Screening for fra(X)(q) in a population of mentally retarded males

Diagnostic investigations in individuals with mental retardation: a systematic literature review of their usefulness

There are no guidelines available for diagnostic studies in patients with mental retardation (MR) established in an evidence-based manner. Here we report such study, based on information from original studies on the results with respect to detected significant anomalies (yield) of six major diagnostic investigations, and evaluate whether the yield differs depending on setting, MR severity, and gender. Results for cytogenetic studies showed the mean yield of chromosome aberrations in classical cytogenetics to be 9.5% (variation: 5.4% in school populations to 13.3% in institute populations; 4.1% in borderline-mild MR to 13.3% in moderate-profound MR; more frequent structural anomalies in females). The median yield of subtelomeric studies was 4.4% (also showing female predominance). For fragile X screening, yields were 5.4% (cytogenetic studies) and 2.0% (molecular studies) (higher yield in moderate-profound MR; checklist use useful). In metabolic investigations, the mean yield of all studies was 1.0% (results depending on neonatal screening programmes; in individual populations higher yield for specific metabolic disorders). Studies on neurological examination all showed a high yield (mean 42.9%; irrespective of setting, degree of MR, and gender). The yield of neuroimaging studies for abnormalities was 30.0% (higher yield if performed on an indicated basis) and the yield for finding a diagnosis based on neuroradiological studies only was 1.3% (no data available on value of negative findings). A very high yield was found for dysmorphologic examination (variation 39-81%). The data from this review allow conclusions for most types of diagnostic investigations in MR patients. Recommendations for further studies are provided.

Concurrence of fragile X syndrome and 47, XYY in an individual with a Prader-Willi-like phenotype

We report on a 34-year-old developmentally disabled man referred to our clinic for evaluation of possible Prader-Willi syndrome on the basis of obesity and voracious appetite. Cytogenetic and molecular analysis revealed a 47, XYY karyotype and the presence of a trinucleotide repeat expansion resulting in fragile X syndrome. To our knowledge, this is the first report of concurrence of XYY and fragile X syndrome in the medical literature. Review of sex chromosome abnormalities associated with fragile X syndrome and phenotypic considerations are presented.

Concurrence of fragile X and Klinefelter syndromes: report of a new case of paternal nondisjunction

The concurrence of fragile X and Klinefelter syndromes would be expected occasionally. Therefore, the analysis of the literature showed that the concurrence of both conditions was found at least 16 times. Among them, only seven cases were analyzed for the parental origin of the extra chromosome X, suggesting that the maternal nondisjunction was preferentially inherited. We present the third patient with the concurrence of fragile X and Klinefelter syndromes, in which the parental origin of the supernumerary chromosome X was paternal. This finding reinforces that the parent-of-origin predisposition of the concurrence of the fragile X and Klinefelter syndromes is a pure coincidence.

Cytogenetic diagnosis of fragile X syndrome: study of 305 suspected cases in Saudi Arabia

BACKGROUND

Fragile X syndrome is the most common cause of inherited mental retardation. Patients with fragile X syndrome show variable mental disability, typical long and narrow facial appearance with large ears and prominent fontanelle and frequent macro-orchidism. It is generally associated with a fragile site at Xq 27.3, which can be observed in the metaphase chromosome following selective culture conditions. At the molecular level, the fragile X syndrome is associated with an amplification of CGG repeat sequence of the FMR1 gene. The prevalence estimates are reported as one per 1500 males and one per 2500 females. Estimated prevalence rates of fragile X syndrome in different ethnic groups range from 0.4-0.8 per 1000 in males and 0.2-0.6 per 1000 in females. In this study, we have determined the frequency of fragile X-positive cases in 305 preselected patients.

MATERIALS AND METHODS

Three hundred and five Saudi patients with mental retardation/developmental delay/clinical suspicion of fragile X syndrome were screened for fragile X chromosome by cytogenetic methods. The majority of patients (95.59%) screened were under the age of 20 years.

RESULTS

Two hundred and ninety-nine patients (98.03%) were in the category of mild to moderate mental retardation. Twenty-four males (7.86%) and two females (0.65%) were found to express fragile X site at q27.3. The frequency of fragile X-positive cells in males ranged between 7% and 58% (mean 26+/-13.11), while in the females it was between 14% and 21% (mean 12.5+/-35), respectively.

CONCLUSION

The frequency of fragile X positive cases found in this study is similar to other reports of fragile X syndrome in preselected patients.

Fragile X syndrome. Clinical and cytogenetic studies

Three families with the fragile X syndrome were studied with the aim to establish the most frequent clinical signs in the affected individuals and heterozygous women. The clinical evaluation, IQ level measurements and cytogenetic studies were performed in 40 subjects, 20 males and 20 females. The fragile X diagnosis was confirmed in all the male individuals with mental retardation. In the postpubertal subjects the most frequent clinical signs were inner canthal distance < 3.5 cm, macro-orchidism, long and narrow face and high arched palate while in the prepubertal subjects the behavioral characteristics as hyperactivity and poor eye contact were the most frequent and were observed in all patients. Twenty six percent of the heterozygous women presented with mental retardation and showed clinical signs rather than behavioral ones. All male individuals with mental retardation were observed as having fragile X [fra(X)] in lymphocytes culture. Sixty three percent of women showed fra(X). There was a positive correlation between the frequency of fra(X) and the clinical characteristics. We emphasize the importance of the clinical evaluation in the study of familial mental retardation and in the screening of isolated cases with suspect of having the fragile X syndrome.

Non-radioactive DNA diagnosis for the fragile X syndrome in mentally retarded Japanese males

A rapid screening test was developed to detect CGG repeat expansion of the FMR-1 gene causing the fragile X syndrome by a non-radioisotope PCR technique. A biotin-labeled primer was initially used and the biotin-labeled PCR product was detected by means of chemiluminescence. The normal PCR product of around 300 bp was not created in the abnormal FMR-1 gene sample with this method. Four positive samples were found among those from 226 mentally retarded males, but the CGG repeat expansion was shown on Southern blot analysis in only one sample. To eliminate false-positive samples, a hybridization method involving a biotin-labeled (CGG)s oligonucleotide was developed for the PCR product and the CGG repeat expansion could be detected. Finally, 256 mentally retarded males in Japan were examined and only 2 abnormal samples were detected. The prevalence of this abnormality was less than 1%, which is relatively lower than those reported previously.

High functioning fragile X males: demonstration of an unmethylated fully expanded FMR-1 mutation associated with protein expression

Fragile X (fra(X)) males with a standardized IQ score of 70 or higher represent a high functioning (HF) or nonretarded fra(X) male group. This group, which does not include nonpenetrant males, has received little research attention to date. Of 221 fra(X) males who had been evaluated through The Children's Hospital in Denver since 1981 and had completed cognitive or developmental testing, 29 (13%) were high functioning by the above definition. We found that HF males on the whole had a lower cytogenetic score and were younger than retarded fra(X) males, but there was no difference between these two groups in the number of typical fra(X) physical manifestations present. FMR-1 DNA testing was performed on 134 fra(X) males and methylation status was determined for 51 of these. A greater percentage of HF males had a mosaic pattern or an incompletely methylated full mutation than did retarded males. A unique DNA pattern, an unmethylated fully expanded mutation, was discovered in 3 of the highest functioning fra(X) males. Protein studies performed on 2 of these males demonstrated the presence of FMR-1 protein, albeit at lower levels than normal. FMR-1 protein was not present in retarded fra(X) males. Significant FMR-1 protein expression may be responsible for higher cognitive functioning in the 2 males with unmethylated fully expanded mutations compared to retarded fra(X) males.

Cytogenetic Study of Mentally Retarded Children in Taipei

560 blood samples collected from mentally retarded children in Taipei were karyotypically analyzed for the incidence of fragile X and other chromosome abnormalities. The fragile site at Xq27.3 was observed in 18 patients (3.21%), 11 males and 7 females, out of the 560 blood cultures using M medium. Down syndrome (6.25%), 24 males and 11 females, was the other major category of abnormality. Other abnormalities, including inversion, translocation, deletion, duplication, ring as well as an extra marker chromosome were observed. The overall incidence of chromosomal abnormalities in these children was 14.82%. Copyright 1994 S. Karger AG, Basel

Fragile-X syndrome in North East Essex: towards systematic screening: clinical selection

A systematic screening for fragile-X syndrome, using various clinical criteria to preselect for cytogenetic testing, was performed throughout the North East Essex Health District on 1100 people attending three different local services for people with learning disability. The selection procedure used varied from a gestalt impression to head, ear and testis measurement depending on the setting. Fifty-nine males and five females who met the selection criteria went on to have chromosome studies. Of these, 23 males and one female were positive (more than 4% positive cells). They came from 19 families. Whilst the true prevalence of fragile-X syndrome is not known in the district, at a minimum, it contributed 3.2% of the institutionalized males (health authority care), 4.4% of the boys and 2.1% of the girls attending special schools for severe learning disability, 7.9% of the boys attending schools for mild learning disability (Local Education Authority), and 3.5% of men attending the two adult training centres within the district (social services). These figures compare well with the yield from reported surveys in which all individuals without a known diagnosis were tested cytogenetically.

Clinical and cytogenetic survey of institutionalized mentally retarded patients with emphasis on the fragile-X syndrome

A detailed clinical and cytogenetic survey for the fragile-X syndrome was undertaken on 201 institutionalized mentally retarded males with no previously recognized cause of retardation, and the causes of mental retardation were summarized from a total of 595 institutionalized male and female patients after the review of their medical records including clinical and cytogenetic data. Among the 201 males clinically and cytogenetically examined, five (2.5%) had abnormal chromosome findings with four (2%) having the fragile-X syndrome. Twelve of the males (6.0%) were diagnosed with a single gene disorder. In the present study, mental retardation was classified as possibly due to multifactorial causes when a genetic syndrome, chromosome abnormality or environmental insult was not identified, but mental retardation was present in one or more first and/or second degree relatives, but did not follow a recognizable inheritance pattern. Hence, mental retardation was recorded in other family members and may indicate possible multifactorial causes in 45 males (22.4%). An environmental insult was noted in 25 males (12.4%); unexplained birth defects in three males (1.5%); a specific condition or diagnosis identified, but cause unknown (e.g. Rubinstein-Taybi syndrome) in 10 males (5%); and no diagnosis made in the remaining 101 males (50.2%). Of all 595 patients (334 males and 261 females), including the 201 males who had undergone a detailed clinical and cytogenetic evaluation, 39 (6.6%) had abnormal chromosome findings, with Down's syndrome noted in 31 of the patients. Twenty-five patients (4.2%) were diagnosed with a single gene disorder while mental retardation was noted in other family members and may indicate possible multifactorial causes in 64 patients (10.8%). An environmental insult was noted in 170 patients (28.6%); unexplained birth defects in 17 patients (2.9%); a specific condition or diagnosis but cause unknown in 27 patients (4.5%); and no diagnosis made in 253 patients (42.5%). Clinical and cytogenetic screening of mentally retarded patients for the fragile-X syndrome and other causes of mental retardation is helpful in identifying individuals and their families who may benefit from genetic services such as counseling and treatment. This study was performed over an approximate 2 year period from 1987 to 1989.

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.

Origin of the supernumerary X chromosome in a patient with fragile X and Klinefelter syndrome

We report on a 10-year-old patient with the fragile X [fra(X)] syndrome and a 47,XXY karyotype. He had Martin-Bell syndrome, including typical craniofacial findings and mental retardation. The fra(X) was detected on both X chromosomes of the patient in 8% of the metaphases examined. DNA analysis using X-chromosome sequences from the pericentromeric region and from distal Xq suggests that the patient is homozygous at the fra(X) locus due to maternal nondisjunction during meiosis II.

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.

Anthropometric comparison of mentally retarded males with and without the fragile X syndrome

An anthropometric survey of 41 variables (weight, height, 10 linear, 4 breadth, 22 craniofacial, 2 skinfold, and testicular volume), including multivariate discriminant analysis, was undertaken on 110 mentally retarded males (39 with and 71 without the fra(X) syndrome). The mean Z scores of the fra(X) syndrome males fell between -2.00 and 8.38 for bizygomatic diameter and testicular volume, respectively, and the range of the mean Z scores of the non-fra(X) males was from -2.64 to 2.26 for hand breadth and testicular volume, respectively. There was a statistically significant difference (P less than .05) between fra(X) and non-fra(X) males for 18 measurements (weight, height, 7 linear, 2 breadth, 5 craniofacial, 1 skinfold, and testicular volume), with the greater measurements (excluding bizygomatic diameter) found in fra(X) males. Sitting height, knee-buttock length, middle finger length, and hand length were negatively correlated (P less than .05) with age, whereas bizygomatic diameter, ear length, and ear width were positively correlated (P less than .05) with age and head circumference, head length, and outer canthal distance were positively correlated (P less than .05) with fra(X) chromosome expression in the fra(X) males. Triceps and subscapular skinfold thicknesses were negatively correlated (P less than .05) with age, whereas ankle breadth, ear length, ear width, and nose length were positively correlated (P less than .05) in the non-fra(X) males. Discriminant analysis of 34 fra(X) and 71 non-fra(X) males resulted in a discriminant function based on 6 of 17 anthropometric variables and age.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Clinico-neurological investigations in the fra(X) form of mental retardation

A clinical, neurological and electroencephalographic investigation was undertaken in 29 previously cytogenetically verified hemizygous males with the fra(X) form of mental retardation (age range 3.5 to 59 years); in addition, 6 heterozygous females were examined. All male patients displayed the known physical aspects of this syndrome together with associated abnormalities of the palate, skeleton, connective tissue and endocrine system. The most prominent neurological features were different forms of oculomotor disturbances, minor motor and pyramidal signs, incoordination, muscle hypotonia, gait and speech abnormalities. There was no increased frequency either in seizures or in epileptic EEG discharges. Some patients had a slowing of background activity in EEG. About 50% of all patients displayed autistic-like behaviour, short attention span and/or hyperactivity. In accordance with the literature, the findings indicate that there are no neurological, electroencephalographic or neuroradiological features which occur specifically in this syndrome. The need to differentiate the findings from those resulting from encephalopathic mechanisms during the gestational and perinatal period is stressed. A distinct typing of seizures and EEG changes is needed in each patient, before definite conclusions about an association of seizures and fra(X) syndrome are drawn. In view of the lack of correlation between IQ and the clinical-neurological measures, a more practical approach to quantifying the mental impairment is proposed.

Martin-Bell syndrome in Greece, with report of another 47,XXY fragile X patient

A cytogenetic investigation was carried out among 200 mentally retarded boys in Greece for the detection of the fragile X [fra(X)] syndrome. Thirteen patients were found to carry fra(X) (6.5%). Of those, six boys had a history of familial X-linked mental retardation, two had the phenotype of the Martin-Bell syndrome, four had only mental retardation of unknown etiology, and one was a mentally retarded patient with Klinefelter syndrome. The remaining 187 boys were fra(X) negative. Our findings emphasize the importance of early identification of this syndrome in the diagnosis and prevention, through proper genetic counselling, of mental retardation.

Prevalence of mental retardation related to fragile X syndrome and other chromosomal abnormalities in the Republic of San Marino

The prevalence of mental retardation related to chromosomal abnormalities, including fragile X syndrome, was studied among 2735 males aged between five and 20 years living in the Republic of San Marino. Five cases of chromosomal abnormalities were found, including one case with fragile X syndrome, with partial epilepsy and a CT scan showing a large arachnoid cyst in the posterior fossa. The prevalence of mental retardation due to chromosomal abnormality was 1.83 per 1000, and that due to fragile X syndrome was 0.37 per 1000. Although these findings relate to only a small population, they are the first from a Mediterranean area.

A cytogenetic study of 47,XXY males of known origin and their parents

A number of patients with both sex chromosome aneuploidy and the fragile X syndrome have been reported and this has led to the hypothesis that females heterozygous for the fragile X mutation have an increased rate of meiotic nondisjunction. Furthermore the suggestion has frequently been made that a predisposition to meiotic nondisjunction is associated with an increase in mitotic nondisjunction. We have tested these two hypotheses by examining the chromosomes of a series of 47,XXY males and their parents. In the majority the parental origin of the additional sex chromosome was known. The cells were cultured under conditions suitable for demonstrating the fragile X and 100 cells were scored 'blind' from the patients and both parents. No fragile X individual was seen and there was no difference in the proportion of aneuploid cells between the parents in whom the nondisjunction event occurred and the control parents. Therefore, our results lend no support to the suggestions that the fragile X is associated with an increase in sex chromosome aneuploidy or that individuals in whom meiotic nondisjunction occurs have an increased level of mitotic nondisjunction.

Cytological evidence of defective template in the fragile X chromosome

In cells of fragile X patients, the changed X segment may appear as a poorly staining region or a gap, or as a deletion, involving one or both chromatids. To find out whether the fragile site represents an incompletely replicated DNA sequence, as has been suggested recently, we analyzed the four chromatids of methotrexate-induced endoreduplicated fragile X chromosomes. Our main observations were: (1) a deleted chromatid was never internal to a poorly staining one; (2) an endoreduplicated X chromosome with a fragile site never included a normal chromatid. These results can be explained by assuming that DNA at the fragile site, when replicated in the presence of methotrexate, may undergo defective replication and give rise to improperly packaged chromatin, appearing as a chromatid with a poorly staining region or a gap in the following metaphase. The same DNA may fail to function as a template in the following S-phase and give rise to a chromatid with a single-stranded segment, appearing as a deleted chromatid in the following metaphase.

X-chromosome polysomy in the male. The Leuven experience 1966-1987

A review of 569 male patients with X-chromosome polysomies (544 Klinefelter and 25 patients with other types of X-chromosome polysomy) is presented here. These patients were detected among the 77,000 persons karyotyped in the Leuven cytogenetic center between the years 1966 and 1987. In the group of 544 Klinefelter patients special attention was paid to (1) the age at diagnosis, (2) social and marital status of the postpubertal males, (3) physical and intellectual abilities of the prepubertal boys, (4) delineation of the concurrence of Klinefelter syndrome and fragile X syndrome, and (5) the frequency of malignancies. In 25 patients with other X-chromosome polysomies (2 n greater than or equal to 48 chromosomes) genotype/phenotype correlation is reviewed, especially for the patients with 48,XXYY and 49,XXXXY karyotypes. Finally, double aneuploidy and rare structural X-chromosome aberrations are briefly discussed.

Spermatogenesis in two patients with the fragile X syndrome. II. First meiosis: light and electron microscopy

Chromosomes at first meiosis from two males with the fra(X) form of mental retardation were studied using pachytene surface spreads and air-dried preparations. The pachytene sex bivalents showed no discontinuation of the synaptonemal complex in the terminal part of Xq corresponding to band Xq27-28 of the mitotic chromosomes. In both cases the frequency of a secondary association of Xq and Yq appeared to be increased compared with controls. The pairing behavior of autosomal bivalents in pachytene and the frequency and distribution of chiasmata in diakinesis were normal. The impairment of spermatogenesis found in these males may not be caused by a meiotic disorder, but could be related to peritubular or intratubular pressure effects on germ cells.

The fragile X-chromosome: an evaluation of the results in a routine cytogenetic laboratory in the period 1981-1986

We report on the cytogenetic studies, performed in a routine cytogenetic laboratory between 1981 and 1986, on 428 subjects: 291 probands with non-specific mental retardation, 101 first-degree relatives of fra(X) positive patients and 36 non-retarded patients, referred for other reasons. As a rule 50 cells, cultured in folate-deficient medium were analysed. The results are compared with data collected from the literature and with the data expected from prior genetic risks and fra(X) penetrance. If no more than 50 cells were analysed, the fragile site was found in a lower than expected proportion (69.2%) of the retarded first-degree male relatives. The conclude that in a substantial number of unselected patients with mental retardation the diagnosis fra(X) syndrome will only be confirmed cytogenetically if at least 100 cells are analysed. Five percent of the male and 10% of the female index patients showed a fragile X-like abnormality, probably not associated with the Martin-Bell syndrome.

Fra(X) frequency on the active X-chromosome and phenotype in heterozygous carriers of the fra(X) form of mental retardation

Female heterozygotes of the fra(X) form of mental retardation show variable degrees of mental impairment and phenotype expression of the disorder. This might be an effect of inactivation of the X-chromosome which carries the fra(X)(q). Prior replication studies in heterozygous carriers gave contradictory results with respect to possible genotype-phenotype correlation. In the interpretation of these studies it is important to understand the effect of BrdU on the fra(X)(q) expression. In a group of 13 hemizygous patients with fra(X)(q) and 7 heterozygous carriers we studied the effect of BrdU on fra(X) expression. In the heterozygous carriers the use of BrdU resulted in a significant suppression of the fra(X)(q), while in hemizygous patients no difference in fra(X)(q) frequency with or without BrdU could be observed. It can be concluded that BrdU suppresses the fra(X)(q) preferentially on the inactive X-chromosome. Thus the fra(X)(q) frequency on the active X-chromosome is of primary importance in phenotype correlation studies among heterozygous carriers. In our group of heterozygous carriers we observed a negative correlation between (IQ) phenotype and fra(X)(q) expression on the active X-chromosome. This suggests that the gene for the fra(X)(q) form of mental retardation is on the X-chromosome and undergoes inactivation.

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)

The concurrence of Klinefelter syndrome and fragile X syndrome

In this paper we report on a third patient with Klinefelter syndrome and fragile X. In the Leuven experience the simultaneous occurrence of both conditions is 1:155 (3 fra(X) positive Klinefelter patients in a total number of 465 fra(X) positive males), a concurrence much higher than expected by chance considering the frequency of both conditions.

Fragile X expression in short-term whole blood cultures is affected by cell density

The effect of cell density on expression of the fragile site at (X)(q27.3) in short-term whole-blood cultures from patients with fragile X [fra(X)] or Martin-Bell syndrome was studied. A significant increase in fra(X) frequency was observed in 7 of 8 samples when cell density was decreased. Higher fra(X) frequency was not always noted at below-routine density, but in some cases fra(X) expression was depressed at above-routine density. We conclude that decay of the FUdR effect explains the fact that fra(X) expression is affected by culture density. It is significant that a relationship exists between the two; it suggests that in order to maximize fra(X) expression in cases with low-percentage fra(X) with standard methods, cell density may have to be adjusted. It is possible that in individuals who are normally nonexpressing, such as some obligate female carriers and nonpenetrant males, fra(X) expression may be sensitive to cell density effects.

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.

Concurrence of the triple-X syndrome and expression of the fragile site Xq27.3

The Xq27.3 fragile site was found to be expressed in an XXX woman, who was mentally and physically normal, and in her son who was mentally retarded and showed behavioural and physical features characteristic of the fragile X syndrome.

Fragile X syndrome

The fragile X syndrome is the most common inherited form of mental retardation known. Its phenotype includes large or prominent ears, macroorchidism, and characteristic behavioral problems. It has attracted the interest of cytogeneticists and molecular biologists because of its characteristic fragile site on the X chromosome. It has puzzled geneticists because of its unusual inheritance pattern involving nonpenetrant males. This syndrome has also spearheaded an appreciation of cytogenetic abnormalities in the etiology of all degrees of developmental delay.

Linkage analysis using multiple Xq DNA polymorphisms in normal families, families with the fragile X syndrome, and other families with X linked conditions

Multipoint linkage analysis was undertaken with eight Xq cloned DNA sequences which identify one or more restriction fragment length polymorphisms in 26 families. These families comprise seven phase known normal families with three or more males in the third generation, seven families segregating for haemophilia B, one large family with dyskeratosis congenita, and 11 families with the fragile X syndrome. Phase known meioses informative for three or more loci supported the order centromere--DXYS1--DXS107--DXS102, DXS51--F9--FRAXA--DXS15, DXS52, F8--Xqter in each group of families studied. One of the normal families was segregating for protan colour blindness and showed a phase known recombination which would support the order centromere--F9--DXS52--CBP--Xqter. With the exception of DXYS1, all of these sequences have been localised to Xq27----qter by in situ hybridisation or hybridisation to Xq fragment panels, and on this basis should lie within 20 cM of one another. No recombination was observed between the sequences localised to Xq28, namely DXS52, F8, and DXS15 (between DXS15 and DXS52 Z = 12.25 at theta = 0 with confidence limits of 0 to 5 cM). However, an excess of recombination was apparent in the region of FRAXA with maximal lod scores as follows: F9 versus FRAXA (Z = 2.05, theta = 0.19), DXS52 versus FRAXA (Z = 1.85, theta = 0.26), and DXS15 versus FRAXA (Z = 1.33, theta = 0.27). No consistent differences were observed in the frequency of recombination when families with the fragile X syndrome were compared with normal families or families segregating for other X linked conditions. These results are compared with other published work and support the conclusion that although measurable linkage exists between these flanking markers and FRAXA, the intervals as measured by the frequency of meiotic recombination will seriously limit their clinical usefulness.

Frequency of rare fragile sites among mentally subnormal schoolchildren

The frequency of rare fragile sites was studied among 240 children in special schools for subnormal intelligence (IQ 52-85). 1/130 boys studied (0.8%) had the fragile site at Xq27.3 while it was not found in any girl (0/110). In two children an autosomal rare fragile site at 2q11.2 (2/240, 0.8%) was seen. In addition a constitutional chromosome abnormality was found in a further seven children (7/240, 2.9%).

Frequency of the fragile X syndrome in Japanese mentally retarded males

Among 243 institutionalized mentally retarded males in Japan, 13 patients (5.3%) with the fra(X)(q27) from nine families were detected. These 13 patients accounted for 8.6% of 152 male inmates with unknown causes of mental retardation in the population. One out of nine pedigrees had an apparently unaffected male transmitter of this disorder. Our data agree with the frequencies of the fra(X) syndrome in various retarded populations, most of which were Caucasians, suggesting that the prevalence of the fra(X) syndrome in Japanese is not significantly different from those in Caucasians.

Prevalence of the fragile X syndrome in an institution for the mentally handicapped

In an investigation to find the prevalence of the fragile X (Martin Bell) syndrome in a mental handicap hospital, chromosomal investigations were carried out in 196 males selected out of a total of 512, and also in 20 female patients who were related to some of the selected males. Fragile X cells were found in 41 of the males and two of the females; in 21 of the males it was associated with macro-orchidism. The overall prevalence in the hospital for males (8.0%) ranks this syndrome next in importance to Down's syndrome as a known cause for mental handicap.

Recently recognized chromosomal defects of clinical importance

We review those conditions which have recently been recognized to be associated with small, sometimes difficult to detect, chromosomal abnormalities. These include the Prader-Willi syndrome and X-linked mental retardation.

Folic acid treatment in males and females with fragile-(X)-syndrome

Ten males with the fragile X (fra(X] syndrome were treated with folic acid (10 mg/day) for 4 months in a double-blind design study. To eight heterozygotes with mental impairment and fra(X), folic acid was given for 4 months (10 mg/day) in an effort to study possible beneficial effects of folic acid. Psychological and cytogenetic testing were carried out during the trial. There was no improvement in concentration, fine motor co-ordination, or comprehension in the adult male and female patients of the study. One patient showed improvement under a control medications. In the females, improvement was seen only in the youngest patient, a 5-year-old girl. Folate treatment does not seem to be effective in fra(X) adults, but may have some effect in children of both sexes with the disorder. Cytogenetic studies using peripheral lymphocytes showed that the fra(X) frequency decreased significantly (t = 0.00856; 1% level) only in cells cultured in a folic acid-free medium but not in cells cultured in a medium with added antifolate (methotrexate). This shows a "contamination effect" of folate-free culture medium after oral folic acid treatment of these patients. The decrease of fra(X) involves primarily the early-replicating X when culturing with folic acid-free medium. A synergistic suppression effect of "external folate" and BrdU is the most likely explanation of this phenomenon.

A profile of cognitive deficit in females from fragile X families

Fragile X, a recently discovered X-linked syndrome, is usually associated with mental retardation in affected males. Less consistent findings have been described for females. neuropsychological evaluation of seven nonretarded females from fragile X families suggested a characteristic profile: on Wechsler IQ tests, a positive Verbal-Performance score difference and lower subtest scaled scores on Arithmetic, Digit Span, Block Design, and Object Assembly; on the Wide Range Achievement Test, a lower score on Arithmetic than on Reading or Spelling; and on the Benton Visual Retention Test, defective recall. These results suggest the existence of X-linked learning disability in females.

Oral folic acid versus placebo in the treatment of males with the fragile X syndrome

A double-blind, crossover study of a 10 mg folic acid per day (vs. placebo) treatment was carried out in 25 fra(X) males (ages 1-31 years). Each treatment period lasted 6 months. Before, during and after the study, the patients were assessed blindly with psychological, language and behavioral evaluations, and parent or caretaker reports were collected. Standardized testing did not show statistically significant changes in the group as a whole; psychological testing demonstrated a statistically significant improvement on folic acid in the prepubertal males. After uncoding, caretaker or parent reports also demonstrated behavioral improvements in the prepubertal males while being treated with folic acid.

A premutation that generates a defect at crossing over explains the inheritance of fragile X mental retardation

The view that the Martin-Bell syndrome (X-linked mental retardation with fragile site at Xq27/8) is inherited in a regular X-linked fashion is becoming untenable with the increasing number of reports of transmission through phenotypically normal males. Analysis of the published pedigrees containing such males shows that their heterozygous daughters are never mentally retarded, and have either no fragile site or very few indeed. By contrast, in the next generation, a third of the female heterozygotes are mentally subnormal with an average of 29% fragile sites. These data suggest a premutation that generates the definitive mutation only when transmitted by a female. We propose an inherited sub-microscopic chromosome rearrangement involving the Xq27/8 region that causes no ill effect per se, but generates a significant genetic imbalance when involved in a recombination event with the other X chromosome. This hypothesis explains many of the puzzling genetic aspects of the Martin-Bell syndrome, but it also complicates the interpretation of linkage analysis with genetic markers.

A community study of severe mental retardation in the West Midlands and the importance of the fragile X chromosome in its aetiology

This paper describes a community based study of 156 boys with idiopathic, severe mental retardation. The boys were examined and a pedigree taken before the cytogenetic results were known. The prevalence of the fragile X chromosome among this group of boys was high: 9% in the whole group and 11% after 39 boys with specific features had been excluded. The fragile X syndrome is therefore an important cause of idiopathic, severe retardation. Its clinical features of large head, large testes, and IQ in the 35 to 70 range were often but not always present in the 14 boys identified in this study. In the whole group, the recurrence of severe mental subnormality was high: 1 in 8 for brothers and 1 in 25 for sisters. This high recurrence was partly due to the fragile X syndrome, partly to X linked mental retardation not accompanied by cytogenetic abnormalities, and partly due to autosomal recessive disease. Autosomal recessive disease was perhaps higher in the West Midlands than elsewhere (such as British Columbia, for example 1) because of the disproportionate contribution by Asian immigrants.

Further segregation analysis of the fragile X syndrome with special reference to transmitting males

A new series of 96 pedigrees with the fra(X) syndrome was analysed using complex segregation analysis with pointers, defining affection as any degree of mental impairment. These families were found to exhibit the same segregation pattern as the first series of 110 pedigrees (Sherman et al. 1984). The best estimate for penetrance of mental impairment in males was 79% and in females was 35% for the combined data. Again, there was little evidence for sporadic cases among affected males. Many more intellectually normal transmitting males have been observed since the existence of such males and the concomitant need to investigate the paternal side of pedigrees was recognized. On further investigation of all 206 pedigrees from the old and new data sets, the sibships of nonexpressing males appeared to be different from those of expressing males. Our analysis, using mental impairment as the phenotype, suggested that obligate carrier mothers and daughters of intellectually normal transmitting males are rarely, if ever, mentally impaired and that the sibs of transmitting males are much less likely to be retarded than the sibs of mentally impaired males. Though mothers and daughters of transmitting males are similar in phenotype, the expression of the gene in their offspring appears to be different: the penetrance of mental impairment is higher in offspring of intellectually normal daughters of transmitting males than in offspring of intellectually normal mothers of transmitting males. The implications of these observations for genetic counseling and for genetic models of the fra(X) syndrome are discussed.

Developmental and behavioural disturbances in 13 boys with fragile X syndrome

Developmental and behavioural aspects were studied in 13 boys aged 2.6-12.5 years from three families with the fragile X syndrome. The following observations were made. Moderate to severe retardation was present in all boys; non-verbal IQs ranged between 25 and 67 (mean 46 +/- 14); IQ and age were negatively correlated (P less than 0.01). Language development was grossly delayed in all boys; most had severe articulation problems. Imitative and symbolic play (e.g. doll play) were strikingly retarded as compared to abstract play (e.g. block design). Autistic features such as no use of eye contact, stereotyped movements and echolalia were found in 9/13 boys; the same number showed aggressive behaviour. General activity was reduced during the 1st year of life; most boys became very hyperactive during the second year; and short attention span and increased distractability were observed in all. Motor development was mildly delayed; all boys were clumsy and moderately hypotonic. The fragile X syndrome ought to be considered in retarded boys with a dissociated developmental pattern, in particular a striking delay in language and play development, and autistic features.

The fragile X syndrome. A study of 83 families

The present report summarizes the experience on the mar(X) syndrome in a total of 157 male patients (44 prepubertal and 113 postpubertal) ascertained through 83 index patients from 83 families under investigation. In one third of the families pedigree data were consistent with X-linked recessive inheritance. In the further two thirds of the families the presenting symptom was familial mental retardation with a mentally retarded mother, or mental subnormality with hyperkinetic behaviour in the male patient. No more than 60% of the adult males presented the typical clinical triad (mental retardation-long face-megalotestes). The most characteristic finding in the mar(X) boy is the psychological profile with severe hyperkinetism, hypersensitivity, handbiting and autistic features in some of them. In 4 of the 27 large mar(X) pedigrees strong evidence was present of a possible transmission of the mar(X) through normal males. The high incidence of mental subnormality in the female offspring of heterozygote carriers, and the relationship between mental status, phenotype, age and expression of the mar(X) in different culture conditions is discussed.

Transmission of the marker X syndrome trait by unaffected males: conclusions from studies of large families

It is well established that apparently unaffected males can be transmitters of the marker X syndrome trait. Cytogenetic and clinical investigations of these male transmitters are only rarely reported for most of these male transmitters are dead by the time the syndrome is diagnosed in their families. We report on cytogenetic and clinical investigations of two unaffected male carriers of the disorder from two large families. Pedigree analysis of these families revealed six other cases of possible male transmission of the marker X syndrome trait. Mental impairment was not reported from the siblings of these unaffected male carriers and could not be observed in their daughters. The mode of transmission of the disorder cannot be fully explained by X-linked inheritance. The phenomenon of unaffected males transmitting the disorder could be due to an autosomal suppressor systeme. Our findings indicate that male transmission may be important for the frequency of the disorder.