A distinct neurocognitive phenotype in female fragile-X premutation carriers assessed with visual attention tasks

Region-Related Differences in Short-Term Synaptic Plasticity and Synaptotagmin-7 in the Male and Female Hippocampus of a Rat Model of Fragile X Syndrome

Fragile X syndrome (FXS) is an intellectual developmental disorder characterized, inter alia, by deficits in the short-term processing of neural information, such as sensory processing and working memory. The primary cause of FXS is the loss of fragile X messenger ribonucleoprotein (FMRP), which is profoundly involved in synaptic function and plasticity. Short-term synaptic plasticity (STSP) may play important roles in functions that are affected by FXS. Recent evidence points to the crucial involvement of the presynaptic calcium sensor synaptotagmin-7 (Syt-7) in STSP. However, how the loss of FMRP affects STSP and Syt-7 have been insufficiently studied. Furthermore, males and females are affected differently by FXS, but the underlying mechanisms remain elusive. The aim of the present study was to investigate possible changes in STSP and the expression of Syt-7 in the dorsal (DH) and ventral (VH) hippocampus of adult males and females in a Fmr1-knockout (KO) rat model of FXS. We found that the paired-pulse ratio (PPR) and frequency facilitation/depression (FF/D), two forms of STSP, as well as the expression of Syt-7, are normal in adult KO males, but the PPR is increased in the ventral hippocampus of KO females (6.4 ± 3.7 vs. 18.3 ± 4.2 at 25 ms in wild type (WT) and KO, respectively). Furthermore, we found no gender-related differences, but did find robust region-dependent difference in the STSP (e.g., the PPR at 50 ms: 50.0 ± 5.5 vs. 17.6 ± 2.9 in DH and VH of WT male rats; 53.1 ± 3.6 vs. 19.3 ± 4.6 in DH and VH of WT female rats; 48.1 ± 2.3 vs. 19.1 ± 3.3 in DH and VH of KO male rats; and 51.2 ± 3.3 vs. 24.7 ± 4.3 in DH and VH of KO female rats). AMPA receptors are similarly expressed in the two hippocampal segments of the two genotypes and in both genders. Also, basal excitatory synaptic transmission is higher in males compared to females. Interestingly, we found more than a twofold higher level of Syt-7, not synaptotagmin-1, in the dorsal compared to the ventral hippocampus in the males of both genotypes (0.43 ± 0.1 vs. 0.16 ± 0.02 in DH and VH of WT male rats, and 0.6 ± 0.13 vs. 0.23 ± 0.04 in DH and VH of KO male rats) and in the WT females (0.97 ± 0.23 vs. 0.31 ± 0.09 in DH and VH). These results point to the susceptibility of the female ventral hippocampus to FMRP loss. Importantly, the different levels of Syt-7, which parallel the higher score of the dorsal vs. ventral hippocampus on synaptic facilitation, suggest that Syt-7 may play a pivotal role in defining the striking differences in STSP along the long axis of the hippocampus.

Disassociation between brain activation and executive function in fragile X premutation females

Executive dysfunction has been demonstrated among premutation (PM) carriers (55-199 CGG repeats) of the Fragile X mental retardation 1 (FMR1) gene. Further, alterations to neural activation patterns have been reported during memory and comparison based functional magnetic resonance imaging (fMRI) tasks in these carriers. For the first time, the relationships between fMRI neural activation during an interleaved ocular motor prosaccade/antisaccade paradigm, and concurrent task performance (saccade measures of latency, accuracy and error rate) in PM females were examined. Although no differences were found in whole brain activation patterns, regions of interest (ROI) analyses revealed reduced activation in the right ventrolateral prefrontal cortex (VLPFC) during antisaccade trials for PM females. Further, a series of divergent and group specific relationships were found between ROI activation and saccade measures. Specifically, for control females, activation within the right VLPFC and supramarginal gyrus correlated negatively with antisaccade latencies, while for PM females, activation within these regions was found to negatively correlate with antisaccade accuracy and error rate (right VLPFC only). For control females, activation within frontal and supplementary eye fields and bilateral intraparietal sulci correlated with prosaccade latency and accuracy; however, no significant prosaccade correlations were found for PM females. This exploratory study extends previous reports of altered prefrontal neural engagement in PM carriers, and clearly demonstrates dissociation between control and PM females in the transformation of neural activation into overt measures of executive dysfunction. Hum Brain Mapp 38:1056-1067, 2017. © 2016 Wiley Periodicals, Inc.

Delineation of the working memory profile in female FMR1 premutation carriers: the effect of cognitive load on ocular motor responses

Fragile X mental retardation 1 (FMR1) premutation carriers (PM-carriers) are characterised as having mid-sized expansions of between 55 and 200 CGG repeats in the 5' untranslated region of the FMR1 gene. While there is evidence of executive dysfunction in PM-carriers, few studies have explicitly explored working memory capabilities in female PM-carriers. 14 female PM-carriers and 13 age- and IQ-matched healthy controls completed an ocular motor n-back working memory paradigm. This task examined working memory ability and the effect of measured increases in cognitive load. Female PM-carriers were found to have attenuated working memory capabilities. Increasing the cognitive load did not elicit the expected reciprocal increase in the task errors for female PM-carriers, as it did in controls. However female PM-carriers took longer to respond than controls, regardless of the cognitive load. Further, FMR1 mRNA levels were found to significantly predict PM-carrier response time. Although preliminary, these findings provide further evidence of executive dysfunction, specifically disruption to working memory processes, which were found to be associated with increases in FMR1 mRNA expression in female PM-carriers. With future validation, ocular motor paradigms such as the n-back paradigm will be critical to the development of behavioural biomarkers for identification of PM-carrier cognitive-affective phenotypes.

Impaired response inhibition is associated with self-reported symptoms of depression, anxiety, and ADHD in female FMR1 premutation carriers

Fragile X Mental Retardation 1 (FMR1) premutation carriers (PM-carriers) have a defective trinucleotide expansion on the FMR1 gene that is associated with continuum of neuropsychological and mental disorders. Currently, little is known about the distinct subcomponents of executive function potentially impaired in female PM-carriers, and there have been no investigations into associations between executive function and incidences of mental disorders. A total of 35 female PM-carriers confirmed by Asuragen triple primed PCR DNA testing and 35 age- and intelligence-matched controls completed tests of executive function (i.e., response inhibition and working memory) and self-reported on social anxiety, depression, and ADHD predominantly inattentive (ADHD-PI) symptoms. Compared to controls, PM-carriers were significantly elevated on self-reported social anxiety and ADHD-PI symptoms. Irrespective of mental symptoms, female PM-carries performed significantly worse than controls on a response inhibition test, and further investigations revealed significant correlations between executive function performance and self-reported symptoms of anxiety, depression and ADHD-PI. Critically, among PM-carriers with good executive function performance, no women exceeded threshold markers for probable caseness of mental disorder. However, rates of probable caseness were elevated in those with average performance (response inhibition: social anxiety: 41.7%; depression: 20%; ADHD: 44.4%; working memory: social anxiety: 27.3%; depression: 9.1%; ADHD: 18.2%) and highly elevated for those with poor executive function performance (response inhibition: social anxiety: 58.3%; depression: 80%; ADHD: 55.6%; working memory: social anxiety: 100%; depression: 50%; ADHD: 83.3%). These data suggest that subtle executive dysfunction may be a useful neuropsychological indicator for a range of mental disorders previously reported in female PM-carriers.

Decreased fragile X mental retardation protein (FMRP) is associated with lower IQ and earlier illness onset in patients with schizophrenia

The purpose of this study was to investigate Fragile X Syndrome (FXS)-related mechanisms in schizophrenia, including CGG triplet expansion, FMR1 mRNA, and fragile X mental retardation protein (FMRP) levels in lymphocytes. We investigated 36 patients with schizophrenia and 30 healthy controls using Southern blot analysis, mRNA assay, and enzyme-linked immunosorbent assay (ELISA). General intellectual functions were assessed with the Wechsler Adult Intelligence Scale-III, and the clinical symptoms were evaluated with the Positive and Negative Syndrome Scale. Results revealed that, relative to healthy controls, CGG triplet size and FMR1 mRNA were unaltered in patients with schizophrenia. However, the FMRP level was significantly reduced in patients compared with controls. We found an association between lower FMRP levels, reduced IQ, and earlier illness onset in schizophrenia. Chlorpromazine-equivalent antipsychotic dose did not correlate with FMRP levels. These results raise the possibility of impaired translation of FMR1 mRNA, altered epigenetic regulation, or increased degradation of FMRP in schizophrenia, which may play a role in dysfunctional neurodevelopmental processes and impaired neuroplasticity.

Why is vision impaired in fragile X premutation carriers? The role of fragile X mental retardation protein and potential FMR1 mRNA toxicity

Dysfunctions of the geniculo-striatal magnocellular (M) visual pathway and its cortical recipients have been documented in fragile X syndrome and in FMR1 premutation carriers. However, the mechanism of this impairment is less clear. To elucidate this issue, we completed the measurement of visual functions at different stages of information processing: low-level mechanisms (contrast sensitivity biasing information processing toward the M and parvocellular [P] pathways), primary visual cortex (motion-defined and static Vernier threshold), and higher-level form and motion processing (coherence thresholds). Results revealed that FMR1 premutation carriers, relative to non-carrier controls, exhibited lower contrast sensitivity for M pathway-biased stimuli, higher Vernier threshold for motion-defined stimuli, and higher global motion coherence threshold. Although both elevated FMR1 mRNA and reduced fragile X mental retardation protein (FMRP) levels were associated with impaired visual functions, regression analysis indicated that FMRP was the primary factor. In premutation carriers, a toxic gain-of-function of elevated FMR1 mRNA has been suggested, whereas reduced FMRP is linked to neurodevelopmental aspects. Here, we showed that FMRP may the primary factor associated with visual dysfunctions.

Fragile X protein expression is linked to visual functions in healthy male volunteers

Fragile X syndrome (FXS) is characterized by the impairment of the magnocellular/dorsal visual system. In this study, we explored how fragile X protein (FMRP) expression may affect visual functions in healthy participants. The percentage of FMRP-positive lymphocytes was measured using a rapid antibody test in blood smears of 100 male volunteers. CGG triplet expansion was also determined. Results revealed that participants with fewer FMRP-positive lymphocytes exhibited lower performances on tests biasing information processing toward the magnocellular pathway and dorsal visual stream (contrast sensitivity at low spatial/high temporal frequency and motion coherence). It was not observed in the case of tests biasing information processing toward the parvocellular pathway and ventral stream (contrast sensitivity at high spatial/low temporal frequency and form coherence). These results suggest that healthy persons with lower peripheral FMRP expression display a visual phenotype similar to that described in patients with FXS.

Motor deficits on a ladder rung task in male and female adolescent and adult CGG knock-in mice

The fragile X premutation is a tandem CGG trinucleotide repeat expansion on the FMR1 gene between 55 and 200 repeats in length. A CGG knock-in (CGG KI) mouse with CGG trinucleotide repeat lengths between 70 and 350 has been developed and used to model the histopathology and cognitive deficits reported in carriers of the fragile X premutation. Previous studies have shown that CGG KI mice show progressive deficits in processing spatial and temporal information. To characterize the motor deficits associated with the fragile X premutation, male and female CGG KI mice ranging from 2 to 16 months of age with trinucleotide repeats ranging from 72 to 240 CGG in length were tested for their ability to perform a skilled ladder rung walking test. The results demonstrate that both male and female CGG KI mice showed a greater number of foot slips as a function of increased CGG repeat length, independent of the age of the animal or general activity level.

Biomarkers in the Study of Families of Individuals with Developmental Disabilities

Research during the past 20 years on families of children with developmental disabilities has yielded a rich body of knowledge about the stress of parenting a child with DD, and the risk and protective factors that result in profiles of family resilience vs. vulnerability at various stages of the family life course. Virtually all of this research has been based on data collected from self-report measures, and has focused on family interactions and relationships, and the psychosocial well-being of individual family members. The present chapter focuses on different sources of data, namely biomarkers, which have the potential to extend our understanding of the biological mechanisms by which the stress of parenting a child with developmental disabilities can take its toll on parents' physical and mental health. We focus on two examples: (1) variations in the FMR1 gene, FMRP, and FMR1 messenger RNA in mothers of children with fragile X syndrome and the association of these measures with maternal depression and anxiety; and (2) profiles of cortisol expression in mothers of children with disabilities and the association of cortisol with daily measures of caregiving stress.

Developmental trajectories of young girls with fragile x syndrome

To describe the early phenotype of girls with full mutation fragile X, we used 54 observations of 15 girls between the ages of 6 months and 9 years to examine developmental trajectories as measured by the Battelle Development Inventory. In this sample, autistic behavior was associated with poorer developmental outcomes, primarily due to interactions of age with autistic behavior, even though autistic behavior, measured continuously, was relatively mild. Although this small sample, ascertained primarily through male relatives with fragile X syndrome, limits generalizability, considerable variability in developmental outcome in young girls was documented. In addition, findings support previous research suggesting that even mild autistic behaviors in girls can be associated with developmental outcomes.

Risk of cognitive impairment in female premutation carriers of fragile X premutation: analysis by means of robust segmented linear regression models

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

Visual pathway deficit in female fragile X premutation carriers: a potential endophenotype

Previous studies indicated impaired magnocellular (M) and relatively spared parvocellular (P) visual pathway functioning in patients with fragile X syndrome. In this study, we assessed M and P pathways in 22 female fragile X premutation carriers with normal intelligence and in 20 healthy non-carrier controls. Testing procedure included visual contrast sensitivity and vernier threshold measurements. Results revealed that carriers were selectively impaired on tests of M pathways (low spatial/high temporal frequency contrast sensitivity and frequency-doubling vernier), whereas they showed intact performance on P pathway tests. These results suggest that the deficit of the M pathway is an endophenotype of fragile X syndrome.

Intersubjectivity, affective neuroscience, and the neurobiology of autistic spectrum disorders: a systematic review

Intersubjectivity is an approach to the study of social interaction viewed from a perspective which rejects the view that reducing any such analysis to study at the level of the individual is adequate to address the issues of social functioning. It also stresses the view that social processes cannot be reduced to cognitive ones - most of the important questions in the study of developmental psychopathology deal with issues which have commonality with many other species and are patent well before the ontological emergence of 'cognitive' abilities. In this paper we review the evidence in this area, and discuss a range of issues relevant to autistic spectrum disorders. We focus in particular on social interaction; the role of the Intrinsic Motive Formation and recent work on mirror neurons in autism; genetic and teratogenic factors in the genesis of autism; and the role of a number of biological factors in pathogenesis - tryptophan; vitamin B12; sterol metabolism; glutamate and GABA; and the Fragile-X expansion.

Language development and fragile X syndrome: profiles, syndrome-specificity, and within-syndrome differences

Fragile X syndrome (FXS) is the leading inherited cause of mental retardation. In this article, we review what is known about the language and related problems of individuals with FXS. In doing so, we focus on the syndrome-specific features of the language phenotype and on the organismic (i.e., genetic and individual neurocognitive and behavioral) and environmental factors associated with within-syndrome variation in the phenotype. We also briefly review those aspects of the behavioral phenotype of FXS that are relevant for understanding syndrome-specific features of, and within-syndrome variability in, language. The review includes summaries of research on the prelinguistic foundations for language development and on each of the major components of language (i.e., vocabulary, morphosyntax, and pragmatics). Throughout the review, we point out implications of existing research for intervention as well as directions for future research.

The Fragile X premutation: new insights and clinical consequences

The Fragile X syndrome (FXS, MIM 309550) is still the most prevalent cause of heritable mental retardation, with a frequency of 1/4000 males and 1/6000 females. The syndrome and its particular pattern of heredity are caused by a dynamic mutation, involving an unstable expansion of a trinucleotide (CGG) repeat at the 5' UTR of the FMR1 gene, located at Xq27.3. Expansion of this repeat region greater than 200 repeats leads to methylation-coupled silencing of the gene and absence of the Fragile X mental retardation protein (FMRP), causing the classical FXS. Individuals with expanded repeat lengths varying from 50 to 200 repeats do not exhibit the classical FXS phenotype, but are considered as fragile X premutation (PM) carriers. These premutation alleles may become unstable, only through maternal transmission, with further expansion in the next generations. For long-time, male and female premutation carriers were considered as asymptomatic. This view was, however, gradually challenged with the description and reports of different premutation-associated clinical phenotypes over the last decade.

Childhood cognitive ability and age at menopause: evidence from two cohort studies

OBJECTIVE

To investigate whether poorer cognitive ability in childhood is associated with an earlier menopause.

DESIGN

Two cohorts were included: a nationally representative British birth cohort study of 1,350 women born in March 1946 and followed up to age 54 years, and an Aberdeen cohort study of 3,465 women born in Aberdeen from 1950 to 1956 and followed up to age 44 to 50 years. Both cohorts had prospective information on childhood cognitive ability at age 7 or 8 years.

RESULTS

In both cohorts, women with lower cognitive scores in childhood reached menopause earlier than women with higher scores. With follow-up of menopause to 49 years, the hazard ratio (HR) for one standard deviation of the cognitive score was 0.80 (95% CI, 0.72-0.90) in the Aberdeen cohort and 0.84 (95% CI, 0.73-0.97) in the older 1946 birth cohort. The effect was still evident in the 1946 birth cohort with follow-up of menopause to 53 years (HR = 0.87; 95% CI, 0.79-0.95). These ratios were weakly attenuated by adjustment for potential confounding effects of lifetime socioeconomic circumstances, parity, and smoking.

CONCLUSIONS

The association between early cognitive ability and timing of menopause only partially reflects common risk factors, although residual confounding remains a possibility. Alternatively, early environmental or genetic programming may explain this association, perhaps through setting lifelong patterns of hormone release or causing transient hormonal changes at sensitive periods of development. These findings have implications for the interpretation of studies investigating an association between age at menopause and adult cognitive function.