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.     

Prevalence of fra(X) and other specific diagnoses in autistic individuals in a Danish county

In a Danish county (the island of Funen) cytogenetic screening for fragile X [fra(X)] of 32 autistic individuals aged 0-23 years showed a prevalence of 2/20 among boys and 0/12 among girls. In both cases additional fra(X) positive relatives were found. In 3 patients other chromosome aberrations were demonstrated and in one female Rett syndrome was diagnosed, initially suspected from observations of her behavior on videotapes. The presence of an underlying cause of autism in 6/32, of the patient group encourages an active search for a specific diagnosis among autistic males and females. Future screening of autistic individuals should include 1) fra(X) search also in females, 2) search for other chromosomal disorders, and 3) observation of behavior, in order to diagnose, i.e., Rett syndrome.     

An analysis of autism in fifty males with the fragile X syndrome

Fifty males with the fragile X [fra(X)] syndrome, which we consider synonymous with the Martin-Bell syndrome, were identified by a chromosome analysis of patients with developmental delays or mental retardation and family studies of known fra(X) pedigrees. These males were evaluated for autism using three criteria: 1) the DSM III diagnostic criteria for Infantile Autism; 2) the Autism Behavior Checklist (ABC); and 3) the Diagnostic Checklist for Behavior Disturbed Children, Form E2. Sixteen percent of patients fulfilled all of the DSM III criteria for Infantile Autism and an additional 30% fulfilled criteria for Infantile Autism Residual State. Thirty-one percent of patients had autism using the ABC checklist but none of the patients fit the classical Kanner syndrome as described by the E2 questionnaire. Some autistic traits were seen in almost all of the 50 fra(X) patients, including eye avoidance in 90%, handflapping, handbiting or handstereotypies in 88%, and language delays with language peculiarities, usually echolalic speech, in 96%. A pervasive lack of responsiveness was seen in 18% at their present age and in 44% in earlier childhood only. Autistic symptoms are common in the fra(X) syndrome. Therefore, any patient with developmental delays and autism or autistic manifestations should have a chromosomal analysis, including fra(X) examination.     

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.     

Fragile site X chromosomes in mentally retarded boys.

The fragile X syndrome is a common X-linked mental retardation and autism, affecting females as well as males. The fragile site X chromosomes were studied in a series of 153 mentally retarded boys of unknown etiology to determine the frequency of fragile X syndrome, and to assess the feasibility of making a clinical diagnosis of the fragile X syndrome in young boys before cytogenetic results were known. The 10 boys (6.4%) were positive for fra (X) (q27). The phenotype of fra (X) (q27) positive patients were typical except one who also had sex chromosomal mosaicism. There were three pairs of siblings among the fra (X) (q27) positive patients. Frequency of expression of the fragile site was in 10 to 47 per cent of cells. In addition, 19 boys showed a previously unsuspected chromosomal abnormality. The frequency of the fragile X syndrome in the present study is not significantly different from those in Caucasians and Japanese population. The fragile X syndrome can be recognized by noting key aspects of family history as well as the clinical features in mentally retarded boys.     

A cytogenetic study in 120 Turkish children with intellectual disability and characteristics of fragile X syndrome

We review the evidence for the frequency of the fragile X syndrome (FXS), other X-linked abnormalities, and other chromosomal disabilities of Turkish pediatric psychiatry outpatients with intellectual disability. Reported clinical features and genetic findings were used in cytogenetic screenings to estimate the prevalence of the fragile X (fra X) and other chromosomal aberrations in 120 patients with mental retardation, language disorders, attention deficit hyperactivity, or developmental delay, in comparison with 30 healthy children. Data on the clinical, intellectual and behavioral findings in 14 fra X positive children (11.7%) is presented. Ten of the 120 patients (8.3%) had enlargement of the heterochromatin region of chromosome 9. Other chromosomal aberrations and autosomal fragile sites (FS) were also observed. There was a statistically significant difference in the autosomal and X-linked FS between the study and control groups (p < 0.05). The tests for the fra X chromosome are likely to be of diagnostic benefit in young children with autism or developmental delay, particularly in speech, and who have large and prominent ears.     

Effects of age and communication level on eye contact in fragile X males and non-fragile X autistic males

Dyadic social gaze and eye contact were examined in fragile X [fra(X)] males and in non-fra(X) autistic males as a function of age and level of communicative ability. Lag sequential analysis showed that responsive eye contact was highly correlated with age and communicative ability in non-fra(X) autistic males but not in fra(X) males. Older, more communicative non-fra(X) autistic males exhibited more responsive eye contact than their fra(X) cohorts. Implications of these observations for theory and intervention are discussed.     

Preliminary communication: neuroanatomical variations of the posterior fossa in men with the fragile X (Martin-Bell) syndrome

Four men with fragile X (fra (X], or Martin-Bell, syndrome were studied by magnetic resonance imaging (MRI) to determine whether detectable abnormalities of the cerebellum were present. The cerebellum was chosen because of the apparently increased tendency for fra (X) patients to demonstrate autistic behavior and accumulating evidence implicating cerebellar abnormalities in autism. Compared with a control group of four normal men, fra (X) patients had a significantly decreased area of the cerebellar vermis, particularly the posterior portion, on planimetric analysis in the midsagittal plane. The pons and fourth ventricular areas also were decreased and increased, respectively, in the fra (X) men. Neuroanatomical and animal research increasingly implicates the cerebellar vermis as an important component in functional brain systems subserving sensory and motor integration, learning, and modulation of affect, motivation, and social behavior. Thus, vermis dysfunction could account for many of the behavioral and cognitive abnormalities observed in fra (X) males, particularly those which overlap with the behavioral syndrome of autism.     

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.     

Fragile-X mutation and Klinefelter syndrome: a reappraisal

To date the concurrent presence of the fragile-X and the Klinefelter syndromes in the same individual has been found at least 8 times either in the course of screening for the fra(X) condition in mentally retarded males or among the relatives of fra(X) propositi. Given the high frequency of both events in the general population and the heterogeneous approaches with which the above cases were ascertained, it has not been possible to determine unequivocally so far whether the finding is purely coincidental or the expression of some underlying biological relationship. To evaluate the issue, we have screened a large population of institutionalized mentally retarded males for microorchidism, and submitted to a full karyotype analysis and fra(X) testing the patients that were found to have marked bilateral microorchidism. Thus, in a total of 32 microorchidism patients identified among 1115 mentally retarded males, we found 6 to have a 47,XXY chromosome complement in all (or in most) of their cells, with one of them having also the fra(X) marker in 9% of the metaphases examined. In addition, another bearer of the fra(X) marker (but only in 4% of his metaphases) was found among 26 47,XXY mentally normal males ascertained throughout routine cytogenetic analysis of males with microorchidism referred to our genetic counseling unit during the last 10 years. In our laboratory the fra(X) marker has never been observed with such a frequency in a total of several hundred normal XY males and XX females studied as control cases in the course of previously reported family and population studies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Behavioral phenotype of fragile X syndrome: DSM-III-R autistic behavior in male children.

Comparison of 34 fragile X [(fra(X)] male children (age 3-18 years) with 32 IQ- and age-matched, non-fra(X) male control children was conducted using specific DSM-III-R criteria for autism. Statistical analyses supported predictions that fra(X) males show increased dysfunction in peer social play, nonverbal communication (e.g., gaze aversion, gesturing), verbal communication (e.g., rate, volume, word/phrase perseveration), and repetitive motor behaviors (e.g., handflapping, rocking). There was a trend for fra(X) children to show abnormal responsivity to sensory stimuli as well such as oversensitivity to sound and increased mouthing or smelling of objects. The investigation supports the contention that fra(X) males manifest a specific subset of behaviors from the autistic spectrum. Implications for treatment are discussed.     

Autism is not associated with the fragile X syndrome

We provided a controlled test of the hypothesis that individuals with the Martin-Bell or Fragile X [fra(x)] syndrome are more autistic than mentally retarded control individuals. A sample of fra(x) individuals was obtained from the register of a clinical genetics unit and compared with mentally retarded control individuals selected from an assessment centre who were individually matched for age, sex, and IQ. A comparison of 45 pairs of fra(x) cases and control individuals on the DSM-III (R) criteria for autism and two standardized "instruments" for the assessment of autism (ABC and ADC) failed to find a higher prevalence of autism among fra(x) individuals. There was no statistically significant difference between fra(x) individuals and control individuals, and the mean differences on both the ABC and ADC scales were in the direction contrary to the hypothesis. An analysis of the study's statistical power suggested that it is unlikely the investigation failed to detect a large to medium difference between fra(x) individuals and control individuals in autistic behaviour. Subsidiary analyses of case-control differences showed that two autistic-like behaviours occurred at a higher rate among fra(x) individuals than other mentally retarded children, namely, gaze avoidance and hand flapping. These abnormalities may have misled clinicians into thinking that autism and fra(x) are associated.     

Fragile X syndrome with extra microchromosome

A mentally retarded male with Martin-Bell syndrome, who has an extra microchromosome and is fra X negative in cytogenetic study is reported. Because of its small size, the origin of the microchromosome could not be determined. Two other affected males in this family (a cousin and a nephew of the proband) were fragile X positive, 24% and 26%, respectively. Cytogenetic studies and DNA analysis with the probe St B 12.3 were performed on several members of the family. The proband and the two other affected males showed a similar full mutation on the molecular study. This study emphasizes the importance of molecular analysis in the diagnosis of fragile X syndrome, particularly when cytogenetic studies demonstrate fra X negative in individuals in families likely to have X-linked mental retardation.     

What is associated with the fragile X syndrome?

In addition to mental retardation (MR), fragile X [fra(X)] syndrome has been associated with a variety of other disorders. Despite earlier reports, it has been shown that MR fra(X) males are at no greater risk for autism than is any MR male. Therefore, studies in which fra(X) has been associated with behavioral, developmental, and psychopathological disabilities were examined to determine whether fra(X) individuals were at an increased risk for these dysfunctions as well. Psychiatric disorders among fra(X) individuals were found not to occur more frequently than in other individuals with cognitive deficits. It was also observed that hyperactivity and attention deficit disorder among MR fra(X) individuals do not occur more frequently than in other MR individuals. Pooled results from studies of cognitive profiles used to characterize fra(X) phenotypes also indicated that there are no consistent patterns in either males or females. Plausible explanations for a variable phenotype include allelic heterogeneity and pleitropy. © 1993 Wiley-Liss, Inc.     

Penetrance estimate of the fra(X) gene using Pointer versus direct estimate.

Direct estimate of the penetrance of the fra(X) gene was compared with the estimate using the Pointer computer program. Direct estimate gave overall penetrances of 85% for male and 64% for female carriers. The estimates calculated by the Pointer program were 82% for males and 38% for females. It is argued that the use of the Pointer program gives incorrect estimates of the penetrance of the fra(X) gene.     

Effect of X inactivation on fragile X frequency and mental retardation

The probability of a heterozygote being affected was estimated from the distribution of frequencies of early-replicating fragile X [fra(X)] chromosome in normal and mentally retarded heterozygotes, taking into account the prior probabilities of 0.35 for mental retardation and 0.65 for normality. The estimated probability of a heterozygote with 100% early-replicating fra(X) being mentally retarded was 78%, which coincides with the value of penetrance in males. Therefore, the manifestation of retardation in females seems to differ from that in males due solely to X inactivation. The frequencies of early-replicating fra(X) were significantly increased among the heterozygotes with the highest frequencies of fra(X) both in the normal group and in the mentally retarded. The mean frequencies of early-replicating fra(X) were 0.42 and 0.68 for normal and mentally retarded heterozygotes, respectively. Considering the overall frequency of retarded heterozygotes as 0.35, the mean frequency of early-replicating fra(X) obtained for all heterozygotes was 0.51, which is in accordance with the hypothesis of random X inactivation. Thus the fragile site appears to have equal chances of being detected when located either on the early- or on the late-replicating X. This leads to the conclusion that the frequency of the fragile site is a consequence of the proportion of cells with the active Martin-Bell syndrome (MBS) gene and not the result of a better visualization of the site on the early-replicating X.     

The strength of association between fragile(X) chromosome presence and mental retardation

In order to obtain a quantitative estimate of the degree of association between presence of fragile X chromosome (fra(X)) and mental retardation (MR), existing data from nonretarded males were analyzed. Clearly, fra(X) occurs less frequently among nonretarded compared to MR males. However, incidence estimates for fra(X) based upon existing data hold open the possibility that there may be significant numbers of nonretarded males with fra(X). Additional analyses of data from families with a pattern of fra(X) linked MR showed: (a) the probability that nonretarded male offspring will have fra(X) is very small, and (b) the probability that MR male offspring will have fra(X) is very large. Thus, accurate prognostic decisions can be based upon prenatal diagnosis of fra(X) presence, especially in families with a pattern of fra(X) linked MR.     

Fragile X screening program in a Spanish region.

In a Spanish region with a population of one million, we screened 371 mentally retarded males, who had no previous diagnosis for fragile X [fra(X))] syndrome. Fifty-three of the 371 males were fra(X) positive. Of these 44 of 362 or 12.1% were unrelated. Family studies identified a large number of obligate carriers and women at risk for being carriers who were given genetic counseling including prenatal diagnostic information. Considering the age of the carriers and the fertility rate, 23 affected males could be born to these women. The prevention potential of this program suggests that it is highly cost-effective.     

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.     

Fragile X screening program in New York State

Most fragile X [fra(X)] males in New York State have not been identified. Hence, a large number of female relatives are unaware of their risks for having an affected child. A program was established in New York State in 1987 to screen for the fra(X) syndrome in mentally retarded males with living relatives. The goal of the program is to identify affected males and inform their families about the diagnosis. In this way relatives would be able to assess their risks for having a fra(X) male. In order to identify the males a screening form was developed to assess 10 features which included physical characteristics, behavior, and family history. Males who exhibited at least 5 of these manifestations were selected for cytogenetic analysis. Any male who had macroorchidism or a family history of mental retardation was also included. A total of 995 males have been screened of which 352 (35%) were selected for cytogenetic analyses. Seventeen (10.5%) of the 161 completed studies were positive for fra(X). A large number of possible female carriers were identified in the families of the propositi. This program identifies fra(X) males in a population of the mentally retarded for whom there had been no previous diagnosis. By using a two-step procedure, it is possible to screen a large population of the mentally retarded for fra(X) without testing each male cytogenetically.