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

Low and High-Normal FMR1 Triplet Cytosine, Guanine Guanine Repeats Affect Ovarian Reserve and Fertility in Women Who Underwent In Vitro Fertilization Treatment? Results from a Cross-Sectional Study

Dynamic mutations in the 5' untranslated region of FMR1 are associated with infertility. Premutation alleles interfere with prenatal development and increase infertility risks. The number of CGG repeats that causes the highest decrease in ovarian reserves remains unclear. We evaluated the effect of FMR1 CGG repeat lengths on ovarian reserves and in vitro fertilization (IVF) treatment outcomes in 272 women with alleles within the normal range. FMR1 CGG repeat length was investigated via PCR and capillary electrophoresis. Alleles were classified as low-normal, normal, and high-normal. Serum levels of follicle-stimulating hormone and anti-Mullerian hormone (AMH) in the follicular phase of the menstrual cycle were measured, and antral follicles (AFC) were counted. IVF outcomes were collected from medical records. Regarding FMR1 CGG repeat length alleles, 63.2% of women presented at least one low-normal allele. Those carrying low-normal alleles had significantly lower AMH levels than women carrying normal or high-normal alleles. Low-normal/low-normal genotype was the most frequent, followed by low-normal/normal and normal/normal. A comparison of ovarian reserve markers and reproductive outcomes of the three most frequent genotypes revealed that AFC in the low-normal/normal genotype was significantly lower than the low-normal/low-normal genotype. The low number of FMR1 CGG repeats affected AMH levels and AFC but not IVF outcomes per cycle of treatment.

Altered GnRH neuron and ovarian innervation characterize reproductive dysfunction linked to the Fragile X messenger ribonucleoprotein (Fmr1) gene mutation

Introduction

Mutations in the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene cause Fragile X Syndrome, the most common monogenic cause of intellectual disability. Mutations of FMR1 are also associated with reproductive disorders, such as early cessation of reproductive function in females. While progress has been made in understanding the mechanisms of mental impairment, the causes of reproductive disorders are not clear. FMR1-associated reproductive disorders were studied exclusively from the endocrine perspective, while the FMR1 role in neurons that control reproduction was not addressed.

Results

Here, we demonstrate that similar to women with FMR1 mutations, female Fmr1 null mice stop reproducing early. However, young null females display larger litters, more corpora lutea in the ovaries, increased inhibin, progesterone, testosterone, and gonadotropin hormones in the circulation. Ovariectomy reveals both hypothalamic and ovarian contribution to elevated gonadotropins. Altered mRNA and protein levels of several synaptic molecules in the hypothalamus are identified, indicating reasons for hypothalamic dysregulation. Increased vascularization of corpora lutea, higher sympathetic innervation of growing follicles in the ovaries of Fmr1 nulls, and higher numbers of synaptic GABAA receptors in GnRH neurons, which are excitatory for GnRH neurons, contribute to increased FSH and LH, respectively. Unmodified and ovariectomized Fmr1 nulls have increased LH pulse frequency, suggesting that Fmr1 nulls exhibit hyperactive GnRH neurons, regardless of the ovarian feedback.

Conclusion

These results reveal Fmr1 function in the regulation of GnRH neuron secretion, and point to the role of GnRH neurons, in addition to the ovarian innervation, in the etiology of Fmr1-mediated reproductive disorders.

Genetic determination of the ovarian reserve: a literature review

The ovarian reserve is one of the most important indicators of female fertility. It allows for the evaluation of the number of viable oocytes. This parameter is actively used in pregnancy planning and in assisted reproductive technology application, as it determines chances of successful fertilization and healthy pregnancy. Due to increased attention towards diagnostic tests evaluating the ovarian reserve, there has been a growing interest in factors that influence the state of the ovarian reserve. True reasons for pathological changes in the ovarian reserve and volume have not yet been explored in depth, and current diagnostic screening methods often fall short in efficacy. In the following review we analyze existing data relating to the study of the ovarian reserve through genetic testing, determining specific characteristics of the ovarian reserve through genetic profiling. We explore existing studies dedicated to finding specific genetic targets influencing the state of the ovarian reserve.

Age of natural menopause onset in BRCA1/2 carriers - systematic review and meta-analysis

Introduction

Germinal pathogenic variants in BRCA1 and BRCA2 genes are associated with high risk of cancers, including breast, ovary, fallopian tubes and primary peritoneal. Non-oncological implications of germline pathogenic variants in BRCA1 and BRCA2 genes, complicating reproductive health are less described. The influence of BRCA1 and BRCA2 on age of natural menopause remains inconclusive and controversial.

Material and methods

PubMed database was searched for potentially relevant abstracts. Studies which were not case-control, cohort or cross-sectional studies were subsequently excluded. Reference lists from systematic reviews or meta-analyses, dealing with the topic of menopause and BRCA1 and BRCA2 germinal pathogenic variants, were also checked to identify eligible studies. We also included our original, unpublished data from families, affected by BRCA1 or BRCA2 pathogenic variant, consisted of at least two postmenopausal female siblings with differing variant status.

Results and conclusions

Initial database search retrieved 193 abstracts. We identified 4 eligible studies for meta-analysis. Two studies not reporting dispersion measures and not reporting age of natural menopause in control group were left in summary for illustrational purposes, yet were excluded from meta-analysis. 4 studies and our original, unpublished data, combining data from 1535 germinal BRCA1 and BRCA2 pathogenic variant carriers and 3191 control individuals, did not support the hypothesis of association between germinal pathogenic variants of “breast cancer genes” and premature menopause.

Association analysis of FMR1 genetic variants and primary ovarian insufficiency in South Indian women with a novel approach of CGG repeats classification

Around 20-28% of FMR1gene CGG premutation (PM) carriers are at augmented risk towards an infertility related disorder, Fragile X-associated primary ovarian insufficiency (FXPOI). Except the effect of CGG repeats, reports are not available on the mechanism through which the cis-acting variations, namely, SNPs involved in POI susceptibility. Addressing the hypothesis that the FMR1 gene polymorphisms [CGG repeats, rs25731(T > A) and rs4949(A > G)] might increase their individual and combined impact in disease predisposition, we tested the genetic variants in 200 south Indian DNA samples consists of 100 patients and 100 healthy volunteers. We used gene scan method to score the CGG repeat length, and ARMS and RFLP methods to genotype the SNPs. Only 0.5% of each Gray zone and PM alleles were found among patient group, however, no disease association was noticed with repeat length. The rs25731 showed protection [OR:0.32; (0.13-0.76), p = 0.006] and rs4949 reported a 2.5-fold risk towards the disease predisposition [OR:2.46; (1.06-5.74), p = 0.031] but, both found insignificant after Bonferroni correction was done under different Genetic Models. Novel classification of genotype combinations, 'Normal&Variant Homozygote' [OR:2.89,(1.12-7.9), p < 0.05] and 'Allele2-T-G' haplotype block (6%vs.1%, p = 0.08) were noticed to be at marginal risk for POI. We demonstrated a susceptible role of the combined effect of variant allele-G and Allele-2 (repeat allele outside the normal range) for FXPOI. To support our findings of its first kind, further studies with large samples are warranted in understanding the role of FMR1 genetic variants in FXPOI etio-pathophysiology, the outcome might help in providing better reproductive treatment options for females, who are at risk for FXPOI.

The prevalence of CGG repeat expansion mutation in FMR1 gene in the northern Chinese women of reproductive age

BACKGROUND

The prevalence of CGG repeat expansion mutation in FMR1 gene varies among different populations. In this study, we investigated the prevalence of this mutation in women of reproductive age from northern China.

METHODS

A total of 11,891 pre-conceptional or pregnant women, including 5037 pregnant women and 7357 women with the history of spontaneous abortion or induced abortion due to delayed growth of the embryos, were recruited. The number of CGG repeats in FMR1 was measured by the TRP-PCR method. We also offered genetic counseling and prenatal diagnosis to the women carrying pre-mutation or full mutation alleles.

RESULTS

The prevalence of pre-mutation in reproductive women in northern China was 1/410, higher than that in southern China and Korea but lower than that in western countries. We also found that the prevalence of pre-mutation was relatively high (1/320) in women with abortion history.

CONCLUSION

Screening for CGG repeat expansion mutation in FMR1 should be recommended to the women with the history of spontaneous abortion or induced abortion due to delayed growth of the embryos.

Female subfertility

Subfertility is common and affects one in six couples, half of whom lack an explanation for their delay in conceiving. Developments in the diagnosis and treatment of subfertility over the past 50 years have been truly remarkable. Indeed, current generations of couples with subfertility are more fortunate than previous generations, as they have many more opportunities to become parents. The timely access to effective treatment for subfertility is important as many couples have a narrow window of opportunity before the age-related effects of subfertility limit the likelihood of success. Assisted reproduction can overcome the barriers to fertility caused by tubal disease and low sperm count, but little progress has been made in reducing the effect of increasing age on ovarian function. The next 5-10 years will likely see further increases in birth rates in women with subfertility, a greater awareness of lifestyle factors and a possible refinement of current assisted reproduction techniques and the development of new ones. Such progress will bring challenging questions regarding the potential benefits and harms of treatments involving germ cell manipulation, artificial gametes, genetic screening of embryos and gene editing of embryos. We hope to see a major increase in fertility awareness, access to safe and cost-effective fertility care in low-income countries and a reduction in the current disparity of access to fertility care.

Fragile X Syndrome: Introduction

Fragile X syndrome (FXS) is one of the most common reasons for intellectual disability (ID). First described in the 1940s, it took many years to understand the disease. The awe-inspiring breakthroughs in both science and technology facilitated the recognition of the unique inheritance pattern and the genetic mechanism of fragile X. In this chapter we describe the history and evolution of our understanding of FXS as mirrored by advances in genetics.

Fragile X syndrome: a review of clinical and molecular diagnoses

Background

Fragile X Syndrome (FXS) is the second cause of intellectual disability after Down syndrome and the most prevalent cause of intellectual disability in males, affecting 1:5000–7000 men and 1:4000–6000 women. It is caused by an alteration of the FMR1 gene, which maps at the Xq27.3 band: more than 99% of individuals have a CGG expansion (>200 triplets) in the 5′ UTR of the gene, and FMR1 mutations and duplication/deletion are responsible for the remaining (<1%) molecular diagnoses of FXS. The aim of this review was to gather the current clinical and molecular knowledge about FXS to provide clinicians with a tool to guide the initial assessment and follow-up of FXS and to offer to laboratory workers and researchers an update about the current diagnostic procedures.

Discussion

FXS is a well-known condition; however, most of the studies thus far have focused on neuropsychiatric features. Unfortunately, some of the available studies have limitations, such as the paucity of patients enrolled or bias due to the collection of the data in a single-country population, which may be not representative of the average global FXS population. In recent years, insight into the adult presentation of the disease has progressively increased. Pharmacological treatment of FXS is essentially symptom based, but the growing understanding of the molecular and biological mechanisms of the disease are paving the way to targeted therapy, which may reverse the effects of FMRP deficiency and be a real cure for the disease itself, not just its symptoms.

Conclusions

The clinical spectrum of FXS is wide, presenting not only as an isolated intellectual disability but as a multi-systemic condition, involving predominantly the central nervous system but potentially affecting any apparatus. Given the relative high frequency of the condition and its complex clinical management, FXS appears to have an important economic and social burden.