Influence of intermediate and uninterrupted FMR1 CGG expansions in premature ovarian failure manifestation

BACKGROUND: Studies attempting to precisely define the range of fragile mental retardation 1 (FMR1) expansions and its inf luence in premature ovarian failure (POF) manifestation are partially lacking. To this aim, we evaluated a large cohort of POF patients for the size and, in selected cases, for the sequence of the CGG expansion. Furthermore, the correlation between POF and X-inactivation was investigated in FRAXA families. METHODS: By fluorescent PCR, 190 POF and 200 control women were sized for the CGG tract; some subjects were also characterized by sequencing and for the FMR1 activation ratio. RESULTS AND CONCLUSION: We found a significant association (19/190, 10%, P < 1 x 10(-6)) between POF and FMR1 premutation (range 63-163 repeats) and a significant enrichment (9/190, 4.7%, P = 0.021) of POF carriers of intermediate expansions (range 41-58 repeats). Interestingly, intermediate alleles were entirely composed of CGG repeats. Furthermore, the analysis of three pairs of siblings with similar FMR1 expansions and discordant for the POF phenotype showed a direct correlation between the expression of the intermediate/premutated allele and POF manifestation. The results obtained strengthen the correlation between FMR1 expansion and POF and suggest that the manifestation of the ovarian dysfunction could be influenced both by the pattern of interruption of the CGG repeat and by X-inactivation.     

Fragile X premutations and (TA)n estrogen receptor polymorphism in women with ovarian dysfunction.

We studied five groups of women with ovarian dysfunction for the CGG expansion in FMR1 and a (TA)n polymorphism in the estrogen receptor gene: a) poor responders to ovarian stimulation as part of in vitro fertilization (n = 13); b) women with familial premature ovarian failure (POF) (n = 7); c) sporadic cases with POF (n = 16); d) FRAXA premutation carriers with POF (n = 7); and e) FRAXA premutation carriers without POF (n = 9). FRAXA premutation was found in one woman with familial POF. A significant association of familial POF and FRAXA premutation carriers with POF having low copy of the (TA)n polymorphism as compared to controls was observed. Our preliminary data suggest a potential role of the estrogen receptor in POF, and it may influence the variable age of menopause of the FRAXA premutation carriers.     

Premature ovarian failure and FRAXA premutation: Positive correlation in a Brazilian survey

Fragile X syndrome (FRAXA) is the most common form of inherited mental retardation (MR). The mutational mechanism leading to the disease involves an expansion of a trinucleotide repeat located at the 5' UTR region of the gene FMR-1. Four types of alleles can be identified in the population, based on the number of repeats: normal (6-40), gray-zone (41-60), premutated (61-200), and fully mutated (>200). Despite only full mutations being associated with the development of the disorder, some authors propose a correlation between FRAXA premutation and the occurrence of premature ovarian failure (POF). We have undertaken a study in 58 women from 24 fragile X syndrome families ascertained for FRAXA testing. Using Southern blotting for direct DNA analysis we have identified 19 normal, 33 premutation carriers, and 6 fully mutated individuals (including 4 somatic mosaics showing premutated and fully mutated alleles). Among the premutated women, 11 experienced menopause before the age of 40 (POF), including one somatic mosaic, which was different from the ones with normal pattern who did not experience POF. Our data corroborate the notion that females carrying alleles in the premutation range are at high risk of experiencing POF.     

Premutation CGG-repeat expansion of the Fmr1 gene impairs mouse neocortical development

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late adult-onset neurodegenerative disorder caused by a premutation CGG-trinucleotide repeat expansion (55-200 CGG repeats) within the 5'-untranslated region of the FMR1 gene. Although FXTAS generally affects premutation carriers over 50 years of age, cognitive and psychological symptoms can appear in carriers during childhood, suggesting that the FMR1 premutation affects brain function early in life. Recent work with cultured hippocampal neurons from a premutation (Fmr1 CGG knock-in) mouse model revealed impaired development of early postnatal neurons, consistent with the developmental clinical involvement of premutation carriers. In the current work, we show that the presence of premutation CGG-repeat expansions in the mouse Fmr1 gene alters embryonic neocortical development. Specifically, embryonic premutation mice display migration defects in the neocortex and altered expression of neuronal lineage markers. The current data demonstrate that premutation alleles of the Fmr1 gene are associated with defects in developmental programs operating during prenatal stages of brain formation and provide further evidence that the FMR1 premutation has a neurodevelopmental component.     

Association between idiopathic premature ovarian failure and fragile X premutation

A total of 106 women affected by premature ovarian failure (POF) were evaluated for fragile X (FRAXA) premutation. The POF patients were classified as having a familial condition (33 women), at least one relative with early menopause (12 women), or a sporadic condition (61 women). The FRAXA premutation was only detected in patients with familial (four out of 33) or sporadic POF (two out of 61). In general, the results obtained indicated that the prevalence [six out of 106, 6%, 95% confidence interval (CI) 3-11%] of FRAXA premutation is significantly higher in women affected by POF than expected (P = 1.24x10(-3)), suggesting a phenotype consequence of the premutation alleles. This relationship is more convincingly derived from the observation in two analysed pedigrees of a co-segregation between FRAXA and POF. These findings suggest a possible involvement of premutated alleles in ovarian failure, and indicate the utility of POF families screening for FRAXA premutation in order to prevent the transmission of mental retardation syndrome.     

Analysis of CGG variation through 642 meioses in Fragile X families

Fragile X syndrome is the commonest familial form of inherited mental retardation. The molecular defect is an expansion of the CGG trinucleotide repeats in the 5' untranslated region of the FMR1 gene that is inherited in an unstable fashion in fragile X families. In an attempt to provide more information about the CGG tract intergenerational variation, we have evaluated 642 transmissions in 175 Fragile X families. PCR and Southern blot (StB12.3) was used to analyse the CGG number. Among premutated alleles, 90.2% showed expansion, two-thirds to a full mutation while the rest remained in the premutation range, 5.5% of alleles did not vary and finally 4.3% of them reduced in size. Premutated females showed an increased risk of expansion to the full mutation depending on the CGG tract. The estimated risk for 80 triplets is more than seven times that of a woman carrying 59 CGG, the risk being 100% for alleles of >100 repeats. Fifty-nine repeats was the smallest allele that expanded to full mutation. Contractions were detected more frequently in males than in females, being statistically significant. This study contributes to the literature by increasing the data available regarding transmissions in Fragile X families and it allows us to perform more precise genetic counselling for women with the CGG repeat in the premutation range.     

Premature ovarian failure in the fragile X syndrome.

The full mutation leading to the fragile X syndrome is a dynamic trinucleotide repeat located in the 5' untranslated region of the FMR1 gene. The premutation allele contains approximately 60 to 199 repeats, is unstable, and originally not considered detrimental; that is, there did not appear to be a phenotype consequence of the long repeat tract. However, in the late 1980s and early 1990s, preliminary findings suggested that nonimpaired heterozygotes were at risk of early menopause and increased rates of twinning, both indications of ovarian failure. Once premutation carriers could be distinguished from full mutation carriers, this phenotype was found to be restricted to premutation carriers only. Based on the recent studies reviewed here, approximately 21% of premutation carriers have premature ovarian failure (POF) compared to only 1% in the general population, or a relative risk of 21. Moreover, among women with idiopathic sporadic or the more rare form of familial POF, approximately 2% and 14%, respectively, carry the premutation. To date, data supporting increased twinning rates are conflicting and need to be resolved. Neither the underlying cellular pathophysiology of POF caused by the premutation allele nor molecular mechanism underlying the presence of the long repeat tract of the premutation allele is understood. Irrespective, women who carry the premutation allele should have not only genetic counseling but also fertility counseling to ensure that they reach their goals for reproduction.     

Very early premature ovarian failure in two sisters compound heterozygous for the FMR1 premutation

Expansion of the CGG trinucleotide repeat in the 5′ untranslated region of the fragile X mental retardation 1 (FMR1) gene within the premutation range is one of the known genetic factors associated with premature ovarian failure and earlier age at menopause. Studies have shown that approximately 16–26% of female carriers will develop premature ovarian failure, and current research is focussed on the identification of molecular factors that predict its occurrence in female carriers. In this report we present two sisters who are compound heterozygous for a premutation, and who were referred because of very early menopause, occurring at the age of 17 years in the youngest sister. Premature ovarian failure associated with FMR1 premutation at such an early age has not been reported in the literature before.     

Premature ovarian failure (POF) and fragile X premutation females: from POF to to fragile X carrier identification, from fragile X carrier diagnosis to POF association data.

Early menopause in the fragile X carriers has been well documented in several reports. All surveys demonstrated that 13-25% of fragile X carriers experienced premature ovarian failure (POF), defined as menopause before the age of 40 years. In 1995 we started screening two groups of subjects as a part of a Fragile X Research Program: 1) women previously diagnosed as fragile X carriers from the register of our center and 2) women with POF and without a family history of fragile X or other forms of mental retardation. In this study we report the preliminary data collected from 75 fragile X families; in 30 of them, POF was present in one or several subjects, all of whom had a fragile X premutation. None of the women with a full mutation experienced POF in our series of patients. We also identified 89 families without a family history of fragile X or mental retardation, and there were 108 subjects who experienced POF, of which 6.5% had a fragile X premutation. This is 70-fold higher than the background prevalence of fragile X premutation in the Italian population and suggests an association with POF. These data confirm the results of other surveys.     

The fragile X syndrome.

The fragile X syndrome is characterised by mental retardation, behavioural features, and physical features, such as a long face with large protruding ears and macro-orchidism. In 1991, after identification of the fragile X mental retardation (FMR1) gene, the cytogenetic marker (a fragile site at Xq27.3) became replaced by molecular diagnosis. The fragile X syndrome was one of the first examples of a "novel" class of disorders caused by a trinucleotide repeat expansion. In the normal population, the CGG repeat varies from six to 54 units. Affected subjects have expanded CGG repeats (>200) in the first exon of the FMR1 gene (the full mutation). Phenotypically normal carriers of the fragile X syndrome have a repeat in the 43 to 200 range (the premutation). The cloning of the FMR1 gene led to the characterisation of its protein product FMRP, encouraged further clinical studies, and opened up the possibility of more accurate family studies and fragile X screening programmes.     

Abnormal elevation of FMR1 mRNA is associated with psychological symptoms in individuals with the fragile X premutation.

Until recently, individuals with premutation alleles (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene were believed to be psychologically unaffected. However, the recent documentation of abnormal elevation of FMR1 mRNA, discovery of fragile X-associated tremor/ataxia syndrome (FXTAS), and reports of psychiatric disorders in children and adults with the premutation have suggested a pathogenic gene-brain-behavior mechanism. In a large collaborative study, 68 men and 144 women with the FMR1 premutation completed a psychological symptoms checklist and FMR1 genetic testing, including determination of CGG repeat size, percentage of FMR1 protein (FMRP)-positive lymphocytes, and FMR1 mRNA levels. Relative to published norms, men and women with FXTAS symptoms reported higher levels of several types of psychological symptoms. In addition, men and women with the premutation and no overt evidence of FXTAS reported higher levels of obsessive-compulsive symptoms. Elevated FMR1 mRNA, but not CGG repeat size or reduced FMRP (as measured by immunocytochemistry), was significantly associated with increased psychological symptoms, predominantly obsessive-compulsive symptoms and psychoticism, in premutation men with and without FXTAS symptoms. There was no relationship between CGG repeat size, FMR1 mRNA or FMRP and psychological symptoms in premutation women unless the sample was restricted to those with skewed X-activation ratio toward >50% active premutation alleles. The results of this study support the hypothesis that FMR1 function is associated with psychological difficulties in individuals with the premutation, and provide evidence concordant with an RNA toxic gain-of-function model in a neuropsychiatric phenotype.     

Population-based estimates of the prevalence of FMR1 expansion mutations in women with early menopause and primary ovarian insufficiency

PurposePrimary ovarian insufficiency before the age of 40 years affects 1% of the female population and is characterized by permanent cessation of menstruation. Genetic causes include FMR1 expansion mutations. Previous studies have estimated mutation prevalence in clinical referrals for primary ovarian insufficiency, but these are likely to be biased as compared with cases in the general population. The prevalence of FMR1 expansion mutations in early menopause (between the ages of 40 and 45 years) has not been published.MethodsWe studied FMR1 CGG repeat number in more than 2,000 women from the Breakthrough Generations Study who underwent menopause before the age of 46 years. We determined the prevalence of premutation (55–200 CGG repeats) and intermediate (45–54 CGG repeats) alleles in women with primary ovarian insufficiency (n = 254) and early menopause (n = 1,881).ResultsThe prevalence of the premutation was 2.0% in primary ovarian insufficiency, 0.7% in early menopause, and 0.4% in controls, corresponding to odds ratios of 5.4 (95% confidence interval = 1.7–17.4; P = 0.004) for primary ovarian insufficiency and 2.0 (95% confidence interval = 0.8–5.1; P = 0.12) for early menopause. Combining primary ovarian insufficiency and early menopause gave an odds ratio of 2.4 (95% confidence interval = 1.02–5.8; P = 0.04). Intermediate alleles were not significant risk factors for either early menopause or primary ovarian insufficiency.ConclusionFMR1 premutations are not as prevalent in women with ovarian insufficiency as previous estimates have suggested, but they still represent a substantial cause of primary ovarian insufficiency and early menopause.Genet Med16 1, 19–24.     

AGG interruptions within the maternal FMR1 gene reduce the risk of offspring with fragile X syndrome

PurposeThe ability to accurately predict the likelihood of expansion of the CGG repeats in the FMR1 gene to a full mutation is of critical importance for genetic counseling of women who are carriers of premutation alleles (55–200 CGG repeats) and who are weighing the risk of having a child with fragile X syndrome. The presence of AGG interruptions within the CGG repeat tract is thought to decrease the likelihood of expansion to a full mutation during transmission, thereby reducing risk, although their contribution has not been quantified.MethodsWe retrospectively analyzed 267 premutation alleles for number and position of AGG interruptions, length of pure CGG repeats, and CGG repeat lengths present in the offspring of the maternal transmissions. In addition, we determined the haplotypes of four markers flanking the 5′-UTR locus in the premutation mothers.ResultsWe found that the presence of AGG interruptions significantly increased genetic stability, whereas specific haplotypes had a marginal association with transmission instability.ConclusionThe presence of AGG interruptions reduced the risk of transmission of a full mutation for all maternal (premutation) repeat lengths below ~100 CGG repeats, with a differential risk (0 vs. 2 AGG) exceeding 60% for alleles in the 70- to 80-CGG repeat range.Genet Med 2012:14(8):729–736     

Expand Long PCR for fragile X mutation detection

Fragile X mutation detection by DNA analysis enables accurate diagnosis of the fragile X syndrome. The mutation involves the expansion of CGG repeats in the FMR1 gene and has been primarily detected by the Southern blotting method. In this study we present a novel, efficient and reliable PCR protocol that is more convenient for routine diagnosis of the fragile X syndrome. This method is based on the use of the Expand Long PCR System, which enables the amplification of normal, premutated and full-mutated alleles, and therefore provides complete CGG repeat analysis of the FMR1 gene. Normal alleles were easily detected by ethidium bromide staining of the agarose gels, suggesting that this assay could be used as a screening test for a large number of referrals. The amplified premutations and full mutations were identified by hybridization with a digoxigenin-labeled 5'-(CGG)_5–3' probe, followed by chemiluminescent detection. The accuracy of our Expand Long PCR protocol was confirmed by Southern blot analysis, illustrating that the Expand Long PCR results concur with those of Southern blotting. In this paper we propose a new strategy for molecular diagnosis of the fragile X syndrome in which our Expand Long PCR assay is used as the first screening test for fragile X mutation detection.     

Prenatal diagnosis of fragile X syndrome and the risk of expansion of a premutation

The aim of the present study was to evaluate prospectively the dynamics of the FMR1 gene. The risk of full mutation among pregnant women and the carriers, and the risk of expansion of a premutation allele to a full mutation were estimated. We identified 89 pregnant women with an expanded FMR1 gene seeking prenatal diagnosis. Amniocentesis or chorion villus sampling (CVS) was offered and a DNA test of the FMR1 gene was carried out in such pregnancies. The overall risk of full mutation among women (N = 21) with a repeat size between 60 and 80 was 4.8% (one fetus with mosaicism), and the risk of expansion of the premutation allele to a full mutation was 14% in those offspring to whom the premutation allele was transmitted. The risk of full mutation among the carriers (N = 13) with a repeat size between 81 and 100 was 61.5% (8/13), and the risk of expansion of a premutation allele to a full mutation was 89%. Only one case fell into the category of 101-200 repeats, and expansion to a full mutation was recorded. Fetuses of full mutation mothers inherited the larger allele in 64% (14/22) of the cases. The range of 40-59 repeats was safe: there were no fetal full mutations. The risk of full mutation was also low among the subjects with a repeat size between 60 and 80, whereas the risk increased significantly after 80 repeats. Maternal premutation size was positively correlated with the risk of having a full mutation offspring.     

Clinical phenotypes of a juvenile sibling pair carrying the fragile X premutation

Individuals with alleles containing 55-200 CGG repeats in the fragile X mental retardation (FMR1) gene are premutation carriers. The premutation allele has been shown to lead to a number of types of clinical involvement, including shyness, anxiety, social deficits, attention deficit hyperactivity disorder (ADHD), and executive function deficits. Some of these problems could be due to mild deficits of the fragile X protein (FMRP) and a possible developmental effect of the elevated FMR1 mRNA observed in carriers. In addition, two abnormal phenotypes specific to the premutation have been described. Primary ovarian insufficiency (FXPOI), defined by cessation of menses prior to age 40, occurs in 20% of females with the premutation. The other phenotype, fragile X-associated tremor/ataxia syndrome (FXTAS), affects some older adult premutation carriers. Premutation females typically have one expanded allele (≥55 CGG repeats) and one normal allele (≤54 CGG repeats). This study describes the cognitive, behavioral, and molecular profile of a female with two alleles in the premutation range (60 and 67 CGG repeats) in comparison to her brother with a similar premutation size (65 CGG repeats). Both exhibited high IQ scores, anxiety, and some physical features associated with fragile X syndrome. This comparison allows us to examine the effect of the premutation in this male-female pair while controlling for environmental and background genetic factors.     

Sleep apnea in fragile X premutation carriers with and without FXTAS

This report seeks to establish the prevalence of sleep apnea in patients with the fragile X mental retardation 1 (FMR1) premutation with and without fragile X-associated tremor/ataxia syndrome (FXTAS) and to determine any correlation between CGG repeat and FMR1 mRNA levels with sleep apnea prevalence. Demographic and medical data from 430 (229 males, 201 females) participants were used in this analysis. Participants included premutation carriers with (n = 118) and without FXTAS (n = 174) as well as controls without the premutation (n = 123). Logistic regression models were employed to estimate the odds ratio of sleep apnea relative to controls, adjusted for age and gender, and also to examine potential association with CGG size and FMR1 mRNA expression level. The observed proportion of sleep apnea in premutation carriers with and without FXTAS and controls are 31.4% (37/118), 8.6% (15/174), and 13.8% (17/123), respectively. The adjusted odds of sleep apnea for premutation carriers with FXTAS is about 3.4 times that compared to controls (odds ratio, OR = 3.4, 95% confidence interval (CI) 1.8-7.4; P = 0.001), and similarly relative to premutation carriers without FXTAS (OR = 2.9, 95% CI 1.2-6.9; P = 0.014). The risk of sleep apnea was not different between controls and premutation carriers without FXTAS. The presence of sleep apnea is not associated with CGG repeat numbers nor FMR1 mRNA expression level among premutation carriers. Our data supports a higher prevalence and risk of sleep apnea in patients with FXTAS. We recommend that all patients diagnosed with FXTAS be screened for sleep apnea given the negative and perhaps accelerative impact sleep apnea may have on their FXTAS progression.     

The number of CGG repeats of the FMR1 locus in premutated and fully mutated heterozygotes and their offspring: Implications for the origin of mosaicism

The size of the CGG repeat of the FMR1 gene was investigated with probe StB12.3 in 154 transmissions to the offspring of heterozygotes for the premutation and the full mutation. Among the 135 offspring of premutated heterozygotes there were three decreases in size of the repeats: in two of these cases a full mutation was present along with the decreased premutation, and in a third mosaic (46,fra(X)(q27.3),Y), a normal allele was observed. In the 19 offspring of fully mutated females with no detected mosaicism, there were three mosaics and three individuals who had full mutations that included a number of repeats smaller than those present in their mothers. Among the 32 offspring who received a premutation from their premutated mothers, 27 alleles were increased in size and 5 remained unaltered. Among 11 mosaic offspring of premutated mothers, the premutation increased in 4, decreased in 3, and was unchanged in 4. In contrast to the trend of an increasing premutation size in the non-mosaic offspring, the premutation present in mosaics can be smaller, larger, or of unaltered size with approximately equal frequencies. These data suggest that the premutations present in mosaics result from mitotic instability of the inherited full mutations. This is further supported by the finding of a mosaic male with a normal sized allele. © 1996 Wiley-Liss, Inc.     

Small CGG repeat expansion alleles of FMR1 gene are associated with parkinsonism

Fragile X-associated tremor/ataxia syndrome (FXTAS) affects older males carrying premutation, that is, expansions of the CGG repeat (in the 55–200 range), in the FMR1 gene. The neurological changes are linked to the excessive FMR1 messenger RNA (mRNA), becoming toxic through a 'gain-of-function'. Because elevated levels of this mRNA are also found in carriers of the smaller expansion (grey zone) alleles, ranging from 40 to 54 CGGs, we tested for a possible role of these alleles in the origin of movement disorders associated with tremor.
We screened 228 Australian males affected with idiopathic Parkinson's disease and other causes of parkinsonism recruited from Victoria and Tasmania for premutation and grey zone alleles. The frequencies of either of these alleles were compared with the frequencies in a population-based sample of 578 Guthrie spots from consecutive Tasmanian male newborns (controls). There was a significant excess of premutation carriers (Fisher's exact test p = 0.006). There was also a more than twofold increase in grey zone carriers in the combined sample of the Victorian and Tasmanian cases, with odds ratio (OR ) = 2.36, and 95% confidence intervals (CI): 1.20–4.63, as well as in Tasmanian cases only (OR = 2.33, 95% CI: 1.06–5.13), compared with controls. The results suggest that the FMR1 grey zone alleles, as well as premutation alleles, might contribute to the aetiology of disorders associated with parkinsonism.