Premature ovarian failure and FMR1 gene mutations: an update

Premature ovarian insufficiency

The natural lifespan of the ovary is occasionally interrupted by pathological processes; some are known, but many are unknown. Premature ovarian insufficiency (POI) can be a devastating diagnosis for an adolescent or for someone who has yet to start a family. Common causes of POI include genetic and chromosomal defects, autoimmune damage, and cancer treatments. Knowledge of the pathogenesis of this condition and an awareness of contemporary hormone replacement and fertility options are required to design a multidisciplinary therapeutic approach comprising reproductive medicine, endocrinology, clinical psychology, and assisted fertility expertise.

Mtor inhibition by INK128 extends functions of the ovary reconstituted from germline stem cells in aging and premature aging mice

Stem cell transplantation has been generally considered as promising therapeutics in preserving or recovering functions of lost, damaged, or aging tissues. Transplantation of primordial germ cells (PGCs) or oogonia stem cells (OSCs) can reconstitute ovarian functions that yet sustain for only short period of time, limiting potential application of stem cells in preservation of fertility and endocrine function. Here, we show that mTOR inhibition by INK128 extends the follicular and endocrine functions of the reconstituted ovaries in aging and premature aging mice following transplantation of PGCs/OSCs. Follicular development and endocrine functions of the reconstituted ovaries by transplanting PGCs into kidney capsule of the recipient mice were maintained by INK128 treatment for more than 12 weeks, in contrast to the controls for only about 4 weeks without receiving the mTOR inhibitors. Comparatively, rapamycin also can prolong the ovarian functions but for limited time. Furthermore, our data reveal that INK128 promotes mitochondrial function in addition to its known function in suppression of immune response and inflammation. Taken together, germline stem cell transplantation in combination with mTOR inhibition by INK128 improves and extends the reconstituted ovarian and endocrine functions in reproductive aging and premature aging mice.

Mutational analysis of theFAM175A gene in patients with premature ovarian insufficiency

RESEARCH QUESTION

The family with sequence similarity 175 member A gene (FAM175A; also known as ABRAXAS1, CCDC98 and ABRA1), a member of the DNA repair family, contributes to the BRCA1 (BRCA1 DNA repair associated)-dependent DNA damage response and is associated with age at natural menopause. However, it remains poorly understood whether sequence variants in FAM175A are causative for premature ovarian insufficiency (POI). The aim of this study was to investigate whether mutations in the gene FAM175A were present in patients with POI.

DESIGN

A total of 400 women with idiopathic POI and 498 control women with regular menstruation (306 age-matched women and 192 women over 40 years old) were recruited. After Sanger sequencing of FAM175A, functional experiments were carried out to explore the deleterious effects of the identified variation. DNA damage was subsequently induced by mitomycin C (MMC), and DNA repair capacity and G2-M checkpoint activation were evaluated by examining the phosphorylation level of H2AX (H2A histone family, member X) and the percentage of mitotic cells, respectively.

RESULTS

One rare single-nucleotide polymorphism, rs755187051 in gene FAM175A, c.C727G (p.L243V), was identified in two patients but absent in the 498 controls. The functional experiments demonstrated that overexpression of variant p.L243V in HeLa cells resulted in a similar sensitivity to MMC-induced damage compared with cells transfected with wild-type FAM175A. Moreover, after treatment with MMC, there were no differences in DNA repair capacity and G2-M checkpoint activation between the mutant and wild-type genes.

CONCLUSION

Our results suggest that the p.L243V variant of FAM175A may not be causative for POI. The contribution of FAM175A to POI needs further exploration.

MiR-219 represses expression of dFMR1 in Drosophila melanogaster

AIMS

Fragile X mental retardation protein (FMRP) plays a vital role in mRNA trafficking and translation inhibition to regulate the synthesis of local proteins in neuronal axons and dendritic terminals. However, there are no reports on microRNA (miRNA)-mediated regulation of FMRP levels in Drosophila. Here, we aimed to identify miRNAs regulating FMRP levels in Drosophila.

MAIN METHODS

Using online software, we predicted and selected 11 miRNAs potentially acting on the Drosophila fragile X mental retardation 1 (dFMR1) transcript. These candidates were screened for modulation of dFMR1 transcript levels at the cellular level using a dual luciferase reporter system. In addition, we constructed a transgenic Drosophila model overexpressing miR-219 in the nervous system and quantified dFMRP by western blotting. The neuromuscular junction phenotype in the model was studied by immunofluorescence staining.

KEY FINDINGS

Among the 11 miRNAs screened, miR-219 and miR-960 reduced luciferase gene activity by binding to the 3'-UTR of the dFMR1 transcript. Mutation of the miR-219 or miR-960 binding sites on the transcript resulted in complete or partial elimination of the miRNA-induced repression. Western blots revealed that dFMRP expression was decreased in the miR-219 overexpression model (Elav>miR-219). Drosophila larvae overexpressing miR-219 showed morphological abnormalities at the neuromuscular junction (increased synaptic boutons and synaptic branches). This finding is consistent with some phenotypes observed in dfmr1 mutants.

SIGNIFICANCE

Our results suggest that miR-219 regulates dFMR1 expression in Drosophila and is involved in fragile X syndrome pathogenesis. Collectively, these findings expand the current understanding of miRNA-mediated regulation of target molecule-related functions.

ESR1, HK3 and BRSK1 gene variants are associated with both age at natural menopause and premature ovarian failure

Background

Premature ovarian failure (POF) is a complex and heterogeneous disorder that is influenced by multiple genetic components. Numerous candidate gene studies designed to identify POF susceptibility loci have been published, but most positive findings have not been confirmed in follow up studies. We sought to determine if sequence variants previously associated with age at natural menopause (AANM) or early menopause (EM) contribute as well to genetic susceptibility to POF.

Methods

Our study was performed on 371 unrelated idiopathic women with POF and 800 women controls, all Chinese Han. Thirty six SNPs from previous genome-wide association studies (GWAS) responsible for AANM or EM and 3 additional SNPs in ESR1, and 2 additional SNPs in PTHB1 were tested using the Sequenom MassARRAY iPLEX platform for genotyping.

Results

Three SNPs - rs2278493 in HK3, rs2234693 in ESR1 and rs12611091 in BRSK1 - showed nominally significant association with POF. Thus, a plausible relationship could exist between ESR1, BRSK1, HK3 and POF.

Conclusions

This largest association study undertaken to determine correlation between POF and AANM/EM revealed three significant SNPs (rs2278493, rs2234693, and rs12611091). All are associated with not only AAWM and EM but also POF. Insights into shared genetic susceptibility between POF and AANM/EM will provide novel entry points for unraveling genetic mechanism involved in ovarian reserve and oocyte aging processes.

A novel assay for evaluating fragile X locus repeats

We have developed a novel fragile X locus repeat assay that is a simple and high-throughput method that, with clinical validation, may be suitable for screening. It uses amplification of the FMR1 trinucleotide repeat region, followed by a hybridization assay to quantify the number of repeats in the amplicons. To our knowledge, this is the first repeat-counting assay that uses fluorescent signals rather than electrophoresis or mass spectrometry as the signaling mechanism. We also report the development of a simple microfluidic electrophoresis reflex test that uses the same amplicons and reduces the need for Southern blots to differentiate homozygous female normal samples from full mutations. The new assay, which is based on a suspension-array hybridization method, was tested on a series of male and female reference samples spanning the range from normal to full mutations. It was also tested on DNA from 1008 dried blood spot samples from pregnant women in their first trimester. The hybridization assay identified 51 of those as potentially expanded alleles of ≥45 repeats or as intermediate or higher in FMR1 repeat classification. Of these screen-positive samples, eight were confirmed by microfluidic electrophoresis as premutations consisting of ≥55 repeats. The FMR1 repeat assay is straightforward to run in high throughput, and the results are in the form of numerical ratios for ease of initial interpretation.

Chromosomal abnormalities in women with premature ovarian failure

Premature ovarian failure is a complex disorder that results in the early loss of ovarian function; however this disease must be separated from early menopause because these patients can sporadically ovulate and in literature are described pregnancies. The aetiology and the patho-physiology of premature ovarian failure are still matter of debate, but is commonly accepted that genetic factors play an important role. This review is aimed to present an overview of known inherited factor implied in the pathogenesis of this disorder to help physician in the counselling of affected pregnant women.