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Since the discovery of the FMR1 gene and the clinical and molecular characterization of Fragile X Syndrome in 1991, more than 141 genes have been identified in the X-chromosome in these 28 years thanks to applying continuously evolving molecular techniques to X-linked intellectual disability (XLID) families. In the past decade, array comparative genomic hybridization and next generation sequencing technologies have accelerated gene discovery exponentially. Classically, XLID has been subdivided in syndromic intellectual disability (S-XLID)-where intellectual disability (ID) is always associated with other recognizable physical and/or neurological features-and non-specific or non-syndromic intellectual disability (NS-XLID) where the only common feature is ID. Nevertheless, new advances on the study of these entities have showed that this classification is not always clear-cut because distinct variants in several of these XLID genes can result in S-XLID as well as in NS-XLID. This review focuses on the current knowledge on the XLID genes involved in non-syndromic forms, with the emphasis on their pathogenic mechanism, thus allowing the possibility to elucidate why some of them can give both syndromic and non-syndromic phenotypes., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder that appears in at least one-third of adult carriers of FMR1 premutation. Several studies have shown that mitochondrial dysfunction may play a role in neurodegenerative disorders. In order to assess whether mitochondrial DNA variants are involved in the risk of developing FXTAS we evaluated the frequency of mitochondrial haplogroups in 132 unrelated Spanish FMR1 premutation carriers. In addition, the entire mitogenome of 26 FMR1 premutation carriers was sequenced using massively parallel sequencing technologies to analyze mitochondrial DNA variants. Statistical analyses reveal a significant difference in the frequency of T haplogroup. Data analysis of mitochondrial DNA sequences evidence an association between FXTAS and the burden of heteroplasmic variants as well as their distribution. Our results suggest that haplogroup T might be a potential protective factor for FXTAS and that FXTAS individuals accumulate higher rates of heteroplasmic variants in compromised regions of the mitochondrial genome. These results may explain, in part, the role of mitochondrial DNA in the development of FXTAS., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

Background: People with fragile X syndrome (FXS) have an intellectual dysfunction that can range from very mild to severe. Symptoms can include speech and language delays and behavioural difficulties such as aggression or self injurious behaviours, emotional lability, and anxiety-related problems (for example obsessive-compulsive symptoms and perseverative behaviours). In some cases, affected people may have an additional diagnosis of attention deficit hyperactivity disorder or an autism spectrum disorder., Objectives: To review the efficacy and safety of L-acetylcarnitine in improving the psychological, intellectual, and social performance of people with FXS., Search Methods: In May 2015 we searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, PsycINFO, Web of Science, and two other databases. We also searched three trials registers, four theses databases, and the reference lists of relevant studies and reviews., Selection Criteria: Randomised controlled trials (RCTs) that assessed the efficacy of L-acetylcarnitine, at any dose, in people of any age diagnosed with FXS compared with placebo., Data Collection and Analysis: For each trial, two review authors independently extracted data on the children included and interventions compared, and assessed the risk of bias of the studies across the following domains: randomisation sequence generation, allocation concealment, blinding (of participants, personnel, and outcome assessors), incomplete outcome data, selective outcome reporting, and other potential sources of bias., Main Results: We found only two RCTs that compared oral L-acetylcarnitine (LAC) with oral placebo in children with FXS. The studies included a total of 83 participants, all of them male, who were treated and followed for one year. The age of participants at the start of treatment ranged from 6 to 13 years, with a mean age of 9 years. Neither study provided information on randomisation, allocation concealment procedures, or blinding of outcome assessment, and we received no responses from the authors we emailed for clarification. We therefore rated studies as being at unclear risk of bias on these domains. We judged both studies to be at low risk of bias for blinding of participants and personnel, incomplete outcome data, and selective reporting, but to be at high risk of other bias, as at least one study was funded by a drug company, and in both studies people working for the company were part of the research team.We used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to rate the quality of the available evidence. Overall, the quality of the evidence was low due to the imprecision of results and high risk of other bias.Regarding the primary outcome of psychological and learning capabilities, both studies assessed the effect of interventions on children's verbal and non-verbal intellectual functioning using the Wechsler Intelligence Scale for Children - Revised. The authors did not provide detailed data on those results but said that they found no important differences between treatment and placebo.Both studies evaluated the impact of the treatment on hyperactive behaviour using the Conners' Abbreviated Parent-Teacher Questionnaire. In one study, teachers' assessments of the children found no clear evidence of a difference (mean difference (MD) 0.50, 95% confidence interval (CI) -5.08 to 6.08, n = 51; low-quality evidence). The other study stated that there were no differences between treated and untreated participants, but did not provide detailed data for inclusion in the meta-analysis.Parents' assessments favoured LAC in one study (MD -0.57, 95% CI -0.94 to -0.19, n = 17; low-quality evidence), but not in the other (MD -2.80, 95% CI -7.61 to 2.01, n = 51; low-quality evidence), though changes were not large enough to be considered clinically relevant.Regarding social skills, one study reported no clear evidence of a difference in Vineland Adaptive Behavior composite scores (MD 8.20, 95% CI -0.02 to 16.42, n = 51; low-quality evidence), yet results in the socialisation domain favoured LAC (MD 11.30, 95% CI 2.52 to 20.08, n = 51; low-quality evidence).Both studies assessed the safety of the active treatment and recorded no side effects. Neither of the included studies assessed the secondary outcome of caregiver burden., Authors' Conclusions: Low-quality evidence from two small trials showed that when compared to placebo, LAC may not improve intellectual functioning or hyperactive behaviour in children with FXS.

Fragile X syndrome is the most common inherited form of intellectual disability. Here we report on a study based on a collaborative registry, involving 12 Spanish centres, of molecular diagnostic tests in 1105 fragile X families comprising 5062 individuals, of whom, 1655 carried a full mutation or were mosaic, three cases had deletions, 1840 had a premutation, and 102 had intermediate alleles. Two patients with the full mutation also had Klinefelter syndrome. We have used this registry to assess the risk of expansion from parents to children. From mothers with premutation, the overall rate of allele expansion to full mutation is 52.5%, and we found that this rate is higher for male than female offspring (63.6% versus 45.6%; P < 0.001). Furthermore, in mothers with intermediate alleles (45-54 repeats), there were 10 cases of expansion to a premutation allele, and for the smallest premutation alleles (55-59 repeats), there was a 6.4% risk of expansion to a full mutation, with 56 repeats being the smallest allele that expanded to a full mutation allele in a single meiosis. Hence, in our series the risk for alleles of <59 repeats is somewhat higher than in other published series. These findings are important for genetic counselling.

During the last few years, several studies have reported an excess of intermediate FMR1 alleles in patients with cognitive and/or behavioural phenotypes. Here, we report the frequency of intermediate alleles (IAs) in three pathologies, intellectual disabilities (IDs), attention-deficit/hyperactivity disorder and autism, from different Spanish regions. We found 142 IAs among 9015 patients with ID (1.6%), 4 among the 415 ADHD patients (0.96%) and 4 among the 300 autistic patients (1.3%), similar to the frequency reported in our control population. No evidence was found of an excess of IA at the FRAXA locus in any of the study populations, although geographical variability was detected. Moreover, the analysis of 100 transmissions of IAs showed that 95% of these alleles were stable. Only 3% expanded within the same range and 2% expanded to a full mutation in two generations. No evidence of an association between IAs and behavioural or cognitive phenotypes was found, suggesting that IAs are not clearly implicated in these pathologies.

Background: It has been argued that individuals with fragile X syndrome could have low folate levels in their bodies and that supplementing their dietary intake might remediate the adverse developmental and behavioural effects of the condition., Objectives: To review the efficacy and safety of folic acid in the treatment of people with fragile X syndrome., Search Strategy: We searched four databases in November 2010: CENTRAL, PubMed, EMBASE and PsycINFO., Selection Criteria: Randomised controlled trials., Data Collection and Analysis: Two review authors independently extracted data and assessed risk of bias using the Cochrane 'Risk of bias' tool., Main Results: We included five trials, which were published between 1986 and 1992. Overall, they included 67 patients, all male, with ages ranging from one to 54 years. Intellectual disability in participants varied from borderline to severe and some studies included patients with an additional diagnosis of autism or autistic behaviour. Four of the studies were placebo-controlled cross-over trials and one study was a parallel design. The duration of follow-up ranged from two months to 12 months and the period on folic acid or placebo ranged from two to eight months. Doses of folic acid ranged from 10 mg to 250 mg per day, 10 mg per day being the most common. Most of the younger patients involved were also taking part in special education programmes (usually involving language and occupational therapy).We were not able to perform meta-analysis to combine results but none of the individual studies found evidence of clinical benefit with the use of folic acid medication in fragile X syndrome patients on any of the areas of interest, either psychological and learning capabilities or behaviour and social performance, as measured with standardised tools. Separate analysis of evidence for patients of different age groups, i.e. prepubertal children and postpubertal young people, found some statistically significant results, but did not show clear evidence of benefit for either group. Adverse effects of folic acid treatment were rare, not serious and transient.Studies were generally poorly reported and we classified only one study as being at low risk of bias., Authors' Conclusions: The quality of available evidence is low and not suitable for drawing conclusions about the effect of folic acid on fragile X syndrome patients. It consists of few studies with small samples of patients, all of them male, with little statistical power to detect anything other than huge effects.

Background: Fragile X syndrome (FXS) is considered the most common cause of inherited mental retardation. Affected people have mental impairment that can include Attention Deficit and/or Hyperactivity Disorder (ADHD), autism disorder, and speech and behavioural disorders. Several pharmacological interventions have been proposed to treat those impairments., Methods: Systematic review of the literature and summary of the evidence from clinical controlled trials that compared at least one pharmacological treatment with placebo or other treatment in individuals with diagnosis of FXS syndrome and assessed the efficacy and/or safety of the treatments. Studies were identified by a search of PubMed, EMBASE and the Cochrane Databases using the terms fragile X and treatment. Risk of bias of the studies was assessed by using the Cochrane Collaboration criteria., Results: The search identified 276 potential articles and 14 studies satisfied inclusion criteria. Of these, 10 studies on folic acid (9 with crossover design, only 1 of them with good methodological quality and low risk of bias) did not find in general significant improvements. A small sample size trial assessed dextroamphetamine and methylphenidate in patients with an additional diagnosis of ADHD and found some improvements in those taking methylphenidate, but the length of follow-up was too short. Two studies on L-acetylcarnitine, showed positive effects and no side effects in patients with an additional diagnosis of ADHD. Finally, one study on patients with an additional diagnosis of autism assessed ampakine compound CX516 and found no significant differences between treatment and placebo. Regarding safety, none of the studies that assessed that area found relevant side effects, but the number of patients included was too small to detect side effects with low incidence., Conclusion: Currently there is no robust evidence to support recommendations on pharmacological treatments in patients with FXS in general or in those with an additional diagnosis of ADHD or autism.

This report describes a study focused on the relationship between CGG repeat length, FMRP, mRNA levels and cognitive functioning in premutation carriers (PM) carriers of Fragile X Syndrome (FXS). We studied 60 females-43 with PM and 17 with normal (N) alleles-from 25 FXS Spanish families. The Wechsler scales were administered to all subjects and new blood samples and hair roots were taken to study mRNA and FMRP levels. Using lowess curves together with segmented models we showed that within the premutation range, IQ scores tend to decrease when the number of CGG repeats increases and the FMRP values decrease. Furthermore, we discovered cut-off points in the molecular variables that seem to change the probability of having some cognitive impairment. Specifically, for those PM females in the upper premutation range (CGG > or = 100) and with FMRP expression < 60% in hair roots, a 10% decrement of FMRP expression represents a significant decrease in IQ scores of about six points, which is more evident for Full-Scale IQ (P-value = 0.035) and Performance IQ (P-value = 0.045) than for Verbal IQ (P-value = 0.074). On the contrary, we did not find any significant correlation between FMR1 mRNA levels and the IQ scores, probably due to the fact that mRNA levels were measured in blood. In conclusion, our findings suggest that the PM can have some effect on cognitive ability in female carriers, although these effects may be subtle. In these cases, it would be advisable to carry out a hair root analysis of FMRP., (2008 Wiley-Liss, Inc.)

Fragile X syndrome is caused by the absence or reduction of the fragile X mental retardation protein (FMRP) because FMR1 gene expression is reduced. Alleles with repeat sizes of 55-200 are classified as premutations, and it has been demonstrated that FMR1 expression is elevated in the premutation range. However, the majority of the studies reported were performed in males. We studied FMR1 expression in 100 female fragile X family members from the northern region of Spain using quantitative (fluorescence) real-time polymerase chain reaction. Of these 100 women, 19 had normal alleles, 19 were full mutation carriers, and 62 were premutation carriers. After confirming differences between the three groups of females, and increased levels of the FMR1 transcript among premutation carriers, we found that the relationship between mRNA levels and repeat size is nonlinear. These results were obtained using a novel methodology that, based on the size of the CGG repeats, allows us to find out the most probable threshold from which the relationship between CGG repeat number and mRNA levels changes. Using this approach, a significant positive correlation between CGG repeats and total mRNA levels has been found in the premutation range <100 CGG, but this correlation diminishes from 100 onward. However, when correcting by the X inactivation ratio, mRNA levels increase as the number of CGG repeats increases, and this increase is highly significant over 100 CGG. We suggest that due to skewed X inactivation, mRNA levels tend to normalize in females when the number of CGG repeats increases.

Introduction: Fragile X syndrome is the most common cause of hereditary mental retardation. Since the molecular mechanism causing it (anomalous expansion of the CGG triplet in the FMR1 gene and hypermethylation of its CpG island) was identified exactly ten years ago, it has been possible to give families in whom the syndrome is transmitted completely reliable prenatal genetic diagnosis of this., Objective: To report and discuss our experience in this field from 1994 to the present time., Patients and Methods: During this period we performed 15 prenatal diagnoses: 14 in samples of chorionic villi from 13 pregnancies (one a twin pregnancy) and 1 using amniotic fluid. In all cases we used Southern blot molecular techniques with the StB12.3 probe, the PCR of CGG triplet and DXS548 in some cases., Results: Nine fetuses were normal. Of the other six foetuses, three had full mutation, one had deletion of the FMR1 gene, another was premutated and another had an allele in the grey zone (50 repetitions)., Conclusions: Molecular prenatal diagnosis of SXF is fast and 100% reliable, although from the technical point of view it is complicated and requires use of various molecular techniques. From the clinical point of view, the low rate of mutations found assures offspring, although molecular studies do not predict mental 'status' in either girls with complete mutation or children with permutation.

A case of mosaic Turner's syndrome with a 45,X/46,XX/47,XXX karyotype, who was also a fragile X obligate carrier as the mother of an affected boy, was identified by molecular diagnosis. Complete haplotyping and direct DNA analysis showed that the X chromosome in all metaphases was the normal X. At the age of 57, she is mentally normal. Her external appearance was typical of Turner's syndrome. This report shows that molecular studies in conjunction with cytogenetic analysis can help in the clinical diagnosis of a rare case and can show the uniqueness of a case such as the one here described.