mutations being associated with the development of the disorder, some authors propose a correlation between FRAXA premutation and the occurrence of premature ovarian failure (POF). We have undertaken a study in 58 women from 24 fragile X syndrome families ascertained for FRAXA testing. Using Southern blotting for direct DNA analysis we have identified 19 normal, 33 premutation carriers, and 6 fully mutated individuals (including 4 somatic mosaics showing premutated and fully mutated alleles). Among the premutated women, 11 experienced menopause before the age of 40 (POF), including one somatic mosaic, which was different from the ones with normal pattern who did not experience POF. Our data corroborate the notion that females carrying alleles in the premutation range are at high risk of experiencing POF.

Selected enquiries into the causation of premature ovarian failure

In most species, reproductive senescence can be explained in the same general terms as physiological senescence. In fact, in some species rapid physiological senescence occurs on the completion of reproduction. The programme in women is unusual in that ovarian function comes to a relatively abrupt halt at 45-50 years of age, when the impact of somatic senescence on most other functions is minimal. Early reproductive senescence has been reported in other species (chimpanzees, macaques and toothed whales) but it is more attenuated and less abrupt. The proximate cause of physiological menopause seems to be oocyte depletion, but less obvious neuroendocrine changes precede or result from the gradual loss of oocytes. This is not surprising as many age-specific processes are controlled by hormones. Hormones provide a way for an animal to co-ordinate the ageing of different tissues. The failure to comprehend completely the reasons for the biological uniqueness of women makes the study of the more extreme examples of premature ovarian failure an important exercise. The premature loss of ovarian function in certain eukaryotic women highlights the role of those special maintenance and repair systems that must be functional in the selection process for healthy germ cells. The purpose of this article is to indicate selected areas of clinical and basic investigation that may provide clues to the mechanisms of untimely ageing of the human ovary. Studies of those human extremes with premature loss, or extended ovarian function, may provide critical insights into the unique discordance between somatic and reproductive senescence that is characteristic of normal women.

Genes and translocations involved in POF

Changes at a single autosomal locus and many X-linked loci have been implicated in women with gonadal dysgenesis [premature ovarian failure (POF) with deficits in ovarian follicles]. For the chromosome 3 locus, a forkhead transcription factor gene (FOXL2) has been identified, in which lesions result in decreased follicles by haploinsufficiency. In contrast, sporadic X; autosomal translocations are distributed at many points on the X, but concentrate in a critical region on Xq. The association of the breakpoints with genes involved in ovarian function is thus far weak (in four analyzed cases) and has not been related to pathology in other POF patients. While many more translocations can be analyzed in detail as the human genome sequence is refined, it remains possible that translocations like X monosomy (Turner syndrome) lead to POF not by interrupting specific genes important in ovarian development, but by causing aberrations in pairing or X-inactivation during folliculogenesis. It is noted that the critical region has unusual features, neighboring the X-inactivation center and including an 18 Mb region of very low recombination. These suggest that chromosome dynamics in the region may be sensitive to structural changes, and when modified by translocations might provoke apoptosis at meiotic checkpoints. Choices among models for the etiology of POF should be feasible based on studies of ovarian follicle development and attrition in mouse models. Studies would prominently include gene expression profiling of developmental-specific pathways in nascent ovaries with controlled levels of Foxl2 and interacting proteins, or with defined changes in the X chromosome.

X/autosomal translocations in the Xq critical region associated with premature ovarian failure fall within and outside genes

Premature ovarian failure curtails female reproductive life and is often linked to balanced Xq/autosomal translocations in a critical region. We mapped regions around translocations at the edges of this zone (one in Xq13.3, two in Xq26) in large-insert clones and analyzed their sequence. One Xq26 region is extensively transcribed and, in agreement with a recent independent analysis, the breakpoint interrupts a gene that encodes a widely expressed peptidase. In contrast 430 kb around the second Xq26 breakpoint has no putative or detected gene content. In 260 kb around the Xq13 translocation, the breakpoint falls among a cluster of repetitive elements at least 59 kb from the only detected gene (a rarely expressed T-box family transcription factor). We discuss our results in relation to models that ascribe premature ovarian failure to interruption of ovarian genes or to a failure of interactions involving DNA of the critical region during follicle development.