Fragile X premutation RNA is sufficient to cause primary ovarian insufficiency in mice

Deregulation of key signaling pathways involved in oocyte maturation in FMR1 premutation carriers with Fragile X-associated primary ovarian insufficiency

FMR1 premutation female carriers are at risk for Fragile X-associated primary ovarian insufficiency (FXPOI). Insights from knock-in mouse model have recently demonstrated that FXPOI is due to an increased rate of follicle depletion or an impaired development of the growing follicles. Molecular mechanisms responsible for this reduced viability are still unknown. In an attempt to provide new data on the mechanisms that lead to FXPOI, we report the first investigation involving transcription profiling of total blood from FMR1 premutation female carriers with and without FXPOI. A total of 16 unrelated female individuals (6 FMR1 premutated females with FXPOI; 6 FMR1 premutated females without FXPOI; and 4 no-FXPOI females) were studied by whole human genome oligonucleotide microarray (Agilent Technologies). Fold change analysis did not show any genes with significant differential gene expression. However, functional profiling by gene set analysis showed large number of statistically significant deregulated GO annotations as well as numerous KEGG pathways in FXPOI females. These results suggest that the impairment of fertility in these females might be due to a generalized deregulation of key signaling pathways involved in oocyte maturation. In particular, the vasoendotelial growth factor signaling, the inositol phosphate metabolism, the cell cycle, and the MAPK signaling pathways were found to be down-regulated in FXPOI females. Furthermore, a high statistical enrichment of biological processes involved in cell death and survival were found deregulated among FXPOI females. Our results provide new strategic approaches to further investigate the molecular mechanisms and potential therapeutic targets for FXPOI not focused in a single gene but rather in the set of genes involved in these pathways.

FMR1 gene mutation screening by TP-PCR in patients with premature ovarian failure and fragile-X

CGG repeat expansion in the FMR1 gene is associated with fragile X syndrome, fragile X-associated tremor/ ataxia syndrome and fragile X-associated primary ovarian insufficiency. In this study, FMR1 gene mutation screening was carried out in 50 patients. Among them, 12 (%24) were POF and 19 (%38) were Fragile-X. We also examined the parents of the Fragile-X patients. DNA was extracted from blood with kit procedure. To examine expansion of the fragile-X CGG repeat, TP-PCR assay was performed and all amplicons were evaluated on an ABI3130XL Genetic Analyzer System by Fragman analysis. The data were analyzed by Gene Mapper Program. As a result of this study, the patients were identified with the fragile-X whose FMR1 gene CGG alleles have been observed in normal range. However, in patients who were referred with premature ovarian failure, pre-mutation frequency was observed as 6.6%. Only limited study in Turkish population reported frequency of pre-mutation carrier in POF and Fragile-X. Detection of pre-mutation carrier is important for next generation to have healthy siblings. We emphasize that TP-PCR technique is clear, reliable, sensitive, easy and fast method to detect pre-mutation. However, full mutations have to be examined by the technique of Southern blot in the diagnosis of fragile-X.

Intermediate CGG repeat length at the FMR1 locus is not associated with hormonal indicators of ovarian age

OBJECTIVE

Premutation and intermediate CGG repeat length at the fragile X mental retardation 1 (FMR1) locus have been associated with premature ovarian failure. We tested whether intermediate length is associated with indicators of ovarian age in a sample of fertile women. Our primary measures of ovarian age were antimüllerian hormone (AMH) and follicle-stimulating hormone (FSH) levels.

METHODS

The cross-sectional sample comprised 258 women with karyotyped spontaneous abortions (140 trisomic spontaneous abortions and 118 chromosomally normal spontaneous abortions or spontaneous abortions with anomalies other than trisomy) and 325 women with recent live births (LBs). We analyzed data from the total sample and data from LBs only. We defined CGG repeat length by the length (both continuous and categorical) on the longer allele.

RESULTS

CGG repeat length was not significantly associated with either hormone measure. A repeat length of 35 to 54 CGG, versus the modal category of 30 CGG, was associated with an approximately 7% increase in median AMH level and a 3% increase in median FSH level. Results were unaltered when analyses were limited to LBs. Analyses of hormone levels using cutpoints to define older ovarian age showed no associations with repeat length. Among 10 women with repeat lengths of 35 to 54 CGG analyzed for AGG sequences, the uninterrupted CGG length was not significantly longer among women with hormonal indicators of "old" versus "young" ovarian age.

CONCLUSIONS

Our data do not support an association between intermediate CGG repeat length and levels of AMH or FSH among fertile women.

Curvilinear association of CGG repeats and age at menopause in women with FMR1 premutation expansions

In a sample of post-menopausal premutation carrier mothers of children with the full mutation of fragile X syndrome (n = 88), this study examined the co-occurrence of the reproductive and psychiatric phenotypes associated with FMR1 premutations. Mean age at menopause was 43.1 years, and 35.2% of premutation carriers reported cessation of menses prior to age 40 (premature ovarian failure), but only 18% of carriers had been medically diagnosed by a physician as having Fragile X-associated Primary Ovarian Insufficiency. There was a significant curvilinear association between CGG repeat length and age at menopause, with women who had mid-range repeats having the earliest menopause, similar to the pattern that has been found for the psychiatric phenotype of the FMR1 premutation.

How the FMR1 gene became relevant to female fertility and reproductive medicine

This manuscript describes the 6 year evolution of our center’s research into ovarian functions of the FMR1 gene, which led to the identification of a new normal CGGn range of 26–34. This “new” normal range, in turn, led to definitions of different alleles (haplotypes) based on whether no, one or both alleles are within range. Specific alleles then were demonstrated to represent distinct ovarian aging patterns, suggesting an important FMR1 function in follicle recruitment and ovarian depletion of follicles. So called low alleles, characterized by CGGn_<26, appear associated with most significant negative effects on reproductive success. Those include occult primary ovarian insufficiency (OPOI), characterized by prematurely elevated follicle stimulating hormone (FSH) and prematurely low anti-Müllerian hormone, and significantly reduced clinical pregnancy rates in association with in vitro fertilization (IVF) in comparison to women with normal (norm) and high (CGGn_>34) alleles. Because low FMR1 alleles present in approximately 25% of all females, FMR1 testing at young ages may offer an opportunity for earlier diagnosis of OPOI than current practice allows. Earlier diagnosis of OPOI, in turn, would give young women the options of reassessing their reproductive schedules and/or pursue fertility preservation via oocyte cryopreservation when most effective.

Understanding decreased fertility in women carriers of the FMR1 premutation: a possible mechanism for Fragile X-Associated Primary Ovarian Insufficiency (FXPOI)

Fragile X syndrome (FXS) and its associated disorders are caused by the expansion of the CGG repeat in the 5′ untranslated region of the fragile X mental retardation 1 gene (FMR1). The full mutation, defined as >200 cytosine-guanine-guanine (CGG) triplet repeats, causes FXS. Individuals with 55–199 CGG repeats, classified as premutation carriers, are affected by two distinct disorders depending on their premutation status. Disorders associated with premutation carriers include: Fragile X-associated Tremor Ataxia Syndrome (FXTAS) and Fragile X-associated Primary Ovarian Insufficiency (FXPOI). The molecular similarities of FXTAS and FXPOI (e.g. overabundance of FMR1 transcript and intranuclear inclusions) suggest that similar molecular mechanisms underlie both FXTAS and FXPOI. The current hypothesis describes the underlying mechanism for FXTAS as an mRNA gain-of-function mutation, however the underlying mechanism for FXPOI remains unresolved. New data suggests that repeat associated non-AUG (RAN) translation could underlie FXPOI.

Use of model systems to understand the etiology of fragile X-associated primary ovarian insufficiency (FXPOI)

Fragile X-associated primary ovarian insufficiency (FXPOI) is among the family of disorders caused by the expansion of a CGG repeat sequence in the 5' untranslated region of the X-linked gene FMR1. About 20% of women who carry the premutation allele (55 to 200 unmethylated CGG repeats) develop hypergonadotropic hypogonadism and cease menstruating before age 40. Some proportion of those who are still cycling show hormonal profiles indicative of ovarian dysfunction. FXPOI leads to subfertility and an increased risk of medical conditions associated with early estrogen deficiency. Little progress has been made in understanding the etiology of this clinically significant disorder. Understanding the molecular mechanisms of FXPOI requires a detailed knowledge of ovarian FMR1 mRNA and FMRP’s function. In humans, non-invasive methods to discriminate the mechanisms of the premutation on ovarian function are not available, thus necessitating the development of model systems. Vertebrate (mouse and rat) and invertebrate (Drosophila melanogaster) animal studies for the FMR1 premutation and ovarian function exist and have been instrumental in advancing our understanding of the disease phenotype. For example, rodent models have shown that FMRP is highly expressed in oocytes where it is important for folliculogenesis. The two premutation mouse models studied to date show evidence of ovarian dysfunction and, together, suggest that the long repeat in the transcript itself may have some pathological effect quite apart from any effect of the toxic protein. Further, ovarian morphology in young animals appears normal and the primordial follicle pool size does not differ from that of wild-type animals. However, there is a progressive premature decline in the levels of most follicle classes. Observations also include granulosa cell abnormalities and altered gene expression patterns. Further comparisons of these models are now needed to gain insight into the etiology of the ovarian dysfunction. Premutation model systems in non-human primates and those based on induced pluripotent stem cells show particular promise and will complement current models. Here, we review the characterization of the current models and describe the development and potential of the new models. Finally, we will discuss some of the molecular mechanisms that might be responsible for FXPOI.

Approaches to identify genetic variants that influence the risk for onset of fragile X-associated primary ovarian insufficiency (FXPOI): a preliminary study

Fragile X-associated primary ovarian insufficiency (FXPOI) is due to an X-linked mutation that results from the expansion of a CGG repeat sequence located in the 5′ untranslated region of the FMR1 gene (premutation, PM). About 20% of women who carry the PM have cessation of menses before age 40, a clinical condition known as premature ovarian failure (POF). This leads to a 20-fold increased risk over women in the general population. Thus, this single gene mutation has a major effect on reducing a woman's reproductive life span. Based on survival analysis of about 1300 women, we showed that the mean age at menopause among PM carriers is reduced compared with noncarriers, even after removing women who reported POF. This suggests that the majority of women with the PM, not just a subset, experience ovarian insufficiency earlier than noncarriers. To better understand the underlying mechanism of the PM and to identify genes that modify the variable expressivity of FXPOI, we conducted two pilot studies. The first focused on five common variants known to reduce age at menopause. We genotyped these SNPs in 72 women with a PM who experienced menopause and found a significant association with the total SNP risk burden and age at menopause. This suggests that these SNPs influence onset of FXPOI, after adjusting for the effect of the PM allele. In the second approach, we conducted whole genome sequencing on 10 PM carriers, five with onset of FXPOI prior to age 30 and five who experienced menopause after age 47 years. Although only a pilot study, we describe our preliminary approach to identify potential variants that may play a role in modifying onset of FXPOI and potentially play a role in idiopathic primary ovarian insufficiency. The overarching goal of both approaches is to identify predictor variants that may identify women predisposed to early onset FXPOI and to further identify genes involved in defining a woman's reproductive life span.

FMR1 premutation is an uncommon explanation for premature ovarian failure in Han Chinese

BACKGROUND

In premature ovarian failure (POF), cessation of menstruation occurs before the expected age of menopause. Approximately 1% of women are affected. FMR1 premutation was reported to be responsible for up to 3.3%-6.7% of sporadic POF and 13% of familial cases in Caucasians, while the data was absent in Chinese population. Therefore, the impact of FMR1 CGG repeat on ovarian reserve is needed to be investigated in large Chinese cohort.

METHODS

The number of FMR1 CGG repeat was determined in 379 Han Chinese women with well-defined 46, XX non-syndromic sporadic POF and 402 controls. The age of menopause onset in respect to CGG repeats was further analyzed.

RESULTS

The frequency of FMR1 premutation in Han Chinese POF was only 0.5% (2/379), although it was higher than that in matched controls (0%, 0/402), it was much lower than that reported in Caucasian with POF (3.3%-6.7%). The prevalence of intermediate FMR1 (41-54) was not increased significantly in sporadic POF than that in controls (2.9% vs. 1.7%, P = 0.343). However, POF patients more often carried a single additional CGG repeat in a single allele than did fertile women (allele-1: 29.7 vs. 28.8, P<0.001; allele-2: 32.6 vs. 31.5, P < 0.001). POF patients with both alleles of CGG repeats outside (below or above) the normal range (26-34) showed an earlier age of cessation of menses than those with two alleles within normal range (hom-high/high vs. norm: 20.4 ± 4.8 vs. 24.7 ± 6.4, p < 0.01; hom-low/high vs. norm: 18.7 ± 1.7 vs. 24.7 ± 6.4, p < 0.01).

CONCLUSIONS

FMR1 premutation seems to be an uncommon explanation for POF in Han Chinese. However, having both alleles with CGG repeats outside the normal range might still adversely affect ovarian aging.

The FMR1 gene, infertility, and reproductive decision-making: a review

The strongest association between FMR1 and the ovary in humans is the increased risk of premature ovarian failure (POF) in women who carry the premutation level of CGG repeats (55–199 CGGs). Research on the FMR1 gene has extended to other endpoints of relevance in the OB/GYN setting for women, including infertility and ovarian hormones. After reviewing the nomenclature changes that have occurred in recent years, this article reviews the evidence linking the length of the FMR1 repeat length to fertility and ovarian hormones (follicle stimulating hormone and anti-mullerian hormone as the primary methods to assess ovarian reserve in clinical settings). The literature is inconsistent on the association between the FMR1 trinucleotide repeat length and infertility. Elevated levels of follicle stimulating hormone have been found in women who carry the premutation; however the literature on the relationship between anti-mullerian hormone and the CGG repeat length are too disparate in design to make a summary statement. This article considers the implications of two transgenic mouse models (FXPM 130R and YAC90R) for theories on pathogenesis related to ovarian endpoints. Given the current screening/testing recommendations for reproductive age females and the variability of screening protocols in clinics, future research is recommended on pretest and posttest genetic counseling needs. Future research is also needed on ovarian health measurements across a range of CGG repeat lengths in order to interpret FMR1 test results in reproductive age women; the inconsistencies in the literature make it quite challenging to advise women on their risks related to FMR1 repeat length.

Blood expression profiles of fragile X premutation carriers identify candidate genes involved in neurodegenerative and infertility phenotypes

Male premutation carriers presenting between 55 and 200 CGG repeats in the Fragile-X-associated (FMR1) gene are at risk of developing Fragile X Tremor/Ataxia Syndrome (FXTAS), and females undergo Premature Ovarian Failure (POF1). Here, we have evaluated gene expression profiles from blood in male FMR1 premutation carriers and detected a strong deregulation of genes enriched in FXTAS relevant biological pathways, including inflammation, neuronal homeostasis and viability. Gene expression profiling distinguished between control individuals, carriers with FXTAS and carriers without FXTAS, with levels of expanded FMR1 mRNA being increased in FXTAS patients. In vitro studies in a neuronal cell model indicate that expression levels of expanded FMR1 5'-UTR are relevant in modulating the transcriptome. Thus, perturbations of the transcriptome may be an interplay between the CGG expansion size and FMR1 expression levels. Several deregulated genes (DFFA, BCL2L11, BCL2L1, APP, SOD1, RNF10, HDAC5, KCNC3, ATXN7, ATXN3 and EAP1) were validated in brain samples of a FXTAS mouse model. Downregulation of EAP1, a gene involved in the female reproductive system physiology, was confirmed in female carriers. Decreased levels were detected in female carriers with POF1 compared to those without POF1, suggesting that EAP1 levels contribute to ovarian insufficiency. In summary, gene expression profiling in blood has uncovered mechanisms that may underlie different pathological aspects of the premutation. A better understanding of the transcriptome dynamics in relation with expanded FMR1 mRNA expression levels and CGG expansion size may provide mechanistic insights into the disease process and a more accurate FXTAS diagnosis to the myriad of phenotypes associated with the premutation.

Genomic markers of ovarian reserve

Ovarian reserve and its utilization, over a reproductive life span, are determined by genetic, epigenetic, and environmental factors. The establishment of the primordial follicle pool and the rate of primordial follicle activation have been under intense study to determine genetic factors that affect reproductive lifespan. Much has been learned from transgenic animal models about the developmental origins of the primordial follicle pool and mechanisms that lead to primordial follicle activation, folliculogenesis, and the maturation of a single oocyte with each menstrual cycle. Recent genome-wide association studies on the age of human menopause have identified approximately 20 loci, and shown the importance of factors involved in double-strand break repair and immunology. Studies to date from animal models and humans show that many genes determine ovarian aging, and that there is no single dominant allele yet responsible for depletion of the ovarian reserve. Personalized genomic approaches will need to take into account the high degree of genetic heterogeneity, family pedigree, and functional data of the genes critical at various stages of ovarian development to predict women's reproductive life span.

RAN translation: fragile X in the running

In this issue of Neuron, Todd et al. (2013) reveal that noncanonical repeat associated non-AUG (RAN) translation occurs on nonexpanded (CGG)30-50 and premutation (CGG)59-160 repeats, associated with the FMR1 gene, suggesting that the polyglycine and polyalanine products might have natural and pathogenic roles.

Fragile X-associated tremor/ataxia syndrome (FXTAS): pathology and mechanisms

Since its discovery in 2001, our understanding of fragile X-associated tremor/ataxia syndrome (FXTAS) has undergone a remarkable transformation. Initially characterized rather narrowly as an adult-onset movement disorder, the definition of FXTAS is broadening; moreover, the disorder is now recognized as only one facet of a much broader clinical pleiotropy among children and adults who carry premutation alleles of the FMR1 gene. Furthermore, the intranuclear inclusions of FXTAS, once thought to be a CNS-specific marker of the disorder, are now known to be widely distributed in multiple non-CNS tissues; this observation fundamentally changes our concept of the disease, and may provide the basis for understanding the diverse medical problems associated with the premutation. Recent work on the pathogenic mechanisms underlying FXTAS indicates that the origins of the late-onset neurodegenerative disorder actually lie in early development, raising the likelihood that all forms of clinical involvement among premutation carriers have a common underlying mechanistic basis. There has also been great progress in our understanding of the triggering event(s) in FXTAS pathogenesis, which is now thought to involve sequestration of one or more nuclear proteins involved with microRNA biogenesis. Moreover, there is mounting evidence that mitochondrial dysregulation contributes to the decreased cell function and loss of viability, evident in mice even during the neonatal period. Taken together, these recent findings offer hope for early interventions for FXTAS, well before the onset of overt disease, and for the treatment of other forms of clinical involvement among premutation carriers.

FMR1 CGG expansions: prevalence and sex ratios

We have estimated the prevalence of FMR1 premutation and gray zone CGG repeat expansions in a population-based sample of 19,996 male and female adults in Wisconsin and compared the observed sex ratios of the prevalence of FMR1 CGG premutation and gray zone expansions to theoretical sex ratios. The female premutation prevalence was 1 in 148 and comparable to past research, but the male premutation prevalence of 1 in 290 is somewhat higher than most previous estimates. The female:male premutation prevalence ratio is in line with the theoretically predicted sex ratio. The prevalence of CGG repeats in the gray zone (45-54 repeats) was 1 in 33 females and 1 in 62 males. The prevalence of the "expanded" gray zone (defined here as 41-54 CGG repeats) was 1 in 14 females and 1 in 22 males, leading to a female:male ratio of 1.62 (95% confidence interval 1.39-1.90). This female:male ratio was significantly lower than the expected ratio of 2.0. We examined results from three previously published FMR1 prevalence studies and found similar female:male ratios for CGG repeats in this "expanded" gray zone range (pooled female:male ratio across all four studies 1.66, 95% confidence interval 1.51-1.82). Further research is needed to understand the apparent excess prevalence of males with CGG repeats in this range.

Activation of mTOR ameliorates fragile X premutation rCGG repeat-mediated neurodegeneration

Fragile X associated tremor/ataxia syndrome (FXTAS) is a late onset neurodegenerative disorder caused by aberrant expansion of CGG repeats in 5′ UTR of FMR1 gene. The elevated mRNA confers a toxic gain-of-function thought to be the critical event of pathogenesis. Expressing rCGG₉₀ repeats of the human FMR1 5′UTR in Drosophila is sufficient to induce neurodegeneration. Rapamycin has been demonstrated to attenuate neurotoxicity by inducing autophagy in various animal models of neurodegenerative diseases. Surprisingly, we observed rapamycin exacerbated rCGG₉₀-induced neurodegenerative phenotypes through an autophagy-independent mechanism. CGG₉₀ expression levels of FXTAS flies exposed to rapamycin presented no significant differences. We further demonstrated that activation of the mammalian target of rapamycin (mTOR) signaling could suppress neurodegeneration of FXTAS. These findings indicate that rapamycin will exacerbate neurodegeneration, and that enhancing autophagy is insufficient to alleviate neurotoxicity in FXTAS. Moreover, these results suggest mTOR and its downstream molecules as new therapeutic targets for FXTAS by showing significant protection against neurodegeneration.

Expression of fragile X mental retardation protein and Fmr1 mRNA during folliculogenesis in the rat

Fragile X mental retardation protein (FMRP) belongs to a small family of RNA-binding proteins. Its absence or inactivity is responsible for fragile X syndrome, the most common cause of inherited mental retardation. Despite its ubiquitous expression, FMRP function and expression remain almost understudied in non-neuronal tissues, though previous studies on germline development during oogenesis may suggest a special function of this protein also in ovarian tissue. In addition, the well-documented association of FMR1 premutation state with fragile X-related premature ovarian insufficiency adds interest to the role of FMRP in ovarian physiology. The aim of the present work was to investigate the expression of Fmr1 mRNA and its protein, FMRP, at different stages of rat follicular development. By immunohistochemical studies we demonstrated FMRP expression in granulosa, theca and germ cells in all stages of follicular development. In addition, changes in Fmr1 expression, both at the protein and mRNA levels, were observed. FMRP levels increased upon follicular development while preantral and early antral follicles presented similar levels of Fmr1 transcripts with decreased expression in preovulatory follicles. These observations suggest that Fmr1 expression in the ovary is regulated at different and perhaps independent levels. In addition, our results show expression of at least four different isoforms of FMRP during all stages of follicular growth with expression patterns that differ from those observed in brain and testis. Our study shows a regulated expression of Fmr1, both at mRNA and protein levels, during rat follicular development.