CGG Expansion Research Articles

White matter changes in basis pontis in small expansion FMR1 allele carriers with parkinsonism

Examples of white matter hyperintensities (wmh) on magnetic resonance images in a basis pontis are presented in two male carriers, each of whom carry a small CGG expansion fragile X mental retardation (FMR1) allele. One carried a premutation (PM) allele of 85 CGG repeats and the other, a gray zone (GZ) allele of 47 repeats. Both were originally diagnosed with idiopathic Parkinson's disease (iPD). Similar changes are also shown in one PM carrier of 99 repeats affected with mild tremor and imbalance, who was ascertained through a fragile X syndrome family. These examples draw attention to the occurrence of wmh in a basis pontis in the carriers of small CGG expansions presenting with tremor and ataxia. Moreover, the presence of this change in GZ, as well as PM, allele carriers originally diagnosed with iPD supports our earlier suggestion that both these alleles may contribute to the neurodegenerative changes in this disorder which, in the examples presented, have been reflected by wmh, most prominent in the cerebellar peduncles and/or pontine area.

Distribution of CGG/GCC Repeats at the FMR1 and FMR2 Genes in an Indian Population with Mental Retardation of Unknown Etiology

Fragile X syndrome is one of the X-linked disorders associated with moderate to severe mental retardation. Fragile X A syndrome (FRAXA) and fragile X E syndrome (FRAXE) are caused by trinucleotide repeat expansion of CGG and GCC repeats at the 5' untranslated region of the FMR1 and FMR2 genes, respectively. The present study was undertaken to identify the repeat polymorphism and to estimate the risk of transmission in Andhra Pradesh and surrounding states of South India. The FRAXA and FRAXE allelic polymorphisms were studied by radioactive polymerase chain reaction that revealed 25 FRAXA among 344 X-chromosomes and 20 FRAXE allelic variants among 212 X-chromosomes in our population. The most frequent FRAXA allele size was of 29 CGG repeats (27.5%) followed by allele sizes of 28 (20.8%) and 31 (7.2%), and that of FRAXE was 15 GCC repeats (24.0%) followed by allele containing 18 repeats (18.4%) and 16 repeats (11.3%). CGG/GCC repeat polymorphism at the FMR1 and FMR2 loci observed in this study demonstrated a racial and ethnic variation among the populations.

Four sisters compound heterozygotes for the pre- and full mutation in fragile X syndrome and a complete inactivation of X-functional chromosome: implications for genetic counseling

Fragile X syndrome (FXS) is a neurodevelopmental disorder and a leading monogenic form of cognitive impairment and autism. It is the most common form of inherited mental retardation in males and a significant cause of mental retardation in females. It is caused by the instability and subsequent expansion of the CGG repeat in the promoter region of the FMR1 (fragile X mental retardation 1) gene at Xq27.3. We describe a double consanguineous family with four sisters compound heterozygotes for the full and pre-mutation CGG repeat size. The index case shows clinical features of the affected males with profound mental retardation; the other three sisters also suffer from mental retardation, ranging from mild to severe. Molecular analysis reveals very similar ranges for the CGG expansions for both chromosomes in all four sisters. The phenotypic differences observed in the index case and her sisters are the total inactivation of X premutated chromosome and the total absence of FMRP (fragile X mental retardation protein). This family case raises important issues for genetic counseling in families with consanguinity and with cases of idiopathic mental retardation.

Linking the FMR1 alleles with small CGG expansions with neurodevelopmental disorders: Preliminary data suggest an involvement of epigenetic mechanisms

American Journal of Medical Genetics Part AVolume 149A, Issue 10 p. 2306-2310 Research Letter Linking the FMR1 alleles with small CGG expansions with neurodevelopmental disorders: Preliminary data suggest an involvement of epigenetic mechanisms† Danuta Z. Loesch, Corresponding Author Danuta Z. Loesch d.loesch@latrobe.edu.au The Olga Tennison Centre for Autism Research, School of Psychological Science, La Trobe University, Melbourne, Victoria, AustraliaSchool of Psychological Science, La Trobe University, Melbourne, VIC 3086, Australia.Search for more papers by this authorDavid E. Godler, David E. Godler Department of Paediatrics, Chromosome and Chromatin Research Laboratory, The Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorMahmoud Khaniani, Mahmoud Khaniani Department of Paediatrics, Chromosome and Chromatin Research Laboratory, The Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorEmma Gould, Emma Gould The Olga Tennison Centre for Autism Research, School of Psychological Science, La Trobe University, Melbourne, Victoria, AustraliaSearch for more papers by this authorFreya Gehling, Freya Gehling Department of Paediatrics, Chromosome and Chromatin Research Laboratory, The Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorCheryl Dissanayake, Cheryl Dissanayake The Olga Tennison Centre for Autism Research, School of Psychological Science, La Trobe University, Melbourne, Victoria, AustraliaSearch for more papers by this authorTrent Burgess, Trent Burgess VCGS Cytogenetics Laboratory, Murdoch Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorFlora Tassone, Flora Tassone Department of Biological Chemistry, School of Medicine, University of California Davis, Sacramento, CaliforniaSearch for more papers by this authorRichard Huggins, Richard Huggins Department of Mathematics and Statistics, University of Melbourne, Melbourne, Victoria, AustraliaSearch for more papers by this authorHoward Slater, Howard Slater VCGS Cytogenetics Laboratory, Murdoch Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorKH Andy Choo, KH Andy Choo Department of Paediatrics, Chromosome and Chromatin Research Laboratory, The Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this author Danuta Z. Loesch, Corresponding Author Danuta Z. Loesch d.loesch@latrobe.edu.au The Olga Tennison Centre for Autism Research, School of Psychological Science, La Trobe University, Melbourne, Victoria, AustraliaSchool of Psychological Science, La Trobe University, Melbourne, VIC 3086, Australia.Search for more papers by this authorDavid E. Godler, David E. Godler Department of Paediatrics, Chromosome and Chromatin Research Laboratory, The Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorMahmoud Khaniani, Mahmoud Khaniani Department of Paediatrics, Chromosome and Chromatin Research Laboratory, The Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorEmma Gould, Emma Gould The Olga Tennison Centre for Autism Research, School of Psychological Science, La Trobe University, Melbourne, Victoria, AustraliaSearch for more papers by this authorFreya Gehling, Freya Gehling Department of Paediatrics, Chromosome and Chromatin Research Laboratory, The Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorCheryl Dissanayake, Cheryl Dissanayake The Olga Tennison Centre for Autism Research, School of Psychological Science, La Trobe University, Melbourne, Victoria, AustraliaSearch for more papers by this authorTrent Burgess, Trent Burgess VCGS Cytogenetics Laboratory, Murdoch Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorFlora Tassone, Flora Tassone Department of Biological Chemistry, School of Medicine, University of California Davis, Sacramento, CaliforniaSearch for more papers by this authorRichard Huggins, Richard Huggins Department of Mathematics and Statistics, University of Melbourne, Melbourne, Victoria, AustraliaSearch for more papers by this authorHoward Slater, Howard Slater VCGS Cytogenetics Laboratory, Murdoch Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this authorKH Andy Choo, KH Andy Choo Department of Paediatrics, Chromosome and Chromatin Research Laboratory, The Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, AustraliaSearch for more papers by this author First published: 24 September 2009 https://doi.org/10.1002/ajmg.a.32990Citations: 22 † How to cite this article: Loesch DZ, Godler DE, Khaniani M, Gould E, Gehling F, Dissanayake C, Burgess T, Tassone F, Huggins R, Slater H, Choo KHA. 2009. Linking the FMR1 alleles with small CGG expansions with neurodevelopmental disorders: Preliminary data suggest an involvement of epigenetic mechanisms. Am J Med Genet Part A 149A:2306–2310. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume149A, Issue10October 2009Pages 2306-2310 RelatedInformation

Do etiologies of premature ovarian aging (POA) mimic those of premature ovarian failure (POF)?

It is unknown whether etiologies differ between milder forms of premature ovarian senescence (the acronym given here 'premature ovarian aging, POA'), and premature ovarian failure (POF). We assessed presumed pathophysiologies in 74 consecutive POA patients, diagnosed based on elevated age-specific baseline follicle stimulating hormone and/or abnormally low anti-Müllerian hormone levels (<1.5 ng/ml). A genetic etiology was presumed with > or = 34 triple CGG expansions on the FMR1 gene. An autoimmune etiology was assumed with at least one abnormality in a laboratory panel, involving antinuclear, antiphospholipid and thyroid antibodies, total immunoglobulin levels and anti-ovarian as well as anti-adrenal autoantibodies. A combined etiology was presumed with both autoimmune and genetic etiologies, and a patient was considered idiopathic when no abnormalities were found. Twelve of 74 (16.2%) women demonstrated a genetic, 28 (37.8%) an autoimmune, 9 (12.2%) combined and 25 (33.8%) idiopathic etiologies. Presumed underlying etiologies with POA follow a similar distribution pattern as reported for POF. POA and POF may, therefore, represent a continuum in phenotypical expression of different etiologies of premature ovarian senescence. Like POF, POA should be considered reason to investigate underlying etiologies.

Is the immunological noise of abnormal autoimmunity an independent risk factor for premature ovarian aging?

The risk for premature ovarian failure increases in association with two principal known etiologies: in the presence of excessive triple CGG expansions on the FMR1 (fragile X) gene (genetic etiology) and in association with a variety of autoimmune conditions (autoimmune etiology). To what degree milder forms of premature ovarian aging are also associated with these two etiologies is, however, unknown. We, therefore, investigated 119 consecutive, so identified, infertile women and statistically correlated by linear and logistic regression analyses ovarian function parameters to markers of a possible genetic etiology (number of CGG triple repeats on the FMR1 gene) and to markers of possible abnormal immune function (immune panel). Sixty (50.4%) of 119 participants demonstrated at least one immune abnormality. Both groups did not differ statistically in age, mean follicle-stimulating hormone, estradiol, and antimüllerian hormone levels, although antimüllerian hormone suggested a trend toward higher levels in autoimmune participants (P = 0.19). Autoimmune participants also demonstrated lower mean triple CGG expansion sizes (P < 0.05) and included fewer women with greater than or equal to 35 triple repeats (relative risk, 4.0; 95% CI, 1.3-11.9; P < 0.01), previously reported to demarcate increased risk for premature ovarian aging. Even minimal evidence of abnormal autoimmune function ("immunological noise") seems to increase risk toward premature ovarian aging, often manifesting as infertility. Evidence of abnormal autoimmune function, such as increased CGG triple expansion sizes, in young women, therefore, warrants vigilance for development of prematurely diminished ovarian reserve and infertility.

Improved Methodology for Assessment of mRNA Levels in Blood of Patients with FMR1 Related Disorders

BackgroundElevated levels of FMR1 mRNA in blood have been implicated in RNA toxicity associated with a number of clinical conditions. Due to the extensive inter-sample variation in the time lapse between the blood collection and RNA extraction in clinical practice, the resulting variation in mRNA quality significantly confounds mRNA analysis by real-time PCR.MethodsHere, we developed an improved method to normalize for mRNA degradation in a sample set with large variation in rRNA quality, without sample omission. Initially, RNA samples were artificially degraded, and analyzed using capillary electrophoresis and real-time PCR standard curve method, with the aim of defining the best predictors of total RNA and mRNA degradation.ResultsWe found that: (i) the 28S:18S ratio and RNA quality indicator (RQI) were good predictors of severe total RNA degradation, however, the greatest changes in the quantity of different mRNAs (FMR1, DNMT1, GUS, B2M and GAPDH) occurred during the early to moderate stages of degradation; (ii) chromatographic features for the 18S, 28S and the inter-peak region were the most reliable predictors of total RNA degradation, however their use for target gene normalization was inferior to internal control genes, of which GUS was the most appropriate. Using GUS for normalization, we examined in the whole blood the relationship between the FMR1 mRNA and CGG expansion in a non-coding portion of this gene, in a sample set (n = 30) with the large variation in rRNA quality. By combining FMR1 3' and 5' mRNA analyses the confounding impact of mRNA degradation on the correlation between FMR1 expression and CGG size was minimized, and the biological significance increased from p = 0.046 for the 5' FMR1 assay, to p = 0.018 for the combined FMR1 3' and 5' mRNA analysis.ConclusionOur observations demonstrate that, through the use of an appropriate internal control and the direct analysis of multiple sites of target mRNA, samples that do not conform to the conventional rRNA criteria can still be utilized to obtain biologically/clinically relevant data. Although, this strategy clearly has application for improved assessment of FMR1 mRNA toxicity in blood, it may also have more general implications for gene expression studies in fresh and archival tissues.

Aetiology of premature ovarian failure

Premature ovarian failure (POF) is the occurrence of hypergonadotropic hypoestrogenic amenorrhoea in women under the age of 40 years. POF is idiopathic in 74-90% of cases but can be familial (4-33%) or sporadic. The known causes are: genetic aberrations; autoimmune ovarian damage; iatrogenic following surgery, radiotherapy or chemotherapy; environmental factors (viruses, toxins, etc.); and metabolic (galactosaemia, 17 OH deficiency, etc.) Genetic aberrations could involve the X chromosome (monosomy, trisomy or translocations) or be autosomal. Genetic mechanisms include reduced gene dosage and non-specific chromosome effect impairing meiosis, decreasing the pool of primordial follicles and increasing atresia due to apoptosis or failure of follicle maturation. The genes for POF-1 are localized to Xq 21.3-Xq27 and for POF-2 to Xq13.3-21.1. The FMR1 gene is responsible for the fragile X syndrome. It occurs due to CGG expansion of more than 55 repeats at the 5'UTR (Xq 27.3), which is associated with gene silence resulting in mental retardation in males, and POF in female carriers. Autoimmune ovarian damage is caused by the alteration of T-cell subsets and T-cell-mediated injury, increase of autoantibody producing B-cells and a low number of effector suppressor/cytotoxic lymphocyte and a decrease of number and activity of natural killer cells. POF can be associated with other non-endocrine and endocrine diseases. The mutations of AIRE gene are responsible for polyendocrinopathies (APS I-III). As the cause of POF is unknown in the majority of cases and the number of women with POF is increasing, the primary goal of scientific groups worldwide should be focused on the study of the aetiology of POF.

Peripheral nervous system pathology in fragile X tremor/ataxia syndrome (FXTAS)

Fragile X tremor/ataxia syndrome (FXTAS) occurs in individuals with moderate CGG expansion of the fragile X mental retardation 1 (FMR1) gene and is associated with intranuclear inclusions in neurons and astrocytes. Although the neuropathologic findings in the brain and spinal cord were described, pathological features in the peripheral nervous system were not reported. Here, we report on novel neuropathological findings in the peripheral nervous system and especially in autonomic ganglia at autopsy in a man with FXTAS. In addition to the characteristic brain and spinal cord findings, typical intranuclear inclusions were identified in the ganglion cells of adrenal medulla, dorsal root ganglia, paraspinal sympathetic ganglia, myenteric ganglia of the stomach and subepicardial autonomic ganglion of the heart. Our findings indicate that FXTAS diffusely involves the central and peripheral nervous systems, which explains the protean neurological symptoms ranging from dementia to dysautonomia.

AETIOLOGY OF PREMATURE OVARIAN FAILURE

Premature ovarian failure (POF) is the occurrence of hypergonadotropic hypoestrogenic amenorrhoea in women under the age of 40 years. POF is idiopathic in 74-90% of cases but can be familial (4-33%) or sporadic. The known causes are: genetic aberrations; autoimmune ovarian damage; iatrogenic following surgery, radiotherapy or chemotherapy; environmental factors (viruses, toxins, etc.); and metabolic (galactosaemia, 17 OH deficiency, etc.) Genetic aberrations could involve the X chromosome (monosomy, trisomy or translocations) or be autosomal. Genetic mechanisms include reduced gene dosage and non-specific chromosome effect impairing meiosis, decreasing the pool of primordial follicles and increasing atresia due to apoptosis or failure of follicle maturation. The genes for POF-1 are localized to Xq 21.3-Xq27 and for POF-2 to Xq13.3-21.1. The FMR1 gene is responsible for the fragile X syndrome. It occurs due to CGG expansion of more than 55 repeats at the 5'UTR (Xq 27.3), which is associated with gene silence resulting in mental retardation in males, and POF in female carriers. Autoimmune ovarian damage is caused by the alteration of T-cell subsets and T-cell-mediated injury, increase of autoantibody producing B-cells and a low number of effector suppressor/cytotoxic lymphocyte and a decrease of number and activity of natural killer cells. POF can be associated with other non-endocrine and endocrine diseases. The mutations of AIRE gene are responsible for polyendocrinopathies (APS I-III). As the cause of POF is unknown in the majority of cases and the number of women with POF is increasing, the primary goal of scientific groups worldwide should be focused on the study of the aetiology of POF.

Replisome stalling and stabilization at CGG repeats, which are responsible for chromosomal fragility

Expanded CGG repeats cause chromosomal fragility and hereditary neurological disorders in humans. Replication forks stall at CGG repeats in a length-dependent manner in primate cells and in yeast. Saccharomyces cerevisiae proteins Tof1 and Mrc1 facilitate replication fork progression through CGG repeats. Remarkably, the fork-stabilizing role of Mrc1 does not involve its checkpoint function. Thus, chromosomal fragility might occur when forks stalled at expanded CGG repeats escape the S-phase checkpoint.

Molecular diagnosis of Fragile X syndrome

Fragile X syndrome, the most prevalent inherited cause of mental retardation, is related to hyperexpansion of a polymorphic CGG repeat of the FMR1 gene. Expansion of 55–200 repeats are called premutations and characterize carriers who usually have no mental impairment. The disease causing full mutations exceed 200 CGG repeats, are hypermethylated and lead to transcriptional silencing of the gene and absence of the Fragile X mental retardation protein (FMRP). Diagnostic approaches involve molecular and immunocytochemical techniques. Southern blot, which allows mutations to be detected and methylation status to be determined in a single test, remains the procedure of choice for most laboratories. Modifications of PCR methods, including methylation specific PCR, are also proposed but their implementation is still in question because of inherent difficulties to amplify CGG repeats, distinguish between mosaic patterns and interpret results in female individuals. The FMRP antibody test is also suitable for large population screening and elucidation of Fragile X syndrome cases with no CGG expansion, but it is not widely applied. In search for novel diagnostic approaches, use of PCR as a first prescreening test followed by Southern blot is considered the most reliable procedure.

A Pseudo-Full Mutation Identified in Fragile X Assay Reveals a Novel Base Change Abolishing an EcoRI Restriction Site

Diagnostic testing for the fragile X syndrome is designed to detect the most common mutation, a CGG expansion in the 5'-untranslated region of the fragile X mental retardation (FMRI) gene. PCR can determine the number of CGG repeats less than 100, whereas Southern analysis can detect large premutations, full mutations, and their methylation status. Bands larger than 5.8 kb observed via Southern analysis are usually considered a methylated full mutation, causing fragile X syndrome in males and varied clinical presentations in females. We observed a 10.9-kb band on a Southern blot assay from an autistic girl with language delay. Further investigation identified a novel G-to-A transition at an EcoRI cleavage site, upstream of the CGG repeat region of the FMRI gene. This base change abolished the EcoRI restriction site, resulting in a 10.9-kb pseudo-full mutation. This G-to-A base change has not been previously reported and was not identified in a subsequent analysis of 105 male and 30 female patient samples. The clear 10.9-kb band detected on a Southern blot assay for fragile X syndrome mimics a large, methylated full mutation, which could result in a misdiagnosis without the benefit of family studies and further testing.

Autoimmune function and number of triple CGG expansions on the FMR1 gene as independent risk factors for premature ovarian senescence

OBJECTIVE: Preliminary data suggest that numbers of triple CGG expansions on the FMR1 gene and the presence of autoimmune laboratory abnormalities distinguish two specific geno- and phenotypes amongst women with premature ovarian senescence (Gleicher et al., Fertil Steril, doi:10/1016/j.fernstert.2008.01.099). This study attempted in a larger patient sample and with higher statistical power, to confirm whether increasing triple CGG expansions sizes and abnormal autoimmune function represent independent risk factors for premature ovarian senescence. DESIGN: Cohort study. MATERIALS AND METHODS: 119 new, consecutive infertility patients with diminished ovarian reserve were investigated for number of CGG triple expansions on the FMR1 gene and evidence of abnormal autoimmune function. Statistical correlations were calculated with the higher of two allele triple repeat counts, designated as allele-2. Below (<) versus above (≥) 35 triple repeats defined the cut off between normal and elevated triple repeats, which denotes genetic risk for premature ovarian senescence (Gleicher et al., Fertil Steril, doi:10/1016/j.fertnstert.2008.01.098). To prevent statistical distortions from only few high triple repeat expansion sizes, associated with pre- and full fragile X mutations, this study was restricted to <55 triple repeats, the upper limit of the intermediate zone. RESULTS: 59/119 women showed no evidence of autoimmunity and 60 did. Mean ages (36.8 ± 5.2 vs. 36.0 ± 4.8 years), baseline follicle stimulating hormone (FSH) (13.6 ± 11.2 vs. 16.0 ± 26.0 mIU/ml), estradiol (51.4 ± 26.8 vs. 52.5 ± 26.2 pg/ml) and anti-Müllerian hormone (AMH) (0.97 ± 1.0 vs. 1.4 ± 2.0 ng/ml) did not differ significantly between both groups. CGG triple repeats on allele-1 also did not differ (28.5 ± 5.6 vs. 27.4 ± 4.4). Allele-2, however demonstrated significantly higher mean allele counts in non-immune than autoimmune patients (33.3 ± 5.6 vs 31.3 ± 4.2; p < 0.05). CONCLUSIONS: These data confirm a high prevalence of abnormal autoimmune function in infertile women with diminished ovarian reserve. They also suggest that abnormal autoimmune function helps to define two etiologically distinct patient subgroups of women with premature ovarian senescence, one autoimmune, defined by abnormal autoimmune function, and the second genetic, defined by abnormal triple CGG expansion sizes.

Triple CGG expansions on the FMR1 gene and response to ovarian stimulation

OBJECTIVE: CGG triple expansion sizes on the FMR1 gene, correlate in normal and in intermediate ranges in younger women with ovarian reserve, reflected by AMH. Whether they also predict response to ovarian stimulation with gonadotropins is unknown and was subject of this investigation.

Relevance of low expansion CGG triple repeats numbers on the FMR1 gene to functional ovarian reserve

OBJECTIVE: A large majority of individuals demonstrate 29-30 CGG repeats on the FMR1 gene. Thirty CGG repeats have also been reported as the switching point between positive and negative effects of the translation product of the FMR1 gene. A minority amongst all ethnicities demonstrate higher or lower expansion sizes. Higher expansion sizes have been statistically correlated to risk towards premature ovarian senescence and diminished ovarian reserve, which seems independent of risk towards premature ovarian senescence associated with abnormal autoimmune function. Whether lower expansions sizes also correlate with ovarian function was subject of this study. DESIGN: Cohort study. MATERIALS AND METHODS: 300 consecutive new infertility patients, of which 81 demonstrated ≤28 triple CGG repeats on the lower count allele (allele-1), represented the study population. Triple CGG expansion sizes on allele-1 were statistically correlated by linear and logistic regression analyses to ovarian reserve parameters [FSH and AMH] in women with ≤28 repeats (low expansion sizes) and ≥ 34 repeats (high expansion sizes), thus excluding women with > 28 – 33 repeats, representing the distribution peak for most humans and, therefore, a large majority of all women (Fu et al, Cell 1991). RESULTS: Low expansion size did not differ from high expansion size patients in age, FSH and AMH levels. Neither FSH nor AMH statistically correlated in linear regression with triple CGG expansions ≤28 repeats. Logistic regression demonstrated, however, that an AMH level ≤0.8 ng/ml (indicative of diminished ovarian reserve at all ages) was significantly associated with triple CGG repeats on allele-1 (p<0.001). An increase by 5 triple expansions ≤28 repeats reduced risk for diminished ovarian reserve by 40%, while an increase by 5 triple expansions in women with ≥34 repeats increased risk by 50% (p= 0.002, each). CONCLUSIONS: High (≥34) and low expansion sizes (≤28) statistically correlate with risk towards diminished ovarian reserve. This for the first time explains the unusual distribution pattern of triple CGG repeats in the population, characterized by a large peak at 29-30 repeats. As Chinese women demonstrate, CGG distribution patterns vary between ethnicities, which may relate to reported differences in prevalence of premature ovarian senescence and IVF outcomes.

Elongation Factor 2 and Fragile X Mental Retardation Protein Control the Dynamic Translation of Arc/Arg3.1 Essential for mGluR-LTD

Group I metabotropic glutamate receptors (mGluR) induce long-term depression (LTD) that requires protein synthesis. Here, we demonstrate that Arc/Arg3.1 is translationally induced within 5 min of mGluR activation, and this response is essential for mGluR-dependent LTD. The increase in Arc/Arg3.1 translation requires eEF2K, a Ca(2+)/calmodulin-dependent kinase that binds mGluR and dissociates upon mGluR activation, whereupon it phosphorylates eEF2. Phospho-eEF2 acts to slow the elongation step of translation and inhibits general protein synthesis but simultaneously increases Arc/Arg3.1 translation. Genetic deletion of eEF2K results in a selective deficit of rapid mGluR-dependent Arc/Arg3.1 translation and mGluR-LTD. This rapid translational mechanism is disrupted in the fragile X disease mouse (Fmr1 KO) in which mGluR-LTD does not require de novo protein synthesis but does require Arc/Arg3.1. We propose a model in which eEF2K-eEF2 and FMRP coordinately control the dynamic translation of Arc/Arg3.1 mRNA in dendrites that is critical for synapse-specific LTD.

Investigation of Phenotypes Associated with Mood and Anxiety Among Male and Female Fragile X Premutation Carriers

The fragile X disorder spectrum, due to a CGG expansion in FMR1, includes fragile X syndrome (>200 repeats) and the premutation-associated disorders of ovarian insufficiency and tremor/ataxia syndrome (approximately 55-199 repeats). Altered neurobehavioral profiles including variation of phenotypes associated with mood and anxiety may be expected among younger premutation carriers given this spectrum of disorders. However, previous studies have produced conflicting findings, providing the motivation to examine these phenotypes further. We investigated measures of mood and anxiety in 119 males and 446 females age 18-50 ascertained from families with a history of fragile X syndrome and from the general population. Scores were analyzed using a linear model with repeat length as the main predictor, adjusting for potential confounders. Repeat length was not associated with anxiety, but was marginally associated with depression and negative affect in males and negative affect only in females. These results suggest that premutation carriers may be at risk for emotional morbidity; however, phenotypic differences were subtle and of small effect size.

Ataxie cérébelleuse tardive due à la prémutation de l’X fragile

Introduction The fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder that affects carriers, principally males after 50 years of age, of premutation alleles of the fragile X mental retardation 1 (FMR1) gene. Clinical features of FXTAS are an intention tremor and/or a cerebellar ataxia, with or without parkinsonism, cognitive disorders, neuropathy and autonomic dysfunction. MRI shows symmetrical signal abnormalities in the middle cerebellar peduncles and deep cerebellar white matter, typically sparing the dentate nucleus, associated with generalized atrophy. We report a case of FXTAS with isolated cerebellar ataxia. Case report We report the case of a 60-year-old right-handed man with an uneventful personal and familial history. Since 2002, he progressively developed gait ataxia associated with paresthesia in the lower limbs. The physical examination revealed static and kinetic cerebellar ataxia with dysarthria. Exhaustive screening tests (inflammatory, immunological, metabolic, infectious and neoplasic) and the cerebrospinal fluid analysis were normal. The brain MRI T2-weighted sequences showed diffuse increased signal in both cerebellar white matter and middle peduncles suggestive of FXTAS. Functional explorations (evoked somesthesic and visual potentials, electromyogram, and cerebral scintigraphy) confirmed the isolated cerebellar involvement. The FXTAS was suggested and the genotype was explored. Southern Blot revealed an expansion of trinucleotide CGG with 107 repetitions, confirming the diagnosis of FXTAS. Discussion In patients with a fragile X premutation, FMR1 protein levels are gradually reduced with increased repeat number, despite elevated FMR1 transcripts levels. Neuropathologic examination reveals eosinophilic intranuclear inclusions in neurons and astrocytes throughout the cortex, subcortical regions, and brain stem. The pathogenic hypothesis would be related to a gain of function with toxic effects of FMR1 messenger RNA on cellular metabolism. Cerebellar ataxia, which may be isolated or not, is the most frequent neurologic manifestation, like many studies showed. Conclusion FXTAS should be suspected in patients with unexplained late-onset cerebellar ataxia. Typical presentation includes a male in his fifties with progressive ataxia and tremor. Brain MRI with symmetrical cerebellar abnormalities is very suggestive of this diagnosis. Genetic screening and advice for the patient and his family must be proposed in order to detect the fragile X syndrome.

Screening for FXTAS in 95 Spanish Patients Negative for Huntington Disease

Fragile X syndrome is the most common form of hereditary mental retardation. The molecular basis of this syndrome is mainly a CGG expansion in the 5' untranslated region of the FMR1 gene. Expansions with more than 200 CGG repeats abolish gene expression causing the classical fragile X phenotype. Premutation carriers (55-200 CGG) have normal cognitive function with increased risk of developing premature ovarian failure and fragile X-associated tremor-ataxia syndrome (FXTAS). Some clinical features associated with FXTAS, such as tremor, gait ataxia, cognitive decline, and generalized brain atrophy, are also seen in other movement disorders. Ninety-five patients referred for HD, who tested negative for the expansion in the IT15 gene, were screened for FMR1 CGG-repeat expansion. One FMR1 premutation male carrier was detected, giving an FXTAS frequency of 1.6%. Our results highlight that FXTAS is still not well diagnosed; therefore, we recommend FMR1 premutation screenings in all patients with late-onset tremor, ataxia, and cognitive dysfunction.