Clinical features and reproductive patterns in fragile X female heterozygotes

The Impact of Mild Chronic Stress and Maternal Experience in the Fmr1 Mouse Model of Fragile X Syndrome

Fragile X syndrome (FXS) is a pervasive developmental disorder and the most common monogenic cause of autism spectrum disorder (ASD). Female heterozygous (HET) carriers play a major role in the transmission of the pathology and present several FXS- and ASD-like behavioral alterations. Despite their clear genetic origins, FXS symptoms are known to be modulated by environmental factors, e.g., exposure to chronic stress, especially during critical life periods, such as pregnancy. Pregnancy, together with pups' care, constitutes maternal experience, i.e., another powerful environmental factor affecting several neurobehavioral functions in females. Here we investigated the impact of maternal experience on the long-term effects of stress in Fmr1-HET female mice. Our findings demonstrated that the behavioral abnormalities of HET females, i.e., hyperactivity and memory deficits, were unaffected by stress or maternal experience. In contrast, stress, independently of maternal experience, induced the appearance of cognitive deficits in WT mice. Maternal experience increased anxiety levels in all mice and enhanced their corticosterone levels, concomitantly promoting the effects of stress on social communication and adrenal glands. In translational terms, these results advance our understanding of the environmental modulation of the behavioral alterations observed in FXS female carriers and highlight the long-term impact of maternal experience and its interactions with chronic stress.

Autistic-like behavioral effects of prenatal stress in juvenile Fmr1 mice: the relevance of sex differences and gene-environment interactions

Fragile X Syndrome (FXS) is the most common heritable form of mental retardation and monogenic cause of autism spectrum disorder (ASD). FXS is due to a mutation in the X-linked FMR1 gene and is characterized by motor, cognitive and social alterations, mostly overlapping with ASD behavioral phenotypes. The severity of these symptoms and their timing may be exacerbated and/or advanced by environmental adversity interacting with the genetic mutation. We therefore tested the effects of the prenatal exposure to unpredictable chronic stress on the behavioral phenotype of juveniles of both sexes in the Fmr1 knock-out (KO) mouse model of FXS. Mice underwent behavioral tests at 7-8 weeks of age, that is, when most of the relevant behavioral alterations are absent or mild in Fmr1-KOs. Stress induced the early appearance of deficits in spontaneous alternation in KO male mice, without exacerbating the behavioral phenotype of mutant females. In males stress also altered social interaction and communication, but mostly in WT mice, while in females it induced effects on locomotion and communication in mice of both genotypes. Our data therefore highlight the sex-dependent relevance of early environmental stressors to interact with genetic factors to influence the appearance of selected FXS- and ASD-like phenotypes.

"Are We Done Yet?" Question-Asking in Boys With Fragile X Syndrome and Idiopathic Autism Spectrum Disorder

Purpose Question-asking serves as a tool to learn new information and is important in both academic and social settings. Boys with idiopathic autism spectrum disorder (ASD) and boys with fragile X syndrome and comorbid ASD (FXS + ASD) have similar social communication deficits, which may have downstream effects on their question-asking ability. This study examined question-asking in school-age boys with idiopathic ASD and FXS + ASD, including the role of ASD severity, expressive grammatical complexity (measured by mean length of utterance [MLU]), and IQ. Method Twenty-five boys with FXS + ASD and 21 boys with idiopathic ASD (ages 9-16 years) were included in this study. Autism Diagnostic Observation Schedule assessments were transcribed and coded for the frequency, function, and appropriateness of spontaneous questions asked. We examined group differences in these aspects of question-asking and relationships between question-asking and ASD severity, MLU, and IQ within each group. Results Boys with FXS + ASD asked more questions than boys with idiopathic ASD, although boys with idiopathic ASD asked a higher proportion of appropriate questions. Boys with idiopathic ASD also asked the examiner more personal questions than the boys with FXS + ASD. ASD severity and MLU were related to the proportion of clarification questions in FXS + ASD, and ASD severity was also related to the proportion of personal questions in this group. For the boys with idiopathic ASD, ASD severity was related to the total number of questions asked. Conclusions Our findings highlight similarities and differences between boys with FXS + ASD and idiopathic ASD in their spontaneous question production and indicate that ASD severity and grammatical language are differentially important for question-asking. This study has implications for targeted treatment in question-asking skills for boys with FXS + ASD and ASD.

Are ovarian response and pregnancy rates similar in selected FMR1 premutated and mutated patients undergoing preimplantation genetic testing?

PURPOSE

To assess if the ovarian response of FMR1 premutated women undergoing preimplantation genetic testing (PGT) for Fragile X syndrome is lower compared with fully mutated patients, due to their frequent premature ovarian failure.

METHODS

In a retrospective cohort study from January 2009 to March 2019, we compared PGT outcomes in 18 FMR1 premutated women and 12 fully mutated women and aimed to identify predictive factors of stimulation outcomes.

RESULTS

Eighty-six IVF/PGT-M cycles for FMR1 PGT were analyzed. Premutation and full mutation patients were comparable in terms of age, body mass index (BMI), basal FSH, antral follicular count, and cycle length. However, premutation carriers had significantly lower AMH (1.9 versus 4.0 ng/mL, p = 0.0167). Premutated patients required higher doses of FSH (2740 versus 1944 IU, p = 0.0069) but had similar numbers of metaphase II oocytes (7.1 versus 6.6, p = 0.871) and embryos (5.6 versus 4.9, p = 0. 554). Pregnancy rates (37.1% versus 13.3%, p = 0.1076) were not statistically different in both groups.

CONCLUSION

In spite of lower ovarian reserve and thanks to an increased total dose of FSH, FMR1 premutated selected patients seem to have similar ovarian response as fully mutated patients. Neither the number of CGG repeats in FMR1 gene nor FMR1 mutation status was good predictors of the number of retrieved oocytes.

Age-specific autistic-like behaviors in heterozygous Fmr1-KO female mice

Fragile X syndrome (FXS) is a major developmental disorder and the most frequent monogenic cause of autism. Surprisingly, most existing studies on the Fmr1-KO mouse model for FXS have focused on males, although FX women, who are mostly heterozygous for the Fmr1 mutation, are known to exhibit several behavioral deficits, including autistic-like features. Furthermore, most animal research has been carried out on adults only; so that little is known about the age progression of the behavioral phenotype of Fmr1 mutants, which is a crucial issue to optimize the impact of therapeutic interventions. Here, we performed an extensive analysis of autistic-like social behaviors in heterozygous (HET) Fmr1-KO females and their WT littermates at different ages. No behavioral difference between HET and WT mice was observed at infancy, but some abnormalities in social interaction and communication were first detected at juvenile age. At adulthood some of these alterations disappeared, but avoidance of social novelty appeared, together with other FXS-relevant behavioral deficits, such as hyperactivity and reduced contextual fear response. Our data provide for the first time evidence for the presence of autistic-relevant behavioral abnormalities in Fmr1-HET female mice, demonstrating the utility of this mouse line to model autistic-like behaviors in both sexes. These results also highlight the importance of taking into account age differences when using the Fmr1-KO mouse model, suggesting that the early post-natal phases are the most promising target for preventive interventions and the adult age is the most appropriate to investigate the behavioral impact of potential therapies. Autism Res 2017. © 2017 International Society for Autism Research, Wiley Periodicals, Inc. Autism Res 2017, 10: 1067-1078. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

Fragile X syndrome screening in Chinese children with unknown intellectual developmental disorder

Background

Fragile X syndrome is the most common genetic disorder of intellectual developmental disorder/mental retardation (IDD/MR). The prevalence of FXS in a Chinese IDD children seeking diagnosis/treatment in mainland China is unknown.

Methods

Patients with unknown moderate to severe IDD were recruited from two children’s hospitals. Informed consent was obtained from the children's parents. The size of the CGG repeat was identified using a commercial TP-PCR assay. The influence of AGG interruptions on the CGG expansion during maternal transmission was analyzed in 24 mother-son pairs (10 pairs with 1 AGG and 14 pairs with 2 AGGs).

Results

553 unrelated patients between six months and eighteen years of age were recruited. Specimens from 540 patients (male:female = 5.2:1) produced high-quality TP-PCR data, resulting in the determination of the FMR1 CGG repeat number for each. The most common repeat numbers were 29 and 30, and the most frequent interruption pattern was 2 or 3 AGGs. Five full mutations were identified (1 familial and 4 sporadic IDD patients), and size mosaicism was apparent in 4 of these FXS patients (4/5 = 80 %). The overall yield of FXS in the IDD cohort was 0.93 % (5/540). Neither the mean size of CGG expansion (0.20 vs. 0.79, p > 0.05) nor the frequency of CGG expansion (2/10 vs. 9/14, p > 0.05) was significantly different between the 1 and 2 AGG groups following maternal transmission.

Conclusions

The FMR1 TP-PCR assay generates reliable and sensitive results across a large number of patient specimens, and is suitable for clinical genetic diagnosis. Using this assay, the prevalence of FXS was 0.93 % in Chinese children with unknown IDD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-015-0394-8) contains supplementary material, which is available to authorized users.

Couples at risk for spinocerebellar ataxia type 2: the Cuban prenatal diagnosis experience

Cuba reports the highest worldwide prevalence of spinocerebellar ataxia type 2 (SCA2) and the greatest number of descendants at risk. A protocol for genetic counseling, presymptomatic testing, and prenatal diagnosis of hereditary ataxias has been under development since 2001. Considering that the revision of the experience with prenatal diagnosis for SCA2 in Cuba would enable comparison of ours with international findings, we designed a descriptive study, based on the retrospective revision of the medical records belonging to the 58 couples that requested their inclusion in the program, during an 11-year period (2001-2011). Most of the participants in the prenatal diagnosis program were known presymptomatic carriers, diagnosed through the presymptomatic testing in the same period of study, for an uptake among them of 22.87 % (51 out of 223). In 28 cases, the fetuses were carriers, 20 of these couples (71.43 %) decided to terminate the pregnancy; the rest continued the pregnancy to term, this resulting in a predictive test for their unborn children. A predominance of females as the at-risk progenitor was observed. Except for a slightly lower average age, the results attained in the Cuban SCA2 prenatal diagnosis program resulted similar to the ones reported for Huntington disease in other countries. It is necessary to have easy access to the Cuban program through its expansion to other genetic centers along the island. Future research is needed to evaluate the long-term impact of both the predictive testing in unborn children and the selection of other reproductive options by the at-risk couples.

Monogenic mouse models of social dysfunction: implications for autism

Autism is a pervasive disorder characterized by a complex symptomatology, based principally on social dysfunction. The disorder has a highly complex, largely genetic etiology, involving an impressive variety of genes, the precise contributions of which still remain to be determined. For this reason, a reductionist approach to the study of autism has been proposed, employing monogenic animal models of social dysfunction, either by targeting a candidate gene, or by mimicking a single-gene disorder characterized by autistic symptoms. In the present review, we discuss this monogenic approach by comparing examples of each strategy: the mu opioid receptor knock-out (KO) mouse line, which targets the opioid system (known to be involved in the control of social behaviors); and the Fmr1-KO mouse, a model for Fragile X syndrome (a neurodevelopmental syndrome that includes autistic symptoms). The autistic-relevant behavioral phenotypes of the mu-opioid and Fmr1-KO mouse lines are described here, summarizing previous work by our research group and others, but also providing novel experimental evidence. Relevant factors influencing the validity of the two models, such as sex differences and age at testing, are also addressed, permitting an extensive evaluation of the advantages and limits of monogenic mouse models for autism.

Comprehensive analysis of ultrasonic vocalizations in a mouse model of fragile X syndrome reveals limited, call type specific deficits

Fragile X syndrome (FXS) is a well-recognized form of inherited mental retardation, caused by a mutation in the fragile X mental retardation 1 (Fmr1) gene. The gene is located on the long arm of the X chromosome and encodes fragile X mental retardation protein (FMRP). Absence of FMRP in fragile X patients as well as in Fmr1 knockout (KO) mice results, among other changes, in abnormal dendritic spine formation and altered synaptic plasticity in the neocortex and hippocampus. Clinical features of FXS include cognitive impairment, anxiety, abnormal social interaction, mental retardation, motor coordination and speech articulation deficits. Mouse pups generate ultrasonic vocalizations (USVs) when isolated from their mothers. Whether those social ultrasonic vocalizations are deficient in mouse models of FXS is unknown. Here we compared isolation-induced USVs generated by pups of Fmr1-KO mice with those of their wild type (WT) littermates. Though the total number of calls was not significantly different between genotypes, a detailed analysis of 10 different categories of calls revealed that loss of Fmr1 expression in mice causes limited and call-type specific deficits in ultrasonic vocalization: the carrier frequency of flat calls was higher, the percentage of downward calls was lower and that the frequency range of complex calls was wider in Fmr1-KO mice compared to their WT littermates.

Fragile X-associated disorders: a clinical overview

Fragile X Syndrome (FraX) is the most common inherited cause of learning disability worldwide. FraX is an X-linked neuro-developmental disorder involving an unstable trinucleotide repeat expansion of cytosine guanine guanine (CGG). Individuals with the full mutation of FraX have >200 GG repeats with premutation carriers having 55-200 GG repeats. A wide spectrum of physical, behavioural, cognitive, psychiatric and medical problems have been associated with both full mutation and premutation carriers of FraX. In this review, we detail the clinical profile and examine the aetiology, epidemiology, neuropathology, neuroimaging findings and possible management strategies for individuals with both the full mutation and premutation of FraX.

Uncommon features in Cuban families affected with Friedreich ataxia

This report describes two families who presented with autosomal recessive ataxia. By means of Polymerase Chain Reaction (PCR) molecular testing we identified expansions in the gene encoding Frataxin (FTX) that is diagnostic of Friedreich ataxia. A history of reproductive loss in the two families, prominent scoliosis deformity preceding the onset of ataxic gait, the presence of a sensitive axonal neuropathy, as well as the common origin of ancestors are unusual features of these families. These cases illustrate the importance of molecular diagnosis in patients with a recessive ataxia. The origin of the expanded gene and the GAA repeat size in the normal population are issues to be further investigated. The molecular diagnosis of Friedreich ataxia is now established in Cuba.

Autism spectrum phenotype in males and females with fragile X full mutation and premutation

The behavioural phenotype of autism was assessed in individuals with full mutation and premutation fragile X syndrome (FXS) using the Autism Diagnostic Observation Scale-Generic (ADOS-G) and the Autism Diagnostic Interview (ADI-R). The participants, aged 5-80 years, comprised 33 males and 31 females with full mutation, 7 males and 43 females with premutation, and 38 non-fragile X relatives (29 males, 9 females). In the full mutation group, a total of 67% males and 23% females met either the Autism Disorder (AD) or the Autism Spectrum Disorder (ASD) criteria on at least one of the diagnostic tests. In the premutation group, 14% males and 5% females met the ADOS-G criteria for ASD. The presence of autism manifestations in males and females with full mutation and premutation provide support for a spectrum view.

[Schizophrenia, human genetics and genetic counselling. Human genetic counselling as part of the psychiatric/psychotherapeutic treatment concept]

The human genome project has substantially increased our knowledge about the genetic basis of psychiatric diseases. In daily clinical practice the physician is asked about the diagnosis of genetically dependent diseases with an increased psychiatric risk, particularly schizophrenia group disorders, about the recurrence risk of psychiatric diseases in the relatives and children of the patients, on the use of psychopharmaceuticals during pregnancy and their potential consequences for the offspring, as well as psychopharmacogenetics. These questions will be dealt with in this contribution. At present, they receive too little attention, although genetic counselling might play an important role within the framework of psychiatric treatment, especially for schizophrenia. Such counselling should be seen as a component of the psychiatric/psychotherapeutic treatment concept and performed according to human genetic guidelines.

Molecular and cognitive predictors of the continuum of autistic behaviours in fragile X

The distributions of scores for autistic behaviours obtained from the Autism Diagnostic Observation Scale-Generic (ADOS-G) were investigated in 147 males and females affected with the full mutation in the fragile X mental retardation 1 (FMR1) gene, in 59 individuals with the premutation, and in 42 non-fragile X relatives, aged 4-70 years. The scores representing communication and social interaction were continuously distributed across the two fragile X groups, and they were significantly elevated compared with the non-fragile X controls. Strong relationships were found between both these scores and FMRP deficits, but they became insignificant for social interaction, and the sum of social interaction and communication scores, when FSIQ was included as another predictor of autism scores. Other significant predictors of these scores in both sexes were those executive skills which related to verbal fluency, and to the regulation and control of motor behaviour. Overall, our data have shown that cognitive impairment, especially of verbal skills, best explains the comorbidity of autism and fragile X. This implies some more fundamental perturbations of specific neural connections which are essential for both specific behaviours and cognition. We also emphasize that FXS offers a unique molecular model for autism since FMRP regulates the translation of many other genes involved in synaptic formation and plasticity which should be natural targets for further exploration.

Biological aging and the etiology of aneuploidy

A prevalent hypothesis concerning the cause of the rise in aneuploid conceptions with maternal age is that the changes that accompany normal ovarian aging increase the rate of meiotic errors in the oocyte. Biological aging of the ovary is accompanied by a decline in both the total oocyte pool and the number of antral follicles maturing per cycle, as well as changes in the levels of circulating reproductive hormones. The biological aging hypothesis predicts that aneuploidy rates should be higher in women with a prematurely reduced oocyte pool, and that women with trisomic conceptions should show signs of earlier ovarian aging than women of the same chronological age without trisomic conceptions. Comprehensive studies of aneuploidy in groups of women with known causes of premature ovarian failure remain to be done, though anecdotal evidence does suggest increased rates of pregnancy loss and aneuploidy. Smoking, which is a well-documented cause of earlier ovarian aging, is not associated with an increase in aneuploid conceptions. Evidence from women with unilateral ovariectomies is inconsistent. Support for the biological aging hypothesis was provided by one study showing that menopause occurred about a year earlier in women with a trisomic spontaneous abortion compared to women with chromosomally normal conceptions. Associations between high FSH and pregnancies with Down syndrome and chromosomally abnormal spontaneous abortions have also been reported. However, the most direct test of the hypothesis, which compared antral follicle counts and hormonal levels in women with trisomic pregnancies and those with chromosomally normal pregnancies, failed to find a difference in the expected direction. A prospective study of FSH levels in women with subfertility also failed to find an association with the rate of pregnancy loss. The bulk of evidence thus suggests that, if the processes of biological aging are indeed related to aneuploidy, they probably involve factors other than those measured by oocyte or antral follicle pool size and reproductive hormone levels.

A new approach to antenatal screening for Fragile X syndrome

OBJECTIVES

To describe a new approach to antenatal screening for Fragile X syndrome and to evaluate its effectiveness.

METHODS

We propose that Fragile X syndrome should be considered as a different disorder in males and in females. We also propose that only male Fragile X syndrome should be screened for, so the initial screening test would be the determination of fetal sex. This can now be performed from eight-weeks gestation using a polymerase chain reaction (PCR) analysis on maternal serum. If this test reveals a male fetus, then the same blood sample can be used to determine the CGG repeat length in the DNA of the mother, again using the PCR technique and a Southern blot analysis where necessary. Mothers with positive results (>58 repeats) would be offered antenatal diagnosis (chorionic villus sampling or amniocentesis) to determine the CGG repeat length in cells from the fetus. The screening performance of this strategy was determined using the performance of the component tests.

RESULTS

The proposed strategy for screening for male Fragile X syndrome would have a 99% detection rate and a 0.1% false-positive rate.

CONCLUSION

After antenatal screening for Down syndrome, the proposed screening strategy would be the most effective method of preventing the birth of males with severe mental retardation. It would have a higher detection rate and a lower false-positive rate than any other antenatal screening programme currently being undertaken, and there would be virtually no prenatal diagnosis of female Fragile X syndrome, which, because such a high proportion are phenotypically normal, has been a barrier to the introduction of screening.

Simple fluorescent PCR assay for discriminating FRAXA fully mutated females from normal homozygotes

Fragile X syndrome linked to the FRAXA locus is the most common inherited genetic disease accounting for mental retardation and is usually caused by the expansion of an unstable CGG repeat in the first exon of the FMR1 gene on the X chromosome. Despite its robustness, Southern blot is not suitable for large-scale routine screening as part of neuropediatric practice. PCR appears as an interesting alternative, and various protocols have been successfully applied to molecular screening in mentally retarded boys and girls. Unfortunately, as of this date these protocols are unable to detect the expanded allele in FRAXA females reliably, thereby failing to discriminate between fully mutated females from normal homozygotes. Therefore, we opted for an alternative approach in designing a semiquantitative PCR assay, based on the amplification of the sole wild-type allele. This method allowed us to detect the presence of one or two normal alleles with the same sizes, thereby discriminating between a FRAXA fully mutated female or a normal homozygote, respectively. A trial on 95 DNA samples from normal and mutated females demonstrated the reliability of the procedure. We believe this simple PCR assay is a powerful approach that would reduce the recourse to Southern blotting in females with mental retardation of unknown etiology.

Brain imaging in neurogenetic conditions: realizing the potential of behavioral neurogenetics research

Behavioral neurogenetics research is a new method of scientific inquiry that focuses on investigation of neurodevelopmental dysfunction associated with specific genetic conditions. This research method provides a powerful tool for scientific inquiry into human gene-brain-behavior linkages that complements more traditional research approaches. In particular, the use of specific genetic conditions as models of common behavioral and cognitive disorders occurring in the general population can reveal insights into neurodevelopmental pathways that might otherwise be obscured or diluted when investigating more heterogeneous, behaviorally defined subject groups. In this paper, we review five genetic conditions that commonly give rise to identifiable neurodevelopmental and neuropsychiatric disability in children: fragile X syndrome, velo-cardio-facial syndrome, Williams syndrome, Turner syndrome, and Klinefelter syndrome. While emphasis is placed on describing the brain morphology associated with these conditions as revealed by neuroimaging studies, we also include information pertaining to molecular genetic, postmortem, and neurobehavioral investigations to illustrate how behavioral neurogenetics research can contribute to an improved understanding of brain disorders in childhood.

Increased transmission of intermediate alleles of the FMR1 gene compared with normal alleles among female heterozygotes

Fragile X syndrome (Fra X) is the most common heritable disease accounting for mental retardation and is caused by an expanded CGG repeat in the first exon of the FMR1gene. Previous studies have shown an increased fertility rate among fragile X carrier mothers and a preponderance of mentally retarded boys among the male offspring. In this study, we examined the transmission of the intermediate allele in the lower range of CGG repeats in carrier mothers found randomly in a screening program of the normal population. We tested 10,587 healthy women with no family history of mental retardation and identified 138 (1.3%) who were carriers of the intermediate allele (51-200 CGG repeats). Of these, 107 underwent prenatal testing during 108 pregnancies for Fra X in the fetus. Of the 108 pregnancies, the abnormal allele was transmitted in 67 (segregation ratio = 0.62, P < 0.012). We found a significant increase in the transmission of the abnormal allele by mothers who had between 51 and 60 repeats (segregation ratio = 0.69 [P < 0.007] for the group with 51-55 repeats, and 0.74 [P < 0.04] for the group with 56-60 repeats), but no increase by mothers who had more than 61 repeats. This suggests a genetic advantage for the abnormal allele in the 51- to 60-repeat range.

Partial seizures with focal epileptogenic electroencephalographic patterns in three related female patients with fragile-X syndrome

Epilepsy and abnormal electroencephalographic (EEG) patterns have been reported in mentally retarded males with fragile-X syndrome, but the high incidence of epilepsy in such persons has been recognized only recently. These individuals have focal spikes in the EEG similar to the benign rolandic pattern. Female carriers have very rarely been reported to have epilepsy or nonspecific abnormal EEG patterns. We report partial seizures with a focal epileptogenic EEG pattern in two sisters and their grandmother, who are all carriers of fragile-X syndrome. The sisters have mild developmental delay, but the grandmother is of normal intelligence. The mother of the two sisters is known to be a carrier of the fragile-X chromosome and is of normal intelligence, with no history of seizures. It is important for physicians to be aware of the possibility that females presenting with partial seizures of unknown cause may be fragile-X carriers, and enquiry for a family history of intellectual disability should be pursued.

The nature of the spatial deficit in young females with Fragile-X syndrome: a neuropsychological and molecular perspective

Spatial performance in a group of young Fragile-X syndrome females with FMR-1 full mutation was compared to two control groups of mainstream schoolchildren. Performance was assessed across a wide range of spatial tasks including visuo-spatial, visuo-construction, visuo-motor, visuo-perception and spatial-memory. A spatial deficit emerged only on those tasks which comprised a visuo-constructive component, with the Fragile-X group performing worse overall. All other tasks were performed at a comparable level across the three groups. Molecular analysis of the lymphocyte DNA found minimal evidence for a correlation between expansion size and spatial performance. In addition, there was no evidence for a correlation between the proportion of active to inactive unmethylated FMR-1 genes (activation ratio) and spatial performance. These results conflict with recent reports of a correlation between activation ratio and intellectual functioning.

"Reduction" of CGG trinucleotide expansion from mother to offspring in seven fragile-X families

Apparent reduction in the size of the CGG repeat is reported from seven fragile-X mothers to nine offspring in seven extended families. The overall frequency of the reduction amongst 121 fragile-X mother-fragile-X child transmissions was 7.4%, compared with an 18% reduction in fragile-X father-fragile-X daughter transmissions, but ascertainment bias may account for some underestimation of the frequency of reductions, especially between mothers and their offspring. In one mother-son transmission, a premutation present in the son (with a full mutation present in the mother) was unmethylated. This may be the result of either demethylation with reduction, or undetected mosaicism in the mother. There was no obvious increase in the level of intellectual performance in female offspring who received a reduced fragment from their mothers. Several mechanisms leading to apparent reduction, such as germline mosaicism, deletion or replication slippage, should be considered.

Reproductive fitness in familial schizophrenia

BACKGROUND

Reproductive fitness is an important factor in understanding inheritance in genetic disorders. The purpose of this study was to determine whether fitness is reduced in familial schizophrenia (FS) and if fitness in siblings differs from the norm.

METHOD

The number of offspring in 36 subjects with RDC schizophrenia or schizoaffective disorder (SZ) and their 101 siblings from large FS families was compared with age-adjusted census figures.

RESULTS

Fitness in the SZ group was significantly reduced: 23% of expected in males and 51% of expected in females. Fitness of unaffected siblings was within census expectations. However, female siblings with schizophrenia spectrum features had increased fitness over census norms. Reduced fitness was correlated with low marital rates, poor functioning and positive symptoms.

CONCLUSIONS

These results indicate that reduced fitness is an important genetic force in FS and is likely inherent to the illness. Sex differences are important and would need to be considered when examining maternal and paternal transmission of schizophrenia. The results support a proposed high mutation rate for schizophrenia, consistent with a dynamic mutation mechanism.

Parents and collateral relatives of children with pervasive developmental disorders: a family history study

The objective of this study was to see whether, using the family history method, the risk for pervasive developmental disorder (PDD), cognitive impairments, and other psychiatric symptoms is greater in the parents and collateral relatives of probands with PDD compared to a control group. A semistructured family history interview was carried out with the parents of 52 probands with PDD and 33 parents of controls. Rates of cognitive impairments and psychiatric problems were not found more frequently in parents or relatives of PDD probands compared to relatives of controls, but four cases of PDD were reported among the extended families of the PDD probands. The relatives with PDD were related to the probands through the maternal line, possibly suggesting some form of maternal influence on inheritance or reduced penetrance in females with the PDD genotype.

Use of robust statistical methods to determine the effect of fragile X on means and variance components of a quantitative trait

Owing to the presence of outliers, an estimated 3.5% in the ridge breadth data and 1.7% in the height data, the effect of fragile X on height and ridge breadth was examined using robust statistical techniques for data collected from 54 families afflicted with this disorder. It is shown that fragile X affects ridge breadth and height in a different manner. Fragile X women had a greater mean ridge breadth than normal women, whereas there was a similar trend, but no significant difference, between normal and fragile X men. Fragile X men were shorter than normal men, but no significant difference between the mean height of normal and fragile X women was observed. However, fragile X girls were shown to grow more quickly and to stop growing earlier than normal girls. An examination of the covariance between relatives classified according to fragile X status showed that for both traits the effect of fragile X was to reduce the covariance between parents and offspring, which produced the effect of departure from an additive polygenic model of inheritance.

Evidence that methylation of the FMR-I locus is responsible for variable phenotypic expression of the fragile X syndrome

DNA at the FMR-1 locus was analyzed by Southern blot using probe StB12.3 in an unusual fragile X family with six brothers, three of whom are affected with fragile X to varying degrees, two of whom are nonpenetrant carriers, and one of whom is unaffected. Fragile X chromosome studies, detailed physical examinations, and psychological testing were completed on all six. Two of the affected brothers and the two nonpenetrant brothers were found to be methylation mosaics. The three affected males spanned the phenotypic and cognitive spectrum of the fragile X syndrome. A correlation was seen between the degree of methylation and the phenotypic expression identified in the three affected males. The two males initially classified as nonpenetrant were found to have mild phenotypic expression which consisted of minor cognitive deficits and a partial physical phenotype. These two, who were negative on fragile X chromosome studies, were found on DNA analysis to have large broad smears, with approximately 97% of the DNA unmethylated. The results described here indicate that some "nonpenetrant" carrier males may have varying amounts of methylation of the FMR-1 region, which can result in mild expression of the fragile X syndrome. The apparently mild phenotypic and cognitive expression of the fragile X syndrome in the two males, initially classified as nonpenetrant, who are mosaic for hypermethylation of an expansion of the CGG repeat in the premutation range, indicates that expression of the syndrome is not confined to males with large, hypermethylated expansions (full mutation) but has instead a gradient effect with a threshold for the full expression of the phenotype.

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.

Between-generation differences in ascertainment and penetrance: relevance to genetic hypotheses in fragile X

Between-generation differences in ascertainment were examined in 54 extended fragile X pedigrees, where all available members were clinically, psychometrically, and cytogenetically investigated. In 24 families a diagnosis was verified by molecular characterization using the pfxa3 fragile X-specific probe. We found considerable differences between generations in relative proportions of affected fragile X subjects versus 'non-penetrant' carriers. We also found deviation in the segregation ratio in unbiased samples of relatives in pedigrees. We claim that these irregularities are influenced by different rates of ascertainment, depending on the clinical expression of the condition (penetrance) and the fertility of fragile X individuals in a pedigree, as well as by the thoroughness of clinical investigation in individual families. Penetrance and fertility were estimated in fragile X females assessed by psychometric tests, and they were compared with earlier estimates based on a subjective judgement of their intellectual status. We suggest that the standard correction for ascertainment bias, such as has been applied in segregation analysis of this condition, is not sufficient to adjust for all types of bias.

Fragile X family with unusual digital and facial abnormalities, cleft lip and palate, and epilepsy

We present a fragile X family with unusual clinical manifestations. These findings, which often occur in the X-linked FG syndrome, include minor limb anomalies, cleft lip and palate, characteristic facial appearance, gastrointestinal problems and epilepsy, and intellectual disability. In a total sample of 54 fra(X) families, the frequency of minor limb anomalies was estimated to be 32% in the affected males and 19% in the female heterozygotes. These anomalies tend to occur in several members of the same family, where some craniofacial abnormalities reported as characteristic of the FG syndrome have also been encountered. Possible mechanisms for the occurrence of these unusual manifestations in the fra(X) families are discussed.

Specific frontal lobe deficits among women with the fragile X gene

The neurocognitive phenotype of fragile X and its relation to cytogenetic expression were examined among 10 fragile X women with > or = 2% expression, 10 0% obligate carriers, and 10 controls. Measures were obtained for intellectual ability, achievement, and verbal, nonverbal, memory, and frontal lobe functions. Results show that no group demonstrated deficits on verbal, nonverbal, or memory measures. In contrast, when controlling for effects of IQ, the expressing fragile X women exhibited (1) deficits on measures of frontal lobe functioning, and (2) enhanced performance on verbal, but not figural, memory. Frontal lobe deficits may account for behavioral and cognitive manifestations of fragile X.

Fixed and random effects in the variation of the finger ridge count: a study of fragile-X families

A maximum-likelihood scoring technique for analysis of pedigree data allows for the concurrent estimation of random and of fixed effects in a quantitative trait. We included both types of effects in genetic models, to study the sources of variation in finger ridge count in 54 large families affected with the fragile-X disorder. The fixed effects were represented by fragile X and sex, and the random effects by environmental and genetic variance. We found a significant effect of fragile X in the mean of the finger ridge count on the thumb (finger 1) and index finger (finger 2), which had the lowest heritability and a negligible nonadditive component of genetic variance. This was in contrast with ridge counts on fingers 3 and 4, which showed little fragile-X effect, but high heritability and a significant nonadditive component. A contrast in genetic properties for ridge counts on fingers 1 and 2, compared with these counts on the remaining three fingers, may be relevant to increased selection pressures on functions of the thumb and of the index finger in evolution of modern man. We have also demonstrated an important effect of fragile X in increasing the additive variance in covariance, especially between male pairs. These findings suggest that the effect of the fragile-X genotype in finger ridge count is additive and superimposed on the normal hereditary variations in this trait.

Problems in ascertainment of transmitting males in Martin-Bell syndrome

The difficulty of assigning families affected with the Martin-Bell syndrome (MBS) into the category of male transmission is emphasised and illustrated by examples of 3 MBS families. These examples demonstrate how the ability to detect transmitting males depends on the number of generations available for investigation, and also on the "spread" of clinical investigation across many branches of the family regardless of what appears to be an unremarkable family history. Some unusual properties of male transmission are shown, and the problem of selective ascertainment of the particular MBS male individuals in different generations in a set of pedigrees is discussed.

Neuropsychological, psychiatric, and physical manifestations in 149 members from 18 fragile X families

One hundred forty-nine subjects from 18 families with fragile X [fra(X)] syndrome were evaluated for their neuropsychological, psychiatric, and physical characteristics. The 36 fra(X) males had intelligence quotients ranging from less than 20 to 61, which prevented the delineation of a reliable neuropsychological profile. Behaviour fitted DSM-III-R and ADI diagnostic criteria of autism in only 2 subjects, both with very low intelligence level (IQ less than 20). Of 36 heterozygotes (HZ), 22 had an IQ between 20 and 80 and 14 between 81 and 99. The neuropsychological profile of the latter was compared with IQ-age-environment-matched 14 normal females and 14 normal males. Significantly poorer results in HZ were found on immediate digit memory and on Raven's progressive matrices (a visuo-spatial test of logical capabilities). The latter result, in conjunction with those results on the Bender visual-motor gestalt test and on some WAIS subtests, suggests a frequent deficit in spatial capabilities in such subjects. Such results tended to be confirmed by the profiles of the 22 HZ with IQ 20-80. No psychiatric abnormalities were found in HZ, except in one subject with IQ less than 20 which fitted DSM-III-R and ADI criteria for autism. Typical physical manifestations, especially cranio-facial, were more frequently present in the HZ group with lower IQ. Subnormal IQ was probably the most reliable abnormality for the detection of HZ in 49 females at 50% and 25% risk of heterozygosity.

Fragile X expression and X inactivation. II. The fragile site at Xq27.3 has a basic function in the pathogenesis of fragile X-linked mental retardation

The major concept of fragile X pathogenesis postulates that the fragile site at band Xq27.3 [fra(X)] represents the primary defect. The expression of fra(X) is predicted to be an intrinsic property of the mutated chromosome and, hence, should not be suppressed by X inactivation in females or induced by X-linked trans-acting factors. We made fibroblast clones of a fra(X)-positive female. Monoclonality was demonstrated using the DNA methylation assay at DXS255. The mutated X chromosomes and their states of genetic activity in the different clones were also defined by molecular methods. Five clones were selected to induce expression of fra(X) by 10(-7) M FUdR; two carried an active mutated X chromosome, in the other three the mutated X chromosome was inactivated. Fra(X) was found expressed in both types of clones. The percentages of positive cells were as high as 7-10%, regardless of the genetic activity of the mutated X chromosomes. DNA replicating patterns, obtained by BUdR labelling, demonstrated that expression occurred only on the mutated X chromosomes previously identified by molecular methods. The concept that the fragile site represents the primary mutation is now strongly supported by experimental evidence. The expression of fra (X) in females is independent of X inactivation and other trans-acting factors.

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.

Expression of fragile-X in a female fetus diagnosed after chorionic villus sampling

Study of different tissues of an aborted female fetus showed similar levels of fragile-X expression (6.3-9.2 per cent) and of early replication of the FRAXA-positive cells (50-66 per cent) in fetal tissues. Different culture media did not significantly affect either investigation. It is suggested that the distribution of X-inactivation in FRAXA-positive chorionic villus cells of a female fetus might indicate her future phenotype.

Heterozygous fragile X female: historical, physical, cognitive, and cytogenetic features

Historical, physical, cognitive, and cytogenetic data were documented in 105 heterozygous fragile X [fra(X)] females and 90 controls in a prospective fashion. For comparisons, we divided heterozygotes and controls into those with cognitive impairment (IQ less than 85) and normal IQ (IQ greater than or equal to 85). The only finding that was significantly more frequent in impaired heterozygotes compared with impaired controls chi 2 analysis was shyness. Features that were more frequent in normal IQ heterozygotes compared with normal controls were voluntary thumb dislocation and hyperextensible metacarpal-phalangeal (MP) joints. Comparisons among heterozygotes demonstrated more math problems, hand biting, strabismus, high-arched palate, hyperextensible finger joints, and flat feet in impaired heterozygotes than in normal heterozygotes. Premature menopause was present in 8 of 61 normal heterozygotes and in none of the impaired heterozygotes. A multiple regression analysis demonstrated a significant inverse correlation between the percent fragility and IQ for the heterozygotes as a group. However, no correlation existed between IQ and fragility when the percent fragility was 2% or greater. However, a higher percentage of fragility was positively correlated with the total number of physical findings present.

Cognitive profiles of the carrier fragile X woman

Cognitive deficits in females with fragile X [fra(X)] syndrome have been reported, but studies have rarely focused on women with normal intelligence, nor have they separated fra(X)-negative carriers from fra(X)-positive carriers. Questions specifically addressed here are: 1) is the degree of fragility predictive of IQ? 2) are cognitive patterns consistent across fragility levels? and 3) do consistent individual profiles exist? These questions were addressed with the help of 74 heterozygous women, 38 of whom were fra(X)-negative carriers. All women completed the WAIS-R, and full-scale IQ was normally distributed (mean = 99.65). A strong inverse relationship between IQ and fragility levels was found. Also, the group of fra(X)-positive women had a significantly different subtest pattern from that of the fra(X)-negative women. However, when results were analyzed individually, no consistent patterns emerged. The cognitive performance of fra(X)-negative carriers has probably been underestimated due to the lack of differentiation between positive and negative carrier females in previous studies. These women appear to be cognitively unimpaired and should be considered separately from fra(X)-positive women. Since consistent WAIS-R patterns are not observable on an individual basis, their use as a diagnostic/predictive tool appears to be inappropriate.

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.

Neuropsychological dimensions of the fragile X syndrome: support for a non-dominant hemisphere dysfunction hypothesis

This study contends that males with the fragile X syndrome feature problems in the visuospatial sphere as compared with Down syndrome males matched on vocabulary ability. Fragile X males suffer impairments of constructional functions, as demonstrated by their poor performance on block construction tests and on drawing tasks. These problems exist in association with visuoperceptive impairments, including the inability to reliably estimate angular relationships (Judgement of Line Orientation). They have shortened Digit and Corsi spans, and may feature some deficits in left hand co-ordination. The observation of a pervasive non-verbal deficit may also apply to carrier females, who despite functioning at an overall higher level, feature a similar pattern of deficits. It is possible that the deficit in non-dominant hemisphere functioning may be a pathognomonic feature of the chromosomal abnormality.

Application of the anthropometric discriminant functions in estimation of carrier probabilities in Martin-Bell syndrome

A method of estimating the likelihood ratio and the risk of an individual being affected with Martin Bell syndrome (MBS) from anthropometric measurements is described. The procedure is based on the discriminant functions (one for each sex), generated in our previous study in order to separate the individuals with MBS from the normal individuals. The procedure is illustrated by the examples of estimating the likelihood and the likelihood ratio in four individuals of either sex, belonging to MBS families, where the discriminant score value obtained from each individual is compared with the empirical (normalized) distribution of discriminant scores from the known MBS and normal subjects of a corresponding sex. The ways in which the risk of an individual being MBS is estimated in the general population or in members of the MBS families are indicated. The limitations of the discriminant diagnosis based on body measurements, as well as its particular applications in studies of the Martin-Bell syndrome, are discussed.

Multivariate analysis of body shape in fragile X (Martin-Bell) syndrome

Human body shape measures can be more informative in studies of developmental abnormalities than distances between body landmarks. Such measures were obtained by an appropriate transformation of 34 distances between trunk/limbs and head/face landmarks in 43 men and 72 women with the Martin-Bell Syndrome (MBS), and in 99 and 103 normal men and women, respectively. The transformation of the original distances was performed by adjusting individual measures for an overall size measure using regression analysis. Thus obtained body shape variables were used in discriminant analysis in order to obtain unbiased classification probabilities of individuals having the MBS or being normal. The average percent correctly classified male and female individuals was high (93 and 87, respectively). Moreover, the body shape variables were used to obtain shape dimensions by means of principal component analysis. There was no difference between the MBS and normal individuals in the first (most important) principal component (shape dimension). This component represents the relative proportions between trunk and limb lengths and widths, or between midfacial lengths and widths. However, there were appreciable differences in some succeeding components. The problem of interpretation of shape dimensions as derived from principal component analysis and of their relevance to abnormal development in the MBS individuals is discussed.