A reexamination of the visuospatial deficit in turner syndrome: Contributions of working memory

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.

Social skills and relationships in Turner syndrome

PURPOSE OF REVIEW

Summarize the literature on the social skills and relationships of women with Turner syndrome and examine the biological and psychological factors that may contribute to social interaction difficulties.

RECENT FINDINGS

Turner syndrome is often associated with impaired social-cognitive processing and executive function deficits. These cognitive abnormalities, together with a range of physical differences, may adversely affect social communication skills, which typically begin to impair quality of life during early adolescence. Parental accounts of their daughter's social skills frequently highlight interaction problems, both in the home and beyond; in contrast, self-reports are usually far more positive. At present, we do not know the extent to which such self-reports reflect a lack of social awareness, or a lack of concern about social difficulties.

SUMMARY

Women with Turner syndrome are likely to experience social interaction challenges (especially in friendships and relationships) across the lifespan. Providing appropriate guidance and support to them demands a better understanding of their strengths and weaknesses.

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.

Face perception in women with Turner syndrome and its underlying factors

Turner syndrome (TS) is a chromosomal condition that affects development in females. It is characterized by short stature, ovarian failure and other congenital malformations, due to a partial or complete absence of the sex chromosome. Women with TS frequently suffer from various physical and hormonal dysfunctions, along with impairments in visual-spatial processing and social cognition difficulties. Previous research has also shown difficulties in face and emotion perception. In the current study we examined two questions: First, whether women with TS, that are impaired in face perception, also suffer from deficits in face-specific processes. The second question was whether these face impairments in TS are related to visual-spatial perceptual dysfunctions exhibited by TS individuals, or to impaired social cognition skills. Twenty-six women with TS and 26 control participants were tested on various cognitive and psychological tests to assess visual-spatial perception, face and facial expression perception, and social cognition skills. Results show that women with TS were less accurate in face perception and facial expression processing, yet they exhibited normal face-specific processes (configural and holistic processing). They also showed difficulties in spatial perception and social cognition capacities. Additional analyses revealed that their face perception impairments were related to their deficits in visual-spatial processing. Thus, our results do not support the claim that the impairments in face processing observed in TS are related to difficulties in social cognition. Rather, our data point to the possibility that face perception difficulties in TS stem from visual-spatial impairments and may not be specific to faces.

The relationship between karyotype and cognitive functioning in Turner syndrome

Objectives: To examine the underlying cognitive abilities of girls with Turner syndrome, as well as to examine the nature, direction and extent of discrepancies between verbal and performance functioning.

Method: Standard tests of intellectual functions (WISC-R and WAIS-R) were administered to 28 girls with Turner syndrome. Subjects varied in age between one year and nine years.

Results: The findings indicate that there is strong, though not entirely consistent, tendency among Turner subjects to show depressed performance scores in comparison with their verbal scores. There was also a tendency toward lower levels of overall cognitive functioning among girls with the classic karyotype over those with mosaic karyotypes.

Conclusions: These findings are in keeping with international findings concerning the intellectual functioning, of girls with Turner syndrome. The findings support the view that the X chromosome is important in regulating the overall balance within the intellectual functioning between verbal and performance domains.

Reduced functional connectivity during working memory in Turner syndrome

Turner syndrome (TS) is a genetic disorder affecting females, resulting from the complete or partial absence of an X chromosome. The cognitive profile of TS shows relative strengths in the verbal domain and weaknesses in the procedural domain, including working memory. Neuroimaging studies have identified differences in the morphology of the parietal lobes, and white matter pathways linking frontal and parietal regions, as well as abnormal activation in dorsal frontal and parietal regions. Taken together these findings suggest that abnormal functional connectivity between frontal and parietal regions may be related to working memory impairments in TS, a hypothesis we tested in the present study. We scanned TS and typically developing participants with functional magnetic resonance imaging while they performed visuospatial and phonological working memory tasks. We generated a seed region in parietal cortex based on structural differences in TS and found that functional connectivity with dorsal frontal regions was reduced during working memory in TS. Finally, we found that connectivity was correlated with task performance in TS. These findings suggest that structural brain abnormalities in TS affect not only regional activity but also the functional interactions between regions and that this has important consequences for behavior.

Effects of treatment with oxandrolone for 4 years on the frequency of severe arithmetic learning disability in girls with Turner syndrome

OBJECTIVES

To study androgen treatment effects on arithmetic performance in girls with Turner syndrome.

STUDY DESIGN

Forty-four girls, ages 10 to 14 years at baseline, completed 4 years of treatment with oxandrolone (Ox) or placebo (Pl). All received growth hormone and estrogen replacement therapy. We assessed the number of girls with severe learning disability (LD, standard score <or=5(th) percentile) on measures of academic arithmetic and reading achievement (WRAT-3, arithmetic and reading), given yearly, and the WIAT numerical operations (NOS) and reading subtests, given at year 4.

RESULTS

On the WRAT-3 arithmetic, the frequency of severe arithmetic LD was similar in the Ox and Pl groups at baseline and at years 1 and 2. At years 3 and 4, fewer girls in the Ox than Pl group had a severe arithmetic LD (year 4: 0/22 vs 5/21, P = .02). On the WIAT NOS (year 4), fewer girls in the Ox than Pl groups had a severe arithmetic LD (3/21 vs 8/20, P = .09). WIAT NOS error analysis suggested that the improved performance in the Ox group was associated with better performance on multiplication and division (P < .01). The frequency of severe LD for the WRAT-3 reading was similar for the Ox and Pl groups (all years) and for the WIAT reading subtest (year 4).

CONCLUSIONS

Androgen treatment for 4 years in girls with Turner syndrome resulted in a small decrease in frequency of severe arithmetic LD, with no effect on reading LD.

Cerebral laterality in Turner syndrome: a critical review of the literature

Turner syndrome (TS) is a genetic disorder in females characterized by the complete or partial absence of one X chromosome. Its most consistent physical features include short stature and ovarian dysgenesis. TS individuals demonstrate a characteristic neurocognitive profile involving weaknesses in visuospatial processing. The hypothesis of defective right hemisphere specialization has been offered to explain the visuospatial deficits in TS. In contrast, an alternative explanation proposes a more uniform dysfunction of the left and right hemispheres, based on findings of symmetrical abnormalities. This article presents an overview of the two hypotheses, along with relevant findings on hemispheric specialization with respect to TS. The impact of the genetic and hormonal mechanisms on the neurocognitive profile of TS is also discussed and directions for further empirical research are identified.

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.

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.

Healthcare for adolescents with Turner syndrome

This review paper highlights important healthcare issues for adolescents with Turner Syndrome. Turner Syndrome potentially affects multiple organ systems including: cardiovascular, renal, endocrine, neurologic, gastrointestinal, skin, skeletal, auditory, and reproductive systems. Congenital and acquired cardiac defects remain the most significant health problem faced by women 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.

Visuospatial executive function in Turner syndrome: functional MRI and neurocognitive findings

Turner syndrome is a genetic disorder that results from an abnormal or missing X chromosome in females and is typically associated with impairments in visuospatial, but not verbal, information processing. These visuospatial processing impairments may be exacerbated with increased task demands, such as those engaged during working memory (WM). While previous studies have examined spatial WM function in Turner syndrome, none have directly compared the neural correlates of spatial and verbal WM processes across the encoding, maintenance and retrieval phases. We employed both neurocognitive assessments and functional MRI (fMRI) to examine the neural circuitry underlying both verbal and visuospatial WM functions in individuals with Turner syndrome and normal controls. We furthermore examined the vulnerability of task-related fMRI activation to distracters presented during WM maintenance. Fifteen healthy female volunteers and eight individuals with Turner syndrome performed a delayed-response WM task during fMRI scanning. Neurocognitive tests revealed impaired performance across both verbal and spatial domains in Turner syndrome, with greater impairment on tasks with WM demands. Frontoparietal regions in controls showed significantly sustained levels of activation during visuospatial WM. This sustained activation was significantly reduced in the group with Turner syndrome. Domain-specific activation of temporal regions, in contrast, did not differ between the two groups. Sensory distraction during the WM maintenance phase did not differentially alter frontoparietal activation between the two groups. The results reveal impaired frontoparietal circuitry recruitment during visuospatial executive processing in Turner syndrome, suggesting a significant role for the X chromosome in the development of these pathways.

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.

A review of neuropsychological and motor studies in Turner Syndrome

We reviewed the literature on Turner Syndrome (TS) from 1962 until March 2003 with respect to the following questions: Is there a consistent pattern of cognitive and/or motor dysfunction in TS girls and if so, is there an explanation for the disturbance? Many studies indicate that girls with TS have a disharmonic IQ profile: a verbal IQ that seems to be at a (nearly) normal level and a decreased PIQ. This profile remains into adulthood. Visual-spatial problems are mentioned most frequently and there is some evidence for a relationship to particular neuro-anatomical structures, hormonal dysfunction, and genotype. Although much less research has been done on motor performance in TS, there is clear evidence that it is disturbed too in TS. Many authors emphasize the interaction between somatic, psychological and social factors, but we did not find a clear theoretical framework explaining this relationship. We argue that there may be two independent problems: a visuospatial and a motor deficit possible related to specific genotypes and both have implications for functioning in daily life.

Child clinical/pediatric neuropsychology: some recent advances

The neuropsychological assets and deficits of several types of pediatric neurological disease, disorder, and dysfunction are described. These are examined from the perspective of the syndrome of nonverbal learning disabilities (NLD) and the "white matter model" designed to explain its complex manifestations. It is concluded that children with some of these diseases exhibit the NLD phenotype, whereas others do not. For the most part, the diseases in which the NLD phenotype is particularly evident are those wherein it has been demonstrated that perturbations of white matter (long myelinated fibers) are particularly prominent.

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.

Visuospatial working memory in Turner's syndrome

Turner's syndrome is a genetic disorder, specific to women, in which one of the X chromosomes is partially or completely deleted. This syndrome is associated with physical features such as short stature or failure in primary and secondary sexual development, together with a specific pattern of cognitive functions. It has been suggested that women affected by Turner's syndrome perform poorly in tasks measuring visuospatial abilities and have a verbal IQ significantly higher than performance IQ. Although this result has received strong empirical support, the nature of the visuospatial deficit is still unclear. Recent studies on visuospatial processes have highlighted that the underlying cognitive structure is more complex than previously suggested and several dissociations have been reported (e.g., visual vs spatial, sequential vs simultaneous, or passive vs active processes). In the present study we analyze in detail the characteristics of the visuospatial deficit associated with Turner's syndrome by presenting four young women with a comprehensive battery of tasks designed to tap all aspects of visuospatial working memory. Results confirm that Turner's syndrome is associated with a general visuospatial working memory deficit, but the pattern of performance of different cases can be different, with a greater emphasis on active visuospatial processes. and on either sequential or simultaneous spatial processes.

Female with autistic disorder and monosomy X (Turner syndrome): parent-of-origin effect of the X chromosome

We have ascertained and examined a patient with autistic disorder (AD) and monosomy X (Turner syndrome). The patient met Diagnostic and Statistical Manual of Mental Disorders (DSM-IV)/International Classification of Diseases (ICD-10) criteria for AD verified by the Autism Diagnostic Interview-Revised. The patient exhibited both social and verbal deficits and manifested the classical physical features associated with monosomy X. Skuse et al. [1997: Nature 387:705-708] reported three such cases of AD and monosomy X in their study of Turner syndrome and social cognition. They observed that monosomy X females with a maternally inherited X chromosome had reduced social cognition when compared with monosomy X females with a paternally inherited X chromosome. All three cases of AD and monosomy X were maternally inherited. Based on their data, they suggested that there was a gene for social cognition on the X chromosome that is imprinted and not expressed when the X chromosome is of maternal origin. Thus, we conducted parent-of-origin studies in our AD/monosomy X patient by genotyping X chromosome markers in the patient and her family. We found that the patient's X chromosome was of maternal origin. These findings represent the fourth documented case of maternal inheritance of AD and monosomy X and provide further support for the hypothesis that parent-of-origin of the X chromosome influences social cognition.

Distinctive patterns of memory function in subgroups of females with Turner syndrome: evidence for imprinted loci on the X-chromosome affecting neurodevelopment

X-monosomy is a form of Turner syndrome (TS) in which an entire X chromosome is missing. It is usually assumed that neuropsychological deficits in females with TS result from insufficient dosage of gene products from alleles on the sex chromosomes. If so, then parental origin of the single X chromosome should be immaterial. However, if there are imprinted genes on the X chromosome affecting brain development, neuropsychological development will depend on the parental origin of the single X chromosome. We contrasted verbal and visuospatial memory in females with a single paternal X chromosome (45,X(p)) and those with a single maternal X (45,X(m)). Neither group showed any impairment on immediate story recall; if anything, performance was above control levels. Groups did not differ on a measure of delayed recall. However, when delayed recall was considered after adjusting for level of immediate recall, 45,X(m) females showed enhanced verbal forgetting relative to controls over a delay. On the Rey figure, both groups were poor at copying the figure, but, after adjusting scores for initial copy score and strategy, only the 45,X(p) females showed disproportionate forgetting relative to controls. We propose there may be one or more imprinted genes on the X chromosome that affect the development of lateralised brain regions important for memory function.