Clinical Phenotype of Adult Fragile X Gray Zone Allele Carriers: a Case Series

CGG repeats in the human FMR1 gene regulate mRNA localization and cellular stress in developing neurons

The human genome has many short tandem repeats, yet the normal functions of these repeats are unclear. The 5' untranslated region (UTR) of the fragile X messenger ribonucleoprotein 1 (FMR1) gene contains polymorphic CGG repeats, the length of which has differing effects on FMR1 expression and human health, including the neurodevelopmental disorder fragile X syndrome. We deleted the CGG repeats in the FMR1 gene (0CGG) in human stem cells and examined the effects on differentiated neurons. 0CGG neurons have altered subcellular localization of FMR1 mRNA and protein, and differential expression of cellular stress proteins compared with neurons with normal repeats (31CGG). In addition, 0CGG neurons have altered responses to glucocorticoid receptor (GR) activation, including FMR1 mRNA localization, GR chaperone HSP90α expression, GR localization, and cellular stress protein levels. Therefore, the CGG repeats in the FMR1 gene are important for the homeostatic responses of neurons to stress signals.

The Frequency of Intermediate Alleles in Patients with Cerebellar Phenotypes

Cerebellar syndromes are clinically and etiologically heterogeneous and can be classified as hereditary, neurodegenerative non-hereditary, or acquired. Few data are available on the frequency of each form in the clinical setting. Growing interest is emerging regarding the genetic forms caused by triplet repeat expansions. Alleles with repeat expansion lower than the pathological threshold, termed intermediate alleles (IAs), have been found to be associated with disease manifestation. In order to assess the relevance of IAs as a cause of cerebellar syndromes, we enrolled 66 unrelated Italian ataxic patients and described the distribution of the different etiology of their syndromes and the frequency of IAs. Each patient underwent complete clinical, hematological, and neurophysiological assessments, neuroimaging evaluations, and genetic tests for autosomal dominant cerebellar ataxia (SCA) and fragile X-associated tremor/ataxia syndrome (FXTAS). We identified the following diagnostic categories: 28% sporadic adult-onset ataxia, 18% cerebellar variant of multiple system atrophy, 9% acquired forms, 9% genetic forms with full-range expansion, and 12% cases with intermediate-range expansion. The IAs were six in the FMR1 gene, two in the gene responsible for SCA8, and one in the ATXN2 gene. The clinical phenotype of patients carrying the IAs resembles, in most of the cases, the one associated with full-range expansion. Our study provides an exhaustive description of the causes of cerebellar ataxia, estimating for the first time the frequency of IAs in SCAs- and FXTAS-associated genes. The high percentage of cases with IAs supports further screening among patients with cerebellar syndromes.

Phenotypic variability to medication management: an update on fragile X syndrome

This review discusses the discovery, epidemiology, pathophysiology, genetic etiology, molecular diagnosis, and medication-based management of fragile X syndrome (FXS). It also highlights the syndrome's variable expressivity and common comorbid and overlapping conditions. FXS is an X-linked dominant disorder associated with a wide spectrum of clinical features, including but not limited to intellectual disability, autism spectrum disorder, language deficits, macroorchidism, seizures, and anxiety. Its prevalence in the general population is approximately 1 in 5000-7000 men and 1 in 4000-6000 women worldwide. FXS is associated with the fragile X messenger ribonucleoprotein 1 (FMR1) gene located at locus Xq27.3 and encodes the fragile X messenger ribonucleoprotein (FMRP). Most individuals with FXS have an FMR1 allele with > 200 CGG repeats (full mutation) and hypermethylation of the CpG island proximal to the repeats, which silences the gene's promoter. Some individuals have mosaicism in the size of the CGG repeats or in hypermethylation of the CpG island, both produce some FMRP and give rise to milder cognitive and behavioral deficits than in non-mosaic individuals with FXS. As in several monogenic disorders, modifier genes influence the penetrance of FMR1 mutations and FXS's variable expressivity by regulating the pathophysiological mechanisms related to the syndrome's behavioral features. Although there is no cure for FXS, prenatal molecular diagnostic testing is recommended to facilitate early diagnosis. Pharmacologic agents can reduce some behavioral features of FXS, and researchers are investigating whether gene editing can be used to demethylate the FMR1 promoter region to improve patient outcomes. Moreover, clustered regularly interspaced palindromic repeats (CRISPR)/Cas9 and developed nuclease defective Cas9 (dCas9) strategies have promised options of genome editing in gain-of-function mutations to rewrite new genetic information into a specified DNA site, are also being studied.

FMR1 CGG Repeats and Stress Influence Self-Reported Cognitive Functioning in Mothers

Variation in the FMR1 gene may affect aspects of cognition, such as executive function and memory. Environmental factors, such as stress, may also negatively impact cognitive functioning. Participants included 1,053 mothers of children with and without developmental disabilities. Participants completed self-report measures of executive function, memory, and stress (i.e., life events, parenting status), and provided DNA to determine CGG repeat length (ranging from 7 to 192 CGGs). Stress exposure significantly predicted greater self-reported difficulties in executive function and the likelihood of memory problems. Cubic CGG effects independently predicted executive function and memory difficulties, suggesting effects of both genetic variation and environmental stress exposure on cognitive functioning.

Connective Tissue Disorders and Fragile X Molecular Status in Females: A Case Series and Review

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disabilities and the second most common cause after Down syndrome. FXS is an X-linked disorder due to a full mutation of the CGG triplet repeat of the FMR1 gene which codes for a protein that is crucial in synaptogenesis and maintaining functions of extracellular matrix-related proteins, key for the development of normal neuronal and connective tissue including collagen. In addition to neuropsychiatric and behavioral problems, individuals with FXS show physical features suggestive of a connective tissue disorder including loose skin and joint laxity, flat feet, hernias and mitral valve prolapse. Disturbed collagen leads to hypermobility, hyperextensible skin and tissue fragility with musculoskeletal, cardiovascular, immune and other organ involvement as seen in hereditary disorders of connective tissue including Ehlers−Danlos syndrome. Recently, FMR1 premutation repeat expansion or carrier status has been reported in individuals with connective tissue disorder-related symptoms. We examined a cohort of females with features of a connective tissue disorder presenting for genetic services using next-generation sequencing (NGS) of a connective tissue disorder gene panel consisting of approximately 75 genes. In those females with normal NGS testing for connective tissue disorders, the FMR1 gene was then analyzed using CGG repeat expansion studies. Three of thirty-nine females were found to have gray zone or intermediate alleles at a 1:13 ratio which was significantly higher (p < 0.05) when compared with newborn females representing the general population at a 1:66 ratio. This association of connective tissue involvement in females with intermediate or gray zone alleles reported for the first time will require more studies on how the size variation may impact FMR1 gene function and protein directly or in relationship with other susceptibility genes involved in connective tissue disorders.

Working memory and arithmetic impairments in children with FMR1 premutation and gray zone alleles

Expansive mutations in familial mental retardation 1 (FMR1) gene have been associated with different phenotypes. Full mutations are associated with intellectual disability and autism spectrum disorder; premutations are associated with math learning difficulties and working memory impairments. In gray zone, neuropsychological development has not yet been described.

Objectives

This study aimed to describe the frequency of FMR1 premutation and gray zone alleles in a school population sample representing a broad spectrum of variation in math achievement and detail school achievement and cognitive performance in the children identified with FMR1 premutation or gray zone alleles.

Methods

We described a two-phase study. In the first phase, 2,195 school-age children were screened for math achievement. In the second phase, 378 children with normal intelligence were neuropsychologically assessed and genotyped for FMR1. Of these, 121 children (61 girls) performed below percentile 25 in mathematics (MD group) and 257 children (146 girls) performed above percentile 25 (control group).

Results

Four pupils presented expanded alleles, one premutation and three gray zone alleles. The girl with the premutation and one boy with a gray zone allele presented impairments in working memory and arithmetic performance below percentile 6, compatible with the diagnosis of developmental dyscalculia. These children's difficulties were not associated with inaccuracy of nonsymbolic number representations or literacy impairments. Dyscalculia in these children seems to be associated mainly with working memory impairments.

Conclusions

FMR1 expansions in the gray zone may contribute to dyscalculia in otherwise healthy and normally intelligent children.

Screening for FMR1 CGG Repeat Expansion in Thai Patients with Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex disorder with a heterogeneous etiology. Fragile X syndrome (FXS) is recognized as the most common single gene mutation associated with ASD. FXS patients show some autistic behaviors and may be difficult to distinguish at a young age from autistic children. However, there have been no published reports on the prevalence of FXS in ASD patients in Thailand. In this study, we present a pilot study to analyze the CGG repeat sizes of the FMR1 gene in Thai autistic patients. We screened 202 unrelated Thai patients (168 males and 34 females) with nonsyndromic ASD and 212 normal controls using standard FXS molecular diagnosis techniques. The distributions of FMR1 CGG repeat sizes in the ASD and normal control groups were similar, with the two most common alleles having 29 and 30 CGG repeats, followed by an allele with 36 CGG repeats. No FMR1 full mutations or premutations were found in either ASD individuals or the normal controls. Interestingly, three ASD male patients with high normal CGG and intermediate CGG repeats (44, 46, and 53 CGG repeats) were identified, indicating that the prevalence of FMR1 intermediate alleles in Thai ASD patients was approximately 1% while these alleles were absent in the normal male controls. Our study indicates that CGG repeat expansions of the FMR1 gene may not be a common genetic cause of nonsyndromic ASD in Thai patients. However, further studies for mutations other than the CGG expansion in the FMR1 gene are required to get a better information on FXS prevalence in Thai ASD patients.

'Essential Tremor' Phenotype in FMR1 Premutation/Gray Zone Sibling Series: Exploring Possible Genetic Modifiers

Fragile X-associated tremor/ataxia syndrome (FXTAS) occurs in carriers of fragile X mental retardation 1 (FMR1) X-linked small CGG expansion (gray zone [GZ] and premutation [PM]) alleles, containing 41-200 repeats. Major features comprise kinetic tremor, gait ataxia, cognitive decline and cerebellar peduncular white matter lesions, but atypical/incomplete FXTAS may occur. We explored the possibility of polygenic effects modifying the FXTAS spectrum phenotypes. We used three motor scales and selected cognitive tests in a series of three males and three females from a single sibship carrying PM or GZ alleles (44 to 75 repeats). The molecular profiles from these siblings were determined by genomewide association study with single-nucleotide polymorphism (SNP) genotyping by Illumina Global Screening Array. Nonparametric linkage analysis was applied and Parkinson's disease (PD) polygenic risk scores (PRSs) were calculated for all the siblings, based on 107 known risk variants. All male and female siblings manifested similar kinetic tremor phenotypes. In contrast to FXTAS, they showed negligible gait ataxia, and few white matter lesions on MRI. Cognitive functioning was unaffected. Suggestive evidence of linkage to a broad region of the short arm of chromosome 10 was obtained, and median PD PRS for the sibship fell within the top 30% of a sample of over 500,000 UK and Australian controls. The genomewide study results are suggestive of modifying effects of genetic risk loci linked to PD, on the neurological phenotype of FMR1-CGG small expansion carriers, resulting in an oligosymptomatic kinetic tremor seen in FXTAS spectrum, but also consistent with essential tremor.

Maternal Mental Health and Parenting Stress and Their Relationships to Characteristics of the Child With Fragile X Syndrome

Although previous research supports the notion that characteristics of both the child and the mother impact maternal well-being and parenting stress in mothers of children with FXS, more work is needed in which self-report measures are supplemented by physiological measures of stress and well-being. The inclusion of physiological measures, such as heart rate variability (HRV), may provide a window into the biological origins and consequences of maternal perceptions of their experiences, including the challenges of raising a child with developmental challenges. The proposed project, therefore, involved the collection of multimodal assessment data from mothers and their school-aged children with FXS. Further, given the importance of understanding how mothers of youth with FXS are faring in their everyday environment, the present study collected all data using telehealth procedures and wearable technology. Participants were 20 biological mothers and their children with FXS between the ages of 6 and 11 years. We measured maternal mental health and parenting stress through self-report as well as through HRV as a more objective measure of psychological well-being. We also examined the associations between these variables and child characteristics such as externalizing and internalizing behaviors as well as autism symptomatology. We found significant support for an elevated rate of depressive symptoms in the sample of mothers (35%) and some potential indicators for heightened rates of anxiety (15%) when compared to normed samples and rates in the general population. We also found that the mothers presented with an atypical HRV profile akin to those experiencing depression or chronic stress, although limitations of the present measure suggest the need for additional confirmatory research. Further, we found that child externalizing behaviors were the primary correlates of maternal well-being. These findings contribute to the growing body of literature regarding the unique challenges faced by these mother-child dyads and supports the importance of increasing the availability of services available to these mothers, not only for meeting the needs of their children's development and behavior, but in supporting their own well-being as well.

Association analysis of FMR1 genetic variants and primary ovarian insufficiency in South Indian women with a novel approach of CGG repeats classification

Around 20-28% of FMR1gene CGG premutation (PM) carriers are at augmented risk towards an infertility related disorder, Fragile X-associated primary ovarian insufficiency (FXPOI). Except the effect of CGG repeats, reports are not available on the mechanism through which the cis-acting variations, namely, SNPs involved in POI susceptibility. Addressing the hypothesis that the FMR1 gene polymorphisms [CGG repeats, rs25731(T > A) and rs4949(A > G)] might increase their individual and combined impact in disease predisposition, we tested the genetic variants in 200 south Indian DNA samples consists of 100 patients and 100 healthy volunteers. We used gene scan method to score the CGG repeat length, and ARMS and RFLP methods to genotype the SNPs. Only 0.5% of each Gray zone and PM alleles were found among patient group, however, no disease association was noticed with repeat length. The rs25731 showed protection [OR:0.32; (0.13-0.76), p = 0.006] and rs4949 reported a 2.5-fold risk towards the disease predisposition [OR:2.46; (1.06-5.74), p = 0.031] but, both found insignificant after Bonferroni correction was done under different Genetic Models. Novel classification of genotype combinations, 'Normal&Variant Homozygote' [OR:2.89,(1.12-7.9), p < 0.05] and 'Allele2-T-G' haplotype block (6%vs.1%, p = 0.08) were noticed to be at marginal risk for POI. We demonstrated a susceptible role of the combined effect of variant allele-G and Allele-2 (repeat allele outside the normal range) for FXPOI. To support our findings of its first kind, further studies with large samples are warranted in understanding the role of FMR1 genetic variants in FXPOI etio-pathophysiology, the outcome might help in providing better reproductive treatment options for females, who are at risk for FXPOI.

Fragile X associated neuropsychiatric disorders in a male without FXTAS

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and autism spectrum disorder. In most cases, it is due to an expansion of the CGG triplet to more than 200 repeats within the promoter region of the FMR1 gene. In the premutation (PM) the trinucleotide is expanded to 55-200 repeats. PM carriers can present with disorders associated with the PM including fragile X-associated tremor/ataxia syndrome (FXTAS) and fragile X-associated ovarian insufficiency (FXPOI). Recently fragile X-associated neuropsychiatric disorders (FXAND) was proposed as an umbrella term to include the neuropsychiatric disorders that are more prevalent in PM carriers compared to the general population such as anxiety, depression, chronic fatigue, alcohol abuse, and psychosis, among others. The patient in our study was evaluated by a team of clinicians from the University del Valle in Cali who traveled to Ricaurte, a Colombian town known for being a genetic geographic cluster of FXS. A detailed medical history was collected and complete physical, neurological and psychiatric evaluations were performed in addition to molecular and neuroradiological studies. We report the case of a 78-year-old man, PM carrier, without FXTAS whose main clinical presentation consists of behavioral changes and psychosis. Brain imaging revealed white matter lesions in the periventricular region and mild cerebral atrophy. Although anxiety and depression are the most common neuropsychiatric manifestations in PM carriers, it is important to perform a complete psychiatric evaluation since some patients may present with behavioral changes and psychosis.

Child Challenging Behavior Influences Maternal Mental Health and Relationship Quality Over Time in Fragile X Syndrome

Parenting children with neurodevelopmental disabilities is often challenging. Biological mothers of children with Fragile X Syndrome (FXS) may be susceptible to increased risk of mental health problems. This study examined the longitudinal relationships between maternal mental health, child challenging behaviors, and mother-child relationship quality in children and adolescents with FXS. Fifty-five mother-child dyads were followed from childhood into adolescence. The findings suggest that child challenging behaviors, maternal mental health, and mother-child relationship quality were stable during that period. Additionally, elevated levels of child challenging behaviors negatively impacted maternal mental health. Finally, child challenging behaviors, in combination with maternal mental health, influenced mother-child relationship quality. Clinical implications are discussed.

Evidence for the role of FMR1 gray zone alleles as a risk factor for parkinsonism in females

Background and Objective There is convincing evidence that small CGG expansion (41-54 repeats): FMR1 "gray zone" alleles (GZ) contribute to the risk of parkinsonism in males, but there is insufficient corresponding data in females. This study intends to fill this gap. Methods We screened whole-blood-derived DNA from a cohort of 601 females diagnosed with idiopathic PD, and from dry Guthrie blood spots from a local sample of 1,005 female newborns (population controls), for the size of the FMR1 CGG repeat using a PCR technique. Results We found a significant excess (8.2%) of GZ carriers compared with 5.2% in the control sample, with a P value of 0.009 for the difference in proportions. Conclusion FMR1 gray zone alleles are a significant risk factor for parkinsonism in females. These population data and occasional reports of FXTAS-like or parkinsonian manifestations in carriers suggest possible mechanisms whereby the effects of these alleles synergize with the existing pathologies underpinning parkinsonism. © 2018 International Parkinson and Movement Disorder Society.

The Spectrum of Neurological and White Matter Changes and Premutation Status Categories of Older Male Carriers of the FMR1 Alleles Are Linked to Genetic (CGG and FMR1 mRNA) and Cellular Stress (AMPK) Markers

The fragile X premutation (PM) allele contains a CGG expansion of 55-200 repeats in the FMR1 gene's promoter. Male PM carriers have an elevated risk of developing neurological and psychiatric changes, including an approximately 50% risk of the fragile X-associated tremor/ataxia syndrome (FXTAS). The aim of this study was to assess the relationships of regional white matter hyperintensities (wmhs) semi-quantitative scores, clinical status, motor (UPDRS, ICARS, Tremor) scales, and cognitive impairments, with FMR1-specific genetic changes, in a sample of 32 unselected male PM carriers aged 39-81 years. Half of these individuals were affected with FXTAS, while the non-FXTAS group comprised subcategories of non-affected individuals and individuals affected with non-syndromic changes. The dynamics of pathological processes at the cellular level relevant to the clinical status of PM carriers was investigated using the enzyme AMP-activated protein kinase (AMPK), which is a highly sensitive cellular stress-sensing alarm protein. This enzyme, as well as genetic markers - CGG repeat number and the levels of the FMR1 mRNA - were assessed in blood lymphoblasts. The results showed that the repeat distribution for FXTAS individuals peaked at 85-90 CGGs; non-FXTAS carriers were distributed within the lowest end of the PM repeat range, and non-syndromic carriers assumed an intermediate position. The size of the CGG expansion was significantly correlated, across all three categories, with infratentorial and total wmhs and with all motor scores, and the FMR1 mRNA levels with all the wmh scores, whilst AMPK activity showed considerable elevation in the non-FXTAS combined group, decreasing in the FXTAS group, proportionally to increasing severity of the wmhs and tremor/ataxia. We conclude that the size of the CGG expansion relates to the risk for FXTAS, to severity of infratentorial wmhs lesions, and to all three motor scale scores. FMR1 mRNA shows a strong association with the extent of wmhs, which is the most sensitive marker of the pathological process. However, the AMPK activity findings - suggestive of a role of this enzyme in the risk of FXTAS - need to be verified and expanded in future studies using larger samples and longitudinal assessment.

Curvilinear Association Between Language Disfluency and FMR1 CGG Repeat Size Across the Normal, Intermediate, and Premutation Range

Historically, investigations of FMR1 have focused almost exclusively on the clinical effects of CGG expansion within the categories of the premutation (55-200 CGG repeats) and fragile X syndrome (>200 CGG repeats). However, emerging evidence suggests that CGG-dependent phenotypes may occur across allele sizes traditionally considered within the "normal" range. This study adopted an individual-differences approach to determine the association between language production ability and CGG repeat length across the full range of normal, intermediate, and premutation alleles. Participants included 61 adult women with CGG repeats within the premutation (n = 37), intermediate (i.e., 41-54 repeats; n = 2), or normal (i.e., 6-40 repeats; n = 22) ranges. All participants were the biological mothers of a child with a developmental disorder, to control for the potential effects of parenting stress. Language samples were collected and the frequency of language disfluencies (i.e., interruptions in the flow of speech) served as an index of language production skills. Verbal inhibition skills, measured with the Hayling Sentence Completion Test, were also measured and examined as a correlate of language disfluency, consistent with theoretical work linking language disfluency with inhibitory deficits (i.e., the Inhibition Deficit Hypothesis). Blood samples were collected to determine FMR1 CGG repeat size. A general linear model tested CGG repeat size of the larger allele (allele-2) as the primary predictor of language disfluency, covarying for education level, IQ, age, and CGG repeats on the other allele. A robust curvilinear association between CGG length and language disfluency was detected, where low-normal (∼ <25 repeats) and mid-premutation alleles (∼90-110 repeats) were linked with higher rates of disfluency. Disfluency was not associated with inhibition deficits, which challenges prior theoretical work and suggests that a primary language deficit could account for elevated language disfluency in FMR1-associated conditions. Findings suggest CGG-dependent variation in language production ability, which was evident across individuals with and without CGG expansions on FMR1.

Fragile X syndrome: a review of clinical and molecular diagnoses

Background

Fragile X Syndrome (FXS) is the second cause of intellectual disability after Down syndrome and the most prevalent cause of intellectual disability in males, affecting 1:5000–7000 men and 1:4000–6000 women. It is caused by an alteration of the FMR1 gene, which maps at the Xq27.3 band: more than 99% of individuals have a CGG expansion (>200 triplets) in the 5′ UTR of the gene, and FMR1 mutations and duplication/deletion are responsible for the remaining (<1%) molecular diagnoses of FXS. The aim of this review was to gather the current clinical and molecular knowledge about FXS to provide clinicians with a tool to guide the initial assessment and follow-up of FXS and to offer to laboratory workers and researchers an update about the current diagnostic procedures.

Discussion

FXS is a well-known condition; however, most of the studies thus far have focused on neuropsychiatric features. Unfortunately, some of the available studies have limitations, such as the paucity of patients enrolled or bias due to the collection of the data in a single-country population, which may be not representative of the average global FXS population. In recent years, insight into the adult presentation of the disease has progressively increased. Pharmacological treatment of FXS is essentially symptom based, but the growing understanding of the molecular and biological mechanisms of the disease are paving the way to targeted therapy, which may reverse the effects of FMRP deficiency and be a real cure for the disease itself, not just its symptoms.

Conclusions

The clinical spectrum of FXS is wide, presenting not only as an isolated intellectual disability but as a multi-systemic condition, involving predominantly the central nervous system but potentially affecting any apparatus. Given the relative high frequency of the condition and its complex clinical management, FXS appears to have an important economic and social burden.

A methylation PCR method determines FMR1 activation ratios and differentiates premutation allele mosaicism in carrier siblings

Background

Epigenetic modifications of the fragile X mental retardation 1 (FMR1) gene locus may impact the risk for reproductive and neurological disorders associated with expanded trinucleotide repeats and methylation status in the 5′ untranslated region. FMR1 methylation is commonly assessed by Southern blot (SB) analysis, yet this method suffers a cumbersome workflow and relatively poor sizing resolution especially for premutation allele characteristic for fragile X-associated disorders. In this study, a methylation PCR (mPCR) assay was used to evaluate correlations among genotype, epitype, and phenotype in fragile X premutation (PM) carrier women in order to advance the understanding of the association between molecular determinants and the presence of fragile X-associated tremor and ataxia (FXTAS).

Results

Activation ratios (ARs) in 39 PM women were determined by mPCR and compared with SB analysis. ARs were distributed across a range of values including five samples with <20% AR and six with >80% AR. The two methods were correlated (R² of 0.87 and F test of <0.001), indicating that mPCR can measure AR in agreement with established assays. However, mPCR was unique in identifying novel and distinct patterns of methylation mosaicism in premutation carrier women, including seven sibling pairs that were assessed using FXTAS clinical rating scales. Of note, four of six pairs with defined age of onset for neurological signs showed ARs consistent with skewed activation of the pathogenic expanded allele. One subject with severe FXTAS had a mosaic full mutation allele identified using mPCR but not detected by SB analysis.

Conclusions

We utilized a repeatable and streamlined methodology to characterize FMR1 inactivation in premutation carrier women. The method was concordant with SB analysis and provided higher resolution information on allele and methylation mosaicism. This approach can facilitate the characterization of epigenetic factors influencing fragile X phenotypes in larger cohort studies that can advance understanding and treatment of fragile X-associated disorders.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0280-8) contains supplementary material, which is available to authorized users.