Full Mutation Research Articles

A Single Common Assay for Robust and Rapid Fragile X Mental Retardation Syndrome Screening From Dried Blood Spots.

Background: FMR1 CGG trinucleotide repeat hyper-expansions are observed in 99% of individuals with fragile X mental retardation syndrome (FXS). We evaluated the reliability of a rapid single-step gender-neutral molecular screen for FXS when performed on DNA isolated from dried blood spots.Methods: DNA was extracted from dried blood spots of 151 individuals with intellectual disability or autism spectrum disorder, whose FMR1 repeat genotypes are known. Dried blood spots were blinded prior to DNA extraction and analysis by triplet primed PCR (TP-PCR) and melt curve analysis (MCA). All expansion-positive and representative expansion-negative samples were also genotyped by fluorescent TP-PCR and capillary electrophoresis (CE) to confirm repeat expansion status.Results: Three males and 12 females were classified as expanded by TP-PCR MCA, and were subsequently sized by fluorescent TP-PCR CE. Two males and four females carried premutations, while one male and eight females carried full mutations. All 19 non-expanded samples that were sized were confirmed as carrying only normal alleles. Replicate analysis of representative expansion-positive samples yielded reproducible melt peak profiles. TP-PCR MCA classifications were completely concordant with FMR1 CGG repeat genotypes.Conclusion: TP-PCR MCA of dried blood spot DNA accurately and reliably identifies presence/absence of FMR1 CGG repeat expansions in both genders simultaneously. This strategy may be suitable for rapid high-throughput first-tier screening for fragile X syndrome.

Fragile X-Associated Neuropsychiatric Disorders (FXAND).

Fragile X syndrome (FXS) is caused by the full mutation (>200 CGG repeats) in the Fragile X Mental Retardation 1 (FMR1) gene. It is the most common inherited cause of intellectual disability (ID) and autism. This review focuses on neuropsychiatric disorders frequently experienced by premutation carriers with 55 to 200 CGG repeats and the pathophysiology involves elevated FMR1 mRNA levels, which is different from the absence or deficiency of fragile X mental retardation protein (FMRP) seen in FXS. Neuropsychiatric disorders are the most common problems associated with the premutation, and they affect approximately 50% of individuals with 55 to 200 CGG repeats in the FMR1 gene. Neuropsychiatric disorders in children with the premutation include anxiety, ADHD, social deficits, or autism spectrum disorders (ASD). In adults with the premutation, anxiety and depression are the most common problems, although obsessive compulsive disorder, ADHD, and substance abuse are also common. These problems are often exacerbated by chronic fatigue, chronic pain, fibromyalgia, autoimmune disorders and sleep problems, which are also associated with the premutation. Here we review the clinical studies, neuropathology and molecular underpinnings of RNA toxicity associated with the premutation. We also propose the name Fragile X-associated Neuropsychiatric Disorders (FXAND) in an effort to promote research and the use of fragile X DNA testing to enhance recognition and treatment for these disorders.

Fragile X-Associated Disorders in Serbia: Baseline Quantitative and Qualitative Survey of Knowledge, Attitudes and Practices Among Medical Professionals.

We conducted a knowledge, attitude, and practice (KAP) survey of fragile X-associated disorders (FXD) in Serbia in order to obtain baseline quantitative and qualitative KAP data on fragile X mental retardation 1 gene (FMR1) pre- and full mutations (PM, FM). The survey's 16-item questionnaire included a knowledge component (12/16), such as self-assessment knowledge (SAK) and factual knowledge (FK, 2/5 questions for PM, FXTAS and FXPOI). Education-directed attitudes in the FXD field and FMR1 DNA testing practices had 4/16 items, including brief case vignettes of FXTAS and FXPOI, respectively. The study's cohort consisted of primary care physicians (referred to as “physicians” in the rest of the text) throughout Serbia (n = 284, aged 26–64 years, 176/284, 62.2% in Belgrade, Serbia) and senior medical students (n = 245, aged 23–30 years; 33.5% males) at the Belgrade School of Medicine. Strikingly, half of the survey respondents indicated “not having any” knowledge for the fragile X gene premutation and FXD. Physicians were more likely to indicate “not having any” knowledge than students (41.2% of physicians vs. 13.1% of students, P < 0.05). Roughly half of the students had “minimal knowledge” (53.5 vs. 30.5% of physicians, P < 0.05). Low FK was common in the cohort, as few physicians had “all correct answers” (7.5 vs. 3.7% of students, P < 0.05; 16.5 vs. 9.5% of students for the 2/5 premutation-related questions). Statistical analyses identified physicians' practice setting and length of clinical experience as predictors of the lack of FK on questions related to FXD. Physicians were more likely than students to indicate “strongly agreed” to expand their knowledge of the gene premutation and FXD (90.9 vs. 66.7% of students, P < 0.01). However, students more frequently indicated that they are willing to recommend DNA testing in their future practices than physicians (93.5 vs. 64.8% of physicians, P < 0.001). In conclusion, there is a major gap in knowledge regarding fragile X gene PM and FXD among the study's participants in Serbia. The study's informative-educational survey serves as an initial step in the process of enhancing the KAP of medical professionals with regards to the fragile X gene premutation and FXD.

Absence of AGG interruptions is a risk factor for a full mutation expansion among Israeli FMR1 premutation carriers

Absence of AGG interruptions is a risk factor for a full mutation expansion among Israeli FMR1 premutation carriers

High expression of miR-510 was associated with CGG expansion located at upstream of FMR1 into full mutation.

MicroRNAs (miRNAs) have been found to play an important role in the regulation of gene expression in eukaryotic organisms at the posttranscriptional level. More than half of miRNA genes have been recognized to be located in different fragile sites. Among them, miR-510 was located on chromosome X in the 27.3Xq region, flanking to a fragile X site. The CGG expansion and its methylation at the promoter of FMR1 located in this fragile site were associated with clinical symptoms of fragile X syndrome (FXS). The aim of the current study was to investigate whether the miR-510 expression was correlated with the CGG expansion of FMR1 in female carriers of full mutation. For this purpose, mesenchymal stem cells were isolated from peripheral blood of FMR1 full mutation female carriers. After differentiation of these cells into neuronal cells, the expression of miR-510 was analyzed by quantitative polymerase chain reaction. Furthermore, the target genes of miR-510 in the nervous system were also predicted by in silico method. The obtained results indicated that the CGG expansion of FMR1 was associated with the enhanced expression of miR-510. Furthermore, the bioinformatics analysis suggested that VHL and PPP2R5E genes could be considered as the most important target genes of miR-510 in the nervous system. This study showed that miR-510 and its target genes, specifically VHL and PPP2R5E, may represent the new targets for future therapy options of FXS.

Sensory Difficulties in Children With an FMR1 Premutation.

Abnormal sensory processing is one of the core characteristics of the fragile X phenotype. Studies of young children with fragile X syndrome (FXS) and the FMR1 premutation have shown sensory challenges as early as infancy and into early childhood. This study sought to examine differences in sensory difficulties in children with an FMR1 premutation compared with children with FXS and typically developing children. We conducted an online survey of 176 parents of affected children (FXS or FMR1 premutation). Most respondents were mothers who are Caucasian (86%), have a 4-year college or graduate degree (68%), and are married (92%). Children ranged in age from 5 to 18, with a mean age of 13.0 years (3.3 SD). Participants completed the BBC Sensory Scales, a 50-item Likert-type scale (1 = Almost Always, 4 = Almost Never) comprised of 8 subscales that assessed auditory processing, visual processing, tactile processing, and eating and feeding behaviors. Mean scores were calculated for the items and each of the subscales. Non-parametric tests examined differences in child and family-level variables. Across all BBCSS subscales, children with an FMR1 premutation displayed more sensory challenges than typically developing children. For six out of the eight subscales, children with the full mutation had the lowest scores indicating more sensory challenges, but this was closely followed by children with an FMR1 premutation. Fragile X status was associated with seven of the eight subscales; children with an FMR1 premutation did not differ from children with FXS on any of the subscales but had more digestive problems than children with no fragile X. Gender, autism status, and family income were also related to sensory sensitivities. In conclusion, these data provide further evidence that some children with an FMR1 premutation experience sensory difficulties that are similar to children with FXS but different than typically developing children.

Epigenetics of fragile X syndrome and fragile X-related disorders.

The fragile X mental retardation 1 gene (FMR1)-related disorder fragile X syndrome (FXS) is the most common heritable form of cognitive impairment and the second most common cause of comorbid autism. FXS usually results when a premutation trinucleotide CGG repeat in the 5' untranslated region of the FMR1 gene (CGG 55-200) expands over generations to a full mutation allele (CGG >200). This expansion is associated with silencing of the FMR1 promoter via an epigenetic mechanism that involves DNA methylation of the CGG repeat and the surrounding regulatory regions. Decrease in FMR1 transcription is associated with loss of the FMR1 protein that is needed for typical brain development. The past decade has seen major advances in our understanding of the genetic and epigenetic processes that underlie FXS. Here we review these advances and their implications for diagnosis and treatment for individuals who have FMR1-related disorders. WHAT THIS PAPER ADDS: Improved analysis of DNA methylation allows better epigenetic evaluation of the fragile X gene. New testing techniques have unmasked interindividual variation among children with fragile X syndrome. New testing methods have also detected additional cases of fragile X.

Skewed X-chromosome inactivation and shorter telomeres associate with idiopathic premature ovarian insufficiency

To analyze whether telomere length, X-chromosome inactivation (XCI), and androgen receptor (AR) GAG polymorphism are related to idiopathic premature ovarian insufficiency (POI). Case-control study. University hospital. A total of 121 women, including 46 nonsyndromic POI and 75 controls. None. Age, weight, height, body mass index (BMI), systolic and diastolic arterial pressure, E2, androstenedione, T, and C-reactive protein were assessed. Telomere length was estimated by quantitative real-time polymerase chain reaction, XCI was measured using the Human Androgen Receptor and X-linked retinitis pigmentosa 2 (RP2) methylation assays. AR and FMR1 polymorphism was assessed by quantitative fluorescent polymerase chain reaction and sequencing. Premature ovarian insufficiency women had a higher mean age, weighed less, and exhibited lower C-reactive protein, E2, and androstenedione levels. The AR polymorphism did not differ between the groups. Four patients had premutation (55-200 CGG repeats), and none displayed a full mutation in the FMR1 gene. However, patients with POI showed shorter telomere length and higher frequency of skewed XCI. Extreme skewing (≥90%) was observed in 15% of women with POI, and shorter telomeres correlated with XCI skewing in both groups. Skewed XCI and shortened telomere length were associated with idiopathic POI, despite no alterations in the AR and FMR1 genes. Additionally, there is a tendency for women with short telomeres to exhibit skewed XCI.

Frajil X Sendromu: Konuşma Gecikmesi Olan Hastalarda Göz Önüne Alınması Gereken Genetik Bir Bozukluk

spectrum disorder (ASD). Comprehensive and multidisciplinary evaluation of patients with ID or ASD is essential for prudent management of any probable underlying condition. Herein we report a 4 years and 3 months old boy with speech delay, previously admitted to other clinics many times without any definite diagnosis. Physical examination revealed that he had hyperactivity, poor eye contact and dysmorphic features. He had global developmental delay and symptoms of ASD. The patient who had dysmorphic features was referred to pediatric genetics department with the suspicion of FXS. Southern Blot analysis revealed CGG repeat expansion in the range of full mutation. Maternal southern blot analysis revealed expanded CGG repeat in the range of premutation, and the family was given genetic counseling. The patient is still being followed-up at the developmental pediatrics department with an individual education program and other supportive treatments. Children with FXS typically present with developmental delay. Although motor delays are often seen, these tend to be mild, and affected males most commonly come to hospital because of speech delay as the patient in this case. The present patient has both FXS and ASD diagnosis. As children with FXS may not have gross physical features, any child who has developmental delay, borderline intellectual abilities, ID or ASD with an unknown etiology should undergo molecular testing for fragile X syndrome. It was aimed in this case to emphasize the importance of comprehensive and multidisciplinary evaluation of all patients referred with speech delay.

Health Profiles of Mosaic Versus Non-mosaic FMR1 Premutation Carrier Mothers of Children With Fragile X Syndrome

The FMR1 premutation is of increasing interest to the FXS community, as questions about a primary premutation phenotype warrant research attention. 100 FMR1 premutation carrier mothers (mean age = 58; 67–138 CGG repeats) of adults with fragile X syndrome were studied with respect to their physical and mental health, motor, and neurocognitive characteristics. We explored the correlates of CGG repeat mosaicism in women with expanded alleles. Mothers provided buccal swabs from which DNA was extracted and the FMR1 CGG genotyping was performed (Amplidex Kit, Asuragen). Mothers were categorized into three groups: Group 1: premutation non-mosaic (n = 45); Group 2: premutation mosaic (n = 41), and Group 3: premutation/full mutation mosaic (n = 14). Group 2 mothers had at least two populations of cells with different allele sizes in the premutation range besides their major expanded allele. Group 3 mothers had a very small population of cells in the full mutation range (>200 CGGs) in addition to one or multiple populations of cells with different allele sizes in the premutation range. Machine learning (random forest) was used to identify symptoms and conditions that correctly classified mothers with respect to mosaicism; follow-up comparisons were made to characterize the three groups. In categorizing mosaicism, the random forest yielded significantly better classification than random classification, with overall area under the receiver operating characteristic curve (AUROC) of 0.737. Among the most important symptoms and conditions that contributed to the classification were anxiety, menopause symptoms, executive functioning limitations, and difficulty walking several blocks, with the women who had full mutation mosaicism (Group 3) unexpectedly having better health. Although only 14 premutation carrier mothers in the present sample also had a small population of full mutation cells, their profile of comparatively better health, mental health, and executive functioning was unexpected. This preliminary finding should prompt additional research on larger numbers of participants with more extensive phenotyping to confirm the clinical correlates of low-level full mutation mosaicism in premutation carriers and to probe possible mechanisms.

Detecting AGG Interruptions in Females With a FMR1 Premutation by Long-Read Single-Molecule Sequencing: A 1 Year Clinical Experience.

The fragile X syndrome arises from the FMR1 CGG expansion of a premutation (55–200 repeats) to a full mutation allele (>200 repeats) and is the most frequent cause of inherited X-linked intellectual disability. The risk for a premutation to expand to a full mutation allele depends on the repeat length and AGG triplets interrupting this repeat. In genetic counseling it is important to have information on both these parameters to provide an accurate risk estimate to women carrying a premutation allele and weighing up having children. For example, in case of a small risk a woman might opt for a natural pregnancy followed up by prenatal diagnosis while she might choose for preimplantation genetic diagnosis (PGD) if the risk is high. Unfortunately, the detection of AGG interruptions was previously hampered by technical difficulties complicating their use in diagnostics. Therefore we recently developed, validated and implemented a new methodology which uses long-read single-molecule sequencing to identify AGG interruptions in females with a FMR1 premutation. Here we report on the assets of AGG interruption detection by sequencing and the impact of implementing the assay on genetic counseling.

Classical fragile-X phenotype in a female infant disclosed by comprehensive genomic studies

BackgroundWe describe a female infant with Fragile-X syndrome, with a fully expanded FMR1 allele and preferential inactivation of the homologous X-chromosome carrying a de novo deletion. This unusual and rare case demonstrates the importance of a detailed genomic approach, the absence of which could be misguiding, and calls for reflection on the current clinical and diagnostic workup for developmental disabilities.Case presentationWe present a female infant, referred for genetic testing due to psychomotor developmental delay without specific dysmorphic features or relevant family history. FMR1 mutation screening revealed a methylated full mutation and a normal but inactive FMR1 allele, which led to further investigation. Complete skewing of X-chromosome inactivation towards the paternally-inherited normal-sized FMR1 allele was found. No pathogenic variants were identified in the XIST promoter. Microarray analysis revealed a 439 kb deletion at Xq28, in a region known to be associated with extreme skewing of X-chromosome inactivation.ConclusionsOverall results enable us to conclude that the developmental delay is the cumulative result of a methylated FMR1 full mutation on the active X-chromosome and the inactivation of the other homologue carrying the de novo 439 kb deletion. Our findings should be taken into consideration in future guidelines for the diagnostic workup on the diagnosis of intellectual disabilities, particularly in female infant cases.

A Novel Radical SAM mechanism mediated by the Interferon‐Inducible Protein Viperin

To survive infection the immune system deploys an arsenal of defensive measures to combat invading pathogens. The type I interferon (IFN) response presents an early host defense by generating an intracellular environment that restricts virus replication and signals the presence of a viral pathogen to the adaptive arm of the immune response. Viperin (virus inhibitory protein, endoplasmic reticulum‐associated, interferon‐inducible) is an interferon stimulated gene (ISG), that is induced by type I, II, and III IFNs, or after infection by a broad range of DNA and RNA viruses. Viperin contains an S‐adenosyl‐L‐methionine (SAM) domain and an N‐terminal amphipathic helix that contributes to its antiviral activity by localizing viperin to ER membranes or lipid droplets. Viperin has been found to require ER localization for full antiviral activity and mutation of the cysteine residues (CX3CX2C motif) ligating the Fe‐S cluster in the central radical SAM domain entirely abolished antiviral activity. Viperin induces a cascade of signaling events to mount an immune response against the viral replication; however, the exact molecular basis for viperin's cellular activity and the role of SAM‐dependent reactions in inhibiting viral synthesis remains unknown. Our studies suggest that the radical SAM activity of viperin is critical for activation of innate immune signaling. The enzyme localizes the E3 ubiquitin ligase TRAF6 and the interleukin 1 receptor‐associated kinase (IRAK1) to the endoplasmic reticulum and activates TRAF6 to catalyze polyubiquitylation of IRAK1, key step in the Toll‐like receptor‐7 (TLR) and TLR‐9 signaling pathways. Our data implicates the radical SAM activity of viperin is essential in this activation step. We found that in presence of IRAK1 and TRAF6 the reductive cleavage of SAM to form 5′‐deoxyadenosine is increased ~ 4‐fold. Thus, our data provides the first evidence that viperin's radical SAM activity is linked to activation of a ubiquitin ligase. This observation has implications for how the enzyme may exert its multifaceted roles in the cellular antiviral response.Support or Funding InformationThis work was supported in part by NIH grants GM 093088 to E.N.G.M. and DK 046960 to R.T.K.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Evidence for a relatively high proportion of DM2 mutations in a large group of Polish patients

IntroductionMyotonic dystrophies (DMs) type 1 (DM1) and type 2 (DM2) are autosomal dominant, multisystem disorders, considered the most common dystrophies in adults. DM1 and DM2 are caused by dynamic mutations in the DMPK and CNBP genes, respectively. MethodsMolecular analyses were performed by PCR and the modified RP-PCR in patients, in their at-risk relatives and prenatal cases. ResultsThe analysis of Polish controls revealed the range of 5-31 CTG repeats for DM1 and 110-228 bp alleles for DM2. Among 318 confirmed probands - 196 (62%) were DM1 and 122 (38%) – DM2. Within DM1families, 10 subjects carried a low expanded CTG tract (< 100 repeats), which resulted in a full mutation in subsequent generations. Two related individuals had unstable alleles–188 bp and 196 bp without common interruptions. ConclusionThe relative frequencies of DM1/DM2 among Polish patients were 68% and 32%, respectively, with a relatively high proportion of DM2 mutations (1.6:1).

Are We Ready for Fragile X Newborn Screening Testing?-Lessons Learnt from a Feasibility Study.

Fragile X syndrome (FXS) is the most prevalent heritable cause of cognitive impairment but is not yet included in a newborn screening (NBS) program within Australia. This paper aims to assess the feasibility and reliability of population screening for FXS using a pilot study in one hospital. A total of 1971 mothers consented for 2000 newborns to be tested using routine NBS dried blood spot samples. DNA was extracted and a modified PCR assay with a chimeric CGG primer was used to detect fragile X alleles in both males and females in the normal, premutation, and full mutation ranges. A routine PCR-based fragile X assay was run in parallel to validate the chimeric primer assay. Babies with CGG repeat number ≥59 were referred for family studies. One thousand nine hundred and ninety NBS samples had a CGG repeat number less than 55 (1986 < 50); 10 had premutation alleles >54 CGG repeats (1/123 females and 1/507 males). There was complete concordance between the two PCR-based assays. A recent review revealed no clinically identified cases in the cohort up to 5 years later. The cost per test was $AUD19. Fragile X status can be determined on routine NBS samples using the chimeric primer assay. However, whilst this assay may not be considered cost-effective for population screening, it could be considered as a second-tier assay to a developed immunoassay for fragile X mental retardation protein (FMRP).

Reevaluation of FMR1 Hypermethylation Timing in Fragile X Syndrome.

Fragile X syndrome (FXS) is one of the most common heritable forms of cognitive impairment. It results from a fragile X mental retardation protein (FMRP) protein deficiency caused by a CGG repeat expansion in the 5′-UTR of the X-linked FMR1 gene. Whereas in most individuals the number of CGGs is steady and ranges between 5 and 44 units, in patients it becomes extensively unstable and expands to a length exceeding 200 repeats (full mutation). Interestingly, this disease is exclusively transmitted by mothers who carry a premutation allele (55–200 CGG repeats). When the CGGs reach the FM range, they trigger the spread of abnormal DNA methylation, which coincides with a switch from active to repressive histone modifications. This results in epigenetic gene silencing of FMR1 presumably by a multi-stage, developmentally regulated process. The timing of FMR1 hypermethylation and transcription silencing is still hotly debated. There is evidence that hypermethylation varies considerably between and within the tissues of patients as well as during fetal development, thus supporting the view that FMR1 silencing is a post-zygotic event that is developmentally structured. On the other hand, it may be established in the female germ line and transmitted to the fetus as an integral part of the mutation. This short review summarizes the data collected to date concerning the timing of FMR1 epigenetic gene silencing and reassess the evidence in favor of the theory that gene inactivation takes place by a developmentally regulated process around the 10th week of gestation.

Genetic cluster of fragile X syndrome in a Colombian district.

Fragile X syndrome (FXS) is the most common cause of inherited intellectual disabilities and autism. The reported prevalence of the full mutation (FM) gene FMR1 in the general population is 0.2-0.4 per 1000 males and 0.125-0.4 per 1000 females. Population screening for FMR1 expanded alleles has been performed in newborns and in an adult population. However, it has never been carried out in an entire town. Ricaurte is a Colombian district with 1186 habitants, with a high prevalence of FXS, which was first described by cytogenetic techniques in 1999. Using a PCR-based approach, screening for FXS was performed on blood spot samples obtained from 926 (502 males and 424 females) inhabitants from Ricaurte, accounting for 78% of total population. A high prevalence of carriers of the expanded allele was observed in all FXS mutation categories. Using the Bayesian methods the carrier frequency of FM was 48.2 (95% Credibility Region CR: 36.3-61.5) per 1000 males and 20.5 (95% CR:13.5-28.6) per 1000 females; the frequency of premutation carrier was 14.1 (95% RC: 8.0-21.7) per 1000 males (95% RC: 8.0-21.7 per 1000 males) and 35.9 (95% RC: 26.5-46.2) per 1000 for females (95% RC: 26.5-46.2 per 1000 females), and gray zone carrier was 13.4 (95% RC: 7.4-20.7) per 1000 males (95% RC: 7.4-20.7 per 1000 males) and 42.2 (95% RC: 32.2-53.8) per 1000 for females (95% RC: 32.2-53.8 per 1000 females). Differences in carrier frequencies were observed for premutation and FM alleles between natives and non-natives. This study shows that in Ricaurte the carrier frequencies of FMR1 expanded alleles (premutations and FMs) are higher than those reported in the literature, suggesting that Ricaurte constitutes a genetic cluster of FXS.

Chapter 25 - Fragile X syndrome and fragile X-associated tremor ataxia syndrome

Fragile X-associated disorders encompass several conditions, which are caused by expansion mutations in the fragile X mental retardation 1 (FMR1) gene. Fragile X syndrome is the most common inherited etiology of intellectual disability and results from a full mutation or >200 CGG repeats in FMR1. It is associated with developmental delay, autism spectrum disorder, and seizures. Fragile X-associated tremor/ataxia syndrome is a progressive neurodegenerative disease that occurs in premutation carriers of 55-200 CGG repeats in FMR1 and is characterized by kinetic tremor, gait ataxia, parkinsonism, executive dysfunction, and neuropathy. Fragile X-associated primary ovarian insufficiency also occurs in premutation carrier women and manifests with infertility and early menopause. The diseases constituting fragile X-associated disorders differ mechanistically, due to the distinct molecular properties of premutation versus full mutations. Fragile X syndrome occurs when there is a lack of fragile X mental retardation protein (FMRP) due to FMR1 methylation and silencing. In fragile X-associated tremor ataxia syndrome, a toxic gain of function is postulated with the production of excess CGG repeat-containing FMR1 mRNA, abnormal translation of the repeat sequence leading to production of polyglycine, polyalanine, and other polypeptides and to outright deficits in translation leading to reduced FMRP at larger premutation sizes. The changes in underlying brain chemistry due to FMR1 mutations have led to therapeutic studies in these disorders, with some progress being made in fragile X syndrome. This paper also summarizes indications for testing, genetic counseling issues, and what the future holds for these disorders.

Fragile X syndrome: diagnosis by molecular characterization of FMR1 gene and clinical correlation

Background One of the most common forms of inherited intellectual disability (ID) is fragile X syndrome (FXS), which is caused by expansion of cytosine–guanine–guanine trinucleotide repeat at the 5′ untranslated region of the fragile X mental retardation gene (FMR1) at Xq27. The cytosine–guanine–guanine repeat expansion leads to hypermethylation and inactive transcription of the gene. The present study aimed to detect expected FMR1 gene alleles by methylation-sensitive PCR and its clinical correlation for rapid screening of FXS among male patients with ID. Patients and methods The study included 50 male patients with ID and clinical features suggestive of FXS, who were compared with 50 healthy age-matched volunteers. All patients were subjected to full history taking, thorough clinical examination using a 15-item checklist [physical (big ears, joint hyperextensibility, Simian crease, wide forehead, macroorchidism, and elongated face) and neurological features (mental retardation, family history of mental retardation, poor eye contact, hand biting, hyperactivity, perservative speech, tactile defensiveness, hand flapping, and short attention span)], and karyotyping using GTG banding. Methylation-sensitive PCR technique after bisulfite treatment of DNA was applied for the detection of expanded alleles of the FMR1 gene. Results Clinical score in patients with abnormal alleles was significantly higher compared with patients with normal alleles. GTG-banding technique showed normal 46XY male karyotype for studied patients. Frequency of normal FMR1 gene alleles was detected in the control group (100%) and 44 (88%) patients. Abnormal alleles were detected in six (12%) patients: three (6%) patients with full mutation (FM) and three (6%) patients with premutation carrier. Conclusion Our study revealed that PCR-positive results of fragile X correlate with the checklist clinical score rather than a single clinical entity.

Fragile X syndrome and fragile X-associated disorders.

Fragile X syndrome (FXS) is caused by a full mutation on the FMR1 gene and a subsequent lack of FMRP, the protein product of FMR1. FMRP plays a key role in regulating the translation of many proteins involved in maintaining neuronal synaptic connections; its deficiency may result in a range of intellectual disabilities, social deficits, psychiatric problems, and dysmorphic physical features. A range of clinical involvement is also associated with the FMR1 premutation, including fragile X-associated tremor ataxia syndrome, fragile X-associated primary ovarian insufficiency, psychiatric problems, hypertension, migraines, and autoimmune problems. Over the past few years, there have been a number of advances in our knowledge of FXS and fragile X-associated disorders, and each of these advances offers significant clinical implications. Among these developments are a better understanding of the clinical impact of the phenomenon known as mosaicism, the revelation that various types of mutations can cause FXS, and improvements in treatment for FXS.