The fragile X syndrome. A study of 83 families

Autism in Fragile X Syndrome; A Functional MRI Study of Facial Emotion-Processing

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and autism spectrum disorder, and among those with fragile X syndrome, approximately 1/3rd meet a threshold for an autism spectrum disorder (ASD) diagnosis. Previous functional imaging studies of fragile X syndrome have typically focused on those with fragile X syndrome compared to either neurotypical or autism spectrum disorder control groups. Further, the majority of previous studies have tended to focus on those who are more intellectually able than is typical for fragile X syndrome. In this study, we examine the impact of autistic traits in individuals with fragile X syndrome on a paradigm looking at facial emotion processing. The study included 17 individuals with fragile X syndrome, of whom 10 met criteria for autism as measured by the Autism Diagnostic Observation Schedule (ADOS). Prior to the scan, participants rehearsed on a mock scanner to help acclimatize to the scanner environment and thus allow more severely affected individuals to participate. The task examined the blood-oxygen-level-dependent (BOLD) response to fearful and neutral faces taken from the Ekman faces series. Individuals in the autism group had a region of significantly reduced activity centered on the left superior temporal gyrus, compared to those with FXS alone, in response to the fearful faces. We suggest that autism in individuals with fragile X syndrome is associated with similar changes in the neurobiology of facial emotion processing as seen in idiopathic autism.

Caregiver Preferences for the Treatment of Males with Fragile X Syndrome

OBJECTIVE

Fragile X syndrome (FXS) is the most common inherited form of intellectual disability. The objective of this study was to determine the relative importance that caregivers place on improving different phenotypic traits observed in males with FXS to better understand the greatest medical needs for developing and evaluating FXS treatments.

METHOD

Fragile X syndrome caregivers (n = 614) compared hypothetical treatments in a discrete-choice experiment. The treatments varied in their effects on 6 outcomes associated with FXS: learning and applying new skills, explaining needs, controlling behavior, taking part in new social activities, caring for oneself, and paying attention. The relative importance was calculated for improving severe or moderate levels of disability and transformed to a 10-point scale. Relative importance was also quantified by patient age group (child, adolescent, and adult).

RESULTS

Most important to caregivers were controlling behavior (10.0) and caring for oneself (9.9). Least important was taking part in new social activities (4.2). A partial improvement in controlling behavior or self-care was more important than full resolution of the least important disabilities. This was consistent across age groups. Improvements from severe to moderate disability were more important than from moderate to no disability.

CONCLUSION

Caregivers expressed strong preferences for improvement in self-care and behavioral control, independent of the age of the individual with FXS. These data may be helpful when designing studies to test the efficacy of FXS treatments because small treatment effects on very important outcomes may be valued more than large treatment effects on less valued outcomes.

Fragile X syndrome: a review of associated medical problems

Fragile X syndrome (FXS) is the most common known genetic cause of inherited intellectual disability and the most common known single-gene cause of autism spectrum disorder. It has been reported that a spectrum of medical problems are commonly experienced by people with FXS, such as otitis media, seizures, and gastrointestinal problems. Previous studies examining the prevalence of medical problems related to FXS have been challenging to interpret because of their marked differences in population, setting, and sampling. Through this comprehensive review, we update the literature by reviewing studies that have reported on prominent medical problems associated with FXS. We then compare prevalence results from those studies with results from a large cross-sectional database consisting of data collected by fragile X clinics that specialize in the care of children with FXS and are part of the Fragile X Clinical and Research Consortium. It is vital for pediatricians and other clinicians to be familiar with the medical problems related to FXS so that affected patients may receive proper diagnosis and treatment; improved care may lead to better quality of life for these patients and their families.

Rescue of fragile X syndrome phenotypes in Fmr1 KO mice by the small-molecule PAK inhibitor FRAX486

Fragile X syndrome (FXS) is the most common inherited form of autism and intellectual disability and is caused by the silencing of a single gene, fragile X mental retardation 1 (Fmr1). The Fmr1 KO mouse displays phenotypes similar to symptoms in the human condition--including hyperactivity, repetitive behaviors, and seizures--as well as analogous abnormalities in the density of dendritic spines. Here we take a hypothesis-driven, mechanism-based approach to the search for an effective therapy for FXS. We hypothesize that a treatment that rescues the dendritic spine defect in Fmr1 KO mice may also ameliorate autism-like behavioral symptoms. Thus, we targeted a protein that regulates spines through modulation of actin cytoskeleton dynamics: p21-activated kinase (PAK). Our results demonstrate that a potent small molecule inhibitor of group I PAKs reverses dendritic spine phenotypes in Fmr1 KO mice. Moreover, this PAK inhibitor--which we call FRAX486--also rescues seizures and behavioral abnormalities such as hyperactivity and repetitive movements, thereby supporting the hypothesis that a drug treatment that reverses the spine abnormalities can also treat neurological and behavioral symptoms. Finally, a single administration of FRAX486 is sufficient to rescue all of these phenotypes in adult Fmr1 KO mice, demonstrating the potential for rapid, postdiagnostic therapy in adults with FXS.

Dampened dopamine-mediated neuromodulation in prefrontal cortex of fragile X mice

Fragile X syndrome (FXS) is the most common form of inheritable mental retardation caused by transcriptional silencing of the Fmr1 gene resulting in the absence of fragile X mental retardation protein (FMRP). The role of this protein in neurons is complex and its absence gives rise to diverse alterations in neuronal function leading to neurological disorders including mental retardation, hyperactivity, cognitive impairment, obsessive-compulsive behaviour, seizure activity and autism. FMRP regulates mRNA translation at dendritic spines where synapses are formed, and thus the lack of FMRP can lead to disruptions in synaptic transmission and plasticity. Many of these neurological deficits in FXS probably involve the prefrontal cortex, and in this study, we have focused on modulatory actions of dopamine in the medial prefrontal cortex. Our data indicate that dopamine produces a long-lasting enhancement of evoked inhibitory postsynaptic currents (IPSCs) mediated by D1-type receptors seen in wild-type mice; however, such enhancement is absent in the Fmr1 knock-out (Fmr1 KO) mice. The facilitation of IPSCs produced by direct cAMP stimulation was unaffected in Fmr1 KO, but D1 receptor levels were reduced in these animals. Our results show significant disruption of dopaminergic modulation of synaptic transmission in the Fmr1 KO mice and this alteration in inhibitory activity may provide insight into potential targets for the rescue of deficits associated with FXS.

Fragile X syndrome: a psychiatric perspective

Fragile X syndrome (FXS) is associated with a complex but relatively consistent psychiatric phenotype. Recent research has suggested neural substrates for the behavioral abnormalities typically seen in FXS, and enhanced treatment strategies for managing disabling psychiatric comorbidity. While disease-specific, and possibly disease-modifying, therapeutics are being developed for FXS, currently available psychiatric medications can provide significant symptomatic relief of the hyperactivity, anxiety disorders, and affective disturbances often seen in the course of FXS. However, patients with fragile X may be especially susceptible to the psychiatric side effects of these medications, requiring particular care in prescribing. Recent findings concerning disease mechanisms and treatment strategies are reviewed from the perspective of a clinical psychiatrist, in an effort to enhance conventional pharmacotherapy of FXS.

The psychiatric presentation of fragile x: evolution of the diagnosis and treatment of the psychiatric comorbidities of fragile X syndrome

Fragile X syndrome (FXS) is the leading inherited cause of mental retardation and autism spectrum disorders worldwide. It presents with a distinct behavioral phenotype which overlaps significantly with that of autism. Unlike autism and most common psychiatric disorders, the neurobiology of fragile X is relatively well understood. Lack of the fragile X mental retardation protein causes dysregulation of synaptically driven protein synthesis, which in turn causes global disruption of synaptic plasticity. Thus, FXS can be considered a disorder of synaptic plasticity, and a developmental disorder in the purest sense: mutation of the FMR1 (fragile X mental retardation 1) gene results in abnormal synaptic development in response to experience. Accumulation of this abnormal synaptic development, over time, leads to a characteristic and surprisingly consistent behavioral phenotype of attention deficit, hyperactivity, impulsivity, multiple anxiety symptoms, repetitive/perseverative/stereotypic behaviors, unstable affect, aggression, and self-injurious behavior. Many features of the behavioral and psychiatric phenotype of FXS follow a developmental course, waxing and waning over the life span. In most cases, symptoms present as a mixed clinical picture, not fitting established diagnostic categories. There have been many clinical trials in fragile X subjects, but no placebo-controlled trials of adequate size or methodology utilizing the most commonly prescribed psychiatric medications. However, large and well-designed trials of investigational agents which target the underlying pathology of FXS have recently been completed or are under way. While the literature offers little guidance to the clinician treating patients with FXS today, potentially disease-modifying treatments may be available in the near future.

Fragile X mental retardation protein has a unique, evolutionarily conserved neuronal function not shared with FXR1P or FXR2P

Fragile X syndrome (FXS), resulting solely from the loss of function of the human fragile X mental retardation 1 (hFMR1) gene, is the most common heritable cause of mental retardation and autism disorders, with syndromic defects also in non-neuronal tissues. In addition, the human genome encodes two closely related hFMR1 paralogs: hFXR1 and hFXR2. The Drosophila genome, by contrast, encodes a single dFMR1 gene with close sequence homology to all three human genes. Drosophila that lack the dFMR1 gene (dfmr1 null mutants) recapitulate FXS-associated molecular, cellular and behavioral phenotypes, suggesting that FMR1 function has been conserved, albeit with specific functions possibly sub-served by the expanded human gene family. To test evolutionary conservation, we used tissue-targeted transgenic expression of all three human genes in the Drosophila disease model to investigate function at (1) molecular, (2) neuronal and (3) non-neuronal levels. In neurons, dfmr1 null mutants exhibit elevated protein levels that alter the central brain and neuromuscular junction (NMJ) synaptic architecture, including an increase in synapse area, branching and bouton numbers. Importantly, hFMR1 can, comparably to dFMR1, fully rescue both the molecular and cellular defects in neurons, whereas hFXR1 and hFXR2 provide absolutely no rescue. For non-neuronal requirements, we assayed male fecundity and testes function. dfmr1 null mutants are effectively sterile owing to disruption of the 9+2 microtubule organization in the sperm tail. Importantly, all three human genes fully and equally rescue mutant fecundity and spermatogenesis defects. These results indicate that FMR1 gene function is evolutionarily conserved in neural mechanisms and cannot be compensated by either FXR1 or FXR2, but that all three proteins can substitute for each other in non-neuronal requirements. We conclude that FMR1 has a neural-specific function that is distinct from its paralogs, and that the unique FMR1 function is responsible for regulating neuronal protein expression and synaptic connectivity.

Systematic review of pharmacological treatments in fragile X syndrome

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.

The Pathophysiology of Fragile X Syndrome

Fragile X syndrome is the most common form of inherited mental retardation. The disorder is mainly caused by the expansion of the trinucleotide sequence CGG located in the 5' UTR of the FMR1 gene on the X chromosome. The abnormal expansion of this triplet leads to hypermethylation and consequent silencing of the FMR1 gene. Thus, the absence of the encoded protein (FMRP) is the basis for the phenotype. FMRP is a selective RNA-binding protein that associates with polyribosomes and acts as a negative regulator of translation. FMRP appears to play an important role in synaptic plasticity by regulating the synthesis of proteins encoded by certain mRNAs localized in the dendrite. An advancing understanding of the pathophysiology of this disorder has led to promising strategies for pharmacologic interventions.

Recruitment of old genes to new functions: evidences obtained by comparing the orthologues of human XLMR genes in mouse and chicken

Gene mapping data indicate that the human X chromosome is enriched in genes that affect both, higher cognitive efficiency and reproductive success. This raises the question whether these functions are ancient, or whether conserved X-linked genes were recruited to new functions. We have studied three X-linked mental retardation (XLMR) genes by RNA in situ hybridization in mouse and in chicken, in which these genes are autosomal: Rho guanine nucleotide exchange factor 6 (ARHGEF6), oligophrenin (OPHN1), and p21 activated kinase 3 (PAK3). In the mouse these genes are specifically expressed in telencephalic regions. Their orthologues in the chicken gave patterns of similar specificity in ancient parts of the brain, i.e. cerebellum and mesencephalon, but were not expressed in the telencephalon. Also in the testes, specific expression was only found in mouse, not in chicken. These data are interpreted such that certain genes on the X chromosome gained novel functions during evolution.

Mental deficiency, alterations in performance, and CNS abnormalities in overgrowth syndromes

Mental deficiency, alterations in performance, and central nervous system (CNS) abnormalities are discussed in the following overgrowth syndromes: Sotos syndrome, Weaver syndrome, Proteus syndrome, neurofibromatosis type 1, fragile X syndrome, syndromes with neonatal hypoglycemia, Simpson-Golabi-Behmel syndrome, hemihyperplasia, Sturge-Weber syndrome, Bannayan-Riley-Ruvalcaba/Cowden syndrome, macrocephaly-autism syndrome, PEHO syndrome, chromosomal syndromes, and other miscellaneous syndromes.

Problems in the diagnosis of fragile X syndrome in young children are still present

Fragile X syndrome is common; its prevalence approaches 1 per 5,000. Fragile X syndrome is the most common inherited cause of mental retardation. Many professionals must deal with fragile X individuals on a daily basis. However, despite the diverse information on the epidemiology, clinical features, unique pattern of inheritance, cytogenetic, and molecular diagnosis and scales for the diagnosis of this syndrome, the diagnosis of fragile X syndrome is still not always made by the patients' specialists. Here we present the difficulties in the diagnosis of fragile X syndrome in 11 children under 8 years of age, 10 boys and one girl. We report data on initial symptoms, behavioral features, and physical and mental development before molecular studies were considered. The possible causes for the diagnosis delay were multiple: nonspecific features (e.g., macrocephaly, overgrowth, obesity), unremarkable physical examination, family history apparently noncontributory, and lack of or delayed molecular testing. Careful clinical examination of young children and DNA screening in case of doubt, and education of professionals in medical specialty areas, behavioral sciences, education, and other fields are recommended.

Epilepsy and EEG findings in 18 males with fragile X syndrome

Of the 24 males identified as having fragile X syndrome in the Northeast Essex screening programme, 25% had epilepsy. Epilepsy in individuals with fragile X syndrome is known to follow a benign course with seizures disappearing before the age of 20. However, half of our sample with a history of epilepsy continued to have seizures after the age of 20. We reviewed the EEG reports of 18 of the 24 individuals (aged between 13 and 63 years) including all six individuals with epilepsy. We had 32 EEG recordings from 18 subjects, with nine people having more than one recording at different points. The EEG showed a definite improvement in only five individuals. Three individuals who had serial recordings (one with epilepsy) showed no significant changes over time and the EEG of one subject with epilepsy deteriorated. The most common abnormal EEG findings were rhythmic theta activity (50%) and a slowing of background activity (28%). There were no characteristic features in the sleep EEGs performed on four subjects. The possible implications of these preliminary findings are discussed.

Chromosomal fragility and human genetic disorders

The first report of X-linked mental retardation correlated with the presence of marker chromosome came in 1940. It was in 1990 that the molecular basis of fragile X syndrome was deciphered. This elucidation marked the discovery of a novel process of mutation designated as dynamic mutations, resulting in the expansion of a triplet repeat sequence within the human genome. Subsequently several human genetic disorders involving triplet repeat expansion have been discovered. Almost all the disorders are known to affect the nervous system and/or the brain. This review presents an overview of fragile sites in the genome and the molecular genetics of fragile X syndrome.

Epilepsy and EEG findings in males with fragile X syndrome

PURPOSE AND METHODS

One hundred and ninety-two fragile X male patients were investigated for seizures and EEG findings, 168 in a retrospective and 24 in another prospective study, to characterize the natural history of seizures, epilepsy, and EEG abnormalities in males with this syndrome.

RESULTS

Seizures were documented in 35 (18.2%) of 192 patients; they never started before the age of 2 years or after the age of 9 years. Seizures were frequently of the complex partial type and less frequently of the partial motor and generalized type. Seizures involving frontal and temporal lobes were commonly seen and were usually well controlled by anticonvulsants. In the majority of young fragile X patients studied, an age-related paroxysmal EEG pattern was found, which showed neurophysiologic characteristics very similar to those of the centrotemporal spikes.

CONCLUSIONS

These findings confirm that fragile X syndrome can be considered a genetic model of epilepsy.

Autism: the point of view from fragile X studies

The relationship between the fragile X syndrome (FXS) and autism is reviewed. Shortly after the FXS was first described, it was noted that certain behaviors commonly found in afflicted individuals resemble certain features of autism. Research concerning a possible relationship between these conditions is summarized. The outcome of this research indicates that FXS is not a common cause of autism, although the number of individuals with FXS who meet diagnostic criteria for autism is higher than can be accounted for by chance. The major focus of this paper highlights that FXS is a well-defined neurogenetic disease that includes a cognitive behavioral phenotype, and has both a known biological cause and an increasing well-delineated pathogenesis. Autism is a behaviorally defined syndrome whose syndromic boundaries and biological causes are not known. These profound differences complicate comparisons and causal discussions. However, the behavioral neurogenetic information available about FXS suggests certain pathways for future research directed at elucidating the syndrome of autism.

Fragile X syndrome among children with mental retardation

Prospective screening for fragile X syndrome was carried out among 1,111 patients with mental retardation who attended the Genetic clinic. Using defined clinical criteria, 55 patients were selected for cytogenetic studies to detect folate sensitive fragile sites. Twenty patients were diagnosed to have the fragile X syndrome. The prevalence of fragile X (A) syndrome was 18 per 1,000 patients of both sexes with mental retardation, 2.8% among male patients with mental retardation, and 5.8% among subjects with nonspecific mental retardation.

Prader-Willi-like phenotype in fragile X syndrome

A 3-year-old boy was referred to the pediatric department because of unexplained extreme obesity. Height and occipitofrontal circumference were just above the 90th centile. Endocrine studies failed to show any significant abnormality. Motor and speech development were generally delayed. On clinical-cytogenetic-molecular grounds, Prader-Willi syndrome was excluded. Fragile X syndrome was diagnosed by the presence of the classical FMR-1 mutation and confirmed by cytogenetic studies, revealing 20% fragile X positive cells. We compare the clinical features in the present patient with the nine reported patients with fra(X) syndrome and extreme obesity. In pathogenesis, hypothalamic dysregulation is hypothesized. In differential diagnosis of Prader-Willi syndrome, fragile X has to be considered, especially when laboratory workup for Prader-Willi syndrome is negative. Clinical behavior can be of help.

Is autism associated with the fragile X syndrome?

In addition to mental retardation (MR), fragile X [fra(X)] has been associated with other developmental disabilities, autism in particular. Recently, several studies have concluded that the association of fra(X) with autism is at best weak and perhaps nonexistent. This study examined reports of previously published data from an epidemiological perspective to determine if the prevalence of fra(X) among autistic males was significantly different from that among MR males. Nineteen studies of autistic males and 21 studies of MR males were analyzed from 59 examined. Of 5601 MR males tested, 307 (5.5%) were cytogenetically positive. Of 1006 autistic males, 54 (5.4%) were positive. Analysis indicated no statistical difference between these proportions (Z = 0.014; p greater than .50). An odds ratio (OR) was also computed to determine the risk of autism from fra(X). Estimated OR approximately 1.0 [0.73, 1.32]. Attributable risk (AR), the proportionate excess risk of autism associated with exposure to fra(X) was AR approximately 0.0. That is, there was no attributable risk of autism from fra(X). The association of fra(X) with autism may reflect the association with MR that generally accompanies autism, as several earlier reports have noted. However, the similarity in prevalence of fra(X) among autistic and MR males may be biased in the studies which find no instances of fra(X) among autistic males represent 12% of the pooled sample.

Factors which contribute to cytogenetic frequency of expression in families of fragile X females

Frequency of expression in mentally retarded (MR) fragile X (fra[X]) males has been shown to be affected by genetic factors and laboratory procedures. Among MR females, factors that contribute to cytogenetic expression have been more problematic in part due to lower frequency of expression and X-inactivation. We examined fra(X) sisters to determine whether genetic factors affecting frequency of expression in sisters were comparable to those in brothers. Evaluations obtained from 2 data sets for a total of 66 families in which at least 2 affected brothers and/or 2 affected sisters were found cytogenetically positive were selected. Of 166 subjects chosen, 118 were male and 48 were female. Sibs were evaluated using an analysis of covariance (ANCOVA) with 2 factors (family, sex) adjusted for the covariate, age. Results indicated that interactive effects (family-by-sex) and main effects (family, sex, age) were significant but the interactive effect of age-by-sex was not. Consequently, one-way analyses of variance (ANOVA) of the effect of family were calculated separately for brothers and sisters. Correlation coefficients between family and cytogenetic frequency was r = .84 for brothers and r = .79 for sisters. Analysis of these coefficients indicated that they were not significantly different from one another (Z = 0.85, p greater than .40). While other factors may affect cytogenetic expression, whatever familial factors control frequency of expression among brothers appear to affect frequency of expression among sisters as well.

Aarskog syndrome: the changing phenotype with age

We describe the Leuven experience with 52 males with Aarskog syndrome particularly with respect to clinical variability, changing phenotype with age, and previously unreported signs. At least 30% of affected males were mentally retarded, two thirds of them at the level of slight mental handicap. Hyperactive behavior and symptoms of attention deficit disorders were frequently observed (61% of the mentally normal and 84% of the mentally subnormal), but regressed completely after the age of 12 to 14 years. The social integration and functioning as adults is satisfactory. Postpubertal males with Aarskog syndrome have only minor remnant manifestations of the prepubertal phenotype, making clinical diagnosis in adults extremely difficult.

Psychological characteristics of Sotos syndrome

A preliminary investigation of the psychological characteristics of 16 children aged between five and 15 years who met the strict diagnostic criteria for Sotos syndrome demonstrated that, while cognitive abilities vary, there are behavioural patterns that are characteristic of the disorder. The children were reported to have high rates of behavioural disturbance at home, particularly tantrums, destructiveness, social withdrawal, and eating and sleeping difficulties. The children were reported to present fewer problems in the school environment. Other difficulties expressed by parents are also described and quantified.

Clinical investigation of females with the Martin-Bell syndrome and risk assessment for carrier status

Anthropometric measurements were made on a series of females heterozygous for the fragile-X syndrome. It was found that there were no simple series of discriminating features separating those of normal IQ from the mentally handicapped, but rather that the carriers studied represented a wide spectrum of phenotype. When measurements performed on 15 FRAXA negative, obligate carriers of normal IQ were considered separately, it was found that there were certain common phenotypic features allowing risk figures to be amended for those females at 50% risk of being a carrier but who are also FRAXA negative.

No genetic linkage detected for schizophrenia to Xq27-q28

The hypothesis that at least a subgroup of familial cases of schizophrenia could be due to a genetic defect on the X chromosome is supported by the observation of an excess of X-chromosome aneuploidies (XXX and XXY) among populations of patients with psychosis. The distal long arm, Xq27-q28, is a candidate region where linkage has been claimed to manic-depressive disorder and a fragile site has been associated with schizophrenia spectrum disorders. The present study excluded linkage to a large part of this region using four polymorphic probes and multipoint lod-score analysis in 10 families with multiple members with schizophrenia.

Sotos syndrome

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The female and the fragile X syndrome: data on clinical and psychological findings in 7 fra(X) carriers

In this report we present precise data on the clinical, intellectual and behavioural findings in 7 young fra(X) positive girls. The two most common and most important findings are an overgrowth syndrome present from birth on and common behavioural features like severe attentional problems and extreme shyness and anxiety. These symptoms seem to constitute the major criteria for fra(X) screening in prepubertal girls. The findings in previous studies are compared with the present observations.

Mental retardation, craniofacial dysmorphism, hypogonadism, diabetes mellitus and epilepsy in four siblings. A "new" mental retardation syndrome

In this report we describe a distinct and apparently new mental retardation syndrome in four siblings: three brothers and one sister. They present slight to moderate mental retardation associated with a peculiar craniofacial dysmorphism (4/4), hypergonadotrophic hypogonadism (4/4), eunuchoid habitus (4/4), diabetes mellitus (4/4) and epilepsy (3/4).

Fragile X frequency in a mentally retarded population in Brazil

Seventy-five male and 50 female students from 2 special schools for mildly, moderately retarded, or borderline individuals were screened clinically and cytogenetically in order to estimate the contribution of fragile X [fra(X)] syndrome to the cause of mental retardation in Brazil. We found 6 males (8%) from 4 families and 2 unrelated females (4%) with fra(X) chromosomes. One male and one female were isolated cases. The estimated frequency of Martin-Bell [fra(X)] syndrome among mentally impaired individuals in Brazil was similar to that previously reported in other countries.

Intelligence and cognitive profile in the fra(X) syndrome: a longitudinal study in 18 fra(X) boys

A longitudinal study of IQ and cognitive profile in 18 fra(X) positive boys is reported. At the time of diagnosis, four of the boys were mildly retarded, seven were moderately retarded, and five were severely mentally retarded. Intelligence was borderline in one child and normal in another. A decline in intellectual performance with age in the fra(X) syndrome indicated in previous studies was not confirmed and we review the reported data on this subject.

A genetic-diagnostic survey in an institutionalized population of 158 mentally retarded patients. The Viaene experience

In this report we summarize the results of a genetic-diagnostic survey of an institutionalized population of 158 severely mentally retarded patients. The etiological study was based on a clinical genetic approach with special attention to dysmorphology and neurological findings. In 72 patients a constitutional cause of their mental impairment was found: a chromosomal abnormality in 21, a Mendelian disorder in 36 (autosomal recessive disorder: 23; autosomal dominant: 12; and X-linked recessive: 1), a MCA/MR syndrome in 9, and a CNS malformation in 6 patients. In 33 patients, a pre- or perinatal cause was found, and 20 patients presented a pre- or perinatal infection of the CNS. Finally, no etiological diagnosis was detected in 28 patients; 6 of them presented a hitherto unclassifiable type of familial mental retardation.

Screening for the fragile X: how many cells should we analyse?

Since nationwide screening for the fragile X would involve the analysis of thousands of individuals within a short period of time, the number of cells, N, which should be analysed is of fundamental importance. When selecting N, the crucial parameter should be the degree of expression of the fragile site in the affected individuals in the population to be screened. However, this degree of expression is not known, and for routine diagnostic purposes, N = 100 has been accepted by many centers. By taking data from two large series of affected males/females with a known degree of expression (one series from New South Wales, one from Belgium), we have estimated the fraction of affected males/females which would have been missed if the two series were rescreened with the analysis of less than 100 cells. Assuming that the degree of expression within these two series is similar to the degree of expression in all affected individuals within the two populations, the results indicate that a reduction of N in a screening program, say from 100 to 50 cells, would reduce the detection rate between 1 and 5%. The reduction would be greater in females than in males, and greater in the Belgian than in the Australian population.

The fragile X in Sicily: an epidemiological survey

We have studied a group of 349 institutionalized propositi with mental retardation, and found 12 fra(X)-positive cases among 155 males (7.7%) and 8 fra(X)-positive cases among 194 females (4.1%). The males had characteristic manifestations of the Martin-Bell syndrome. Another 7 males, who were initially considered "borderline", having expression of fra(X) less than 4% and a non-characteristic phenotype, were eventually considered negative. Among 5,624 patients (2,764 males and 2,860 females) that were admitted to the Pediatric Department of the University of Catania during the period July 1986 - June 1987, 210 (120 males and 90 females) had mental retardation. Of these, 75 were analyzed for the presence of fra(X) (q27.3); 5 males (0.18% of all males) and 2 females (0.07% of all females) were fra(X)-positive. The males had the Martin Bell syndrome phenotype. The presence of fra(X) (q27) was confirmed in another 4 male propositi that were referred to our outpatient services with a clinical diagnosis of Martin-Bell syndrome.

Early manifestations of the Martin-Bell syndrome based on a series of both sexes from infancy

A small series of male and female fra(X) positive children is reviewed retrospectively clinically and photographically to identify a profile of age-related manifestations and behavioral traits of predictive value. This method involves a crossmatch with the cases and trait lists in the POSSUM Data Base. The plan then is to test the sensitivity and specificity in a prospective series. If this proves reliable, a request for a fra(X) cytogenetic analysis could be limited to the clinically screened matching cases, rather than the present costly exercise of testing all undiagnosed intellectually handicapped children.

Investigation of the segregation of the fragile X mutation in daughters of obligate carrier women

Two reports have suggested that over 50% of the offspring of obligate carrier women receive the mutation for the fra(X) or the Martin-Bell syndrome [Webb et al, 1986; Fryns, 1984]. Such a segregation distortion is difficult to assess for the fra(X) syndrome because of incomplete penetrance, variable expression and probable ascertainment biases. We have attempted to evaluate this possible segregation distortion in daughters of obligate carriers in a large sample of sibships ascertained in a survey of New South Wales, Australia. We used two definitions of expression: 1) presence of fra(X) positive cells if daughters were tested cytogenetically, and 2) mental impairment if daughters were not tested cytogenetically. The segregation frequency was estimated in different types of sibships of obligate carriers based on the way they were ascertained. This was done in order to have an internal check on possible ascertainment biases. Among the 189 cytogenetically tested daughters, 81 were fra(X) positive. Among the 97 untested daughters, 24 were mentally impaired in some way. Therefore, the segregation frequency as defined by fra(X) expression and/or mental impairment was 37%. Thus, no evidence was detected for segregation distortion. These data were significantly different than those collected by Webb et al [1986] and scored by the same method as the present data set.

Screening developmentally disabled male populations for fragile X: the effect of sample size

The fra(X) or Martin-Bell syndrome is the most common cause of inherited mental retardation (MR) in males. It is also associated with a variety of unusual behavioral and developmental disorders. Recent studies found great variability in the estimated strength of association between "autism" and the fra(X) syndrome, but not between MR and fra(X). We examined 31 studies which investigated the association of fra(X) syndrome with either MR or "autism" and found that the conclusion of those researchers could be significantly affected by sample size. Different behavioral and cytogenetic protocols will also influence the strength of association between fra(X) and autism.

Growth pattern in boys with fragile X

The impression that a proportion of boys with fra(X) may show overgrowth in early infancy was investigated in a small series of 7 boys born after 1970. The fra(X) positive boys had been referred for mental retardation, or were identified in investigations of familial mental retardation. The mean birth weight was increased, and average linear growth was consistently above the mean for Danish boys with the greatest increase in the second year of life. In contrast, the weight measurements were on average below the mean until age 2 years. It is suggested that in fra(X) patients there is a disturbance of early infantile growth.

Anthropometry in Martin-Bell syndrome

Thirty anthropometric measurements were analyzed in 147 adults with Martin-Bell syndrome (MBS) (56 men and 91 women) and in a random sample of 108 normal women and 111 men. Results of the univariate comparison of the age, height, or weight-adjusted variables between MBS and normal individuals of either sex indicated that a decrease in stature, in upper limb length, and in upper face height, and an increase in jaw length, chest circumference, and waist width occurred in both affected men and in heterozygous women. While the increase in ear height and breadth and in hypermobility of finger joints and decrease in palm width and bigonial diameter occurred only in affected men, increased bispinal and bitrochanteric diameters, upper arm circumference, and palm and wrist widths were characteristic deviations in heterozygous women. Multivariate analysis in the form of principal components showed some differences in the pattern of interrelationships in individual measures between MBS and normal individuals. In particular, and in contrast with both normal groups, height and weight tended to load on separate components (as did head and midfacial measures) in MBS individuals. A discriminant function based on all body measurements included in this study resulted in almost complete separation of discriminant scores of normal from those of MBS men and in good separation of the scores from normal and heterozygous women. Classification rates based on these functions were from 95% in men to 85% in women. These already high classification rates may be further improved mainly by enlarging the samples and including some other category of traits such as dermatoglyphic measurements.

Fragile X expression in normal and mentally retarded subjects: effect of treatment with an antifolic agent

Expression of the fragile site fra(X) (q27.3) in peripheral lymphocytes was evaluated in mentally retarded patients and in normal control individuals before and after administration of the antifolic agent trimethoprim for 7 days. This treatment was effective in converting the status of some individuals from fra(X)-negative to fra(X)-positive. However, the induced level of fra(X) expression was very low and not significantly different in patients and in control subjects and did not increase in those individuals where it was already present before treatment. These data support the contention that fra(X)(q27.3) is a common fragile site and that treatment in vivo with an antifolic agent is not effective in enhancing its degree of expression in vitro. Therefore, such treatment seems to be of no diagnostic value in those cases where the fra(X) syndrome is suspected clinically, but where there is no or very low cytogenetic expression of the fra(X).

Suggestively increased rate of infant death in children of fra(X) positive mothers

A review of the Leuven data on the fragile X syndrome indicates that sudden infant death is frequently observed in the progeny of obligate female carriers. This observation may be another indication of a central nervous dysfunction in infants with this type of X-linked mental retardation.

The fragile-X syndrome

The variability in behavioral manifestations of the fragile-X syndrome and the lack of a well-defined psychological profile require the attention of behavioral geneticists and other behavioral scientists. The association with autism suggests that the fra(X) may be responsible for a genetic subtype of autism. While the fragile-X syndrome is considered an X-linked disorder, several aspects of observed transmission patterns do not follow those of classical X-linked inheritance. In particular, the finding of genetic transmission via intellectually normal males is surprising and has important implications for genetic counseling, as well as for genetic models of the fragile-X syndrome. Reports on folic acid treatment are encouraging, but not conclusive. The mechanisms involved in the association between the fra(X) chromosome and its particular phenotype are still unknown. Current investigations applying advanced techniques in molecular biology are likely to provide insight into this unique genetic disorder.

Autism: familial aggregation and genetic implications

A review of the current literature suggests that genetic factors play an important role in the etiology of autism. It is likely that the etiology of currently idiopathic cases of autism will be shown to be heterogeneous, just as the few known etiologies are both environmental and genetic. Moreover, we would speculate that within the group of cases shown to have genetic etiologies, more than one genetic locus will be found. Some evidence suggests that quite often it is not autism itself that is inherited but rather some genetic abnormality of language or sociability that interacts with other factors to produce autism.

Fragile-X syndrome: a particular epileptogenic EEG pattern

A clinical and EEG study of 12 fragile-X syndrome subjects (six with epilepsy) is presented. All subjects had clinical-family history examinations, EEG evaluations, and karyotyping. Spikes were present in the sleep EEG of one nonepileptic and four epileptic subjects: these spikes were similar in location, occurrence, voltage, frequency, and morphology (and similar to those of the Rolandic spikes). These data, together with the clinical similarities (type of epilepsy, responses to drugs, ages of seizure onset, etc.), have resulted in the postulation of EEG characteristics of epileptic and nonepileptic fragile-X patients. However, further studies with fragile-X patients are needed to confirm this hypothesis.

A peculiar subphenotype in the fra(X) syndrome: extreme obesity-short stature-stubby hands and feet-diffuse hyperpigmentation. Further evidence of disturbed hypothalamic function in the fra(X) syndrome?

In this report we describe two fra(X) adults and two prepubertal fra(X) brothers with a combination of distinct phenotypic findings: extreme obesity, short stature, stubby hands and feet and diffuse hyper-pigmentation. These clinical abnormalities may be an additional indication of a specific hypothalamic disturbance in the fra(X) syndrome.

A comparison of language characteristics of mentally retarded adults with fragile X syndrome and those with nonspecific mental retardation and autism

Fragile X syndrome is a recently identified form of mental retardation that is associated with a chromosomal abnormality and inherited in an X-linked manner. Previous studies have suggested that distinctive speech and language characteristics are associated with the syndrome. Twelve adult male residents of an institution for the retarded (aged 23 to 51 years) were compared on a series of speech and language measures to 12 adult males with nonspecific forms of MR who were residents of the same institution and were matched on age and IQ. A second contrast group consisted of similarly matched autistic men. Results revealed that there were no significant differences among the groups' performance, with the exception of increased rates of echolalia in the autistic group. A nonsignificant trend toward poorer performance on expressive measures on the part of the fragile X group was noted. The implications of these findings for further research on the syndrome are discussed.