Cytosine-guanine-guanine repeats of FMR1 gene negatively affect ovarian reserve and response in Chinese women

RESEARCH QUESTION

Do cytosine-guanine-guanine (CGG) repeats of the FMR1 gene affect ovarian function, ovarian response and assisted reproductive technology (ART) outcomes in Chinese women?

DESIGN

A retrospective cohort study of 5869 women who underwent 8932 ART cycles at Women's Hospital, School of Medicine, Zhejiang University between January 2018 and June 2021. Basic hormone level, oocyte yield, embryo quality and the rate of live birth were considered as main outcome measures to evaluate the effects of CGG repeats on ovarian function, ovarian response and ART outcomes.

RESULTS

The CGG repeats were negatively related to serum anti-Müllerian hormone (AMH), oestradiol, antral follicle count (AFC) and oocyte yield. A significant association was found between serum AMH, oestradiol and AFC even after age was controlled for. No statistically significant association, however, was found between CGG repeats and embryo quality or live birth rate. Ovarian function mediated the association between CGG repeats and ovarian response.

CONCLUSION

Increased CGG repeats on the FMR1 gene were associated with diminished ovarian function and poor ovarian response, and ovarian function played an intermediary role in the relationship between CGG repeats and ovarian response.

High normal sized CGG repeat on the FMR1 gene reduces live birth rates after in vitro fertilization in Han Chinese

Substantial evidence now suggests an association between the FMR1 genotype and female fertility. The aim of this study was to determine whether a high normal FMR1 allele (35-54 repeats) affects in vitro fertilization (IVF) outcomes in Chinese women. A total of 120 women with 210 IVF cycles were retrospectively recruited in this study. The patients were divided into two groups based on the FMR1 repeat lengths at allele 2 (normal repeat group: <35 repeats; high repeat group: 35-54 repeats). The observed primary outcomes were the clinical pregnancy rate and live birth rate. No associations were observed between the high normal FMR1 allele and lower clinical pregnancy rate or live birth rate after adjusting for maternal age, education, work status, duration of infertility and number of embryos transferred (aOR 0.633, 95% CI 0.249-1.601, p = 0.337; aOR 0.325, 95% CI 0.094-1.118, p = 0.075; respectively). However, after additionally adjusting for anti-Müllerian hormone (AMH) level, there was a weak but significant association between high normal sized CGG repeats and a lower live birth rate (aOR 0.218, 95% CI 0.057-0.836, p = 0.026). The rate of available embryos showed a decreasing trend in patients with a high normal FMR1 allele, although the difference was not statistically significant after adjusting for maternal age, education, work status, duration of infertility and AMH level (aOR 0.905, 95% CI 0.810-1.011, p = 0.078). Furthermore, the number of CGG repeats in either allele was not associated with the live birth rate after adjusting for all confounding factors (aOR 0.832, 95% CI 0.677-1.023, p = 0.081; aOR 0.865, 95% CI 0.651-1.148, p = 0.315; respectively). In addition, no significant differences were found in the rates of good-quality embryos (p = 0.263), miscarriage (p = 0.861) or cycle cancellation (p = 0.295) between the groups. Taken together, in the Chinese population, individuals with high normal sized CGG repeats on the FMR1 gene have a higher risk of reduced live birth rates in childbearing age. Therefore, we recommend enhanced screening for fragile X syndrome in women of childbearing age in China. This study also suggests that the association between the FMR1 genotype and fertility in Chinese women merits further research.

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.

Does theFMR1 gene affect IVF success?

FMR1 CGG trinucleotide repeat expansions are associated with Fragile X syndrome (full mutations) and primary ovarian insufficiency (premutation range); the effect of FMR1 on the success of fertility treatment is unclear. The effect of FMR1 CGG repeat lengths on IVF outcomes after ovarian stimulation was reviewed. PubMed was searched for studies on IVF-related outcomes reported by FMR1 trinucleotide repeat length published between 2002 and December 2017. For women with CGG repeats in the normal (<45 CGG), intermediate range (45-54 CGG), or both, research supports a minimal effect on IVF outcomes, including pregnancy rates; although one study reported lower oocyte yields after IVF stimulation in women with lower CGG repeat lengths and normal ovarian reserve. Meta-analysis revealed no association within subcategories of normal repeat length (<45 CGG) and IVF pregnancy rates (summary OR 1.0, 95% CI 0.87 to 1.15). Premutation carriers (CGG 55-200) may have reduced success with IVF treatment (lower oocyte yield) than women with a normal CGG repeat length or a full mutation, although findings are inconsistent. Direct implications of the repeat length on inheritance and the risk of Fragile X syndrome have been observed. Patients may require clinical and psychological counselling, and further preimplantation genetic testing options should be considered. Thus, there are clinical and psychological counseling implications for patients and potential further patient decisions regarding preimplantation genetic testing options.

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.

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.

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.

The Bologna criteria for poor ovarian response: a contemporary critical appraisal

Postponement of child bearing and maternal age at first pregnancy are on the rise, contributing considerably to an increase in age-related infertility and the demand for assisted reproductive technologies (ART) treatment. This brings to the infertility clinics many women with low ovarian reserve and poor ovarian response (POR) to conventional stimulation. The Bologna criteria were released to standardize the definition of POR and pave the way for the formulation of evidence-based, efficient modalities of treatment for women undergoing IVF-ET. More than four years have passed since the introduction of these criteria and the debate is still ongoing whether a revision is due. Women with POR comprise several sub-groups with diverse baseline distinctiveness, a major issue that has fueled the discussion. Although antral follicle count (AFC) and anti-Müllerian hormone (AMH), are considered good predictors of ovarian reserve, their threshold values are still not universally standardized. Different definitions for sonographic AFC and diverse assays for AMH are held responsible for this delay in standardization. Adding established risk factors to the criteria will lead to more reliable and reproducible definition of a POR, especially in young women. The original criteria did not address the issue of oocyte quality, and the addition of risk factors may yield specific associations with quality vs. quantity. Patient’s age is the best available criterion, although limited, to predict live-birth and presumably oocyte quality. High scale studies to validate these criteria are still missing while recent evidence raises concern regarding over diagnosis.

Early decline in functional ovarian reserve in young women with low (CGGn < 26) FMR1 gene alleles

Mouse fmr1 models, and recent cross-sectional human data, suggest that different triple CGGn ranges of the fragile X mental retardation 1 (FMR1) gene are associated with variations in ovarian aging and infertility treatment outcomes. The FMR1 mutation affecting reproductive function most negatively in humans is the so-called low mutation, characterized by CGGn < 26. We here present a first longitudinal study of selected young women with normal functional ovarian reserve (FOR). In a prospective cohort study, we selected among 233 young oocyte donors (mean age 24.8 ± 3.3 years) as study population of 66 who had more than 1 anti-Müllerian hormone (AMH) level drawn over a 4-year period. AMH curves, as reflection of FOR, were then statistically compared between women with and without low FMR1 alleles. Biallelic low FMR1 (hom-low/low) donors already at initial presentation demonstrated significantly lower FOR than donors with biallelic normal (norm) FMR1 (CGGn = 26-34; P = 0.001). Although monoallelic low FMR1 at initial presentation was not yet associated with decreased FOR, it over 4 years did demonstrate significantly enhanced declines in FOR (P = 0.046). Including repeat measurements, low/low (P = 0.006) and high/high (CGGn > 34) alleles (P < 0.001) demonstrated lower FOR by AMH than norm donors. Even monoallelic low FMR1 alleles are, thus, already at young female ages associated with accelerated declines in FOR. Low FMR1 alleles, therefore, potentially represent a screening tool for women at genetic risk toward premature ovarian senescence, representing in all races circa 10% of the female population.

Diminished ovarian reserve is not observed in infertility patients with high normal CGG repeats on the fragile X mental retardation 1 (FMR1) gene

STUDY QUESTION

Does an association exist between high normal numbers of CGG trinucleotide repeats on the fragile X mental retardation 1 (FMR1) gene and diminished ovarian reserve (DOR)?

SUMMARY ANSWER

This large data set demonstrated that a high normal number of CGG repeats (35-54 repeats) on the FMR1 gene was not significantly correlated with DOR.

WHAT IS KNOWN ALREADY

The FMR1 premutation (55-200 repeats) is a known cause of primary ovarian insufficiency. However, the relationship between high normal CGG repeat numbers (35-54 repeats) and ovarian reserve has yet to be conclusively demonstrated.

STUDY DESIGN, SIZE, DURATION

This is a retrospective data analysis conducted between January 2012 and February 2014 that included 1287 women. Over 1140 women had complete data.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All women, excluding oocyte donors, who presented to a large private practice specializing in reproductive endocrinology and infertility for treatment and who underwent both fragile X and ovarian reserve testing were included. All fragile X testing was performed using triplet repeat PCR, with confirmation of positives by Southern blot. CGG repeat numbers from both alleles were recorded, and the allele with the higher number of repeats was used for statistical calculations. We did not differentiate between patients with one or two high normal alleles. Women with >54 CGG repeats were excluded from the analysis. For our analysis, we considered both a 'high normal' number of CGG repeats (35-44) and an intermediate number of GCC repeats (45-54) as 'high normal'. Ovarian reserve testing was carried out on Cycle Day 2 or 3 and included measurements of FSH, anti-Müllerian hormone (AMH) and antral follicle count (AFC). A generalized linear regression model assuming gamma distribution and log link function that controlled for age was used to assess correlation between CGG repeat number and FSH, AMH and AFC.

MAIN RESULTS AND THE ROLE OF CHANCE

As expected, there was a significant correlation between increasing age and increasing FSH and decreasing AFC and AMH for the patients in this study. For every 1-year increase in age, FSH increased by a factor of 1.04, AFC decreased by a factor of 0.93 and AMH decreased by a factor of 0.89. After controlling for age, there was no significant correlation between FMR1 CGG trinucleotide repeat number and FSH (P = 0.23), AFC (P = 0.14) or AMH (P = 0.53). Three subgroup analyses were also performed. We found a significant relationship between increasing CGG repeat number and decreasing AMH levels (P = 0.01) in women >44 years old. The second subgroup analysis included only Caucasian patients and found no significant correlation between CGG repeat number and DOR. In a subgroup analysis comparing women with at least one allele <26 repeats, at least one allele >35 and women with both alleles between 29 and 32, there were no significant associations regarding ovarian reserve in any of these groups.

LIMITATIONS, REASONS FOR CAUTION

One limitation of this study is that it involved a heterogeneous population of infertile women with mixed diagnoses. Factors that could affect ovarian reserve, such as medical comorbidities, prior surgeries, family history and endometriosis, were not accounted for. Finally, there was a lack of racial diversity, with Caucasians representing 67.8% of the total population.

WIDER IMPLICATIONS OF THE FINDINGS

The findings of this study are generalizable to an infertility population and are in line with several previously published studies. Women who are found to have high normal CGG repeat numbers can be counseled that this is not causative for DOR. Further studies are needed to investigate whether increasing CGG repeat numbers are associated with ovarian responsiveness to gonadotrophin stimulation or IVF outcome.

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.

Utilizing FMR1 gene mutations as predictors of treatment success in human in vitro fertilization

CONTEXT

Mutations of the fragile X mental retardation 1 (FMR1) gene are associated with distinct ovarian aging patterns.

OBJECTIVE

To confirm in human in vitro fertilization (IVF) that FMR1 affects outcomes, and to determine whether this reflects differences in ovarian aging between FMR1 mutations, egg/embryo quality or an effect on implantation.

DESIGN, SETTING, PATIENTS

IVF outcomes were investigated in a private infertility center in reference to patients' FMR1 mutations based on a normal range of CGG(n = 26-34) and sub-genotypes high (CGG(n>34)) and low (CGG(<26)). The study included 3 distinct sections and study populations: (i) A generalized mixed-effects model of morphology (777 embryos, 168 IVF cycles, 125 infertile women at all ages) investigated whether embryo quality is associated with FMR1; (ii) 1041 embryos in 149 IVF cycles in presumed fertile women assessed whether the FMR1 gene is associated with aneuploidy; (iii) 352 infertile patients (< age 38; in 1st IVF cycles) and 179 donor-recipient cycles, assessed whether the FMR1 gene affects IVF pregnancy chances via oocyte/embryo quality or non-oocyte maternal factors.

INTERVENTIONS

Standardized IVF protocols.

MAIN OUTCOME MEASURES

Morphologic embryo quality, ploidy and pregnancy rates.

RESULTS

(i) Embryo morphology was reduced in presence of a low FMR1 allele (P = 0.032). In absence of a low allele, the odds ratio (OR) of chance of good (vs. fair/poor) embryos was 1.637. (ii) FMR1 was not associated with aneuploidy, though aneuploidy increased with female age. (iii) Recipient pregnancy rates were neither associated with donor age or donor FMR1. In absence of a low FMR1 allele, OR of clinical pregnancy (vs. chemical or no pregnancy) was 2.244 in middle-aged infertility patients.

CONCLUSIONS

A low FMR1 allele (CGG(<26)) is associated with significantly poorer morphologic embryo quality and pregnancy chance. As women age, low FMR1 alleles affect IVF pregnancy chances by reducing egg/embryo quality by mechanisms other than embryo aneuploidy.

FMR1-dependent variability of ovarian aging patterns is already apparent in young oocyte donors

BACKGROUND

Hypothesizing that redundant functional ovarian reserve (FOR) at young ages may clinically obfuscate prematurely diminished FOR (PDFOR), we investigated in young oocyte donors genotypes and sub-genotypes of the FMR1 gene, in prior studies associated with specific ovarian aging patterns, and determined whether they already at such young age were associated with variations in ovarian reserve (OR). We also investigated racial as well as FMR1 associations with menarcheal age in these donors.

METHODS

In a cohort study we investigated 157 oocyte donor candidates and, based on the 95% CI of AMH, divided them into normal age-specific (AMH greater or equal to 2.1 ng/mL; n = 121) and PDFOR (AMH < 2.1 ng/mL; n = 36). We then assessed associations between numbers of trinucleotide repeat (CGGn) on the FMR1 gene and FOR (based on anti-Müllerian hormone, AMH).

RESULTS

FMR1 did not associate with AMH overall. Amongst 36 donors with PDFOR, 17 (42%) presented with at least one low (CGGn < 26 ) allele. Remaining donors with normal FOR presented with significantly more CGGn greater or equal to 26 (73.6% vs. 26.4%; P = 0.024) and higher AMH (P = 0.012). This finding was mostly the consequence of interaction between FMR1 (CGGn < 26 vs. CGGn greater or equal to 26) and race (P = 0.013), with Asians most responsible (P = 0.009). Menarcheal age was in donors with normal FOR neither associated with race nor with FMR1 status. In donors with PDFOR race was statistically associated with CGGn (P = 0.018), an association primarily based on significantly delayed age of menarche in African donors with CGGn < 26 in comparison to African donors with CGGn greater or equal to 26 (P = 0.019), and Caucasian (P = 0.017) and Asian donors (P = 0.025) with CGGn < 26.

CONCLUSIONS

CGGn on FMR1 already at young ages affects FOR, but is clinically apparent only in cases of PDFOR. Screening for low FMR1 CGGn < 26 at young age, thus, appears predictive of later PDFOR.