Frontal lobe function and executive skills in children with turner's syndrome

The speech and language profile of a child with Turner Syndrome- a case study

BACKGROUND

Turner syndrome is a genetic disorder that affects only females. It has specific cognitive characteristics, but speech and language data are scarce.

METHODS AND PROCEDURES

Prospective case report; we report a girl aged seven's cognitive and speech and language profile.

RESULTS

Cognitive assessment shows higher performance IQ (PIQ), and atypical cognitive profile for Turner syndrome. Speech and language assessment show a significant difference between receptive and expressive language levels. Although the girl did comprehend most of the language structure, there was a lack of it in spontaneous speech. She demonstrated inconsistency in the use of language morphology and complex linguistic structures, primarily because of significant inconsistency in her sound production. Although she produced the majority of phonemes correctly in isolation, her spontaneous speech production was incomprehensible.

CONCLUSION

Case studies of speech and language development may reveal a specific characteristic in the cases with Turner syndrome to delineate genetic factors from individual developmental variabilities.

Which tasks measure what? Reflections on executive function development and a commentary on Podjarny, Kamawar, and Andrews (2017)

This article provides a selective review of the literature on executive function development and related topics, focusing on the conceptual and terminological confusions that might hinder communication among researchers in the field. The distinctions between working memory and updating, and between shifting and flexibility, are discussed. Methodological problems, which have implications regarding whether a certain task can be considered a measure of a psychological construct, are also discussed. Research on preschoolers is examined with particular attention because it is a rapidly growing but controversial field that seems in particular need of greater conceptual clarity. As a specific touchstone case, we discuss whether the Multidimensional Card Selection Task (MCST) created by Podjarny, Kamawar, and Andrews (2017) should better be considered a measure of concurrent cognitive flexibility or working memory capacity. It is argued that connecting tasks to theoretical constructs is not warranted unless based on rigorous empirical testing of well-formulated models.

Mapping the effect of the X chromosome on the human brain: Neuroimaging evidence from Turner syndrome

In addition to determining sex, the X chromosome has long been considered to play a crucial role in brain development and intelligence. Turner syndrome (TS) is caused by the congenital absence of all or part of one of the X chromosomes in females. Thus, Turner syndrome provides a unique "knock-out model" for investigating how the X chromosome influences the human brain in vivo. Numerous cutting-edge neuroimaging techniques and analyses have been applied to investigate various brain phenotypes in women with TS, which have yielded valuable evidence toward elucidating the causal relationship between the X chromosome and human brain structure and function. In this review, we comprehensively summarize the recent progress made in TS-related neuroimaging studies and emphasize how these findings have enhanced our understanding of X chromosome function with respect to the human brain. Future investigations are encouraged to address the issues of previous TS neuroimaging studies and to further identify the biological mechanisms that underlie the function of specific X-linked genes in the human brain.

Skill-related physical fitness versus aerobic fitness as a predictor of executive functioning in children with intellectual disabilities or borderline intellectual functioning

Children with intellectual disabilities (ID) or borderline intellectual disabilities (BIF) often demonstrate impairments in executive functioning (EF). Studies in typically developing children show that aerobic fitness (AF) is positively related with EF. Skill-related physical fitness (SF) might, however, be a stronger predictor of EF than AF, as cognitive challenges are inherent in application of these skills. In this study, AF and SF were examined simultaneously in relationship with domains of EF in children with ID or BIF. Seventy-three children (age range 8-11; 51 boys) with ID (IQ range 56-79) or BIF (IQ range 71-79) were measured annually over a period of 4 years on AF (20-m endurance shuttle run test) and SF (plate tapping and 10×5m run). EF was measured with the Stroop Color-Word test (inhibition), Trailmaking and Fluency test (cognitive flexibility), Self-ordered pointing task (working memory) and the Tower of London (planning). Multilevel models showed that SF was significantly associated with inhibition and both measures of cognitive flexibility, but in the same models no significant associations between AF and EF were found. In addition, age was significantly related to working memory and cognitive flexibility, favouring the older children. In children with ID or BIF, SF is of greater importance than AF in relationship with core domains of EF.

The role of short-term memory and visuo-spatial skills in numerical magnitude processing: Evidence from Turner syndrome

Most studies on magnitude representation have focused on the visual modality with no possibility of disentangling the influence of visuo-spatial skills and short-term memory (STM) abilities on quantification processes. This study examines this issue in patients with Turner syndrome (TS), a genetic condition characterized by a specific cognitive profile frequently associating poor mathematical achievement, low spatial skills and reduced STM abilities. In order to identify the influence of visuo-spatial and STM processing on numerical magnitude abilities, twenty female participants with TS and twenty control female participants matched for verbal IQ and education level were administered a series of magnitude comparison tasks. The tasks differed on the nature of the magnitude to be processed (continuous, discrete and symbolic magnitude), on visuo-spatial processing requirement (no/high) and on STM demands (low in simultaneous presentation vs. high in sequential presentation). Our results showed a lower acuity when participants with TS compared the numerical magnitudes of stimuli presented sequentially (low visuo-spatial processing and high STM load: Dot sequence and Sound sequence) while no difference was observed in the numerical comparison of sets presented simultaneously. In addition, the group difference in sequential tasks disappeared when controlling for STM abilities. Finally, both groups demonstrated similar performance when comparing continuous or symbolic magnitude stimuli and they exhibited comparable subitizing abilities. These results highlight the importance of STM abilities in extracting numerosity through a sequential presentation and underline the importance of considering the impact of format presentation on magnitude judgments.

The processing of number scales beyond whole numbers in development: Dissociations in arithmetic in Turner's syndrome

The arithmetical skills in two children with Turner's syndrome (TS), each the focus of a case study, were analysed in whole numbers and other number scales that have not been systematically explored previously, fractions, decimals, percentages, and negative numbers. The intention was to identify the fractionation of arithmetical skills. The two girls with TS showed dissociations of arithmetical skill in the calculation system of whole numbers that support its modular organization. Fractionation of skills was observed in some components of the other number scales, suggesting an analogous organization within these scales. The operational specificity of impairment within number scales but not others argued against a unitary arithmetical system but rather for autonomous operational scales within distinct number scales. A general model of arithmetic is proposed.

Human 45,X fibroblast transcriptome reveals distinct differentially expressed genes including long noncoding RNAs potentially associated with the pathophysiology of Turner syndrome

Turner syndrome is a chromosomal abnormality characterized by the absence of whole or part of the X chromosome in females. This X aneuploidy condition is associated with a diverse set of clinical phenotypes such as gonadal dysfunction, short stature, osteoporosis and Type II diabetes mellitus, among others. These phenotypes differ in their severity and penetrance among the affected individuals. Haploinsufficiency for a few X linked genes has been associated with some of these disease phenotypes. RNA sequencing can provide valuable insights to understand molecular mechanism of disease process. In the current study, we have analysed the transcriptome profiles of human untransformed 45,X and 46,XX fibroblast cells and identified differential expression of genes in these two karyotypes. Functional analysis revealed that these differentially expressing genes are associated with bone differentiation, glucose metabolism and gonadal development pathways. We also report differential expression of lincRNAs in X monosomic cells. Our observations provide a basis for evaluation of cellular and molecular mechanism(s) in the establishment of Turner syndrome phenotypes.

Effects of a psychosocial intervention on the executive functioning in children with ADHD

The purpose of this study was to analyze the effects of an intensive psychosocial intervention on the executive functioning (EF) in children with ADHD. The treatment was carried out in a coordinated manner over a period of 10 weeks with 27 children with ADHD aged 7 to 10, their parents, and their teachers. A battery of neuropsychological tasks was applied to evaluate attention, interference control, verbal and visuospatial working memory, planning ability, and flexibility. The comparative analysis of the treated group of ADHD children and an untreated ADHD group showed significant differences that were especially important in visuospatial memory and planning in favor of the treated children, even when the scores in the pretreatment phase were included as covariables. Likewise, improvements were observed in the parents' and teachers' behavioral ratings of hyperactivity or impulsivity and inattention. The conclusion was drawn that psychosocial interventions with children with ADHD can have a positive effect on some executive functions.

Exceptional lexical skills but executive language deficits in school starters and young adults with Turners syndrome: implications for X chromosome effects on brain function

TS school starters had enhanced receptive and expressive language on standardised assessment (CELF-P) and enhanced rhyme judgements, spoonerisms, and lexical decision, indicating enhanced phonological skills and word representations. There was marginal but consistent advantage across lexico-semantic tasks. On executive tasks, speeded naming of numbers was impaired but not pictures. Young TS adults had enhanced naming and receptive vocabulary, indicating enhanced semantic skills. There were consistent deficits in executive language: phonemic oral fluency, rhyme fluency, speeded naming of pictures, numbers and colours; sentence completion requiring supression of prepotent responses. Haploinsufficiency of X-chromosome drives mechanisms that affect the anatomical and neurochemical development of the brain, resulting in enhanced temporal lobe aspects of language. These strengths co-exist with impaired development of frontal lobe executive language systems. This means not only that these elements of language can decouple in development but that their very independence is driven by mechanisms linked to the X-chromosome.

Impact of cognitive profile on social functioning in prepubescent females with Turner syndrome

Social deficits are prevalent in Turner syndrome (TS); however, the extent to which these difficulties are secondary to characteristic cognitive impairments is not well known. Here, we sought to establish the relative contribution of executive functions, visuospatial abilities, and IQ to social difficulties in young girls with TS. Forty TS girls and 19 typically developing (TD) children were assessed with the Social Responsiveness Scale (SRS), the Motor-Free Visual Spatial Test (MVPT-3), the Behavior Rating Inventory of Executive Function (BRIEF), and an IQ test. Hierarchical multiple regression analyses were conducted with the SRS subscales as outcome variables. In a first step, the cognitive factors were entered (verbal IQ, BRIEF global score, MVPT-3, and age), followed by the group variable in a second step. In comparison to TD, TS participants were significantly impaired on all main measures. All six regression models with the SRS subscales were significant and revealed that global executive functions explained the largest portion of the variance on all subscales and the total score. Even after controlling for cognitive elements, the group factor still explained a significant portion of the variance of the Social Cognition, Social Awareness, and Autistic Mannerisms subscales. In contrast, the group factor was not a significant predictor of Social Motivation and Social Communication scores. These results suggest that executive dysfunctions play a role in social impairments encountered in TS, but also that some specific aspects of social behavior are altered beyond what can be attributed to cognitive difficulties in this population.

Wisconsin Card Sorting Test performance in children with developmental coordination disorder

The primary purpose of this study was to investigate and compare the executive functions measured by the Wisconsin Card Sorting Test (WCST) between children with developmental coordination disorder (DCD) and age-matched normal controls. A second purpose was to examine the relations between executive functions and school functions in DCD children. Seventy-one children with DCD and 70 children without motor problems were recruited from 14 public schools. Executive functions and school functions were assessed using the WCST, and the School Function Assessment--Chinese Version (SFA-C) respectively. Univariate analyses demonstrated significant between-group differences in five WCST measures. The logistic regression analysis showed differences between two groups on eight SFA-C subscales, and significant correlation between items measured on WCST and SFA-C was also found. The result of the study provides further evidence of impaired sub-domains of executive functions (i.e., mental shifting, flexibility) in children with DCD. The finding also adds to recent investigations into the relationship between executive functions and school functions in DCD. Implications for rehabilitation professionals and recommendations for further research are discussed.

Executive function in adolescents with Down Syndrome

BACKGROUND

The present work is aimed at analysing executive function (EF) in adolescents with Down Syndrome (DS). So far, EF has been analysed mainly in adults with DS, showing a pattern of impairment. However, less is known about children and adolescents with this syndrome. Studying adolescents with DS might help us better understand whether performances on EF tasks of individuals with DS are determined by age or by Alzheimer disease, as some studies suggest, or whether their performances are directly related to DS cognitive profile.

METHOD

A battery of EF tasks assessing set shifting, planning/problem-solving, working memory, inhibition/perseveration and fluency, as well as a tasks assessing sustained attention has been administered to a group of 15 adolescents with DS and 15 typically developing children matched for mental age. All EF tasks were selected from previous studies with individuals with intellectual disabilities or from developmental literature and are thought to be useful for the samples considered.

RESULTS

The present results revealed that the group of individuals with DS performed at a significantly lower level on tasks assessing set shifting, planning/problem-solving, working memory and inhibition/perseveration, but not on the tasks assessing fluency. In addition, individuals with DS demonstrated a greater number of errors and less strategy use for the sustained attention task.

CONCLUSIONS

The results suggest a broad impairment in EF in adolescents with DS, and are consistent with several similar studies conducted with adults with DS. We assume that EF deficit is a characteristic of DS.

Cognitive profile of Turner syndrome

Turner syndrome (TS) is a relatively common neurogenetic disorder characterized by complete or partial monosomy-X in a phenotypic female. TS is associated with a cognitive profile that typically includes intact intellectual function and verbal abilities with relative weaknesses in visual-spatial, executive, and social cognitive domains. In this report, we review previous and current research related to the cognitive profile of TS. We also discuss how cognitive impairments in this syndrome may reflect integrative rather than modular deficits. For example, the less commonly reported areas of verbal difficulty in TS and certain visual-spatial deficits seem significantly influenced by impairments in executive function and spatially loaded stimuli. We provide a summary of cognitive testing measures used in the assessment of visual-spatial and executive skills, which includes test domain descriptions as well as a comprehensive examination of social cognitive function in TS. This review concludes with a discussion of ecological interpretations regarding the meaning of cognitive deficits in TS at the individual level.

Converging pharmacological and genetic evidence indicates a role for steroid sulfatase in attention

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a complex neurodevelopmental disorder characterized by deficits in attention, increased motor impulsivity, and hyperactivity. Preliminary work in mice and humans has suggested the X-linked gene STS (which encodes the enzyme steroid sulfatase) as a mediator of attentional functioning and as a candidate gene for ADHD.

METHODS

The effects of modulating the murine steroid sulfatase axis pharmacologically (through administration of the substrate dehydroepiandrosterone sulfate [DHEAS], 0-40 mg/kg, or acute inhibition of the enzyme by COUMATE, 10mg/kg) or genetically (through loss of the gene in 39,X(Y)*O mice) were assayed using the 5-choice serial reaction time task (5-CSRTT) a test of visuospatial attention and response control, and a locomotor activity paradigm.

RESULTS

DHEAS administration improved 5-CSRTT performance under attentionally demanding conditions, whereas steroid sulfatase inhibition impaired accuracy under the same conditions. Loss of Sts expression constitutively throughout development in 39,X(Y)*O mice resulted in deficits in 5-CSRTT performance at short stimulus durations and reduced anticipatory responding. Neither the pharmacologic nor the genetic manipulations affected basic locomotor activity.

CONCLUSIONS

These data provide converging evidence indicating a role for steroid sulfatase in discrete aspects of attentional functioning and are suggestive of a role in motor impulsivity. The findings provide novel insights into the neurobiology of attention and strengthen the notion of STS as a candidate gene for the attentional component of ADHD.

Mathematics learning disabilities in girls with fragile X or Turner syndrome during late elementary school

The present study focuses on math and related skills among 32 girls with fragile X (n = 14) or Turner (n = 18) syndrome during late elementary school. Performance in each syndrome group was assessed relative to Full Scale IQ-matched comparison groups of girls from the general population (n = 32 and n = 89 for fragile X syndrome and Turner syndrome, respectively). Differences between girls with fragile X and their comparison group emerged on untimed arithmetic calculations, mastery of counting skills, and arithmetic problem verification accuracy. Relative to girls in the comparison group, girls with Turner syndrome did not differ on untimed arithmetic calculations or problem verification accuracy, but they had limited mastery of counting skills and longer response times to complete the problem verification task. Girls with fragile X or Turner syndrome also differed from their respective comparison groups on math-related abilities, including visual-spatial, working memory, and reading skills, and the associations between math and those related skills. Together, these findings support the notion that difficulty with math and related skills among girls with fragile X or Turner syndrome continues into late elementary school and that the profile of math and related skill difficulty distinguishes the two syndrome groups from each other.

X-monosomy effects on visuospatial attention in mice: a candidate gene and implications for Turner syndrome and attention deficit hyperactivity disorder

BACKGROUND

The loss of all, or part of an X chromosome, in Turner syndrome (TS, 45,XO) results in deficits in attentional functioning.

METHODS

Using a 39,XO mouse model, we tested the hypothesis that X-monosomy and/or parental origin of the single X chromosome may influence visuospatial attentional functioning in a 5-choice serial reaction time task (5-CSRTT).

RESULTS

Under attentionally demanding conditions 39,XO mice displayed impaired discriminative response accuracy and slowed correct reaction times relative to 40,XX mice; these deficits were alleviated in a version of the task with reduced attentional demands. Parental origin of the X did not affect performance of the 5-CSRTT. In contrast, the attentional phenotype was rescued in 40,XY*X mice possessing a single maternally inherited X chromosome and a small Y*X chromosome that comprises a complete pseudoautosomal region (PAR), and a small X-specific segment.

CONCLUSIONS

Our findings are consistent with an X-monosomy effect on attention and suggest the existence of X-linked gene(s) that escape X-inactivation, are present on the small Y*X chromosome and impact on attentional functioning; the strongest candidate gene is Sts, encoding steroid sulfatase. The data inform the TS literature and indicate novel genetic mechanisms that may be of general significance to the neurobiology of attention.

Ocular motor indicators of executive dysfunction in fragile X and Turner syndromes

Fragile X and Turner syndromes are two X-chromosome-related disorders associated with executive function and visual spatial deficits. In the present study, we used ocular motor paradigms to examine evidence that disruption to different neurological pathways underlies these deficits. We tested 17 females with fragile X, 19 females with Turner syndrome, and 40 females with neither disorder who comprised the comparison group. Group differences emerged for both the fragile X and Turner syndrome groups, each relative to the comparison group: Females with fragile X had deficits in generating memory-guided saccades, predictive saccades, and saccades made in the overlap condition of a gap/overlap task. Females with Turner syndrome showed deficits in generating memory-guided saccades, but not during either the predictive saccade or gap/overlap task. Females with Turner syndrome, but not females with fragile X, showed deficits in visually guided saccades and anti-saccades. These findings indicate that different brain regions are affected in the two disorders, and suggest that different pathways lead to the similar cognitive phenotypes described for fragile X and Turner syndromes.

The 39,XO mouse as a model for the neurobiology of Turner syndrome and sex-biased neuropsychiatric disorders

Turner syndrome (TS) is a developmental disorder most frequently arising from the loss of a complete X chromosome (karyotype 45,XO). The disorder is characterised by physiological abnormalities (notably short stature and ovarian dysfunction), emotional anomalies (including heightened anxiety) and by a neuropsychological profile encompassing deficits in visuospatial skills, memory, attention, social cognition and emotion recognition. Moreover, TS subjects are at significantly increased risk of developing attention deficit hyperactivity disorder (ADHD) and autism. At the neuroanatomical level, TS subjects display abnormalities across a number of brain structures, including the amygdala, hippocampus and orbitofrontal cortex. The TS phenotype arises due to reduced dosage of X-linked genes, and may also be modulated by parental origin of the single X chromosome. In this review, we discuss the utility of a mouse model of TS, the 39,XO mouse, in which the parental origin of the single X chromosome can be varied. This model provides the opportunity to investigate the effects of X-linked gene dosage/parent-of-origin effects on neurobiology in the absence of gross physiological abnormalities. Initial findings indicate that several features of the TS behavioural phenotype may be accurately recapitulated in the mouse. Furthermore, as X-linked gene dosage/imprinting can influence sex-specific neurobiology, investigations in the 39,XO mouse are also likely to offer insights into why certain neuropsychiatric disorders (including ADHD and autism) affect the sexes differently.

The cognitive phenotype of Turner syndrome: Specific learning disabilities

Global descriptors of the cognitive phenotype of Turner syndrome are well established and are thus commonly referred to. For example, Turner syndrome is a proposed etiology of the nonverbal learning disability - because of reported relative strengths in verbal skills, and relatively weaker nonverbal skills - particularly in arithmetic, select visuospatial skills, and processing speed. This profile is observed throughout and beyond the school age years. Reliance on this gross level description of the cognitive profile (e.g., nonverbal learning disability) may be helpful as a starting point when determining whether an individual with Turner syndrome has educational needs, but it carries limited practical significance when determining the specific nature of these needs. The limitations stem from the fact that the severity of the cognitive profile is highly variable among individuals with Turner syndrome; that the "nonverbal" difficulties are specific rather than widespread; and that any individual with Turner syndrome may also manifest cognitive characteristics independent of Turner syndrome. In view of the increased risk for specific cognitive difficulties, a detailed assessment prior to the onset of formal schooling (or at the time of diagnosis, when diagnosis occurs after 5 years of age) can play an important role in determining school readiness and potential need for educational support among individual girls with Turner syndrome.

Visuospatial skills and their association with math performance in girls with fragile X or Turner syndrome

The present study was designed to assess object identification ("what") and location ("where") skills among girls with fragile X or Turner syndrome and girls with neither disorder. Participants completed standardized subtests of visual perception and tasks of visuospatial "what" and "where" memory. Girls with fragile X had average performance on most object identification tasks, yet 53% failed to accurately recreate the gestalt of a design during the "where" memory task. Fewer than 7% of girls in the Turner or comparison group made this error. Girls with Turner syndrome had lower scores and longer response times on object perception tasks and had poorer recall of location for internal features of the design on the "where" memory task, relative to girls in the comparison or fragile X group. When limiting analyses to IQ-matched samples, correlations between math and visual perception tasks emerged, but only for girls with fragile X. These results reflect important differences between two cognitive phenotypes and have implications for the role of visuospatial processing in early math performance.

Mathematics learning disability in girls with Turner syndrome or fragile X syndrome

Two studies were carried out to examine the persistence (Study 1) and characteristics (Study 2) of mathematics learning disability (MLD) in girls with Turner syndrome or fragile X during the primary school years (ages 5-9 years). In Study 1, the rate of MLD for each syndrome group exceeded the rate observed in a grade-matched comparison group, although the likelihood of MLD persisting through the primary school years was comparable for all three groups. In Study 2, formal and informal math skills were compared across the syndrome groups, a normative group, and children from the normative group who had MLD. Few differences were observed between the Turner syndrome and normative groups. Despite having rote counting and number representation skills comparable to those in the normative group, girls with fragile X had difficulty with counting rules (e.g., cardinality, number constancy). However, this difficulty did not distingush them from the MLD group. Overall, counting skills appear to distinguish the Turner syndrome and fragile X groups, suggesting that the specificity of math deficits emerges earlier for fragile X than Turner syndrome.

Planning and problem solving: from neuropsychology to functional neuroimaging

This article provides an overview of recent research on human planning and problem solving. As an introduction, these two cognitive domains will be described and discussed from the perspective of experimental and cognitive psychology. The following sections will focus on the role of the prefrontal cortex in planning and problem solving and on disorders of these functions in patients with frontal-lobe lesions. Specific emphasis will be placed on the Tower of London task, a well established and widely used neuropsychological test of planning ability. We will present an overview of recent behavioural and neuroimaging studies that have employed the Tower of London task to draw specific conclusions about the likely neural and cognitive basis of planning function. Finally, we turn to a number of new directions and recent studies exploring different aspects of planning and problem solving and their association to related cognitive dimensions.

Increased prevalence of ADHD in Turner syndrome with no evidence of imprinting effects

BACKGROUND

Turner syndrome (TS) results from the loss of part or all of one X chromosome in females. It can result in short stature, various dysmorphic findings, and difficulties with psychosocial adjustment. Girls with TS have previously been found to exhibit increased levels of hyperactivity and inattention. However, no studies have assessed whether individuals with TS meet strict (DSM-IV) criteria for attention-deficit/hyperactivity disorder (ADHD).

OBJECTIVE

We looked at the prevalence of ADHD in girls with TS and evaluated the contribution of imprinting on cognitive performance (IQ) and ADHD.

METHODS

We tested 50 girls with TS for ADHD, IQ, academic performance, and parental origin of the X chromosome.

RESULTS

We report an 18-fold increase in the prevalence of ADHD in girls with TS (24%) compared with girls in the general population (1.3%) (p < .01) and a 4.8 fold increase when compared with boys and girls in the general population (5%) (p < .05). In contrast to previous reports, our molecular studies in females with 45,X also showed no association between IQ scores and the parental origin of the intact X chromosome.

CONCLUSIONS

We find an increased prevalence of ADHD in girls with TS but no evidence for imprinting effects for cognitive performance.

Assessing Executive Dysfunction in Girls With Fragile X or Turner Syndrome Using the Contingency Naming Test (CNT)

The aim of this study was to examine executive function (EF) skills in girls with fragile X or Turner syndrome, using the Contingency Naming Test (CNT). The CNT is a Stroop-like task involving a 1- or 2-attribute contingency rule. We predicted that girls with fragile X would make errors reflecting poor cognitive flexibility and working memory limitations. We predicted that girls with Turner syndrome would have sufficient cognitive flexibility to perform the CNT accurately, but would have difficulty with verbal inhibition and would thus make more self-corrections than girls in a comparison group. The hypotheses were partially supported: relative to their Full Scale IQ-matched comparison group, girls with fragile X or Turner syndrome were slower on the warm-up naming task; girls with fragile X made more errors on the 1-attribute task, and girls with Turner syndrome were less efficient on both the 1- and 2-attribute tasks, without making more self-corrections. These results support previous findings of executive dysfunction associated with fragile X or Turner syndrome. The results suggest that both low IQ and fragile X status contribute to working memory limitations in girls with fragile X and that EF inefficiency in girls with Turner syndrome is due to both working memory limitations and slower response times.

Effect of Turner's syndrome and X-linked imprinting on cognitive status: analysis based on pedigree data

The effects of a monosomy of either the maternally or paternally derived X chromosome in Turner's syndrome (TS) on general neurocognitive status and some executive abilities were assessed using the maximum likelihood estimators for pedigree data. This method increases the power of analysis by accounting for the effect of background heritable variation on a trait. The sample comprised 42 females with regular non-mosaic X monosomy and their non-affected relatives. Wechsler neurocognitive scores and several executive function tests' scores, including the Behaviour Dyscontrol Scale (BDS-2), the Wisconsin Card Sorting Test (WCST), and the Rey Complex Figure Test (RCFT), were considered in the analysis. Results showed a significant effect of TS on all Wechsler index and subtest scores, with greatest deficits observed in Arithmetic, Block Design, Object Assembly and Picture Arrangement, and on the total BDS, RCFT and WCST scores, regardless of parental origin of the single X-chromosome. Our data also showed a significantly higher effect of a paternally derived X chromosome in diminishing the performance on several Wechsler scores relevant to verbal skills, which might suggest X-linked imprinting loci relevant to these skills. Possible reasons for the inconsistency of the results concerning X-linked imprinting of cognitive loci using TS patients are discussed, and the relevance of pedigree analysis to future studies of this problem is emphasized.

An investigation of executive function abilities in adults with Prader-Willi syndrome

BACKGROUND

Prader-Willi syndrome (PWS) is a genetic disorder caused by the absence of expression of maternally imprinted genes on the long arm of chromosome 15 (15q 11-13). There are two main genetic sub-types: (1) deletion, caused by the absence of paternally derived genetic material; and (2) uniparental disomy (UPD), where two copies of maternally derived chromosome 15 are present. In addition to generally mild/borderline intellectual disability (ID) and the almost universal feature of hyperphagia, PWS is associated with high rates of behaviour problems including temper tantrums, compulsive behaviour, perseverative speech, skin picking and rigid thinking. The present study seeks to explore whether these behaviours are associated with relative deficits in executive function (EF), which comprises the set of non-automatic processes utilized by an individual when faced with a novel situation.

METHODS

Eighteen adult participants with a clinical diagnosis of PWS (12 with deletion sub-type, 6 with UPD) were recruited from a UK Health Service PWS clinic, and compared with 15 participants of similar age and verbal ability on a series of EF tasks and also Digit Span Forwards. An informant completed two ratings of behaviour, the Aberrant Behavior Checklist (ABC) and the Dysexecutive Questionnaire (DEX).

RESULTS

The PWS group had significantly higher scores on the ABC but not on the DEX. There were no significant differences between the whole PWS group and the comparison group on any of the EF tasks. The deletion sub-type group was significantly poorer at a non-executive task, Digit Span Forwards. There was an unexpected trend for the deletion sub-type group to show more efficient performance on a visuospatial planning task, the Tower of London (TOL), but this trend did not reach significance.

CONCLUSIONS

The lack of relative deficits in EF task performance does not support the hypothesis that EF differences could account for the high levels of behaviour problems found in PWS. Applying the Baddeley and Hitch model of working memory it is suggested that the PWS group have a relatively intact central executive and visuospatial sketchpad but a relative impairment in the phonological loop, perhaps relating to the capacity of the phonological store. This latter finding seems to be particularly salient for those with a deletion. As differences in EF ability were not found, it is suggested that a region of the brain involved in the modulation of emotion but not particularly with EF, the orbitofrontal cortex (OFC), may be implicated in the behaviour problems reported in PWS.

The Tower of London: the impact of instructions, cueing, and learning on planning abilities

The Tower of London (ToL) is a well-known test of planning ability, and commonly used for the purpose of neuropsychological assessment and cognitive research. Its widespread application has led to numerous versions differing in a number of respects. The present study addressed the question whether differences in instruction, cueing, and learning processes systematically influence ToL performance across five difficulty levels (three to seven moves). A total of 81 normal adults were examined in a mixed design with the between-subject factor instruction (online versus mental preplanning) and the within-subject factors cueing (cue versus non-cue test version) and learning processes (first block and second block). We also assessed general intelligence for further analyses of differences between instruction groups. In general, there was a significant main effect across the difficulty levels indicating that the rate of incorrect solutions increased with problem difficulty. The participants who were instructed to make full mental plans before beginning to execute movements (preplanning) solved significantly more problems than people who started immediately with task-related movements (online). As for the cueing conditions, participants with the minimum number of moves predetermined (cue) could solve more trials than people who were only instructed to solve the problems in as few moves as possible (non-cue). Participants generally increased performance in the second part of the test session. However, an interaction of presentation order of the cueing condition with learning indicated that people who started the tasks with the non-cue version showed significantly better performance in the following cue condition, while participants who started with the cue condition stayed at the same performance level for both versions. These findings suggest that instruction, cueing conditions, and learning processes are important determinants of ToL performance, and they stress the necessity of standardized application in research and clinical practice.

Executive skills in Klinefelter's syndrome

Executive skills are those involved in concept formation, problem solving, switching tasks, inhibiting inappropriate responses, initiating rapid and fluent responses, planning and sustained attention. Different patterns of disorder amongst these skills have been found in several developmental abnormalities including autism, attention deficit hyperactivity disorder (ADHD) and Turner's syndrome (TS). This study explored, for the first time, executive skills in children with Klinefelter's syndrome (KS), a sex chromosome abnormality in which there is one or more additional X-chromosomes. Intelligence in KS is normal but there is academic underachievement. A battery of executive tasks was administered, in a series of case studies, to three 10-year-old boys with KS and to controls matched for age, sex and intelligence. The results demonstrate that children with KS have impairments in executive skills. However, the pattern of impairment is task-specific. There is evidence from multiple tasks of impairment in inhibitory skills, for each case of KS. In contrast, concept formation, problem solving, task switching and speeded responding are normal. These results support theories that argue for distinct sub-components of executive skills within development that may develop relatively independently. The results have relevance for modelling both child and adult executive systems. They also confirm that an additional X-chromosome has highly selective effects upon the consequent cognitive phenotype seen in development.

The importance of head growth patterns in predicting the cognitive abilities and literacy skills of small-for-gestational-age children

This study evaluated the effects of head growth compromise beginning in utero and continuing, in some cases, through the first 9 months of life on the cognitive and literacy skills of school-age small-for-gestational-age (SGA) children. Seventy-one SGA children, aged 7 to 9 years (gestational ages, 24-41 weeks) and 16 full-term appropriate-for-gestational-age control children of comparable socioeconomic backgrounds and age at testing completed tests assessing intelligence, receptive language, working memory, problem solving, visual-motor integration, phonological awareness, reading, and spelling. SGA children were subdivided into head-growth pattern groups based on their head circumference at birth and at 9 months postterm. Analyses showed that SGA children with poor prenatal and postnatal head growth had the worst outcomes, followed by those with prenatal brain compromise, but good postnatal head growth. SGA children with preserved head growth in utero as well as good head growth after birth demonstrated the best outcomes, although spelling skills were deficient relative to full-term peers. The Verbal and Full Scale IQ ratings of the SGA children who had experienced brain compromise in utero declined significantly from 5 to 8 years of age. We conclude that mild intrauterine growth retardation (IUGR) has a minimal effect on the development of cognitive or academic abilities, providing that brain growth in utero is not affected. IUGR that slows brain growth in utero impairs the acquisition of some cognitive and academic abilities, even when followed by good catch-up head growth after birth, whereas poor brain growth in utero followed by little or no catch-up head growth results in widespread impairments. Findings highlight the limits to brain plasticity and emphasize the importance of optimal prenatal and postnatal brain growth.

Oral fluency and narrative production in children with Turner's syndrome

Despite good verbal skills, children with Turner's syndrome (TS) have been found to perform poorly on oral fluency tasks. Explanations for this impairment were explored in a study of 9-12-year-old children with TS. The children with TS were found, as expected, to have impaired levels of retrieval on initial letter fluency tasks, in comparison to their peers. Children with TS were also found to have receptive vocabularies which were significantly better than controls, indicating that the weak performance on oral fluency cannot be attributed to lower vocabulary levels. Naming skills were normal for children with TS, indicating that oral fluency scores cannot be attributed to generalised problems with lexical access. Analysis of the content of fluency performance indicated clusters of words within sub-categories which were of normal size but there were fewer switches between clusters than for controls and fewer returns to previously successful clusters. Additionally, a significantly larger proportion of the words generated were of low frequency (e.g. Assyrian, antediluvian) and the children with TS did not thereby show a normal frequency effect in word retrieval. One explanation is that these reflect abnormal action of executive language retrieval processes. Within narrative production, picture description was normal. However, in relation to narrative tasks, hypothesised to place greater executive demands, there was impairment which was significantly greater for narratives of yesterday than narratives of organising a party. This impairment within the narrative generation tasks could be attributable to a selective impairment within executive retrieval skills, or could represent an impairment in episodic memory or the executive processes involved in its retrieval.

Syntactic processing in Turner's syndrome

A significant controversy concerning language development in Turner's syndrome has been found. Whereas some authors have observed that girls with Turner's syndrome maintain their verbal abilities intact, others have reported significant differences in Wechsler Verbal IQ when compared with normal controls. However, little has been studied about the linguistic characteristics of these patients when using tests to evaluate different linguistic levels. With the aim of assessing syntactic processes, 15 patients with Turner's syndrome (aged 8 to 19 years) were compared with 15 healthy girls, matched by age, Wechsler Full-Scale IQ range, type of school (private or public), and school grade. A syntactic processing battery including 11 different subtests was developed. Compared with controls, the participants with Turner's syndrome obtained a fewer number of correct answers in most of the subtests and shorter latencies in some of them. We concluded that the subjects with Turner's syndrome have difficulties in using syntactic structures. It is suggested that some of these language difficulties are related to disturbances in using spatial-language relationships.

Representation and retrieval of arithmetical facts: developmental difficulties

One form of developmental difficulty with arithmetic affects the storage or retrieval of arithmetical facts, such as tables, which are required to implement arithmetical computations (Temple, 1991, 1994). Such difficulties may arise because of impairment in a specialized system for the storage of arithmetical facts or as a result of causally linked impairment in another cognitive domain. This study explored issues concerning the representation and retrieval of arithmetical facts in children with number fact disorders (NF) and in normal children, in particular the status of hypothesized linked impairments: short-term memory (STM) spans, counting skills, speed of speech, and speed of number fact and lexical retrieval. There was no evidence that NF children had weak STM spans on any span measure or that STM spans related to arithmetical fact skills. There was also no evidence that NF children had weak counting abilities or free counting speeds. The NF children were slower in speeded counting, which also correlated with number fact skill. The significance or not of this is discussed. The NF children were also slower than controls in speed of speech and on some measures of speed of access. However, the absence of correlation with number fact skill, the absence of generality across tasks, and the possibility that delayed speeds in fact retrieval reflect the use of alternative strategies, together suggest that the increased speeds are not causally linked to number fact skill. The results are consistent with modular accounts, in which there is a specialized system for the storage and retrieval of arithmetical facts.

An attempt to discriminate different types of executive functions in the Wisconsin Card Sorting Test

This study examined the roles of the phonological working memory and the central executive in the Wisconsin Card Sorting Test by altering the materials and the procedure of the task and using a dual-task design, in which cognitive abilities of normal participants were manipulated by performance of the secondary tasks selectively taxing the phonological loop or the central executive. The present study used three novel versions of the Wisconsin Card Sorting Test, namely the WCST-4 stimuli, the WCST-12-stimuli, and the WCST-12-stimuli-box, in all of which the participants were given the exact sorting criterion. So the tasks did not involve processes such as maintenance of inferences about the sorting criterion which would require phonological memory load. However, the tasks were assumed to require the executive process of response inhibition. In the WCST-4-stimuli condition no change was made to the WCST materials. In the other two conditions, relying on the assumption that the three-dimensional nature of the cards triggers inappropriate responses, unidimensional stimulus cards were used instead of the four normal three-dimensional WCST stimulus cards. The difference between these two conditions was that, in the WCST-12-stimuli-box condition, boxes were used to conceal the response cards previously sorted. The results supported Dunbar and Sussman's (1995) argument that some executive processes in the Wisconsin Card Sorting Test require the use of phonological store, and the present design was able to differentiate the type of executive functions that do not involve the use of a phonological loop from the ones that do. In addition, the results concerning manipulations of the visual aspects of the Wisconsin Card Sorting Test suggest that the three-dimensional nature of the WCST stimulus cards leads to an increase in the number of inappropriate responses produced with the executive secondary task interference.

Cognitive and behavioral characteristics of turner syndrome: exploring a role for ovarian hormones in female sexual differentiation

To better understand factors contributing to behavioral development, we studied patients with Turner syndrome (TS), a disorder typically marked by prenatal onset of ovarian dysfunction. We compared girls and women (ages 12 and up) with TS (n = 21) to matched controls (n = 21) in cognitive and motor skills, as well as sex-typed personality characteristics and activity preferences. Measures were categorized (based on prior studies) as showing an average male advantage (male-superior measures), female advantage (female-superior measures), or no sex difference (sex-neutral measures). It was hypothesized that, if gonadal function contributes to behavioral development, effects of this deficiency would be more prominent on sexually differentiated than sex-neutral measures and thus that patient-control differences would be most marked for measures that show sex differences. Our findings indicated that TS patients and controls differed more on cognitive and motor domains that show sex differences than on sex-neutral domains. Patients also had more "undifferentiated" personalities and showed reduced sex-typed interests and activities. Differing experiences, as indexed by interests and activities, did not explain the observed cognitive and motor differences. These results are consistent with a role for ovarian hormones acting on the brain to influence cognitive and behavioral development, although they do not rule out other possible interpretations.

Math learning disability and math LD subtypes: evidence from studies of Turner syndrome, fragile X syndrome, and neurofibromatosis type 1

The present study examined whether indicators of math learning disability are observed in 5- and 6-year-olds with neurofibromatosis type 1 (NF1) and in 5- to 6-year-old girls with Turner syndrome or fragile X syndrome. Data from 14 girls with Turner syndrome, 9 girls with fragile X syndrome, and 11 children with NF1 were compared to data from control participants matched on age, sex, IQ score, and grade level. The results indicate that girls with fragile X syndrome or Turner syndrome are significantly more likely to have specific math difficulties relative to their control group, with a larger effect size demonstrated by the group with Turner syndrome. Young children with NF1 had a heterogeneous profile not suggestive of specific math disability. The results are discussed in terms of their implications for understanding math disability subtypes and the identification of math difficulty in the early school years.

Preliminary evidence for a cognitive phenotype in Barth syndrome

Barth syndrome (BTHS) is a rare, X-linked, recessive disorder that affects almost exclusively males. It is characterized by short stature, cardioskeletal myopathy, cyclic neutropenia, increased excretion of 3-methylglutaconic acid in the urine, and moderate hypocholesterolemia. The objective of the present study was to assess whether BTHS presents with a cognitive phenotype. Preliminary data were collected from five kindergarten or first-grade boys with BTHS. An abbreviated psychoeducational test battery was administered to each boy, and parents of each boy completed standardized behavior rating scales. Data from 120 boys of similar age or grade level were used for one comparison group; a subset of this sample comprised a comparison group that was individually matched on age and grade level to one of the five boys with BTHS. Preliminary data reflect a higher incidence of cognitive difficulties in boys with BTHS relative to both comparison groups. Boys with BTHS had significantly lower visual spatial skills, but comparable reading-related skills, when compared with either group. Although based on a small sample size, the preliminary data presented in this work are the first indication of a cognitive phenotype associated with BTHS.

Mental planning and the Tower of London task

The Tower of London (TOL) task has been used extensively as a test of planning ability in neuropsychological patients and normal populations. Participants are asked to preplan mentally a sequence of moves to match a start set of discs to a goal, and then to execute the moves one by one. The mental preplanning stage has been identified as critical to efficient performance. The current experiments examined whether manipulations of mental preplanning influence performance on the TOL. In Experiment 1, the effect of different planning instructions was examined. Those told to make full mental plans spent considerably longer in planning than participants given no specific planning instructions, yet there was no effect of instruction condition on the efficiency of executing plans. Experiment 2 investigated whether people were able to plan mentally, by looking at their ability to identify intermediate states of an optimum mental plan. Results indicated that most individuals could make accurate preplans up to two subgoals ahead, but not three. However, making an efficient preplan did not result in better subsequent execution of moves to solve the TOL trial. It is concluded that people can make effective mental plans for a limited number of moves. However, on the TOL task, mental preplanning does not offer benefits in terms of quicker performance, or more accurate solution. The nature of planning in the TOL task is therefore questioned.

The role of memory in the Tower of London task

The Tower of London (TOL) task is widely used as a neuropsychological test of planning. Relatively little is known of the cognitive components of the task, and in particular the role of memory in performance. The current studies on normal adults looked at the role of verbal and spatial working memory in the TOL. The effects of verbal and visuospatial dual-task manipulations on TOL performance were examined in an experiment with 36 participants. Both verbal and visuospatial executive secondary tasks caused poorer performance on the TOL; however, concurrent articulatory suppression enhanced performance. The results suggest that executive and spatial components are important in the task, and raise questions about the role of preplanning in the TOL.

Cognitive neuropsychology and its application to children

Cognitive neuropsychology has been used successfully in the analysis of adult neuropsychological disorders in both verbal and nonverbal domains. When applied to children, it aims to construct models on the basis of functional lesions manifest within developing systems and provides a theoretical framework within which patterns of intact and deficient skills can be charted over time. These patterns constrain possible underlying models. In highlighting potential individual differences in the acquisition of skills and indicating intact skills within subjects, cognitive neuropsychology may also enable a precise description of the locus of difficulty and potential circumventory routes for remediation around it. The theoretical assumptions of cognitive neuropsychology and issues relevant to its methodology are discussed, including the terminology and principles of modularity, the significance of individual differences and the use of case studies, the dynamics of developing systems, current views on plasticity, and distinctions between developmental and acquired disorders. The application of cognitive neuropsychology to children is discussed in relation to three cognitive areas: face recognition disorders, language disorders and arithmetical disorders. These illustrate the similarities that there are between many developmental cognitive neuropsychological disorders and those seen in adults following brain injury. Models derived from studies of adults are helpful in enabling understanding of both face recognition disorders and arithmetical disorders in childhood. Within language systems, a variety of different types of disorder are evident, which not only relate to receptive and productive difficulties but differentially affect the core components of the language system. All of the disorders discussed illustrate the limitations of functional plasticity in development. In each case, there is not a generalised deficit resulting from degradation of capabilities independent of task requirements. Rather, there are focal and selective disorders which affect subcomponents of cognitive systems. In some cases, genetic factors may constrain compensatory mechanisms.

Reading skills in children with Turner's syndrome: an analysis of hyperplexia

Most neuropsychological studies of cases of chromosomal abnormalities report associations with disorders or disabilities. Studies of Turner's Syndrome (TS), in which their is functional absence of the information carried on the short arm of the second X chromosome, have emphasised disorders of spatial skill and potential abnormality of the parietal lobes or right hemisphere. In contrast, language skills have received little investigation despite suggestions by Shaffer (1962) of considerable verbal skill. This paper reports on an analysis of reading skill, in girls with TS. The girls with TS attained reading levels higher than those predicted on the basis of their age and intelligence. Moreover, they attained significantly higher reading levels than controls. Unlike many previous studies of hyperlexia, reading comprehension was also better than controls. The hyperlexia of the girls with TS was characterised by strength in both lexical reading systems, as assessed by the ability to read irregular words, and strength in alphabetical or phonological reading skills, as assessed by the ability to read long unfamiliar regular words. Hyperlexia need not therefore co-occur with comprehension difficulties nor need it reflect strength in only part of the reading system. In TS it appears to represent a genuine hyperdevelopment of a skill. The strength of reading skill counterbalances the spatial difficulties of a comparable sample of girls with TS (Temple and Carney, 1995), and with other verbal skills may potentially be exploited in remedial enterprises.