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

Is FMR1 CGG Repeat Number Polymorphism Associated With Phenotypic Variation in the General Population? Report From a Cohort of 5,499 Adults

FMR1 CGG repeat length was assayed in 5499 research participants (2637 men and 2862 women) in the Wisconsin Longitudinal Study (WLS), a population-based cohort. Most past research has focused on clinically-ascertained individuals with expansions in CGG repeats, either those with fragile X syndrome (> 200 CGG repeats), the FMR1 premutation (55-200 repeats), or in the gray zone (variously defined as 45-54 or 41-54 repeats). In contrast, the WLS is a unique source of data that was obtained from an unselected cohort of individuals from the general population for whom FMR1 CGG repeat length was assayed. The WLS is a random sample of one-third of all high school seniors in the state of Wisconsin in 1957. The most recent round of data collection was in 2011; thus, the study spanned over 50 years. Saliva samples were obtained from 69% of surviving members of the cohort in 2008 and 2011, from which CGG repeats were assayed. With one exception, the CGG repeat length of all members of this cohort was below 100 (ranging from 7 to 84). The present study evaluated the genotype-phenotype associations of CGG repeat number and IQ, college graduation, age at menopause, number of biological children, having a child with intellectual or developmental disabilities, and the likelihood of experiencing an episode of depression during adulthood. Linear and curvilinear effects were probed. Although effect sizes were small, significant associations were found between CGG repeat length and high school IQ score, college graduation, number of biological children, age at menopause, and the likelihood of having an episode of depression. However, there was no significant association between repeat length and having a child diagnosed with an IDD condition. This study demonstrates a continuum of phenotype effects with FMR1 repeat lengths and illustrates how research inspired by a rare genetic condition (such as fragile X syndrome) can be used to probe genotype-phenotype associations in the general population.

Curvilinear Association Between Language Disfluency and FMR1 CGG Repeat Size Across the Normal, Intermediate, and Premutation Range

Historically, investigations of FMR1 have focused almost exclusively on the clinical effects of CGG expansion within the categories of the premutation (55-200 CGG repeats) and fragile X syndrome (>200 CGG repeats). However, emerging evidence suggests that CGG-dependent phenotypes may occur across allele sizes traditionally considered within the "normal" range. This study adopted an individual-differences approach to determine the association between language production ability and CGG repeat length across the full range of normal, intermediate, and premutation alleles. Participants included 61 adult women with CGG repeats within the premutation (n = 37), intermediate (i.e., 41-54 repeats; n = 2), or normal (i.e., 6-40 repeats; n = 22) ranges. All participants were the biological mothers of a child with a developmental disorder, to control for the potential effects of parenting stress. Language samples were collected and the frequency of language disfluencies (i.e., interruptions in the flow of speech) served as an index of language production skills. Verbal inhibition skills, measured with the Hayling Sentence Completion Test, were also measured and examined as a correlate of language disfluency, consistent with theoretical work linking language disfluency with inhibitory deficits (i.e., the Inhibition Deficit Hypothesis). Blood samples were collected to determine FMR1 CGG repeat size. A general linear model tested CGG repeat size of the larger allele (allele-2) as the primary predictor of language disfluency, covarying for education level, IQ, age, and CGG repeats on the other allele. A robust curvilinear association between CGG length and language disfluency was detected, where low-normal (∼ <25 repeats) and mid-premutation alleles (∼90-110 repeats) were linked with higher rates of disfluency. Disfluency was not associated with inhibition deficits, which challenges prior theoretical work and suggests that a primary language deficit could account for elevated language disfluency in FMR1-associated conditions. Findings suggest CGG-dependent variation in language production ability, which was evident across individuals with and without CGG expansions on FMR1.

Are expanded alleles of the FMR1 gene related to unexplained recurrent miscarriages?

BACKGROUND

In women with recurrent miscarriages, up to 50 % of those cases remain unexplained. In this study, we evaluated the impact of Cytosine/Guanine/Guanine (CGG)  trinucleotide expansions of the fragile-X mental retardation 1 (FMR1) gene in women with unexplained recurrent miscarriages.

METHODS

This is a prospective case-control pilot study involving 49 women with unexplained recurrent miscarriages and 49 age-matched controls with documented fertility. The case group consisted of women with a history of two or more consecutive miscarriages, in whom no known factor could be identified. The maximum age of recruitment was 40 years. We obtained blood samples that were checked, using polymerase chain reaction with electrophoresis, for the presence of expanded alleles of the FMR1 gene. We further evaluated using sequencing analysis, those women marked as positive. We set the limit at more than 40 repeats.

RESULTS

The repeat sizes of CGG expansion in the FMR1 gene differ significantly in the two population groups (p =0.027). We found four women in the miscarriage group and one in the control group positive for carrying premutation alleles (Odds ratio: 4.267, confidence interval: 0.459-39.629). All the positive cases involved intermediate zone carriers. We found no association between the number of abortions each woman had, and her respective CGG repeat number (p =0.255).

CONCLUSIONS

Many couples are desperately looking for the cause of their recurrent miscarriage suffering. The CGG expanded allele of the FMR1 gene is possibly to be blamed in some of these cases. More studies are needed to support the results of this prototype study. HIPPOKRATIA 2018, 22(3): 132-136.

Expanded alleles of the FMR1 gene are related to unexplained recurrent miscarriages

Up to 50% of recurrent miscarriage cases in women occur without an underlying etiology. In the current prospective case-control study, we determined the impact of CGG trinucleotide expansions of the fragile-X mental retardation 1 (FMR1) gene in 49 women with unexplained recurrent miscarriages. Case group consisted of women with two or more unexplained consecutive miscarriages. Blood samples were obtained and checked for the presence of expanded alleles of the FMR1 gene using PCR. Patients harboring the expanded allele, with a threshold set to 40 repeats, were further evaluated by sequencing. The number of abortions each woman had, was not associated with her respective CGG repeat number (P=0.255). The repeat sizes of CGG expansion in the FMR1 gene were significantly different in the two population groups (P=0.027). All the positive cases involved intermediate zone carriers. Hence, the CGG expanded allele of the FMR1 gene might be associated with unexplained multiple miscarriages; whether such an association is coincidental or causal can be confirmed by future studies using a larger patient cohort.

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.

FMR1 genotype interacts with parenting stress to shape health and functional abilities in older age

This study investigated the association of genotype (CGG repeats in FMR1) and the health and well-being of 5,628 aging adults (mean age = 71) in a population-based study. Two groups were contrasted: aging parents who had adult children with developmental or mental health disabilities (n = 785; the high-stress parenting group) and aging parents of healthy children who did not have disabilities (n = 4843; the low-stress parenting group). There were significant curvilinear interaction effects between parenting stress group and CGG repeats for body mass index and indicators of health and functional limitations, and the results were suggestive of interactions for limitations in cognitive functioning. Parents who had adult children with disabilities and whose genotype was two standard deviations above or below the mean numbers of CGGs had poorer health and functional outcomes at age 71 than parents with average numbers of CGGs. In contrast, parents who had healthy adult children and who had similarly high or low numbers of CGG repeats had better health and functional outcomes than parents with average numbers of CGGs. This pattern of gene by environment interactions was consistent with differential susceptibility or the flip-flop phenomenon. This study illustrates how research that begins with a rare genetic condition (such as fragile X syndrome) can lead to insights about the general population and contributes to understanding of how genetic differences shape the way people respond to environments. © 2017 Wiley Periodicals, Inc.

Correlation of normal-range FMR1 repeat length or genotypes and reproductive parameters

PURPOSE

This study aims to ascertain whether the length of normal-ranged CGG repeats on the FMR1 gene correlates with abnormal reproductive parameters.

METHODS

We performed a retrospective, cross-sectional study of all FMR1 carrier screening performed as part of routine care at a large university-based fertility center from January 2011 to March 2014. Correlations were performed between normal-range FMR1 length and baseline serum anti-Müllerian hormone (AMH), cycle day 3 follicle stimulating hormone (FSH), ovarian volumes (OV), antral follicle counts (AFC), and incidence of diminished ovarian reserve (DOR), while controlling for the effect of age.

RESULTS

Six hundred three FMR1 screening results were collected. One subject was found to be a pre-mutation carrier and was excluded from the study. Baseline serum AMH, cycle day 3 FSH, OV, and AFC data were collected for the 602 subjects with normal-ranged CGG repeats. No significant difference in median age was noted amongst any of the FMR1 repeat genotypes. No significant correlation or association was found between any allele length or genotype, with any of the reproductive parameters or with incidence of DOR at any age (p > 0.05). However, subjects who were less than 35 years old with low/low genotype were significantly more likely to have below average AMH levels compared to those with normal/normal genotype (RR 3.82; 95 % CI 1.38-10.56).

CONCLUSIONS

This large study did not demonstrate any substantial association between normal-range FMR1 repeat lengths and reproductive parameters.

Is FMR1 CGG repeat length a predictor of in vitro fertilization stimulation response or outcome?

OBJECTIVE

To study a broad range of FMR1 CGG repeat lengths and assisted reproduction technology (ART) outcomes.

DESIGN

Retrospective cohort study.

SETTING

Private ART practice.

PATIENT(S)

Fresh autologous ART stimulation cycles.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Oocyte yield, live birth.

RESULT(S)

We screened 14,088 fresh autologous ART cycles from 2012 to 2015, of which 4,690 cycles in 3,290 patients met the inclusion criteria. The FMR1 repeat length was statistically significantly but weakly associated with oocyte yield and other markers of ovarian response. The receiver operating characteristic curve analysis suggested extremely limited predictive ability. Moreover, the FMR1 repeat length was not statistically significantly associated with outcomes in multivariable models, including other markers of ovarian reserve. The FMR1 repeat length was not associated with embryo quality or live birth. Only patient age had a strong ability to predict live birth.

CONCLUSION(S)

The FMR1 repeat length is associated with ART response, but only weakly. It provides no incremental predictive ability beyond the conventionally used predictors, including patient age, antimüllerian hormone concentration, antral follicle count, and follicle-stimulating hormone level. These data suggest a possible role of the FMR1 repeat length within the normal range in ovarian response but demonstrate no clinically relevant indication for testing FMR1 as a predictor of ART outcomes.

Evidence of an age-related correlation of ovarian reserve and FMR1 repeat number among women with "normal" CGG repeat status

PURPOSE

The objective of this analysis is to examine the relationship between Fragile X Mental Retardation 1 gene (FMR1) cytosine-guanine-guanine (CGG) repeat number and ovarian reserve, with a particular focus exclusively on the range of CGG repeat number below the premutation (PM) range (<55 CGG repeats).

METHODS

Our study included female patients who underwent assessment of FMR1 CGG repeat number and serum anti-Mullerian hormone (AMH) in 2009-2014. To examine the association between FMR1 repeat number and serum AMH, we created three summary measures of CGG repeat number for the two alleles-"Sum," "Max," and "Gap" (absolute difference). Using multivariable regression models, controlling for age, we then analyzed the impact of these summary measures on AMH.

RESULTS

A total of 566 patients were included in our study. Using multivariable regression models, we found that the relationship between CGG repeat number and AMH differed depending on age. Specifically, in younger women, AMH increased by 7-8 % (Sum p < 0.01, Max p = 0.04) for every 1 unit increase in CGG repeat number. In contrast, starting at age 40, there was a 3 to 5 % decline in AMH for every 1 unit increase in CGG repeat number (Sum p < 0.01, Max p = 0.04).

CONCLUSIONS

This is the first study to report a statistically significant correlation of ovarian reserve and CGG repeat number in women with <55 CGG repeats. Although these women are generally considered to have a normal phenotype, our data suggest that increasing CGG repeat number within this normal range is associated with a more rapid decline in ovarian reserve.

Maximizing the clinical utility of antimüllerian hormone testing in women's health

Purpose of review

To provide an update on the latest clinical applications of serum antimüllerian hormone (AMH) testing with practical approaches to mitigate the impact of significant variability in AMH results.

Recent findings

Recent studies continue to demonstrate that AMH is the best single serum test for ovarian response management with, at most, a weak-to-moderate age-independent association with live-birth rate and time to conception. Data confirm serum AMH levels improve menopause prediction, monitoring of ovarian damage, and identification of women at risk for several ovary-related disorders such as polycystic ovary syndrome and premature or primary ovarian insufficiency. However, it is now recognized that serum AMH results can have dramatic variability due to common, biologic fluctuations within some individuals, use of hormonal contraceptives or other medications, certain surgical procedures, specimen treatment, assay changes, and laboratory calibration differences. Practical guidelines are provided to minimize the impact of variability in AMH results and maximize the accuracy of clinical decision-making.

Summary

AMH is an ovarian biomarker of central importance which improves the clinical management of women's health. However, with the simultaneous rapid expansion of AMH clinical applications and recognition of variability in AMH results, consensus regarding the clinical cutpoints is increasingly difficult. Therefore, a careful approach to AMH measurement and interpretation in clinical care is essential.

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.

AMH in women with diminished ovarian reserve: potential differences by FMR1 CGG repeat level

PURPOSE

We explored whether AMH, as a surrogate for oocyte supply, varies by FMR1 genotype in women diagnosed with diminished ovarian reserve (DOR), a subset of the Primary Ovarian Insufficiency phenotype. Research is inconsistent on the relationship between AMH and FMR1 repeat length, controlling for age.

METHOD

Seventy-nine cycling women diagnosed with DOR, and without a family history of fragile X syndrome, provided blood for FMR1 and AMH testing. DOR was defined as elevated FSH and/or low AMH and/or low antral follicle count, with regular menses. FMR1 CGG repeats were stratified by the larger allele <35 repeats (n = 70) v. ≥35 repeats (n = 9). Quadratic and linear models were fit to predict log (AMH) controlling for age. The AMH sample used as the outcome variable was drawn at a later date than the diagnostic AMH.

RESULTS

Serum AMH concentration median was 0.30 ng/mL; Ages ranged from 26-43 years. A quadratic model (including age(2)) did not show a relationship with FMR1 CGG level (p-value = 0.25). A linear model of log (AMH), corresponding to an exponential decline of AMH with increasing age, was significantly different, and had a steeper slope, for women with ≥ 35 CGG repeats than women with < 35 repeats (p = 0.035).

CONCLUSION

Findings suggest a greater rate of follicular loss that starts at later ages in women with DOR and ≥ 35 CGG repeats.