Ovarian dysfunction and FMR1 alleles in a large Italian family with POF and FRAXA disorders: case report

DNA Hypermethylation and Unstable Repeat Diseases: A Paradigm of Transcriptional Silencing to Decipher the Basis of Pathogenic Mechanisms

Unstable repeat disorders comprise a variable group of incurable human neurological and neuromuscular diseases caused by an increase in the copy number of tandem repeats located in various regions of their resident genes. It has become clear that dense DNA methylation in hyperexpanded non-coding repeats induces transcriptional silencing and, subsequently, insufficient protein synthesis. However, the ramifications of this paradigm reveal a far more profound role in disease pathogenesis. This review will summarize the significant progress made in a subset of non-coding repeat diseases demonstrating the role of dense landscapes of 5-methylcytosine (5mC) as a common disease modifier. However, the emerging findings suggest context-dependent models of 5mC-mediated silencing with distinct effects of excessive DNA methylation. An in-depth understanding of the molecular mechanisms underlying this peculiar group of human diseases constitutes a prerequisite that could help to discover novel pathogenic repeat loci, as well as to determine potential therapeutic targets. In this regard, we report on a brief description of advanced strategies in DNA methylation profiling for the identification of unstable Guanine-Cytosine (GC)-rich regions and on promising examples of molecular targeted therapies for Fragile X disease (FXS) and Friedrich ataxia (FRDA) that could pave the way for the application of this technique in other hypermethylated expansion disorders.

Epigenetic Aberration of FMR1 Gene in Infertile Women with Diminished Ovarian Reserve

OBJECTIVES

The diminished ovarian reserve (DOR) is a condition characterized by a reduction in the number and/or quality of oocytes. This primary infertility disorder is usually accompanied with an increase in the follicle-stimulating hormone (FSH) levels and regular menses. Although there are many factors contributing to the DOR situation, it is likely that many of idiopathic cases have genetic/epigenetic bases. The association between the FMR1 premutation (50-200 CGG repeats) and the premature ovarian failure (POF) suggests that epigenetic disorders of FMR1 can act as a risk factor for the DOR as well. The aim of this study was to analyze the mRNA expression and epigenetic alteration (histone acetylation/methylation) of the FMR1 gene in blood and granulosa cells of 20 infertile women.

MATERIALS AND METHODS

In this case-control study, these women were referred to the Royan Institute, having been clinically diagnosed as DOR patients. Our control group consisted of 20 women with normal antral follicle numbers and serum FSH level. All these women had normal karyotype and no history of genetic disorders. The number of CGG triplet repeats in the exon 1 of the FMR1 gene was analyzed in all samples.

RESULTS

Results clearly demonstrated significantly higher expression of the FMR1 gene in blood and granulosa cells of the DOR patients with the FMR1 premutation compared to the control group. In addition, epigenetic marks of histone 3 lysine 9 acetylation (H3K9ac) and di-metylation (H3K9me2) showed significantly higher incorporations in the regulatory regions of the FMR1 gene, including the promoter and the exon 1, whereas tri-metylation (H3K9me3) mark showed no significant difference between two groups.

CONCLUSIONS

Our data demonstrates, for the first time, the dynamicity of gene expression and histone modification pattern in regulation of FMR1 gene, and implies the key role played by epigenetics in the development of the ovarian function.

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.

Development and validation of a multiplex-PCR assay for X-linked intellectual disability

Background

X-linked intellectual disability is a common cause of inherited cognitive deficit affecting mostly males. There are several genetic causes implicated in this condition, which has hampered the establishment of an accurate diagnosis. We developed a multiplex-PCR assay for the mutational hotspot regions of the FMR1, AFF2 and ARX genes.

Methods

The multiplex-PCR was validated in a cohort of 100 males selected to include known alleles for the FMR1 repetitive region: five full mutations (250–650 CGGs), ten premutations (70–165 CGGs) and eighty-five in the normal range (19–42 CGGs). Sequencing or Southern blotting was used to confirm the results, depending on the allele class. In this cohort, with the exception of one sample showing an AFF2 intermediate-sized allele, all other samples were normal (8–34 CCGs). No ARX variant was found besides the c.429_452dup. The validated assay was applied to 5000 samples (64.4% males and 35.6% females).

Results

The normal-allelic range of both FMR1 and AFF2 genes as well as the nature of ARX variants identified was similar in both genders. The rate of homozygosity observed in female samples, 27.5% for FMR1 and 17.8% for AFF2 alleles, is comparable to that published by others. Two FMR1 premutations were identified, in a male (58 CGGs) and a female case [(CGG)₄₇/(CGG)₆₁], as well as several FMR1 or AFF2 intermediate-sized alleles. One AFF2 premutation (68 CCGs) and two putative full expansions were picked up in male subjects, which seems relevant considering the rarity of reported AFF2 mutations found in the absence of a family history.

Conclusions

We developed a robust multiplex-PCR that can be used to screen the mutational hotspot regions of FMR1, AFF2 and ARX genes. Moreover, this strategy led to the identification of variants in all three genes, representing not only an improvement in allele-sizing but also in achieving a differential diagnosis. Although the distinction between females who are truly homozygous and those with a second pre- or full mutation sized allele, as well as a definitive diagnosis, requires a specific downstream technique, the use of this multiplex-PCR for initial screening is a cost-effective approach which widens the scope of detection.

Genetic and molecular analysis of a new unbalanced X;18 rearrangement: localization of the diminished ovarian reserve disease locus in the distal Xq POF1 region

BACKGROUND

Diminished ovarian reserve (DOR) is a heterogeneous disorder causing infertility, characterized by a decreased number of oocytes, the genetic cause of which is still unknown.

METHODS AND RESULTS

We describe a family with a new unbalanced X;18 translocation der(X) associated with either fully attenuated or DOR phenotype in the same family. Cytogenetics and array comparative genomic hybridization (aCGH) studies have revealed the same partial Xq monosomy and partial 18q trisomy in both the 32-year-old female with DOR and the unaffected mother. The genetic analysis has defined a subtelomeric deletion spanning 13.3 Mb from Xq27.3 to -Xqter, which covers the premature ovarian failure locus 1 (POF1); and a duplication spanning 13.4 Mb, from 18q22.1 to 18qter. From a parental-origin study, we have inferred that the rearranged X chromosome is maternally derived. The Xq27 and 18q22 breakpoint regions fall in a region extremely rich in long interspersed nuclear element, a class of retrotransposons able to trigger mispairing and unusual crossovers. X-inactivation studies reveal a skewing of der(X) both in the mother and the proband. Therefore, the phenotypic expression of der(X) is fully attenuated in the fertile mother and partially attenuated in the DOR daughter.

CONCLUSIONS

We report on an unbalanced maternally derived translocation (X;18)(q27;q22) with different intra-familial reproductive performances, ranging from fertility to DOR. Skewed X-inactivation seems to restore the unbalanced genetic make-up, fully silencing the 18q22 trisomy and at least in part the Xq27 monosomy. The chromosomal abnormality observed in this family supports the presence of a DOR susceptibility locus in the distal Xq region and targets the POF1 region for further investigation.

A molecular and cytogenetic investigation of FMR1 gene premutations in Polish patients with primary ovarian insufficiency

OBJECTIVE

The aim of this study was to determine the prevalence of premutations in the FMR1 gene that cause primary ovarian insufficiency (POI) in a group of affected women.

STUDY DESIGN

Forty DNA samples were purified from peripheral blood collected from women with ovarian failure who were under 40 years of age. A routine cytogenetic test was performed to eliminate chromosomal aberrations as the cause of POI. The DNA was analysed by polymerase chain reaction (PCR) with primers specific to the FMR1 gene region. The PCR products were then separated in denaturing polyacrylamide gels using an ABI Prism 377 sequencer.

RESULTS

Cytogenetic analysis of the samples revealed two X/autosome translocations. DNA analysis identified FMR1 gene premutations in three patients. The frequency of X/autosome translocations in the studied group was 2/40 (5.0%), and the frequency of FMR1 gene premutations was 3/38 cases (7.9%). Thus, genetic tests allowed for the identification of POI in five (12.5%) out of 40 women.

CONCLUSION

FMR1 gene premutation is a common genetic cause of POI.

X-chromosome terminal deletion in a female with premature ovarian failure: Haploinsufficiency of X-linked genes as a possible explanation

Background

Premature ovarian failure (POF) has repeatedly been associated to X-chromosome deletions. FMR1 gene premutation allele's carrier women have an increased risk for POF. We intent to determine the cause of POF in a 29 year old female, evaluating both of these situations.

Methods

Concomitant analysis of FMR1 gene CGG repeat number and karyotype revealed an X-chromosome terminal deletion. Fluorescence in situ further characterized the breakpoint. A methylation assay for FMR1 gene allowed to determine its methylation status, and hence, the methylation status of the normal X-chromosome.

Results

We report a POF patient with a 46,X,del(X)(q26) karyotype and with skewed X-chromosome inactivation of the structural abnormal X-chromosome.

Conclusions

Despite the hemizygosity of FMR1 gene, the patient does not present Fragile X syndrome features, since the normal X-chromosome is not subject to methylation. The described deletion supports the hypothesis that haploinsufficiency of X-linked genes can be on the basis of POF, and special attention should be paid to X-linked genes in region Xq28 since they escape inactivation and might have a role in this disorder. A full clinical and cytogenetic characterization of all POF cases is important to highlight a pattern and help to understand which genes are crucial for normal ovarian development.

Premature ovarian failure and FMR1 gene mutations: an update

Screening for fragile X premutations is recommended for the routine work-up for any woman presenting with premature ovarian failure (POF). The reason for this is that women with POF have an approximate 5% chance of conceiving and this possibility may be increased further in the FRAXA premutation subgroup. Women need to be informed if they are at risk of having a child with fragile X syndrome. In addition, the identification of a family in which the fragile X repeat site is expanded can lead to the identification of other female family members at risk of transmitting fragile X syndrome. The identification of an index case should therefore trigger genetic counseling throughout the pedigree according to the wishes of the family.

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.

Reproductive health of adolescent girls who carry the FMR1 premutation: expected phenotype based on current knowledge of fragile x-associated primary ovarian insufficiency

The fragile X mental retardation 1 (FMR1) gene, located on the X chromosome, is characterized by a dynamic CGG repeat expansion in the 5' untranslated region. It has long been known that female carriers of the FMR1 premutation allele (55-199 CGG) are at risk for passing the FMR1 full mutation (> or =200 repeats) to their offspring, which results in a common form of mental retardation known as fragile X syndrome. The FMR1 premutation allele, however, also places female carriers at significantly increased risk for prematurely diminished ovarian function, which we refer to as fragile X-associated primary ovarian insufficiency (FXPOI). Although of particular concern for younger women, to date, studies of FXPOI have been restricted to women > or =18 years of age and have not specifically addressed ovarian reserve and menstrual cycle characteristics among adolescent carriers. We discuss the expected reproductive phenotype among FMR1 premutation carriers during adolescence, the associated health considerations based on our current understanding of FXPOI, and the directions for future studies.