FMR1 CGG Repeats: Reference Levels and Race-Ethnic Variation in Women With Normal Fertility (Study of Women's Health Across the Nation)

Low normal FMR1 genotype in older adult women: Psychological well-being and motor function

The FMR1 gene plays a key role in adult neurogenesis and neuroplasticity, and thus may contribute to age-related health in the population. The current study focused on the "low normal" FMR1 genotype, defined by lower-than-typical numbers of FMR1 CGG repeats (<26), as a potential genetic determinant of age-related health. We characterized the effect of the low normal FMR1 genotype on psychological well-being and motor function in a racially diverse non-clinical sample of older adult women. Women with low CGG repeats were distinguished from those with CGGs falling within the mid-high end of the normal range by reduced performance on multimodal assessments of motor function and psychological well-being, with large effect sizes. Robust continuous associations were also detected between lower CGG repeat length and reduced psychological well-being, balance, and dexterity. Findings suggest that FMR1 may represent an important mediator of individual differences in age-related health; larger epidemiological studies are needed. Given that approximately 23-35% of females carry the low normal genotype, efforts to understand its clinical effects have relevance a broad swath of the aging population.

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.

Novel variants in women with premature ovarian function decline identified via whole-exome sequencing

PURPOSE

To investigate the potential etiologies of premature ovarian insufficiency (POI) and diminished ovarian reserve (DOR).

METHODS

Fourteen women with sporadic POI and 6 women with DOR were enrolled. We used whole-exome sequencing (WES) and bioinformatics analysis to identify variants in a subset of 599 selected POI candidate genes. The identified genes were subjected to gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment and protein-protein interaction (PPI) network analyses to uncover key genes and pathways.

RESULTS

Among the 20 patients, 79 heterozygous variants were detected in 49 genes, which were classified as "likely pathogenic" or "variants of uncertain significance" according to the guidelines of the American College of Medical Genetics and Genomics. Most patients (17/20) carried two or more variants. Monoacylglycerol O-acyltransferase 1 mutations were found in six patients, and cytochrome P450 family 26 subfamily B member 1 and Bardet-Biedl syndrome 9 mutations were each found in four patients. Some variants were shared between DOR and POI. Enrichment analyses showed that the identified genes participate in key ovarian processes, such as follicular development, gonadal development, meiosis, Fanconi anemia, homologous recombination, and transforming growth factor β signaling. A PPI network revealed interactions between these proteins.

CONCLUSION

Premature ovarian function decline may be polygenic, and overlap exists between the genetic backgrounds of DOR and POI. WES and in silico analyses may be a useful clinical tool for etiological diagnosis and risk prediction for high-risk women in the future.

The significance of FMR1 CGG repeats in Chinese women with premature ovarian insufficiency and diminished ovarian reserve

BACKGROUND

Previous studies have shown that there is an association between FMR1 CGG repeats and ovarian dysfunction. The aim of this study is to assess the association between the number of CGG repeats in FMR1 in Chinese patients with premature ovarian insufficiency (POI) and diminished ovarian reserve (DOR).

METHODS

This is a cross-sectional, case-control study, which enrolled 124 patients with POI, 57 patients with DOR and 111 normal menopausal controls. The demographic details along with other clinical data were recorded. The FMR1 CGG repeats were analyzed by polymerase chain reaction and microfluidic capillary electrophoresis.

RESULTS

We could detect two premutation carriers in the POI group (1.6%) and one in the control group (0.9%). No premutation carriers were identified in the DOR group. The frequency of FMR1 premutations was not different between POI or DOR and controls. The most common CGG repeat was 29 and 30, and the repeat length for allele 2 had a secondary peak around 36-39 repeats. The CGG repeats were divided into groups of five consecutive values, and the distribution of allele 1 in the POI group was different from that in the control group (P < 0.001). No statistically significant differences were found for allele 1 between DOR group vs. controls, and for allele 2 between three groups (P > 0.05).

CONCLUSIONS

The study shows that the frequency of FMR1 premutations is relatively low (1.6%) in Chinese women with POI. The distribution of allele 1 CGG repeat in patients with POI showed difference from that in healthy women.

Chinese women with 29-30 FMR1 CGG repeats have an earlier menopause

Purpose: A strong, well-established non-linear relationship exists between fragile X mental retardation (FMR1) premutation and menopausal age. The aim of this study is to evaluate whether this relationship continues into the normal CGG repeat range.Methods: FMR1 CGG repeats of 111 Chinese postmenopausal women from a prospective cohort and the relationship with age at menopause were analyzed. Associations of FMR1 genotypes with annually measured estradiol and follicle stimulating hormone (FSH) levels were also assessed.Results: One premutation and two intermediate carriers were identified, with a prevalence of 0.90% and 1.80%, respectively. The age at menopause differed with statistical significance (p = 0.007) between women carrying bi-allelic 29-30 repeats (49.66 ± 3.26 years) and those carrying a different number of repeats (51.26 ± 2.74 years). Age at menopause among subgroups (≤28, 29-30, and ≥31 repeats) of alleles 1 and 2 were also different (p = 0.014, p = 0.044). FSH trajectories to final menstrual period differed between women with the bi-allelic 29-30 repeats and others (p = 0.019).Conclusions: Women with 29-30 FMR1 CGG repeats may experience menopause approximately 2 years earlier than those carrying ≤28 or ≥31 CGG repeats, and have a longer FSH fluctuant period.

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.

Study of the Genetic Etiology of Primary Ovarian Insufficiency: FMR1 Gene

Menopause is a period of women’s life characterized by the cessation of menses in a definitive way. The mean age for menopause is approximately 51 years. Primary ovarian insufficiency (POI) refers to ovarian dysfunction defined as irregular menses and elevated gonadotrophin levels before or at the age of 40 years. The etiology of POI is unknown but several genes have been reported as being of significance. The fragile X mental retardation 1 gene (FMR1) is one of the most important genes associated with POI. The FMR1 gene contains a highly polymorphic CGG repeat in the 5′ untranslated region of exon 1. Four allelic forms have been defined with respect to CGG repeat length and instability during transmission. Normal (5–44 CGG) alleles are usually transmitted from parent to offspring in a stable manner. The full mutation form consists of over 200 repeats, which induces hypermethylation of the FMR1 gene promoter and the subsequent silencing of the gene, associated with Fragile X Syndrome (FXS). Finally, FMR1 intermediate (45–54 CGG) and premutation (55–200 CGG) alleles have been principally associated with two phenotypes, fragile X tremor ataxia syndrome (FXTAS) and fragile X primary ovarian insufficiency (FXPOI).

Distribution of the FMR1 gene in females by race/ethnicity: women with diminished ovarian reserve versus women with normal fertility (SWAN study)

OBJECTIVE

To study whether reported, but inconsistent, associations between the FMR1 CGG repeat lengths in the intermediate, high normal, or low normal range differentiate women diagnosed with diminished ovarian reserve (DOR) from population controls and whether associations vary by race/ethnic group.

DESIGN

Case-control study.

SETTING

Academic and private fertility clinics.

PATIENT(S)

DOR cases (n = 129; 95 Whites, 22 Asian, 12 other) from five U.S. fertility clinics were clinically diagnosed, with regular menses and no fragile X syndrome family history. Normal fertility controls (n = 803; 386 Whites, 219 African-Americans, 102 Japanese, 96 Chinese) from the United States-based SWAN Study had one or more menstrual period in the 3 months pre-enrollment, one or more pregnancy, no history of infertility or hormone therapy, and menopause ≥46 years. Previously, the SWAN Chinese and Japanese groups had similar FMR1 CGG repeat lengths, thus they were combined.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

FMR1 CGG repeat lengths.

RESULT(S)

Median CGG repeats were nearly identical by case/control group. DOR cases had fewer CGG repeats in the shorter FMR1 allele than controls among Whites, but this was not significant among Asians. White cases had fewer CGG repeats in the shorter allele than Asian cases. No significant differences were found in the high normal/intermediate range between cases and controls or by race/ethnic group within cases in the longer allele.

CONCLUSION(S)

This study refutes prior reports of an association between DOR and high normal/intermediate repeats and confirms an association between DOR and low normal repeats in Whites.