X/autosomal translocations in the Xq critical region associated with premature ovarian failure fall within and outside genes

Skewed X-chromosome inactivation drives the proportion of DNAAF6-defective airway motile cilia and variable expressivity in primary ciliary dyskinesia

BACKGROUND

Primary ciliary dyskinesia (PCD) is a rare airway disorder caused by defective motile cilia. Only male patients have been reported with pathogenic mutations in X-linked DNAAF6, which result in the absence of ciliary dynein arms, whereas their heterozygous mothers are supposedly healthy. Our objective was to assess the possible clinical and ciliary consequences of X-chromosome inactivation (XCI) in these mothers.

METHODS

XCI patterns of six mothers of male patients with DNAAF6-related PCD were determined by DNA-methylation studies and compared with their clinical phenotype (6/6 mothers), as well as their ciliary phenotype (4/6 mothers), as assessed by immunofluorescence and high-speed videomicroscopy analyses. The mutated X chromosome was tracked to assess the percentage of cells with a normal inactivated DNAAF6 allele.

RESULTS

The mothers' phenotypes ranged from absence of symptoms to mild/moderate or severe airway phenotypes, closely reflecting their XCI pattern. Analyses of the symptomatic mothers' airway ciliated cells revealed the coexistence of normal cells and cells with immotile cilia lacking dynein arms, whose ratio closely mirrored their XCI pattern.

CONCLUSION

This study highlights the importance of searching for heterozygous pathogenic DNAAF6 mutations in all female relatives of male PCD patients with a DNAAF6 defect, as well as in females consulting for mild chronic respiratory symptoms. Our results also demonstrate that about one-third-ranging from 20% to 50%-normal ciliated airway cells sufficed to avoid severe PCD, a result paving the way for gene therapy.

Current understanding of the genomic abnormities in premature ovarian failure: chance for early diagnosis and management

Premature ovarian failure (POF) is an insidious cause of female infertility and a devastating condition for women. POF also has a strong familial and heterogeneous genetic background. Management of POF is complicated by the variable etiology and presentation, which are generally characterized by abnormal hormone levels, gene instability and ovarian dysgenesis. To date, abnormal regulation associated with POF has been found in a small number of genes, including autosomal and sex chromosomal genes in folliculogenesis, granulosa cells, and oocytes. Due to the complex genomic contributions, ascertaining the exact causative mechanisms has been challenging in POF, and many pathogenic genomic characteristics have yet to be elucidated. However, emerging research has provided new insights into genomic variation in POF as well as novel etiological factors, pathogenic mechanisms and therapeutic intervention approaches. Meanwhile, scattered studies of transcriptional regulation revealed that ovarian cell function also depends on specific biomarker gene expression, which can influence protein activities, thus causing POF. In this review, we summarized the latest research and issues related to the genomic basis for POF and focused on insights gained from their biological effects and pathogenic mechanisms in POF. The present integrated studies of genomic variants, gene expression and related protein abnormalities were structured to establish the role of etiological genes associated with POF. In addition, we describe the design of some ongoing clinical trials that may suggest safe, feasible and effective approaches to improve the diagnosis and therapy of POF, such as Filgrastim, goserelin, resveratrol, natural plant antitoxin, Kuntai capsule et al. Understanding the candidate genomic characteristics in POF is beneficial for the early diagnosis of POF and provides appropriate methods for prevention and drug treatment. Additional efforts to clarify the POF genetic background are necessary and are beneficial for researchers and clinicians regarding genetic counseling and clinical practice. Taken together, recent genomic explorations have shown great potential to elucidate POF management in women and are stepping from the bench to the bedside.

Short stature and primary ovarian insufficiency possibly due to chromosomal position effect in a balanced X;1 translocation

BACKGROUND

Primary ovarian insufficiency (POI) is defined as a primary ovarian defect characterized by absent menarche (primary amenorrhea), a decrease in the initial primordial follicle number, high follicle-stimulating hormone (FSH) levels and hypoestrogenism. Although the etiology of a majority of POI cases is not yet identified, several data suggest that POI has a strong genetic component. Conventional cytogenetic and molecular analyses have identified regions of the X chromosome that are associated with ovarian function, as well as POI candidate genes, such as FMR1 and DIAPH2. Here we describe a 10.5-year-old girl presenting with high FSH and luteinizing hormone (LH) levels, pathologic GH stimulation arginine and clonidine tests, short stature, pterygium, ovarian dysgenesis, hirsutism and POI.

RESULTS

Cytogenetic analysis demonstrated a balanced reciprocal translocation between the q arms of chromosomes X and 1, with breakpoints falling in Xq21 and 1q41 bands. Molecular studies did not unravel any chromosome microdeletion/microduplication, and no XIST-mediated inactivation was found on the derivative chromosome 1. Interestingly, through immunofluorescence assays, we found that part of the Xq21q22 trait, translocated to chromosome 1q41, was late replicating and therefore possibly inactivated in 30 % metaphases both in lymphocytes and skin fibroblasts, in addition to a skewed 100 % inactivation of the normal X chromosome. These findings suggest that a dysregulation of gene expression might occur in this region. Two genes mapping to the Xq translocated region, namely DIAPH2 and FMR1, were found overexpressed if compared with controls.

CONCLUSIONS

We report a case in which gonadal dysgenesis and POI are associated with over-expression of DIAPH2 gene and of FMR1 gene in wild type form. We hypothesize that this over-expression is possibly due to a phenomenon known as "chromosomal position effect", which accounts for gene expression variations depending on their localization within the nucleus. For the same effect a double mosaic inactivation of genes mapping to the Xq21-q22 region, demonstrated by immunofluorescence assays, may be the cause of a functional Xq partial monosomy leading to most Turner traits of the proband's phenotype.

Genetic mechanisms leading to primary amenorrhea in balanced X-autosome translocations

OBJECTIVE

To map the X-chromosome and autosome breakpoints in women with balanced X-autosome translocations and primary amenorrhea, searching candidate genomic loci for female infertility.

DESIGN

Retrospective and case-control study.

SETTING

University-based research laboratory.

PATIENT(S)

Three women with balanced X-autosome translocation and primary amenorrhea.

INTERVENTION(S)

Conventional cytogenetic methods, genomic array, array painting, fluorescence in situ hybridization, and quantitative reverse transcription-polymerase chain reaction.

MAIN OUTCOME MEASURE(S)

Karyotype, copy number variation, breakpoint mapping, and gene expression levels.

RESULT(S)

All patients presented with breakpoints in the Xq13q21 region. In two patients, the X-chromosome breakpoint disrupted coding sequences (KIAA2022 and ZDHHC15 genes). Although both gene disruptions caused absence of transcription in peripheral blood, there is no evidence that supports the involvement of these genes with ovarian function. The ZDHHC15 gene belongs to a conserved syntenic region that encompasses the FGF16 gene, which plays a role in female germ line development. The break in the FGF16 syntenic block may have disrupted the interaction between the FGF16 promoter and its cis-regulatory element. In the third patient, although both breakpoints are intergenic, a gene that plays a role in the DAX1 pathway (FHL2 gene) flanks distally the autosome breakpoint. The FHL2 gene may be subject to position effect due to the attachment of an autosome segment in Xq21 region.

CONCLUSION(S)

The etiology of primary amenorrhea in balanced X-autosome translocation patients may underlie more complex mechanisms than interruption of specific X-linked candidate genes, such as position effect. The fine mapping of the rearrangement breakpoints may be a tool for identifying genetic pathogenic mechanisms for primary amenorrhea.

Genetics of female infertility due to anomalies of the ovary and mullerian ducts

Genetic factors are pivotal in reproductive development and subsequent reproductive processes. If disturbed, infertility can occur. In the female, genetic factors affecting the ovary and the uterus are not uncommon causes of infertility. Terminal deletions on the X long arm and X short arm and X chromosomal mosaicism have long been accepted as causes of premature ovarian failure (POF). Responsible genes on the X have not yet elucidated. Attractive candidate genes for POF also exist on autosomes, and in over a dozen genes molecular perturbations are documented in non-syndromic POF. The most common single-gene cause of POF is premutation carriers for FMR1 (fragile X syndrome). As other candidate genes and additional ethnic groups are interrogated, the proportion of POF cases due to single-gene mutation will increase. Among uterine anomalies, incomplete mullerian fusion is most common. Increased recurrence risks for first-degree relatives confirm a role for genetic factors; interrogation of candidate genes is under way.

Disruption of HDX gene in premature ovarian failure

We present a case of a 19-year-old phenotypically normal girl with premature ovarian failure. Cytogenetic analysis using G banding and fluorescence in situ hybridization (FISH) from cultured peripheral blood lymphocytes of the patient and the family revealed a de novo X;15 translocation and the imbalance to be 46,X,t(X;15)(Xpter → Xq21::15q11 → 15qter;15pter → 15q11::Xq21 → Xqter). ish (CEPX+, wep15+, ISNRPN+, PML+, D15S10+, wcp15-, SNRRN-, PML-)[20]. The X chromosome inactivation (XCI) assay revealed a completely skewed XCI pattern in which selective pressure favors an active maternal allele. The Affymetrix 2.7 M cytogenetics whole-Genome array confirmed the chromosomal imbalance and identified disruption of the HDX gene at Xq21, the translocation breakpoint.

Translocation t(X;11)(q22;q25) in a woman with premature ovarian failure

Genetic, autoimmune, environmental, iatrogenic, and idiopathic factors are known to cause premature ovarian failure (POF). This report describes an X;11 translocation, t(X;11)(q22;q25), in a woman diagnosed with POF. The FSH level was found to be elevated. Menstrual cycle was regular initially, and she had a spontaneous abortion at the 5th month of gestation at 16 years of age. Her mother was karyotypically normal while her father was not investigated. Male carriers of X;autosome translocations are mostly infertile, and hence the translocation is presumed to be of de novo origin. Fluorescence in situ hybridization using whole chromosome paint probes confirmed the rearrangement.

A family with Xq22.3q25 interstitial deletion and normal ovarian function

OBJECTIVE

To investigate genomic changes in a family with deletion of X chromosome q22.3-q25 associated with normal constitutional and reproductive phenotypes.

DESIGN

Case report.

SETTING

Academic district hospital genetic laboratory.

PATIENT(S)

A family incidentally found to have deletion of X chromosome q22.3-q25.

INTERVENTION(S)

Cytogenetic analysis and array-based comparative genomic hybridization for amniotic fluid and peripheral blood lymphocyte of family members.

MAIN OUTCOME MEASURE(S)

Ovarian function and menstrual cycles.

RESULT(S)

The proband and two daughters showed deletion of Xq22.3q25. This region spans 17.4 Mb and contains 121 genes.

CONCLUSION(S)

Female subjects with deletion of Xq22.3q25 may present with normal constitutional and reproductive phenotypes.

Cytogenetics of premature ovarian failure: an investigation on 269 affected women

The importance of X chromosome in the aetiology of premature ovarian failure (POF) is well-known but in many cases POF still remains idiopathic. Chromosome aneuploidy increase is a physiological phenomenon related to aging, but the role of low-level sex chromosome mosaicism in ovarian function is still undiscovered. Standard cytogenetic analysis was carried out in a total of 269 patients affected by POF: 27 chromosomal abnormalities were identified, including X chromosome and autosomal structural and numerical abnormalities. In 47 patients with 46,XX karyotype we performed interphase FISH using X alpha-satellite probe in order to identify X chromosome mosaicism rate. Aneuploidy rate in the patient group was significantly higher than the general population group. These findings underline the importance of X chromosome in the aetiology of POF and highlight the potential role of low-level sex chromosome mosaicism in ovarian aging that may lead to a premature onset of menopause.

Similar phenotype characteristics comparing familial and sporadic premature ovarian failure

OBJECTIVE

Premature ovarian failure (POF) is characterized by secondary amenorrhea before the age of 40 years, along with repeated increased follicle-stimulating hormone and low estrogen concentrations. POF is considered a complex genetic disease with a familial presentation in 12% to 50% of cases. POF may originate from different genes and various gene-environment interactions. The aim of this study was to identify possible differences in phenotype comparing women with familial and women with sporadic POF.

METHODS

A multicenter study was initiated in the Netherlands using standardized phenotyping. For each woman, medical history, menstrual cycle, and fertility and smoking status were assessed and a standardized examination was performed. Based on a detailed three-generation family history, women were identified as having either familial (defined as having at least one relative with POF) or sporadic POF.

RESULTS

A total of 58 familial cases and 142 sporadic cases of POF were identified. Maternal age at menopause was significantly lower in the women with familial compared with the women with sporadic POF (41.0 +/- 7.5 and 49.7 +/- 2.6 y, respectively; P < 0.001). Sex hormone-binding globulin concentration was significantly higher in the women with familial than in the women with sporadic POF (73.6 +/- 37.1 and 55.2 +/- 26.9 nmol/L, respectively; P = 0.002). All other characteristics, such as parity, bone mineral density, and serum follicle-stimulating hormone and lipid levels were similar, as was the incidence of autoimmunity and cytogenetic abnormalities.

CONCLUSIONS

Familial and sporadic POF do not differ in phenotype except for maternal menopause age and sex hormone-binding globulin concentration. Future studies are needed to unravel the genotype-phenotype interactions in POF.

Analysis of X chromosome genomic DNA sequence copy number variation associated with premature ovarian failure (POF)

BACKGROUND

Premature ovarian failure (POF) is a heterogeneous disease defined as amenorrhoea for >6 months before age 40, with an FSH serum level >40 mIU/ml (menopausal levels). While there is a strong genetic association with POF, familial studies have also indicated that idiopathic POF may also be genetically linked. Conventional cytogenetic analyses have identified regions of the X chromosome that are strongly associated with ovarian function, as well as several POF candidate genes. Cryptic chromosome abnormalities that have been missed might be detected by array comparative genomic hybridization.

METHODS

In this study, samples from 42 idiopathic POF patients were subjected to a complete end-to-end X/Y chromosome tiling path array to achieve a detailed copy number variation (CNV) analysis of X chromosome involvement in POF. The arrays also contained a 1 Mb autosomal tiling path as a reference control. Quantitative PCR for selected genes contained within the CNVs was used to confirm the majority of the changes detected. The expression pattern of some of these genes in human tissue RNA was examined by reverse transcription (RT)-PCR.

RESULTS

A number of CNVs were identified on both Xp and Xq, with several being shared among the POF cases. Some CNVs fall within known polymorphic CNV regions, and others span previously identified POF candidate regions and genes.

CONCLUSIONS

The new data reported in this study reveal further discrete X chromosome intervals not previously associated with the disease and therefore implicate new clusters of candidate genes. Further studies will be required to elucidate their involvement in POF.

Chromosome territories, X;Y translocation and Premature Ovarian Failure: is there a relationship?

BACKGROUND

Premature ovarian failure (POF) is a secondary hypergonadotrophic amenorrhea occurring before the age of 40 and affecting 1-3% of females. Chromosome anomalies account for 6-8% of POF cases, but only few cases are associated with translocations involving X and Y chromosomes.This study shows the cytogenetic and molecular analysis of a POF patient came to our attention as she developed a left ovary choriocarcinoma at the age of 10 and at 14 years of age she presented secondary amenorrhea with elevated levels of gonadotropins.

RESULTS

Breakpoint position on X and Y chromosomes was investigated using Fluorescent In Situ Hybridisation (FISH) with a panel of specific BAC probes, microsatellite analysis and evaluation of copy number changes and loss of heterozigosity by Affymetrix(R) GeneChip platform (Santa Clara, CA, USA). Patient's karyotype resulted 46, X, der(Y)t(X;Y)(q13.1;q11.223). X inactivation study was assessed by RBA banding and showed preferential inactivation of derivative chromosome. The reciprocal spatial disposition of sexual chromosome territories was investigated using whole chromosome painting and centromeres probes: patient's results didn't show a significant difference in comparison to normal controls.

CONCLUSION

The peculiar clinical case come to our attention highlighted the complexity of POF aetiology and of the translocation event, even if our results seem to exclude any effect on nuclear organisation. POF phenotype could be partially explained by skewed X chromosome inactivation that influences gene expression.

Epigenetic control of the critical region for premature ovarian failure on autosomal genes translocated to the X chromosome: a hypothesis

Chromosomal rearrangements in Xq are frequently associated to premature ovarian failure (POF) and have contributed to define a POF "critical region" from Xq13.3 to Xq26. Search for X-linked genes responsible for the phenotype has been elusive as most rearrangements did not interrupt genes and many were mapped to gene deserts. We now report that ovary-expressed genes flanked autosomal breakpoints in four POF cases analyzed whose X chromosome breakpoints interrupted a gene poor region in Xq21, where no ovary-expressed candidate genes could be found. We also show that the global down regulation in the oocyte and up regulation in the ovary of X-linked genes compared to the autosomes is mainly due to genes in the POF "critical region". We thus propose that POF, in X;autosome balanced translocations, may not only be caused by haploinsufficiency, but also by a oocyte-specific position effect on autosomal genes, dependent on dosage compensation mechanisms operating on the active X chromosome in mammals.

A Case of 46,X,der(X)t(X;X)(q22.1;p11) Xq22.1→Xqter in a 12-Year-Old Girl with Premature Ovarian Failure

Premature ovarian failure due to Xp duplication and Xq deletion has been reported in four patients, the youngest of whom was 18 years old. The diagnosis has been made with new techniques for genetic analysis, such as comparative genomic hybridization and fluorescence in situ hybridization. We report the youngest case (a 12-year-old who presented with irregular menses), of premature ovarian failure due to Xp duplication and Xq deletion and the first with 46,X,der(X)t(X;X)(q22.1;p11). The diagnosis was made using C-banding and fluorescent in situ hybridization with locus-specific probes. This case highlights the need to use advanced genetic strategies to determine karyotypic and phenotypic abnormalities.

X-linked premature ovarian failure: a complex disease

Involvement of the X chromosome in premature ovarian failure was demonstrated by the relatively frequent chromosomal rearrangements in patients, but the requirement of two X chromosomes for ovarian function was quite unexplained until recently. Review of the data on chromosomal rearrangements suggests that several genes along the X chromosomes contribute to ovarian function. In most instances, no single X chromosome gene has a causative role in premature ovarian failure, and the phenotype is likely to derive from the additive effect of X-linked and non-X-linked factors. Recent data on a small group of balanced X-autosome translocations showed that X-linked premature ovarian failure might also be caused by a different mechanism, namely position effect of the X chromosome on non-X-linked genes, and suggest a peculiar organization of the X chromosome during oogenesis.

Chromosomal rearrangements in Xq and premature ovarian failure: mapping of 25 new cases and review of the literature

BACKGROUND

Chromosomal rearrangements in Xq are frequently associated with premature ovarian failure (POF) and have defined a POF 'critical region'. Search for genes responsible for the disorder has been elusive.

METHODS

We report mapping of novel breakpoints of X;autosome-balanced translocations and interstitial deletions and a review of published X chromosome rearrangements.

RESULTS

All the novel POF-associated rearrangements were mapped outside and often very distant from genes. The majority mapped to a gene-poor region in Xq21. In the same region, deletions were reported in women who apparently did not have problems conceiving. Expression analysis of genes flanking breakpoints clustered in a 2-Mb region of Xq21 failed to demonstrate ovary-specific genes.

CONCLUSIONS

Our results excluded most of the possible explanations for the POF phenotype and suggested that POF should be ascribed to a position effect of the breakpoints on flanking genes. We also showed that while the X breakpoint may affect X-linked genes in the distal part of Xq, from Xq23 to Xq28, interruption of the critical region in Xq21 could be explained by a position effect of the Xq critical region on genes flanking the autosomal breakpoints.

A susceptibility gene for premature ovarian failure (POF) maps to proximal Xq28

Terminal deletions of the long arm of the human X chromosome have been described in women with premature ovarian failure (POF). We report here the molecular characterization of an inherited deletion in two affected women and in their mother. The two daughters presented secondary amenorrhea at 17 or 22 years respectively, while the mother was fertile. She had four children, but she eventually had premature menopause at 43 years of age. The fine molecular analysis of the deletion showed that the three women carried an identical deletion. We conclude that the phenotypic difference within the family must be attributed to genetic or environmental factors and not to the presence of different extent deletions. By comparison with other deletions in the region, we map a susceptibility gene for POF to 4.5 Mb, in the distal part of Xq.

Mutation analysis of two candidate genes for premature ovarian failure, DACH2 and POF1B

BACKGROUND

Balanced X;autosome translocations interrupting the 'critical region' of the long arm of the human X chromosome are often associated with premature ovarian failure (POF). However, the mechanisms leading to X-linked ovarian dysfunction are largely unknown, as the majority of the X chromosome breakpoints have been mapped to gene-free genomic regions. A few genes have been found to be interrupted, but their role has never been clarified.

METHODS AND RESULTS

By fine mapping of the X chromosome breakpoint of an X;autosome balanced translocation, we identified a new interrupted gene, POF1B. We performed a mutation analysis of POF1B and of another gene previously identified, DACH2, localized approximately 700 kb distal in Xq21, in a cohort of >200 Italian POF patients. Rare mutations were found in patients in both genes.

CONCLUSIONS

Our findings could not demonstrate any involvement of POF1B, but suggest that rare mutations in the DACH2 gene may have a role in the POF phenotype.

Premature ovarian failure and fragile X premutation: a study on 45 women

OBJECTIVE

The aim of this study was to test for the presence of the fragile X (FRAXA) premutation a group of women with early menopause.

STUDY DESIGN

45 women with idiopathic premature ovarian failure (POF), five with a familial and 40 with a sporadic form, were screened for the presence of FRAXA premutation. A control group of 28 women >45 years, with one or more children and no signs of POF, was also studied.

RESULTS

We found three cases of fragile X premutations in women all belonging to the group with sporadic POF.

CONCLUSION

Our results seems to confirm previous observations on the non random association between POF and FRAXA premutation.

Fertility, sex determination, and the X chromosome

Because of its function, the X chromosome has a special status in mammalian genomes, with the specific occurrence of genes that influence both female and male fertility. Long ago, the XO karyotype (Turner syndrome) was associated with infertility, proving the correlation between normal X chromosome dosage and normal female fertility. Nevertheless, the search for specific X-borne fertility genes was not completely successful and suggested, instead, that female X-linked fertility, for example, depends upon groups of X-linked genes. Conversely, X-linked hyperfertility has been observed in sheep, where a mutation in BMP15 leads to a hyperfertile phenotype, but only in the heterozygous state. Many male fertility genes map to the X chromosome, consistent with a genetic model developed in the early 1990s. Ironically, NR0B1 (formerly DAX1), once presented as the paradigm of genes responsible for ovarian development and function, is probably one of these male fertility factors and is active in the maintenance of spermatogenesis. Indeed, duplications of this gene on the human X chromosome lead to XY sex reversal, as NR0B1 is able to counterbalance the effect in humans. Nevertheless, invalidation experiments in mice demonstrate the effect of this factor on male germ-cell production.

Skewed X-chromosome inactivation is associated with trisomy in women ascertained on the basis of recurrent spontaneous abortion or chromosomally abnormal pregnancies

An increase in extremely skewed X-chromosome inactivation (XCI) (> or = 90%) among women who experienced recurrent spontaneous abortion (RSA) has been previously reported. To further delineate the etiology of this association, we have evaluated XCI status in 207 women who experience RSA. A significant excess of trisomic losses was observed among the women who had RSA with skewed XCI versus those without skewed XCI (P=.02). There was also a significant excess of boys among live births in this group (P=.04), which is contrary to expectations if the cause of skewed XCI was only that these women carried X-linked lethal mutations. To confirm the association between skewed XCI and the risk of trisomy, an independent group of 53 women, ascertained on the basis of a prenatal diagnosis of trisomy mosaicism, were investigated. Only cases for which the trisomy was shown to be of maternal meiotic origin were included. The results show a significantly higher level of extreme skewing (> or = 90%) in women whose pregnancies involved placental trisomy mosaicism (17%) than in either of two separate control populations (n=102 and 99) (P=.02 compared with total control subjects). An additional 11 cases were ascertained on the basis of one or more trisomic-pregnancy losses. When all women in the present study with a trisomic pregnancy (n=103) were considered together, skewed XCI was identified in 18%, as compared with 7% in all controls (n=201) (P=.005). This difference was more pronounced when a cutoff of extreme skewing of 95% was used (10% vs. 1.5% skewed; P=.002). Maternal age was not associated with skewing in either the patient or control populations and therefore cannot account for the association with trisomy. Previous studies have shown that a reduced ovarian reserve is associated with increased risk of trisomic pregnancies. We hypothesize that the association between skewed XCI and trisomic pregnancies is produced by a common mechanism that underlies both and that involves a reduction of the size of the follicular pool.