Association between idiopathic premature ovarian failure and fragile X premutation

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.

Laboratory testing for fragile X, 2021 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG)

Molecular genetic testing of the FMR1 gene is commonly performed in clinical laboratories. Pathogenic variants in the FMR1 gene are associated with fragile X syndrome, fragile X-associated tremor ataxia syndrome (FXTAS), and fragile X-associated primary ovarian insufficiency (FXPOI). This document provides updated information regarding FMR1 pathogenic variants, including prevalence, genotype-phenotype correlations, and variant nomenclature. Methodological considerations are provided for Southern blot analysis and polymerase chain reaction (PCR) amplification of FMR1, including triplet repeat-primed and methylation-specific PCR.The American College of Medical Genetics and Genomics (ACMG) Laboratory Quality Assurance Committee has the mission of maintaining high technical standards for the performance and interpretation of genetic tests. In part, this is accomplished by the publication of the document ACMG Technical Standards for Clinical Genetics Laboratories, which is now maintained online ( http://www.acmg.net ). This subcommittee also reviews the outcome of national proficiency testing in the genetics area and may choose to focus on specific diseases or methodologies in response to those results. Accordingly, the subcommittee selected fragile X syndrome to be the first topic in a series of supplemental sections, recognizing that it is one of the most frequently ordered genetic tests and that it has many alternative methods with different strengths and weaknesses. This document is the fourth update to the original standards and guidelines for fragile X testing that were published in 2001, with revisions in 2005 and 2013, respectively.This versionClarifies the clinical features associated with different FMRI variants (Section 2.3)Discusses important reporting considerations (Section 3.3.1.3)Provides updates on technology (Section 4.1).

RNA contributions to the form and function of biomolecular condensates

Biomolecular condensation partitions cellular contents and has important roles in stress responses, maintaining homeostasis, development and disease. Many nuclear and cytoplasmic condensates are rich in RNA and RNA-binding proteins (RBPs), which undergo liquid-liquid phase separation (LLPS). Whereas the role of RBPs in condensates has been well studied, less attention has been paid to the contribution of RNA to LLPS. In this Review, we discuss the role of RNA in biomolecular condensation and highlight considerations for designing condensate reconstitution experiments. We focus on RNA properties such as composition, length, structure, modifications and expression level. These properties can modulate the biophysical features of native condensates, including their size, shape, viscosity, liquidity, surface tension and composition. We also discuss the role of RNA-protein condensates in development, disease and homeostasis, emphasizing how their properties and function can be determined by RNA. Finally, we discuss the multifaceted cellular functions of biomolecular condensates, including cell compartmentalization through RNA transport and localization, supporting catalytic processes, storage and inheritance of specific molecules, and buffering noise and responding to stress.

A study on the role of FMR1 CGG trinucleotide repeats in Jordanian poor ovarian responders

The expansion of trinucleotide CGG repeats in the promoter of fragile X mental retardation 1 (FMR1) gene is associated with fragile X and fragile X associated tremor/ataxia syndromes. While the expansion of CGG repeats has been associated with such neuro/psychiatric diseases, the contraction of CGG repeats has been recently suggested as an indication of ovarian dysfunction. This study aimed to evaluate a possible association of the short CGG repeats with poor ovarian responders (POR) and to test for a possible correlation between the CGG size and different known markers of the ovarian reserve, namely FSH, AMH, and the number of retrieved oocytes from Jordanian females. We found a significant difference between the CGG median allele size between the cases and the controls (p < 0.001), where poor ovarian responders had shorter CGG repeats compared to the healthy controls. Also, females with alleles <26 had twice the odds to be presented in the POR compared to the controls. However, we did not find a significant correlation between CGG sizes and the markers of ovarian reserve. We conclude that although low CGG repeats appear to be linked to POR, the clinical utility of FMR1 for predicting ovarian response needs further investigation.

Premature ovarian insufficiency in adolescence: a chance for early diagnosis?

Premature ovarian insufficiency (POI) is typically diagnosed when amenorrhea is combined with high gonadotrophins and hypoestrogenemia in a woman under 40 years of age, although, more rarely, POI can develop in adolescence and present with delayed puberty or amenorrhea, depending on the timing of follicular depletion or insult to the ovary. In a proportion of girls, the diagnosis may be made at an early stage of POI, presenting with abnormal uterine bleeding, when some follicular function is still retained. The natural history of POI in this group of patients is not clear; however, they could represent a subgroup with a unique opportunity for early intervention and thus the provision of fertility preservation options. While the etiology of POI in a large number of girls remains unknown, a growing number will be identified as carriers of genetic mutations, offering clinicians a yet greater opportunity to provide genetic counseling to other female family members. The aim of this review is to provide information regarding the etiology, diagnosis, and treatment of POI in adolescents while detailing the new options for fertility preservation when POI is diagnosed at an early stage.

Fragile X syndrome and fragile X-associated tremor ataxia syndrome

Fragile X-associated disorders encompass several conditions, which are caused by expansion mutations in the fragile X mental retardation 1 (FMR1) gene. Fragile X syndrome is the most common inherited etiology of intellectual disability and results from a full mutation or >200 CGG repeats in FMR1. It is associated with developmental delay, autism spectrum disorder, and seizures. Fragile X-associated tremor/ataxia syndrome is a progressive neurodegenerative disease that occurs in premutation carriers of 55-200 CGG repeats in FMR1 and is characterized by kinetic tremor, gait ataxia, parkinsonism, executive dysfunction, and neuropathy. Fragile X-associated primary ovarian insufficiency also occurs in premutation carrier women and manifests with infertility and early menopause. The diseases constituting fragile X-associated disorders differ mechanistically, due to the distinct molecular properties of premutation versus full mutations. Fragile X syndrome occurs when there is a lack of fragile X mental retardation protein (FMRP) due to FMR1 methylation and silencing. In fragile X-associated tremor ataxia syndrome, a toxic gain of function is postulated with the production of excess CGG repeat-containing FMR1 mRNA, abnormal translation of the repeat sequence leading to production of polyglycine, polyalanine, and other polypeptides and to outright deficits in translation leading to reduced FMRP at larger premutation sizes. The changes in underlying brain chemistry due to FMR1 mutations have led to therapeutic studies in these disorders, with some progress being made in fragile X syndrome. This paper also summarizes indications for testing, genetic counseling issues, and what the future holds for these disorders.

Premutations of FMR1 CGG repeats are not related to idiopathic premature ovarian failure in Iranian patients: A case control study

Premature ovarian failure (POF) is a reproductive disease which affects 1 in 100 under 40 years women. FMR1 premutation carriers of CGG repeats are supposed to be at increased risk for POF. We have examined the 5'UTR region of the gene to find any association between the repeat size and the disease etiology in Iranian population. 30 women with early idiopathic POF and 30 fertile control women were selected. We used triplet repeat primed PCR (TP PCR) assay and gene-specific primers to amplify the CpG Island of FMR1 gene promoter region. The amplification results were analyzed by capillary electrophoresis and Gene Marker software. Among 30 patients, two had intermediate repeat size, one had premutation and the rest had CGG repeat of the normal range. Two of controls had intermediate repeats and none had a premutation. Two groups had significant differences in the repeat number average (p = 0.007) and in the average length of the smallest allele (p < 0.001), but had no promising difference in average length of the longest allele (p = 0.453). Although the two groups showed a significant difference in the length of alleles, their length was within normal range. Perhaps the polymorphism, in connection with the genome's entire network, has been involved in the development of the disease, or there has been a fundamentally different mechanism for the disease in Iranian population. A larger number of Iranian POF patients should be investigated for any probable relationship between the CGG triplet repeat length and the etiology of the disease.

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.

Molecular Characterization of FMR1 Gene by TP-PCR in Women of Reproductive Age and Women with Premature Ovarian Insufficiency

BACKGROUND

Fragile X syndrome is caused by CGG repeat expansion mutation in the FMR1 gene. Normal alleles have 5-44 CGG repeats with AGG interruptions. The expanded gray zone (GZ) (45-54 repeats) and premutation (PM) (55-200 repeats) alleles are often uninterrupted and are unstably inherited in subsequent generations. The prevalence of PM and GZ carriers is high in the female population, at 1/66 and 1/113, respectively, and PM is associated with fertility problems in 20% of cases.

OBJECTIVE

Our objective was to molecularly characterize CGG repeats and AGG interruption sequences in the FMR1 gene in women of reproductive age and in women with premature ovarian insufficiency (POI).

MATERIALS AND METHODS

We conducted molecular analysis of the FMR1 gene from 300 women of reproductive age and 140 women with POI using triplet primed-polymerase chain reaction. This enabled us to identify carriers and to document CGG repeat size and the AGG interruption pattern.

RESULTS

In women of reproductive age, 1.7% were GZ carriers and 0.3% were PM carriers; in women with POI, 3.6% were GZ carriers and 2.14% were PM carriers. The frequency of GZ and PM carriers did not significantly differ between the cohorts (Fisher's exact test: p < 2.23 for GZ vs. control and p < 0.101 for PM vs. control). Carriers received genetic counselling; family screening identified an additional seven carriers.

CONCLUSION

We documented preliminary data on the prevalence of GZ and PM carriers among the studied cohorts. The identification of PM carriers among women with POI serves a dual purpose of recognizing a cause for ovarian dysfunction and enabling genetic counselling, which will help carriers when making reproductive decisions.

Polycystic ovarian syndrome and the risk of subsequent primary ovarian insufficiency: a nationwide population-based study

OBJECTIVE

To evaluate the risk of subsequent primary ovarian insufficiency (POI) amongst patients with a history of polycystic ovarian syndrome (PCOS).

METHODS

This nationwide, population-based study is an inspection and review of data from the 1998 to 2012 Taiwan National Health Insurance Research Database. In a sample of 1,000,000 randomly sampled individuals, women with PCOS (exposure group; n = 7,049) and women without PCOS (contrast group; n = 70,490) were compared. Women initially diagnosed with PCOS at less than 15 or more than 35 years of age were excluded. Each woman with PCOS was age-matched to 10 women without PCOS. The diagnoses of PCOS and POI (coded using International Classification of Diseases, 9th Revision, Clinical Modification) were further confirmed with blood test results and ultrasonographic findings to ensure the accuracy of the diagnoses.

RESULTS

POI occurred more among women with PCOS compared with women without PCOS (3.73% vs 0.44%; P < 0.001). Using Kaplan-Meier survival analysis, the POI-free survival rates were significantly different between the exposure and contrast groups (P < 0.001). During 10 years of follow-up, Cox proportional-hazard analysis revealed that the risk for POI was significantly higher in the exposure than in the contrast group (hazard ratio [HR] 8.64, 95% confidence interval [CI] 7.33-10.18) and remained similar after adjustment for covariates (adjusted HR 8.31, 95% CI 7.05-9.81). Compared with that of women without PCOS, the risk of POI was even higher for women with PCOS who did not receive metformin treatment (adjusted HR 9.93, 95% CI 8.28-11.90). However, the risk for POI was significantly reduced for women with PCOS who received metformin treatment (adjusted HR 5.66, 95% CI 4.36-7.35).

CONCLUSIONS

As a possible precursor stage, prior PCOS is a significant and independent risk factor for development of POI. The use of metformin reduces the risk of POI.

FMR1 premutation: not only important in premature ovarian failure but also in diminished ovarian reserve

It is recognized that FMR1 premutation expansions are associated with premature ovarian failure (POF), but their role in diminished ovarian reserve (DOR) is not clearly established. Moreover, the impact of smaller repeats at the boundary of premutation and normal is less clear. Therefore, we have compared the frequency of these intermediate (45-54 repeats) and premutation (>55) sized FMR1 CGG repeats among a patients group including 188 DOR and 173 POF women and 200 controls. FSH and LH concentrations were also compared between intermediate and premutation ranges in patients. The 5' UTR of FMR1 gene was amplified using PCR. The numbers of trinucleotide repeats were confirmed by the Sanger sequencing method. The frequency of premutation was higher in POF and DOR patients in comparison with controls, but the difference in the incidence of intermediate alleles was not statistically significant among these groups. The mean level of serum FSH was higher in patients with premutation than patients with intermediate alleles. Based on the current evidence, we concluded that intermediate-sized FMR1 CGG repeat alleles should not be considered as a high-risk factor for POF and DOR.

The impact of FMR1 gene mutations on human reproduction and development: a systematic review

PURPOSE

This is a comprehensive review of the literature in this field attempting to put the FMR1 gene and its evaluation into context, both in general and for the reproductive health audience.

METHODS

Online database search of publications with systematic review of all papers relevant to ovarian reserve and assisted reproduction was done.

RESULTS

Relevant papers were identified and assessed, and an attempt was made to understand, rationalize and explain the divergent views in this field of study. Seminal and original illustrations were employed.

CONCLUSIONS

FMR1 is a highly conserved gene whose interpretation and effect on outcomes remains controversial in the reproductive health setting. Recent re-evaluations of the commonly accepted normal range have yielded interesting tools for possibly explaining unexpected outcomes in assisted reproduction. Fragile X investigations should perhaps become more routinely assessed in the reproductive health setting, particularly following a failed treatment cycle where oocyte quality is thought to be a contributing factor, or in the presence of a surprise finding of diminished ovarian reserve in a young patient.

Current Concepts in Premature Ovarian Insufficiency

Premature ovarian insufficiency (POI) is a life-changing diagnosis, with profound physical and psychological consequences. Unfortunately, there are many deficiencies in our understanding of the condition as the underlying etiology and optimum management strategies are poorly understood. Improved awareness of POI and its long-term implications has led to increased research interest in recent years. Current research has allowed a greater understanding of the changing epidemiology in POI, genetic factors in its etiology and randomized controlled trials of hormone therapy are underway to provide evidence for treatment. This article reviews the latest literature on POI to summarize current understanding and future directions.

Germ cell-specific Atg7 knockout results in primary ovarian insufficiency in female mice

Primary ovarian insufficiency (POI) is a common cause of infertility in around 1–2% of women aged <40 years. However, the mechanisms that cause POI are still poorly understood. Here we showed that germ cell-specific knockout of an essential autophagy induction gene Atg7 led to subfertility in female mice. The subfertility of Atg7 deletion females was caused by severe ovarian follicle loss, which is very similar to human POI patients. Further investigation revealed that germ cell-specific Atg7 knockout resulted in germ cell over-loss at the neonatal transition period. In addition, our in vitro studies also demonstrated that autophagy could protect oocytes from over-loss by apoptosis in neonatal ovaries under the starvation condition. Taken together, our results uncover a new role for autophagy in the regulation of ovarian primordial follicle reservation and hint that autophagy-related genes might be potential pathogenic genes to POI of women.

EMQN best practice guidelines for the molecular genetic testing and reporting of fragile X syndrome and other fragile X-associated disorders

Different mutations occurring in the unstable CGG repeat in 5' untranslated region of FMR1 gene are responsible for three fragile X-associated disorders. An expansion of over ∼200 CGG repeats when associated with abnormal methylation and inactivation of the promoter is the mutation termed ‘full mutation' and is responsible for fragile X syndrome (FXS), a neurodevelopmental disorder described as the most common cause of inherited intellectual impairment. The term ‘abnormal methylation' is used here to distinguish the DNA methylation induced by the expanded repeat from the ‘normal methylation' occurring on the inactive X chromosomes in females with normal, premutation, and full mutation alleles. All male and roughly half of the female full mutation carriers have FXS. Another anomaly termed ‘premutation' is characterized by the presence of 55 to ∼200 CGGs without abnormal methylation, and is the cause of two other diseases with incomplete penetrance. One is fragile X-associated primary ovarian insufficiency (FXPOI), which is characterized by a large spectrum of ovarian dysfunction phenotypes and possible early menopause as the end stage. The other is fragile X-associated tremor/ataxia syndrome (FXTAS), which is a late onset neurodegenerative disorder affecting males and females. Because of the particular pattern and transmission of the CGG repeat, appropriate molecular testing and reporting is very important for the optimal genetic counselling in the three fragile X-associated disorders. Here, we describe best practice guidelines for genetic analysis and reporting in FXS, FXPOI, and FXTAS, including carrier and prenatal testing.

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.

Identification of genes promoting skin youthfulness by genome-wide association study

To identify genes that promote facial skin youthfulness (SY), a genome-wide association study on an Ashkenazi Jewish discovery group (n=428) was performed using Affymetrix 6.0 Single-Nucleotide Polymorphism (SNP) Array. After SNP quality controls, 901,470 SNPs remained for analysis. The eigenstrat method showed no stratification. Cases and controls were identified by global facial skin aging severity including intrinsic and extrinsic parameters. Linear regression adjusted for age and gender, with no significant differences in smoking history, body mass index, menopausal status, or personal or family history of centenarians. Six SNPs met the Bonferroni threshold with Pallele<10(-8); two of these six had Pgenotype<10(-8). Quantitative trait loci mapping confirmed linkage disequilibrium. The six SNPs were interrogated by MassARRAY in a replication group (n=436) with confirmation of rs6975107, an intronic region of KCND2 (potassium voltage-gated channel, Shal-related family member 2) (Pgenotype=0.023). A second replication group (n=371) confirmed rs318125, downstream of DIAPH2 (diaphanous homolog 2 (Drosophila)) (Pallele=0.010, Pgenotype=0.002) and rs7616661, downstream of EDEM1 (ER degradation enhancer, mannosidase α-like 1) (Pgenotype=0.042). DIAPH2 has been associated with premature ovarian insufficiency, an aging phenotype in humans. EDEM1 associates with lifespan in animal models, although not humans. KCND2 is expressed in human skin, but has not been associated with aging. These genes represent new candidate genes to study the molecular basis of healthy skin aging.

Maternal FMR1 premutation allele expansion and contraction in fraternal twins

Fragile X syndrome results from an expansion of the CGG trinucleotide repeat in the 5' untranslated region of the Fragile X Mental Retardation 1 (FMR1) gene. Expansion of a maternal premutation allele is the mechanism by which a full mutation allele arises; contraction of a maternal premutation allele is rare. Here we report on both an expansion and contraction of a maternal FMR1 premutation allele in fraternal twins. The propositus was the product of a 29-week gestation twin pregnancy and was referred for FMR1 testing due to developmental delay. A FMR1 full mutation with complete methylation was observed on Southern blot analysis. Evaluation of the maternal FMR1 gene by PCR revealed a normal and premutation allele with CGG repeat numbers of 30 and 93, respectively. Subsequent FMR1 testing on the twin sister of the propositus detected CGG repeat numbers of 30 and 54. The FMR1 CGG repeat number of the reproductive partner was 30. The FMR1 CGG repeat 30 allele in the twin sister was determined to be of paternal origin and the FMR1 allele with a CGG repeat number of 54 was of maternal origin. This observation is particularly interesting not only because of the concomitant donation of a FMR1 expanded and contracted premutation allele in a twin pregnancy but also because of the significant degree of contraction (39 repeats) of the maternal premutation allele.

ACMG Standards and Guidelines for fragile X testing: a revision to the disease-specific supplements to the Standards and Guidelines for Clinical Genetics Laboratories of the American College of Medical Genetics and Genomics

Molecular genetic testing of the FMR1 gene is commonly performed in clinical laboratories. Mutations in the FMR1 gene are associated with fragile X syndrome, fragile X tremor ataxia syndrome, and premature ovarian insufficiency. This document provides updated information regarding FMR1 gene mutations, including prevalence, genotype-phenotype correlation, and mutation nomenclature. Methodological considerations are provided for Southern blot analysis and polymerase chain reaction amplification of the FMR1 gene, including triplet repeat-primed and methylation-specific polymerase chain reaction. In addition to report elements, examples of laboratory reports for various genotypes are also included.

Genetic association studies in female reproduction: from candidate-gene approaches to genome-wide mapping

Many genetic association studies have been performed to investigate disorders of female reproduction, such as polycystic ovary syndrome, premature ovarian failure and endometriosis. These disorders typically manifest heterogeneously, and their pathogeneses are influenced by polygenic and environmental factors. Researchers evaluating these genetic associations have chosen candidate genes related to hormone action, steroid biosynthesis, inflammatory cytokines and autoimmune factors. Several of these genes have yielded statistically significant associations with female reproductive disorders; however, few associations have been robust and reproducible. Whole-genome association studies generate more reliable and unbiased results and represent a breakthrough in genetic studies of female reproduction. Nevertheless, to date only a very small fraction of the overall heritability has been identified and so further studies are needed.

Population-based estimates of the prevalence of FMR1 expansion mutations in women with early menopause and primary ovarian insufficiency

PURPOSE

Primary ovarian insufficiency before the age of 40 years affects 1% of the female population and is characterized by permanent cessation of menstruation. Genetic causes include FMR1 expansion mutations. Previous studies have estimated mutation prevalence in clinical referrals for primary ovarian insufficiency, but these are likely to be biased as compared with cases in the general population. The prevalence of FMR1 expansion mutations in early menopause (between the ages of 40 and 45 years) has not been published.

METHODS

We studied FMR1 CGG repeat number in more than 2,000 women from the Breakthrough Generations Study who underwent menopause before the age of 46 years. We determined the prevalence of premutation (55-200 CGG repeats) and intermediate (45-54 CGG repeats) alleles in women with primary ovarian insufficiency (n = 254) and early menopause (n = 1,881).

RESULTS

The prevalence of the premutation was 2.0% in primary ovarian insufficiency, 0.7% in early menopause, and 0.4% in controls, corresponding to odds ratios of 5.4 (95% confidence interval = 1.7-17.4; P = 0.004) for primary ovarian insufficiency and 2.0 (95% confidence interval = 0.8-5.1; P = 0.12) for early menopause. Combining primary ovarian insufficiency and early menopause gave an odds ratio of 2.4 (95% confidence interval = 1.02-5.8; P = 0.04). Intermediate alleles were not significant risk factors for either early menopause or primary ovarian insufficiency.

CONCLUSION

FMR1 premutations are not as prevalent in women with ovarian insufficiency as previous estimates have suggested, but they still represent a substantial cause of primary ovarian insufficiency and early menopause.

Somatic expansion in mouse and human carriers of fragile X premutation alleles

Repeat expansion diseases result from expansion of a specific tandem repeat. The three fragile X-related disorders (FXDs) arise from germline expansions of a CGG•CCG repeat tract in the 5' UTR (untranslated region) of the fragile X mental retardation 1 (FMR1) gene. We show here that in addition to germline expansion, expansion also occurs in the somatic cells of both mice and humans carriers of premutation alleles. Expansion in mice primarily affects brain, testis, and liver with very little expansion in heart or blood. Our data would be consistent with a simple two-factor model for the organ specificity. Somatic expansion in humans may contribute to the mosaicism often seen in individuals with one of the FXDs. Because expansion risk and disease severity are related to repeat number, somatic expansion may exacerbate disease severity and contribute to the age-related increased risk of expansion seen on paternal transmission in humans. As little somatic expansion occurs in murine lymphocytes, our data also raise the possibility that there may be discordance in humans between repeat numbers measured in blood and that present in brain. This could explain, at least in part, the variable penetrance seen in some of these disorders.

Ovarian abnormalities in a mouse model of fragile X primary ovarian insufficiency

FMR1 premutation (PM) alleles have 55-200 CGG·CCG-repeats in their 5' UTR. PM carriers are at risk of fragile X-associated tremor and ataxia syndrome (FXTAS). Females are also at risk for FX primary ovarian insufficiency (FXPOI). PM pathology is generally attributed to deleterious properties of transcripts with long CGG-tracts. For FXPOI, hormone changes suggest a reduced residual follicle pool. Whether this is due to a smaller than normal original follicle pool or an increased rate of follicle depletion is unclear. A FX-PM mouse the authors generated with 130 CGG·CCG-repeats in the endogenous Fmr1 gene recapitulates features of FXTAS. Here the authors demonstrate that the gross development of the ovary and the establishment of the primordial follicle pool is normal in these mice. However, these animals show a faster loss of follicles of all follicle classes, suggesting that the problem is intrinsic to the ovary. In addition, many oocytes show aberrant nuclear accumulation of FMRP and elevated levels of ubiquitination. Furthermore, PM follicles are smaller and have fewer granulosa cells (GCs) than normal. Thus, these animals have ovarian abnormalities involving both the oocytes and GCs that may shed light on the molecular basis of FXPOI in humans.

Number of CGG repeats in the FMR1 gene of Japanese patients with primary ovarian insufficiency

OBJECTIVE

To define the number of CGG repeats in the FMR1 gene of Japanese patients with primary ovarian insufficiency (POI) and normal controls.

DESIGN

Retrospective, controlled cohort study.

SETTING

Outpatient department of an academic tertiary center.

PATIENT(S)

One hundred twenty-eight consecutive Japanese patients with sporadic, nonsyndromic POI and 98 controls with normal menstruation.

INTERVENTION(S)

Deoxyribonucleic acid was obtained from the plasma of each subject.

MAIN OUTCOME MEASURE(S)

Differences in the distribution of CGG repeat numbers between patients with POI and controls.

RESULT(S)

Six alleles in the intermediate range and two in the premutation range were found in five and two patients with POI, respectively, but none were identified in normal controls. The prevalence of FMR1 premutation among Japanese POI patients was 1.56% (2 of 128). The prevalence of having >36 CGG repeats in the FMR1 gene was significantly higher in patients with POI than in controls, and age at the onset of amenorrhea was significantly lower in patients with >38 repeats.

CONCLUSION(S)

More than 36 CGG repeats in the FMR1 might intensify the etiology of POI, at least up to the premutation range.

Initiation of translation of the FMR1 mRNA Occurs predominantly through 5'-end-dependent ribosomal scanning

The fragile X mental retardation 1 (FMR1) gene contains a CGG repeat within its 5' untranslated region (5'UTR) that, when expanded to 55-200 CGG repeats (premutation allele), can result in the late-onset neurodegenerative disorder, fragile X-associated tremor/ataxia syndrome. The CGG repeat is expected to form a highly stable secondary structure that is capable of inhibiting 5'-cap-dependent translation. Paradoxically, translation in vivo is only mildly impaired within the premutation range, suggesting that other modes of translation initiation may be operating. To address this issue, we translated in vitro a set of reporter mRNAs containing between 0 and 99 CGG repeats in either native (FMR1) or unrelated (heterologous) 5'UTR context. The 5'-cap dependence of translation was assessed by inserting a stable hairpin (HP) near the 5' end of the mRNAs. The results of the current studies indicate that translation initiation of the FMR1 mRNA occurs primarily by scanning, with little evidence of internal ribosome entry or shunting. Additionally, the efficiency of translation initiation depends on transcription start site selection, with the shorter 5'UTR (downstream transcription start site I) translating with greater efficiency compared to the longer mRNA (start site III) for all CGG-repeat elements studied. Lastly, an HP previously shown to block translation gave differing results depending on the 5'UTR context, in one case initiating translation from within the HP.

Depression in women with spontaneous 46, XX primary ovarian insufficiency

CONTEXT

A high prevalence of depressive symptoms is observed in women with primary ovarian insufficiency (POI) compared with women in whom the menopause is normally timed. Indeed, studies suggest that depression and/or its pharmacological treatment contribute to the onset of POI.

OBJECTIVES

We characterize the prevalence of psychiatric disorders and the timing of onset of clinically significant depression relative to both the diagnosis of POI and the onset of menstrual irregularity in women with POI.

DESIGN AND SETTING

We conducted a cross-sectional clinic-based study at the National Institutes of Health Clinical Research Center.

PATIENTS

A total of 174 women with spontaneous 46, XX POI and 100 women with Turner syndrome participated in the study.

MAIN OUTCOME MEASURES

The structured clinical interview for DSM-IV was performed.

RESULTS

Lifetime histories of depression in POI exceeded rates of depression reported in women with Turner syndrome and community-based samples of women (P < 0.001). The onset of depression frequently preceded the diagnosis of POI but occurred after the onset of menstrual irregularity. Analyses standardizing the periods of risk for depression showed that similar numbers of depressions occurred before and after these events.

CONCLUSIONS

POI is associated with an increased lifetime risk for major depression. Attention to the presence of depression in POI should become an important part of the care for these women. The onset of depression frequently occurs after signs of altered ovarian function but before the diagnosis of POI. Thus, in some women the association between POI and depression suggests an overlapping pathophysiology rather than a causal relationship.

A molecular and cytogenetic investigation of FMR1 gene premutations in Polish patients with primary ovarian insufficiency

OBJECTIVE

The aim of this study was to determine the prevalence of premutations in the FMR1 gene that cause primary ovarian insufficiency (POI) in a group of affected women.

STUDY DESIGN

Forty DNA samples were purified from peripheral blood collected from women with ovarian failure who were under 40 years of age. A routine cytogenetic test was performed to eliminate chromosomal aberrations as the cause of POI. The DNA was analysed by polymerase chain reaction (PCR) with primers specific to the FMR1 gene region. The PCR products were then separated in denaturing polyacrylamide gels using an ABI Prism 377 sequencer.

RESULTS

Cytogenetic analysis of the samples revealed two X/autosome translocations. DNA analysis identified FMR1 gene premutations in three patients. The frequency of X/autosome translocations in the studied group was 2/40 (5.0%), and the frequency of FMR1 gene premutations was 3/38 cases (7.9%). Thus, genetic tests allowed for the identification of POI in five (12.5%) out of 40 women.

CONCLUSION

FMR1 gene premutation is a common genetic cause of POI.

Cytogenetics of premature ovarian failure: an investigation on 269 affected women

The importance of X chromosome in the aetiology of premature ovarian failure (POF) is well-known but in many cases POF still remains idiopathic. Chromosome aneuploidy increase is a physiological phenomenon related to aging, but the role of low-level sex chromosome mosaicism in ovarian function is still undiscovered. Standard cytogenetic analysis was carried out in a total of 269 patients affected by POF: 27 chromosomal abnormalities were identified, including X chromosome and autosomal structural and numerical abnormalities. In 47 patients with 46,XX karyotype we performed interphase FISH using X alpha-satellite probe in order to identify X chromosome mosaicism rate. Aneuploidy rate in the patient group was significantly higher than the general population group. These findings underline the importance of X chromosome in the aetiology of POF and highlight the potential role of low-level sex chromosome mosaicism in ovarian aging that may lead to a premature onset of menopause.

Four sisters compound heterozygotes for the pre- and full mutation in fragile X syndrome and a complete inactivation of X-functional chromosome: implications for genetic counseling

Fragile X syndrome (FXS) is a neurodevelopmental disorder and a leading monogenic form of cognitive impairment and autism. It is the most common form of inherited mental retardation in males and a significant cause of mental retardation in females. It is caused by the instability and subsequent expansion of the CGG repeat in the promoter region of the FMR1 (fragile X mental retardation 1) gene at Xq27.3. We describe a double consanguineous family with four sisters compound heterozygotes for the full and pre-mutation CGG repeat size. The index case shows clinical features of the affected males with profound mental retardation; the other three sisters also suffer from mental retardation, ranging from mild to severe. Molecular analysis reveals very similar ranges for the CGG expansions for both chromosomes in all four sisters. The phenotypic differences observed in the index case and her sisters are the total inactivation of X premutated chromosome and the total absence of FMRP (fragile X mental retardation protein). This family case raises important issues for genetic counseling in families with consanguinity and with cases of idiopathic mental retardation.

Premature ovarian failure and FMR1 gene mutations: an update

Screening for fragile X premutations is recommended for the routine work-up for any woman presenting with premature ovarian failure (POF). The reason for this is that women with POF have an approximate 5% chance of conceiving and this possibility may be increased further in the FRAXA premutation subgroup. Women need to be informed if they are at risk of having a child with fragile X syndrome. In addition, the identification of a family in which the fragile X repeat site is expanded can lead to the identification of other female family members at risk of transmitting fragile X syndrome. The identification of an index case should therefore trigger genetic counseling throughout the pedigree according to the wishes of the family.

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.

Aetiology of premature ovarian failure

Premature ovarian failure (POF) is the occurrence of hypergonadotropic hypoestrogenic amenorrhoea in women under the age of 40 years. POF is idiopathic in 74–90% of cases but can be familial (4–33%) or sporadic. The known causes are: genetic aberrations; autoimmune ovarian damage; iatrogenic following surgery, radiotherapy or chemotherapy; environmental factors (viruses, toxins, etc.); and metabolic (galactosaemia, 17 OH deficiency, etc.) Genetic aberrations could involve the X chromosome (monosomy, trisomy or translocations) or be autosomal. Genetic mechanisms include reduced gene dosage and non-specific chromosome effect impairing meiosis, decreasing the pool of primordial follicles and increasing atresia due to apoptosis or failure of follicle maturation. The genes for POF-1 are localized to Xq 21.3–Xq27 and for POF-2 to Xq13.3–21.1. The FMR1 gene is responsible for the fragile X syndrome. It occurs due to CGG expansion of more than 55 repeats at the 5′UTR (Xq 27.3), which is associated with gene silence resulting in mental retardation in males, and POF in female carriers. Autoimmune ovarian damage is caused by the alteration of T-cell subsets and T-cell-mediated injury, increase of autoantibody producing B-cells and a low number of effector supressor/cytotoxic lymphocyte and a decrease of number and activity of natural killer cells. POF can be associated with other non-endocrine and endocrine diseases. The mutations of AIRE gene are responsible for polyendocrinopathies (APS I–III). As the cause of POF is unknown in the majority of cases and the number of women with POF is increasing, the primary goal of scientific groups worldwide should be focused on the study of the aetiology of POF.

Very early premature ovarian failure in two sisters compound heterozygous for the FMR1 premutation

Expansion of the CGG trinucleotide repeat in the 5' untranslated region of the fragile X mental retardation 1 (FMR1) gene within the premutation range is one of the known genetic factors associated with premature ovarian failure and earlier age at menopause. Studies have shown that approximately 16-26% of female carriers will develop premature ovarian failure, and current research is focussed on the identification of molecular factors that predict its occurrence in female carriers. In this report we present two sisters who are compound heterozygous for a premutation, and who were referred because of very early menopause, occurring at the age of 17 years in the youngest sister. Premature ovarian failure associated with FMR1 premutation at such an early age has not been reported in the literature before.

Reproductive health of adolescent girls who carry the FMR1 premutation: expected phenotype based on current knowledge of fragile x-associated primary ovarian insufficiency

The fragile X mental retardation 1 (FMR1) gene, located on the X chromosome, is characterized by a dynamic CGG repeat expansion in the 5' untranslated region. It has long been known that female carriers of the FMR1 premutation allele (55-199 CGG) are at risk for passing the FMR1 full mutation (> or =200 repeats) to their offspring, which results in a common form of mental retardation known as fragile X syndrome. The FMR1 premutation allele, however, also places female carriers at significantly increased risk for prematurely diminished ovarian function, which we refer to as fragile X-associated primary ovarian insufficiency (FXPOI). Although of particular concern for younger women, to date, studies of FXPOI have been restricted to women > or =18 years of age and have not specifically addressed ovarian reserve and menstrual cycle characteristics among adolescent carriers. We discuss the expected reproductive phenotype among FMR1 premutation carriers during adolescence, the associated health considerations based on our current understanding of FXPOI, and the directions for future studies.

Variation in bone morphogenetic protein 15 is not associated with spontaneous human dizygotic twinning

BACKGROUND

Spontaneous dizygotic (DZ) twinning in humans is under genetic control. In sheep, heterozygous loss of function mutations in bone morphogenetic protein 15 (BMP15) increase ovulation and hence twinning rates.

METHODS

To investigate the role of BMP15 in human twinning, we typed 14 common variants, 4 rare novel variants initially detected by sequencing 279 mothers of DZ twins (MODZT) and 17 variants previously associated with premature ovarian failure (POF) in 933 DZ twinning families. We also typed five additional POF associated GDF9 variants.

RESULTS

There was some evidence for association between DZ twinning and a common intronic BMP15 variant (rs3897937), but this was not significant after correction for multiple testing. Three of the four novel variants (p.Pro174Ser, p.Ala311Thr and p.Arg392Thr) occurred in 1-5 MODZT but were not detected in 1512 controls. We also detected three POF associated mutations in both BMP15 and GDF9 at low frequencies in MODZT and controls.

CONCLUSIONS

We conclude that neither rare nor common BMP15 variants play a significant role in the variation in human DZ twinning.

The fragile X continuum: new advances and perspectives

Fragile X syndrome is the world's most common hereditary cause of intellectual disability in men and to a lesser extent in women. The disorder is caused by the silencing of a single gene on the X chromosome, the Fragile X Mental Retardation Gene-1. A substantial body of research across the disciplines of molecular genetics, child psychiatry and developmental neuroscience bears testament to a decade of exciting and innovative science that has advanced our knowledge about the fragile X 'signature' or influence across cognitive and social development. The core aims of this review are to first discuss fragile X syndrome and premutation involvement in the context of current advances that demonstrate the dynamic nature of the genotype on phenotypic outcomes. Second, to discuss the implications of these recent advances for the development of clinical and educational interventions and resource tools that target specific phenotypic 'signatures' within the fragile X continuum.

Spontaneous premature ovarian failure: management challenges

Premature ovarian failure (POF) generally describes a syndrome consisting of amenorrhea, sex steroid deficiency, and elevated/menopausal levels of ganadotropins in a woman aged more than two standard deviations below the mean age at menopause estimated for the reference population. Numerous questions relating to this condition remain unanswered, and several important management issues are yet to be addressed. The challenges posed by this important condition range from difficulties with nomenclature to the absence of standardized diagnostic criteria and management guidelines. In the present paper we discuss the management of spontaneous premature ovarian failure, highlight the challenging issues, review the current literature and propose a practical management outline based on our local practice. Women with POF have unique needs that require special attention. There is an urgent need for a more suitable terminology and evidence-based guidelines on which to establish the diagnosis and manage this difficult condition.

Anti-Mullerian hormone indicates early ovarian decline in fragile X mental retardation (FMR1) premutation carriers: a preliminary study

BACKGROUND

Women who carry the fragile X mental retardation (FMR1) premutation are at risk for fragile X-associated primary ovarian insufficiency. Past studies have shown that carriers who are still cycling have increased levels FSH compared with non-carriers. As anti-Mullerian hormone (AMH) has been shown as an excellent marker of ovarian decline, we examined AMH levels among premutation carriers to characterize their ovarian function.

METHODS

We determined the level of FSH and AMH in serum samples collected during early follicular phase from women who carried longer FMR1 repeat alleles (defined as >or=70 repeats, n = 40) and those with shorter repeat alleles (<70 repeats, n = 75), identified by DNA analysis. Comparisons were made stratified by age and carrier status.

RESULTS

For all age groups, AMH levels were significantly lower among longer repeat allele carriers compared to shorter repeat allele carriers (P = 0.002, 0.006 and 0.020 for women ages 18-30, 31-40 and 41-50 years, respectively). In contrast, increased FSH indicative of early ovarian decline was only evident for longer repeat allele carriers aged 31-40 years (P = 0.089, 0.001 and 0.261 for women ages 18-30, 31-40 and 41-50 years, respectively).

CONCLUSIONS

These preliminary data suggest that AMH levels indicate early ovarian decline among women with longer FMR1 repeat alleles; moreover, AMH appears to be a better marker than FSH in identifying this early decline.

Dynamic mutations as digital genetic modulators of brain development, function and dysfunction

A substantial portion of the human genome has been found to consist of simple sequence repeats, including microsatellites and minisatellites. Microsatellites, tandem repeats of 1-6 nucleotides, form the template for dynamic mutations, which involve heritable changes in the lengths of repeat sequences. In recent years, a large number of human disorders have been found to be caused by dynamic mutations, the most common of which are trinucleotide repeat expansion diseases. Dynamic mutations are common to numerous nervous system disorders, including Huntington's disease, various spinocerebellar ataxias, fragile X syndrome, fragile X tremor/ataxia syndrome, Friedreich ataxia and other neurodegenerative disorders. The involvement of dynamic mutations in brain disorders will be reviewed, with a focus on the large group caused by CAG/glutamine repeat expansions. We will also outline a proposed role of tandem repeat polymorphisms (TRPs), with unique 'digital' genetic distributions, in modulating brain development and normal function, so as to generate additional mutational diversity upon which natural selection may act.

Examination of reproductive aging milestones among women who carry the FMR1 premutation

BACKGROUND

The fragile X premutation is characterized by a large CGG repeat track (55-199 repeats) in the 5' UTR of the FMR1 gene. This X-linked mutation leads to an increased risk for premature ovarian failure; interestingly, the association of repeat size with risk is non-linear. We hypothesize that the premutation-associated ovarian insufficiency is due to a diminished oocyte pool and examined reproductive aging milestones by repeat size group to determine if the same non-linear association is observed.

METHODS

We analyzed cross-sectional reproductive history questionnaire data from 948 women with a wide range of repeat sizes.

RESULTS

We have confirmed the non-linear relationship among premutation carriers for ovarian insufficiency. The mid-range repeat size group (80-100 repeats), not the highest group, had an increased risk for: altered cycle traits (shortened cycle length, irregular cycles and skipped cycles), subfertility and dizygotic twinning. Smoking, a modifiable risk, decreased the reproductive lifespan of women with the premutation by about 1 year, similar to its effect on non-carriers. As expected, premutation carriers were found to be at an increased risk for osteoporosis.

CONCLUSIONS

Possible molecular mechanisms to explain the non-linear repeat size risk for ovarian insufficiency are discussed.

Elevated FMR1 mRNA in premutation carriers is due to increased transcription

Carriers of premutation alleles (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene have levels of FMR1 mRNA that are elevated by as much as 10-fold in peripheral blood leukocytes and CNS tissue. The excess expanded-repeat mRNA, per se, is now believed to result in forms of clinical involvement that are largely restricted to premutation carriers, including the neurodegenerative disorder, fragile X-associated tremor/ataxia syndrome (FXTAS). Although evidence to date suggests that the elevated mRNA is not due to increased stability, the basis for the increase is not known. In the current study, we have determined the relative transcriptional activities of premutation and normal FMR1 alleles using a highly sensitive nuclear run-on assay that involves immunocapture of digoxigenin-modified run-on transcripts followed by PCR amplification of the nascent transcripts. Using the nuclear run-on approach, we demonstrate that the rate of run-on synthesis of FMR1 transcripts is increased in premutation alleles. The current run-on assay should be broadly applicable to studies of other genes with promoters of weak to moderate strength. The fraction of capped FMR1 mRNA remains unaltered for premutation transcripts, indicating that elevated message levels are not due to premature escape from the cotranscriptional capping process. We also show that, in contrast to the situation with myotonic dystrophy, there is no net nuclear sequestration of premutation FMR1 mRNA. Finally, we have demonstrated that AGG interruptions within the CGG repeat element do not influence FMR1 mRNA levels.