Skewed X-chromosome inactivation is associated with primary but not secondary ovarian failure

Epigenetic regulation in premature ovarian failure: A literature review

Premature ovarian failure (POF), or premature ovarian insufficiency (POI), is a multifactorial and heterogeneous disease characterized by amenorrhea, decreased estrogen levels and increased female gonadotropin levels. The incidence of POF is increasing annually, and POF has become one of the main causes of infertility in women of childbearing age. The etiology and pathogenesis of POF are complex and have not yet been clearly elucidated. In addition to genetic factors, an increasing number of studies have revealed that epigenetic changes play an important role in the occurrence and development of POF. However, we found that very few papers have summarized epigenetic variations in POF, and a systematic analysis of this topic is therefore necessary. In this article, by reviewing and analyzing the most relevant literature in this research field, we expound on the relationship between DNA methylation, histone modification and non-coding RNA expression and the development of POF. We also analyzed how environmental factors affect POF through epigenetic modulation. Additionally, we discuss potential epigenetic biomarkers and epigenetic treatment targets for POF. We anticipate that our paper may provide new therapeutic clues for improving ovarian function and maintaining fertility in POF patients.

Tet1 Deficiency Leads to Premature Ovarian Failure

Tet enzymes participate in DNA demethylation and play critical roles in stem cell pluripotency and differentiation. DNA methylation alters with age. We find that Tet1 deficiency reduces fertility and leads to accelerated reproductive failure with age. Noticeably, Tet1-deficient mice at young age exhibit dramatically reduced follicle reserve and the follicle reserve further decreases with age, phenomenon consistent with premature ovarian failure (POF) syndrome. Consequently, Tet1-deficient mice become infertile by reproductive middle age, while age matched wild-type mice still robustly reproduce. Moreover, by single cell transcriptome analysis of oocytes, Tet1 deficiency elevates organelle fission, associated with defects in ubiquitination and declined autophagy, and also upregulates signaling pathways for Alzheimer's diseases, but down-regulates X-chromosome linked genes, such as Fmr1, which is known to be implicated in POF. Additionally, Line1 is aberrantly upregulated and endogenous retroviruses also are altered in Tet1-deficient oocytes. These molecular changes are consistent with oocyte senescence and follicle atresia and depletion found in premature ovarian failure or insufficiency. Our data suggest that Tet1 enzyme plays roles in maintaining oocyte quality as well as oocyte number and follicle reserve and its deficiency can lead to POF.

Skewed X-chromosome inactivation and shorter telomeres associate with idiopathic premature ovarian insufficiency

OBJECTIVE

To analyze whether telomere length, X-chromosome inactivation (XCI), and androgen receptor (AR) GAG polymorphism are related to idiopathic premature ovarian insufficiency (POI).

DESIGN

Case-control study.

SETTING

University hospital.

PATIENT(S)

A total of 121 women, including 46 nonsyndromic POI and 75 controls.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Age, weight, height, body mass index (BMI), systolic and diastolic arterial pressure, E₂, androstenedione, T, and C-reactive protein were assessed. Telomere length was estimated by quantitative real-time polymerase chain reaction, XCI was measured using the Human Androgen Receptor and X-linked retinitis pigmentosa 2 (RP2) methylation assays. AR and FMR1 polymorphism was assessed by quantitative fluorescent polymerase chain reaction and sequencing.

RESULT(S)

Premature ovarian insufficiency women had a higher mean age, weighed less, and exhibited lower C-reactive protein, E₂, and androstenedione levels. The AR polymorphism did not differ between the groups. Four patients had premutation (55-200 CGG repeats), and none displayed a full mutation in the FMR1 gene. However, patients with POI showed shorter telomere length and higher frequency of skewed XCI. Extreme skewing (≥90%) was observed in 15% of women with POI, and shorter telomeres correlated with XCI skewing in both groups.

CONCLUSION(S)

Skewed XCI and shortened telomere length were associated with idiopathic POI, despite no alterations in the AR and FMR1 genes. Additionally, there is a tendency for women with short telomeres to exhibit skewed XCI.

A pharmacogenetic approach to improve low ovarian response: The role of CAG repeats length in the androgen receptor gene

The AR (androgen receptor) polymorphism is associated with POR risk. Furthermore, the use of androgens in POR remains controversial. Our data could clarify the effectiveness of androgen pretreatment. AR genotyping could help us to identify patients at risk for POR and POR patients that will be benefited of androgen pretreatment.

OBJECTIVE

The aim of this project was to investigate if the AR (androgen receptor) polymorphism could be used to identify patients at risk for POR and that will benefit from androgens pretreatment.

STUDY DESIGN

To evaluate the POR risk we performed a cohort study including 231 patients (54 POR and 177 control). Moreover, we included 88 IVF-cycles performed by 44 POR-patients to assess the effect on ovarian response. All patients performed two cycles: a standard ovarian stimulation and a second one with androgen preparation. We compare the results in pair from each.

RESULTS

POR showed the highest frequency of CAG repeats at 24 vs 22 in controls. Only 33% of POR have alleles with a repeat number below 23, compared with 50% of controls (p < 0.05). According to AR polymorphism ovarian response differences were shown. Patients that carried CAG repeats in AR gene between 22 and 24 showed an increased in the number of oocytes (2.61 in cycles without androgens vs 5.11 when they were pretreated with androgens; p < 0.05). For the patients that carried repeats lower than 22 and higher than 24, no differences were reported in the number of oocytes obtained in the cycle with or without androgens (2.94 vs 2.56; p = 0.88). Similar results were obtained for mature oocytes in patients that carry a number of CAG repeats between 22 and 24 (1.86 MII in cycles without androgens vs 4.04 MII when they were pretreated with androgens; p < 0.05). No differences in the number of MII oocytes were found in patients that get out of 22 and 24 repeats between the two cycles (2.31 vs 2.13; p = 0.88).

CONCLUSION

The AR polymorphism is associated with POR risk, patients with repeats greater than 22 show a higher risk. Our data suggest that AR genotype could play a role in natural ovarian aging. Furthermore, the use of androgens in POR remains controversial. Our data suggest that the AR genotype could clarify the effectiveness of the androgen pretreatment. AR genotyping could help us to identify patients at risk of POR and POR patients that could benefit from transdermal testosterone pretreatment.

Role of polymorphism of the androgen receptor gene and non-random X chromosome inactivation in the genesis of androgenic alopecia in women of childbearing potential

The authors describe the results of a study of polymorphism of the androgen receptor gene by the number of CAG repeats in exon 1 of the androgen receptor gene and non-random X chromosome inactivation in 87 women of childbearing potential (at the average age of 29.5 ± 5.4 years) suffering from androgenic alopecia. They revealed an association between the presence of 'short' (≤ 22) CAG repeats in both alleles of the androgen receptor gene (р < 0,05) and a reliable growth of prevalence of non-random X chromosome inactivation in patients with androgenic alopecia as compared to healthy women (50.7% (39/77) and 16.1% (9/56), respectively, р < 0.05). These data demonstrate a pathogenetic role of polymorphism of the androgen receptor gene and non-random X chromosome inactivation in the development of androgenic alopecia in women of childbearing potential as well as urgency of using molecular and genetic studies to study pathogenetic mechanisms of the disease.

Skewed X chromosome inactivation may be not associated with premature ovarian failure

BACKGROUND

In view of the controversies about the skewed X chromosome inactivation (XCI) and premature ovarian failure (POF) association, a meta-analysis of the published data was performed to evaluate the relationship between XCI skewing and POF.

METHODS

We searched for all published articles indexed in MEDLINE (1950 approximately 2009) and CNKI (1994 approximately 2009). Any case-control or cohort study that tested the association between skewed XCI and POF was included and data were extracted independently by two reviewers. We performed this meta-analysis involving 325 cases and 403 controls with Review Manager 4.2 software.

RESULTS

Four eligible studies were selected for meta-analysis. It suggested that there was no significant difference between the incidence of skewed XCI (XCI >or=70% skewing) in POF cases comparing to healthy controls, odds ratio (OR) = 1.13 [95% confidence interval (CI): 0.84 approximately 1.53, P = 0.42]. The link between extremely skewed XCI (XCI >or=90% skewing) and POF was also analysed, and no significant difference was found, either, OR = 1.46 (95% CI: 0.79 approximately 2.69, P = 0.22).

CONCLUSIONS

Skewed XCI had no association with POF. However, more case-control and cohort studies are needed in the future.

X chromosome inactivation does not define the development of premature ovarian failure in fragile X premutation carriers

Since only 20% of female fragile X premutation carriers develop premature ovarian failure (POF, i.e., amenorrhea before age of 40 years), and since X chromosome inactivation (XCI) determines the phenotypic severity of full mutation women, we reasoned that the development of POF in fragile X premutation carriers could be due to skewed XCI (XCI ratio >80:20). To determine inactivation ratios and activities of the premutations, inactivation patterns were assessed in peripheral blood samples from 101 fragile X premutation carriers (mean age 47.1 years, range 12-72) through analysis of the AR and FMR1 loci, respectively. In addition, AR inactivation patterns were assessed in peripheral blood samples from 25 women with idiopathic POF (mean age 31.7 years, range 19-48). We addressed the association between age and skewed XCI because older women are prone to XCI skewness. The median XCI ratios were 68% for premutation carriers with POF (N = 37), 67% for premutation carriers without POF (N = 64) and 61% for women with idiopathic POF (N = 25). The incidence of skewing was similar in all groups, that is, 7 of 37 (18.9%) in premutation carriers with POF, 11 of 64 (17.2%) in premutation carriers without POF, and 3 of 25 (12%) in women with idiopathic POF. There was good concordance between inactivation ratios at the two loci tested in 62 premutation carriers (intraclass correlation coefficient = 0.86; P < 0.01). No age-specific skewing was observed. Skewed XCI and activity of the premutation are not associated with POF in fragile X premutation carriers.

Skewed X chromosome inactivation and trisomic spontaneous abortion: no association

Several studies suggest that highly skewed X chromosome inactivation (HSXI) is associated with recurrent spontaneous abortion. We hypothesized that this association reflects an increased rate of trisomic conceptions due to anomalies on the X chromosome that lead both to HSXI and to a diminished oocyte pool. We compared the distribution of X chromosome inactivation (XCI) skewing percentages (range: 50%-100%) among women with spontaneous abortions in four karyotype groups-trisomy (n = 154), chromosomally normal male (n = 43), chromosomally normal female (n = 38), nontrisomic chromosomally abnormal (n = 61)-to the distribution for age-matched controls with chromosomally normal births (n = 388). In secondary analyses, we subdivided the nontrisomic chromosomally abnormal group, divided trisomies by chromosome, and classified women by reproductive history. Our data support neither an association of HSXI with all trisomies nor an association of HSXI with chromosomally normal male spontaneous abortions. We also find no association between HSXI and recurrent abortion (n = 45).

Extreme clonality in lymphoblastoid cell lines with implications for allele specific expression analyses

Lymphoblastoid cell lines (LCL) are being actively and extensively used to examine the expression of specific genes and genome-wide expression profiles, including allele specific expression assays. However, it has recently been shown that approximately 10% of human genes exhibit random patterns of monoallelic expression within single clones of LCLs. Consequently allelic imbalance studies could be significantly compromised if bulk populations of donor cells are clonal, or near clonal. Here, using X chromosome inactivation as a readout, we confirm and quantify widespread near monoclonality in two independent sets of cell lines. Consequently, we recommend where possible the use of bulk, non cell line, ex vivo cells for allele specific expression assays.