Klinefelter's syndrome as a model of anomalous cerebral laterality: testing gene dosage in the X chromosome pseudoautosomal region using a DNA microarray

Sex chromosome trisomies are not associated with atypical lateralization for language

AIM

To test the hypothesis that sex chromosome trisomies (SCTs) are associated with reduced left lateralization for language.

METHOD

Using a cross-sectional design, language laterality was measured during an animation description task using functional transcranial Doppler ultrasonography. Data were available for 75 children with an SCT (47,XXX females [n=26], 47,XXY males [n=25], 47,XYY males [n=24]; mean age 11y 4mo [SD 3y 10mo]) and 132 comparison children with typical karyotypes (69 males, 63 females; mean age 9y 1mo [SD 1y 7mo]).

RESULTS

Lateralization for language did not differ between the SCT and comparison groups, either in mean laterality index or relative frequency of each laterality category. There were no differences when splitting the group with an SCT by trisomy. Handedness showed no group effects.

INTERPRETATION

Our data provide no evidence for disrupted lateralization for language in SCTs. The brain basis of the cognitive phenotype in SCTs is unlikely to be a failure of the left hemisphere to specialize for language, as previously suggested.

WHAT THIS PAPER ADDS

Children with a sex chromosome trisomy (SCT) have typically lateralized language. This disproves theories linking language problems to hemispheric specialization in SCTs.

Klinefelter Syndrome: Integrating Genetics, Neuropsychology, and Endocrinology

Although first identified over 70 years ago, Klinefelter syndrome (KS) continues to pose substantial diagnostic challenges, as many patients are still misdiagnosed, or remain undiagnosed. In fact, as few as 25% of patients with KS are accurately diagnosed and most of these diagnoses are not made until adulthood. Classic characteristics of KS include small testes, infertility, hypergonadothropic hypogonadism, and cognitive impairment. However, the pathophysiology behind KS is not well understood, although genetic effects are also thought to play a role. For example, recent developments in genetics and genomics point to a fundamental change in our understanding of KS, with global epigenetic and RNA expression changes playing a central role for the phenotype. KS is also associated with more general health markers, including higher morbidity and mortality rates and lower socioeconomic status (which likely affect both morbidity and mortality). In addition, hypogonadism is associated with greater risk of metabolic syndrome, type 2 diabetes, cardiovascular disease, breast cancer, and extragonadal germ cell tumors. Medical treatment typically focuses on testosterone replacement therapy (TRT), although the effects of this therapy have not been studied rigorously, and future studies need to evaluate the effects of TRT on metabolic risk and neurocognitive outcomes. This review presents a comprehensive interdisciplinary examination of recent developments in genetic, endocrine, and neurocognitive science, including the study of animal models. It provides a number of recommendations for improving the effectiveness of research and clinical practice, including neonatal KS screening programs, and a multidisciplinary approach to KS treatment from childhood until senescence.

Androgen Treatment Effects on Motor Function, Cognition, and Behavior in Boys with Klinefelter Syndrome

OBJECTIVES

To examine the effects of early low-dose androgen on motor, cognitive, and behavioral function in prepubertal boys with Klinefelter syndrome (47,XXY).

STUDY DESIGN

Double-blind trial of 84 boys, ages 4-12 years, randomized to oxandrolone (Ox; 0.06?mg/kg daily; n?=?43) or placebo (Pl; n?=?41) for 24 months. Standardized assessments were performed at baseline and every 12 months for 24 months evaluating motor, cognitive, and behavioral function.

RESULTS

The 24-month outcomes were better in the Ox vs. Pl group on 1 of 5 primary endpoints (motor function/strength): Bruininks Visual-Motor scale (P?=?.005), without significant differences between the 2 groups for the other 4 components. Secondary analyses suggested improvement in the Ox vs. Pl group in the anxiety/depression (P?=?.03) and social problems (P?=?.01) scales on the Child Behavior Checklist, anxiety (P?=?.04) on the Piers Harris Self Concept Scale, and interpersonal problems (P?=?.02) on the Children's Depression Inventory, without significant differences in hyperactive or aggressive behaviors.

CONCLUSIONS

This double-blind, randomized trial demonstrates that 24 months of childhood low-dose androgen treatment in boys with Klinefelter syndrome benefited 1 of 5 primary endpoints (visual-motor function). Secondary analyses demonstrated positive effects of androgen on aspects of psychosocial function (anxiety, depression, social problems), without significant effects on cognitive function, or hyperactive or aggressive behaviors.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00348946.

The role of genes, intelligence, personality, and social engagement in cognitive performance in Klinefelter syndrome

INTRODUCTION

The determinants of cognitive deficits among individuals with Klinefelter syndrome (KS) are not well understood. This study was conducted to assess the impact of general intelligence, personality, and social engagement on cognitive performance among patients with KS and a group of controls matched for age and years of education.

METHODS

Sixty-nine patients with KS and 69 controls were assessed in terms of IQ, NEO personality inventory, the Autism Spectrum Quotient (AQ) scale, and measures of cognitive performance reflecting working memory and executive function.

RESULTS

Patients with KS performed more poorly on memory and executive-function tasks. Patients with KS also exhibited greater neuroticism and less extraversion, openness, and conscientiousness than controls. Memory deficits among patients with KS were associated with lower intelligence, while diminished executive functioning was mediated by both lower intelligence and less social engagement.

CONCLUSION

Our results suggest that among patients with KS, memory deficits are principally a function of lower general intelligence, while executive-function deficits are associated with both lower intelligence and poorer social skills. This suggests a potential influence of social engagement on executive cognitive functioning (and/or vice-versa) among individuals with KS, and perhaps those with other genetic disorders. Future longitudinal research would be important to further clarify this and other issues discussed in this research.

Neuropsychology and socioeconomic aspects of Klinefelter syndrome: new developments

PURPOSE OF REVIEW

To summarize recent important studies on neuropsychology and epidemiology of Klinefelter syndrome. PubMed was searched for 'Klinefelter', 'Klinefelter's' and 'XXY' in titles and abstracts. Relevant studies were obtained and reviewed, as well as other articles selected by the authors.

RECENT FINDINGS

Klinefelter syndrome is the most common sex-chromosome disorder in humans, affecting one in 660 men. The key findings in Klinefelter syndrome are small testes, hypergonadotropic hypogonadism and cognitive impairment. Klinefelter syndrome scores significantly below education matched controls on a range of cognitive tests with verbal skills displaying the largest effects. Boys with Klinefelter syndrome are often in the need of speech therapy and many suffer from learning disability and may benefit from special education. New studies are elucidating aspects of cognitive functioning and suggesting that neuropsychological treatment may be of value. The socioeconomic status and educational level of Klinefelter syndrome is severely affected with many struggling to achieve any or only shorter education, resulting in low-income levels and early retirement. In addition, few become fathers and fewer live with a partner compared with controls. Medical treatment is mainly testosterone replacement therapy in order to alleviate acute and long-term consequences of hypogonadism, as well as, treating or preventing the frequent comorbidity.

SUMMARY

The neurocognitive phenotype of Klinefelter syndrome is being unraveled and the need for psychological and cognitive treatment in many cases is evident. The neurocognitive deficits no doubt influence the socioeconomic status of many Klinefelter syndrome patients, which is clearly inferior to age-matched controls.

Neuroanatomical correlates of Klinefelter syndrome studied in relation to the neuropsychological profile

Brain imaging in Klinefelter syndrome (47, XXY) (KS), a genetic disorder characterized by the presence of an extra X chromosome, may contribute to understanding the relationship between gene expression, brain structure, and subsequent cognitive disabilities and psychiatric disorders. We conducted the largest to date voxel-based morphometry study of 65 KS subjects and 65 controls matched for age and education and correlated these data to neuropsychological test scores. The KS patients had significantly smaller total brain volume (TBV), total gray matter volume (GMV) and total white matter volume (WMV) compared to controls, whereas no volumetric difference in cerebral spinal fluid (CSF) was found. There were no differences in TBV, GMV, WMV or CSF between testosterone treated KS (T-KS) and untreated KS (U-KS) patients. Compared to controls, KS patients had significantly decreased GMV bilaterally in insula, putamen, caudate, hippocampus, amygdala, temporal pole and frontal inferior orbita. Additionally, the right parahippocampal region and cerebellar volumes were reduced in KS patients. KS patients had significantly larger volumes in right postcentral gyrus, precuneus and parietal regions. Multivariate classification analysis discriminated KS patients from controls with 96.9% (p < 0.001) accuracy. Regression analyses, however, revealed no significant association between GMV differences and cognitive and psychological factors within the KS patients and controls or the groups combined. These results show that although gene dosage effect of having and extra X-chromosome may lead to large scale alterations of brain morphometry and extended cognitive disabilities no simple correspondence links these measures.

The Sex Chromosome Trisomy mouse model of XXY and XYY: metabolism and motor performance

Background

Klinefelter syndrome (KS), caused by XXY karyotype, is characterized by low testosterone, infertility, cognitive deficits, and increased prevalence of health problems including obesity and diabetes. It has been difficult to separate direct genetic effects from hormonal effects in human studies or in mouse models of KS because low testosterone levels are confounded with sex chromosome complement.

Methods

In this study, we present the Sex Chromosome Trisomy (SCT) mouse model that produces XXY, XYY, XY, and XX mice in the same litters, each genotype with either testes or ovaries. The independence of sex chromosome complement and gonadal type allows for improved recognition of sex chromosome effects that are not dependent on levels of gonadal hormones. All mice were gonadectomized and treated with testosterone for 3 weeks. Body weight, body composition, and motor function were measured.

Results

Before hormonal manipulation, XXY mice of both sexes had significantly greater body weight and relative fat mass compared to XY mice. After gonadectomy and testosterone replacement, XXY mice (both sexes) still had significantly greater body weight and relative fat mass, but less relative lean mass compared to XY mice. Liver, gonadal fat pad, and inguinal fat pad weights were also higher in XXY mice, independent of gonadal sex. In several of these measures, XX mice also differed from XY mice, and gonadal males and females differed significantly on almost every metabolic measure. The sex chromosome effects (except for testis size) were also seen in gonadally female mice before and after ovariectomy and testosterone treatment, indicating that they do not reflect group differences in levels of testicular secretions. XYY mice were similar to XY mice on body weight and metabolic variables but performed worse on motor tasks compared to other groups.

Conclusions

We find that the new SCT mouse model for XXY and XYY recapitulates features found in humans with these aneuploidies. We illustrate that this model has significant promise for unveiling the role of genetic effects compared to hormonal effects in these syndromes, because many phenotypes are different in XXY vs. XY gonadal female mice which have never been exposed to testicular secretions.

The protocadherin 11X/Y (PCDH11X/Y) gene pair as determinant of cerebral asymmetry in modern Homo sapiens

Annett's right-shift theory proposes that human cerebral dominance (the functional and anatomical asymmetry or torque along the antero-posterior axis) and handedness are determined by a single “right-shift” gene. Familial transmission of handedness and specific deviations of cerebral dominance in sex chromosome aneuploidies implicate a locus within an X–Y homologous region of the sex chromosomes. The Xq21.3/Yp11.2 human-specific region of homology includes the protocadherin 11X/Y (PCDH11X/Y) gene pair, which encode cell adhesion molecules subject to accelerated evolution following the separation of the human and chimpanzee lineages six million years ago. PCDH11X and PCDH11Y, differentially regulated by retinoic acid, are highly expressed in the ventricular zone, subplate, and cortical plate of the developing cerebral cortex. Both proteins interact with β-catenin, a protein that plays a role in determining axis formation and regulating cortical size. In this way, the PCDH11X/Y gene pair determines cerebral asymmetry by initiating the right shift in Homo sapiens.

Discovering tumor suppressor genes through genome-wide copy number analysis

Classical tumor suppressor gene discovery has largely involved linkage analysis and loss-of-heterozygosity (LOH) screens, followed by detailed mapping of relatively large chromosomal regions. Subsequent efforts made use of genome-wide PCR-based methods to detect rare homozygous deletions. More recently, high-resolution genomic arrays have been applied to cancer gene discovery. However, accurate characterization of regions of genomic loss is particularly challenging due to sample heterogeneity, the small size of deleted regions and the high frequency of germline copy number polymorphisms. Here, we review the application of genome-wide copy number analysis to the specific problem of identifying tumor suppressor genes.

48,XXYY, 48,XXXY and 49,XXXXY syndromes: not just variants of Klinefelter syndrome

Sex chromosome tetrasomy and pentasomy conditions occur in 1:18,000-1:100,000 male births. While often compared with 47,XXY/Klinefelter syndrome because of shared features including tall stature and hypergonadotropic hypogonadism, 48,XXYY, 48,XXXY and 49,XXXXY syndromes are associated with additional physical findings, congenital malformations, medical problems and psychological features. While the spectrum of cognitive abilities extends much higher than originally described, developmental delays, cognitive impairments and behavioural disorders are common and require strong treatment plans. Future research should focus on genotype-phenotype relationships and the development of evidence-based treatments.

CONCLUSION

The more complex physical, medical and psychological phenotypes of 48,XXYY, 48,XXXY and 49,XXXXY syndromes make distinction from 47,XXY important; however, all of these conditions share features of hypergonadotropic hypogonadism and the need for increased awareness, biomedical research and the development of evidence-based treatments.

The cognitive phenotype in Klinefelter syndrome: a review of the literature including genetic and hormonal factors

Klinefelter syndrome (KS) or 47,XXY occurs in approximately 1 in 650 males. Individuals with KS often present with physical characteristics including tall stature, hypogonadism, and fertility problems. In addition to medical findings, the presence of the extra X chromosome can lead to characteristic cognitive and language deficits of varying severity. While a small, but significant downward shift in mean overall IQ has been reported, the general cognitive abilities of patients with KS are not typically in the intellectual disability range. Most studies support that males with KS have an increased risk of language disorders and reading disabilities. Results of other studies investigating the relationship between verbal and nonverbal/spatial cognitive abilities have been mixed, with differing results based on the age and ascertainment method of the cohort studied. Executive function deficits have been identified in children and adults with KS, however, the research in this area is limited and further investigation of the neuropsychological profile is needed. In this article, we review the strengths and weaknesses of previous cognitive and neuropsychological studies in males with KS in childhood and adulthood, provide historical perspective of these studies, and review what is known about how hormonal and genetic factors influence cognitive features in 47,XXY/KS.

Allelic genome structural variations in maize detected by array comparative genome hybridization

DNA polymorphisms such as insertion/deletions and duplications affecting genome segments larger than 1 kb are known as copy-number variations (CNVs) or structural variations (SVs). They have been recently studied in animals and humans by using array-comparative genome hybridization (aCGH), and have been associated with several human diseases. Their presence and phenotypic effects in plants have not been investigated on a genomic scale, although individual structural variations affecting traits have been described. We used aCGH to investigate the presence of CNVs in maize by comparing the genome of 13 maize inbred lines to B73. Analysis of hybridization signal ratios of 60,472 60-mer oligonucleotide probes between inbreds in relation to their location in the reference genome (B73) allowed us to identify clusters of probes that deviated from the ratio expected for equal copy-numbers. We found CNVs distributed along the maize genome in all chromosome arms. They occur with appreciable frequency in different germplasm subgroups, suggesting ancient origin. Validation of several CNV regions showed both insertion/deletions and copy-number differences. The nature of CNVs detected suggests CNVs might have a considerable impact on plant phenotypes, including disease response and heterosis.

Cognitive mechanisms underlying disorganization of thought in a genetic syndrome (47,XXY)

Because of the risk for development of psychopathology such as psychotic symptoms, it has been suggested that studying men with the XXY karyotype may help in the search for underlying cognitive, neural and genetic mechanisms. The aim of this study was to identify cognitive mechanisms that may contribute to disorganization of thought in XXY men. A group of 24 XXY men and two non-clinical control groups (N=20, N=18) participated in the study. The level of disorganization of thought was measured using the Schizotypal Personality Questionnaire. We assessed IQ, lateralization of verbal information processing and executive functions including inhibition and mental flexibility. XXY men with high levels of disorganization showed more severe impairments in mental flexibility and inhibition as compared to non-clinical controls and other XXY men. This subgroup also showed a stronger reduction in lateralization of verbal information processing. IQ measures did not differentiate XXY men with high versus low levels of disorganization. These findings indicate that executive impairments in the domains of inhibition and mental flexibility might play a role in the increased vulnerability for disorganized thought in the XXY group. Reduced lateralization of verbal information processing points to non-optimal cerebral specialization in the XXY group, especially in XXY men with high levels of disorganization. This fits with deficits in brain functions most vulnerable to such maturational disruptions, i.e. executive dysfunctions. Our findings are in line with those reported for schizophrenia patients with thought disorder. We speculate that the underlying mechanisms of thought disorder probably are deficit specific rather than disorder specific.

The influence of sex chromosome aneuploidy on brain asymmetry

The cognitive deficits present in individuals with sex chromosome aneuploidies suggest that hemispheric differentiation of function is determined by an X-Y homologous gene [Crow (1993); Lancet 342:594-598]. In particular, females with Turner's syndrome (TS) who have only one X-chromosome exhibit deficits of spatial ability whereas males with Klinefelter's syndrome (KS) who possess a supernumerary X-chromosome are delayed in acquiring words. Since spatial and verbal abilities are generally associated with right and left hemispheric function, such deficits may relate to anomalies of cerebral asymmetry. We therefore applied a novel image analysis technique to investigate the relationship between sex chromosome dosage and structural brain asymmetry. Specifically, we tested Crow's prediction that the magnitude of the brain torque (i.e., a combination of rightward frontal and leftward occipital asymmetry) would, as a function of sex chromosome dosage, be respectively decreased in TS women and increased in KS men, relative to genotypically normal controls. We found that brain torque was not significantly different in TS women and KS men, in comparison to controls. However, TS women exhibited significantly increased leftward brain asymmetry, restricted to the posterior of the brain and focused on the superior temporal and parietal-occipital association cortex, while KS men showed a trend for decreased brain asymmetry throughout the frontal lobes. The findings suggest that the number of sex chromosomes influences the development of brain asymmetry not simply to modify the torque but in a complex pattern along the antero-posterior axis.

Molekulare Karyotypisierung in der klinischen Anwendung

In den vergangenen Jahren hat sich die Anwendung der Mikroarraytechnologie für die Detektion von putativ pathologischen submikroskopischen Copy-Number-Variationen (CNV) einen festen Platz in der molekularen Zytogenetik erobert. Neben der Identifikation somatischer CNV in der onkologischen Diagnostik wird diese Technologie nunmehr für die Analyse von konstitutionellen CNV bei Patienten mit mentaler Retardierung genutzt. Arraybasierte genomische Hybridisierungen zeigen eine deutliche Verbesserung zu der bereits seit Jahren angewendeten komparativen genomischen Hybridisierung (CGH). Insbesondere weisen die dazugehörigen Technologien eine verbesserte Auflösung von weniger als 100 kb für Deletionen und Duplikationen auf und haben damit eine deutlich bessere Aufklärungsrate von Krankheiten mit Behinderungen ungeklärter Ursache. In einigen Zentren gehört die Arraytechnologie daher bereits zur Routinetechnologie der Syndromabklärung. Im vorliegenden Beitrag soll deshalb auch auf die Gemeinsamkeiten bzw. Unterschiede der verschiedenen Basistechnologien der Arraytechnik eingegangen werden.

Genomic imprinting in the development and evolution of psychotic spectrum conditions

I review and evaluate genetic and genomic evidence salient to the hypothesis that the development and evolution of psychotic spectrum conditions have been mediated in part by alterations of imprinted genes expressed in the brain. Evidence from the genetics and genomics of schizophrenia, bipolar disorder, major depression, Prader-Willi syndrome, Klinefelter syndrome, and other neurogenetic conditions support the hypothesis that the etiologies of psychotic spectrum conditions commonly involve genetic and epigenetic imbalances in the effects of imprinted genes, with a bias towards increased relative effects from imprinted genes with maternal expression or other genes favouring maternal interests. By contrast, autistic spectrum conditions, including Kanner autism, Asperger syndrome, Rett syndrome, Turner syndrome, Angelman syndrome, and Beckwith-Wiedemann syndrome, commonly engender increased relative effects from paternally expressed imprinted genes, or reduced effects from genes favouring maternal interests. Imprinted-gene effects on the etiologies of autistic and psychotic spectrum conditions parallel the diametric effects of imprinted genes in placental and foetal development, in that psychotic spectrum conditions tend to be associated with undergrowth and relatively-slow brain development, whereas some autistic spectrum conditions involve brain and body overgrowth, especially in foetal development and early childhood. An important role for imprinted genes in the etiologies of psychotic and autistic spectrum conditions is consistent with neurodevelopmental models of these disorders, and with predictions from the conflict theory of genomic imprinting.

Characterization of hemizygous deletions in citrus using array-comparative genomic hybridization and microsynteny comparisons with the poplar genome

BACKGROUND

Many fruit-tree species, including relevant Citrus spp varieties exhibit a reproductive biology that impairs breeding and strongly constrains genetic improvements. In citrus, juvenility increases the generation time while sexual sterility, inbreeding depression and self-incompatibility prevent the production of homozygous cultivars. Genomic technology may provide citrus researchers with a new set of tools to address these various restrictions. In this work, we report a valuable genomics-based protocol for the structural analysis of deletion mutations on an heterozygous background.

RESULTS

Two independent fast neutron mutants of self-incompatible clementine (Citrus clementina Hort. Ex Tan. cv. Clemenules) were the subject of the study. Both mutants, named 39B3 and 39E7, were expected to carry DNA deletions in hemizygous dosage. Array-based Comparative Genomic Hybridization (array-CGH) using a Citrus cDNA microarray allowed the identification of underrepresented genes in these two mutants. Subsequent comparison of citrus deleted genes with annotated plant genomes, especially poplar, made possible to predict the presence of a large deletion in 39B3 of about 700 kb and at least two deletions of approximately 100 and 500 kb in 39E7. The deletion in 39B3 was further characterized by PCR on available Citrus BACs, which helped us to build a partial physical map of the deletion. Among the deleted genes, ClpC-like gene coding for a putative subunit of a multifunctional chloroplastic protease involved in the regulation of chlorophyll b synthesis was directly related to the mutated phenotype since the mutant showed a reduced chlorophyll a/b ratio in green tissues.

CONCLUSION

In this work, we report the use of array-CGH for the successful identification of genes included in a hemizygous deletion induced by fast neutron irradiation on Citrus clementina. The study of gene content and order into the 39B3 deletion also led to the unexpected conclusion that microsynteny and local gene colinearity in this species were higher with Populus trichocarpa than with the phylogenetically closer Arabidopsis thaliana. This work corroborates the potential of Citrus genomic resources to assist mutagenesis-based approaches for functional genetics, structural studies and comparative genomics, and hence to facilitate citrus variety improvement.

Effects of an extra X chromosome on language lateralization: an fMRI study with Klinefelter men (47,XXY)

De novo occurring genetic variations provide an opportunity to study the effects of genes on structure and function of the brain. The presence of an extra X chromosome in men (XXY karyotype) has been associated with language deficits. Recently, schizophrenia spectrum traits have been observed in XXY men, which is of interest as language deficits are prominent in schizophrenia. One possible neural mechanism underlying these deficits is reduced hemispheric specialization for language. However, there has been no study of brain activity patterns during language processing in XXY men. Also, it remains unclear whether reduced language lateralization may be related to mental functioning in these men. We used functional Magnetic Resonance Imaging (fMRI) to study language lateralization in 15 XXY men as compared to 14 control men. We used a psychiatric interview and a schizotypy questionnaire to explore the relation between language lateralization and mental functioning in these men, with special interest in disorganization of thought and language. Compared to controls, the XXY group showed reduced hemispheric specialization for language, which was due to decreased functional asymmetry in the superior temporal gyrus (STG) and the supramarginal gyrus (part of Wernicke's area). Reduced lateralization in the STG correlated significantly with disorganization traits. These findings suggest the X chromosome may be involved in hemispheric specialization for language. Moreover, reduced hemispheric specialization for language processing in the superior temporal gyrus may have important consequences for mental functioning, as it was associated with disorganization of thought and language as seen in the schizophrenia spectrum.

Identification of origin of unknown derivative chromosomes by array-based comparative genomic hybridization using pre- and postnatal clinical samples

Microarray-based comparative genomic hybridization (array CGH) is a high-resolution and comprehensive method for detecting both genome-wide and chromosome-specific copy-number imbalance. We have developed an array CGH analysis system (consisting of an array CGH chip plus its exclusive analysis software) for constitutional genetic diagnosis and have evaluated the suitability of our system for molecular diagnosis using pre- and postnatal clinical samples. In a blind study, each of the 264 sample karyotypes identified by array CGH analysis was consistent with that identified by traditional karyotype analysis--with one exception, case (47, XXX)--and we were able to identify origins, such as small supernumerary marker chromosomes, which cannot be determined by conventional cytogenetics. We also acquired very accurate, fast and reliable results using a diminutive amount of clinical samples. Taken together, the array CGH platform developed in this study is a rapid, powerful and sensitive technology for pre- and postnatal diagnosis using a very small amount of clinical sample.

The impact of array genomic hybridization on mental retardation research: a review of current technologies and their clinical utility

Our understanding of the causes of mental retardation is benefiting greatly from whole-genome scans to detect submicroscopic pathogenic copy number variants (CNVs) that are undetectable by conventional cytogenetic analysis. The current method of choice for performing whole-genome scans for CNVs is array genomic hybridization (AGH). Several platforms are available for AGH, each with its own strengths and limitations. This review discusses considerations that are relevant to the clinical use of whole-genome AGH platforms for the diagnosis of pathogenic CNVs in children with mental retardation. Whole-genome AGH studies are a maturing technology, but their high diagnostic utility assures their increasing use in clinical genetics.

Autism spectrum disorder and Klinefelter syndrome

BACKGROUND

Autism is a severe handicapping disorder of early childhood characterized by a distinct pattern of social and communication impairment with rigid ritualistic interests. In about 10-25% of cases, it is associated with known medical conditions. Population-based studies of autism have found that Klinefelter's syndrome (KS), a common chromosome abnormality, is sometimes associated with autism. However, few detailed case descriptions of patients with KS and autism have not been published.

CASE REPORT

In this paper, we describe the occurrence of autistic features in two cases of Klinefelter syndrome, one with the typical XXY karyotype and the other with the XXYY variant.

CONCLUSION

Autistic features may be more common in persons with Klinefelter syndrome than generally believed. We propose that all patients with KS should be screened for the presence of autism.

Heritability and linkage analysis of hand, foot, and eye preference in Mexican Americans

Functional lateralities are of interest due to their relationship with cerebral lateralisation and language development. However, genes influencing sidedness remain elusive. We measured direction and consistency of hand, foot, and eye preference in 584 Mexican-Americans from families participating in the San Antonio Family Diabetes/Gallbladder Study. Using maximum-likelihood-based variance components methods, we estimated weak (.11 <or= h2<or=.17) but significant heritability for foot preference, eye preference, several hand preferences (writing, drawing, throwing, using scissors, using spoon, striking match), and a composite hand preference trait. Self-reported handedness was significantly heritable (h2=.57), whereas hand preference for opening a box or using a toothbrush or knife was not. Many trait pairs had significant genetic correlations, and all had significant environmental correlations. Using genome-wide multipoint linkage screens using 382 highly informative autosomal STR markers, we identified suggestive linkage signals for drawing (LOD 2.10) and writing (LOD 2.00) hand preference on chromosome 12q21-23, in the region flanked by markers D12S1300 and PAH. A suggestive signal (LOD 2.46) for eye preference occurred on chromosome 22pter, near marker D22S420. No obvious candidate genes occur in these regions. Our results indicate that genes are an important component of side preferences, and suggest chromosomal regions for further investigation.

XXY (Klinefelter syndrome): a pediatric quantitative brain magnetic resonance imaging case-control study

OBJECTIVE

An extra X chromosome in males (XXY), known as Klinefelter syndrome, is associated with characteristic physical, cognitive, and behavioral features of variable severity. The objective of this study was to examine possible neuroanatomical substrates of these cognitive and behavioral features during childhood and adolescence.

METHODS

MRI brain scans were acquired for 42 XXY and 87 healthy XY age-matched control males. We compared these 2 groups on regional brain volumes and cortical thickness.

RESULTS

Total cerebral volume and all lobar volumes except parietal white matter were significantly smaller in the XXY group, whereas lateral-ventricle volume was larger. Consistent with the cognitive profile, the cortex was significantly thinner in the XXY group in left inferior frontal, temporal, and superior motor regions.

CONCLUSION

The brain-imaging findings of preferentially affected frontal, temporal, and motor regions and relative sparing of parietal regions are consistent with observed cognitive and behavioral strengths and weaknesses in XXY subjects.

WebaCGH: an interactive online tool for the analysis and display of array comparative genomic hybridisation data

Gene copy number variations occur both in normal cells and in numerous pathologies including cancer and developmental diseases. Array comparative genomic hybridisation (aCGH) is an emerging technology that allows detection of chromosomal gains and losses in a high-resolution format. When aCGH is performed on cDNA and oligonucleotide microarrays, the impact of DNA copy number on gene transcription profiles may be directly compared. We have created an online software tool, WebaCGH, that functions to (i) upload aCGH and gene transcription results from multiple experiments; (ii) identify significant aberrant regions using a local Z-score threshold in user-selected chromosomal segments subjected to smoothing with moving averages; and (iii) display results in a graphical format with full genome and individual chromosome views. In the individual chromosome display, data can be zoomed in/out in both dimensions (i.e. ratio and physical location) and plotted features can have 'mouse over' linking to outside databases to identify loci of interest. Uploaded data can be stored indefinitely for subsequent retrieval and analysis. WebaCGH was created as a Java-based web application using the open-source database MySQL.

AVAILABILITY

WebaCGH is freely accessible at http://129.43.22.27/WebaCGH/welcome.htm

CONTACT

Xiaolin Wu (forestwu@mail.nih.gov) or Ulises Urzúa (uurzua@med.uchile.cl).

Puberty-related influences on brain development

Puberty is a time of striking changes in cognition and behavior. To indirectly assess the effects of puberty-related influences on the underlying neuroanatomy of these behavioral changes we will review and synthesize neuroimaging data from typically developing children and adolescents and from those with anomalous hormone or sex chromosome profiles. The trajectories (size by age) of brain morphometry differ between boys and girls, with girls generally reaching peak gray matter thickness 1-2 years earlier than boys. Both boys and girls with congenital adrenal hyperplasia (characterized by high levels of intrauterine testosterone), have smaller amygdala volume but the brain morphometry of girls with CAH did not otherwise significantly differ from controls. Subjects with XXY have gray matter reductions in the insula, temporal gyri, amygdala, hippocampus, and cingulate-areas consistent with the language-based learning difficulties common in this group.

Methylation of two Homo sapiens-specific X-Y homologous genes in Klinefelter's syndrome (XXY)

An increased incidence of psychiatric and structural brain abnormalities in individuals with Klinefelter syndrome (KS, 47 XXY) could be due to the presence of extra copies of X-Y homologous genes that escape X inactivation. Of particular interest are the two brain-expressed genes Protocadherin11XY (PCDH11XY) and the Synaptobrevin-like gene (SYBL1) which have been duplicated from the X chromosome to the Y chromosome to give X-Y homologous gene pairs that are specific to modern humans. We examined the DNA of KS individuals reported recently by DeLisi et al. 2005 and determined the parental origin of the X alleles, the degree of skewed X inactivation and investigated the CpG island methylation status of PCDH11XY and SYBL1 by bisulphite sequencing and quantification of methylated HpaII sites. We used a novel method for quantification of unmethylated CpGs with the restriction enzyme McrBC which cuts methylated but not unmethylated CpGs. The results showed that KS individuals have two methylated and one unmethylated SYBL1 allele whereas PCDH11XY is unmethylated and escapes X inactivation on the extra X chromosome. Overexpression of PCDH11XY in KS is probable and variable escape from inactivation of this Homo sapiens-specific gene could account for some abnormalities in KS. The origin of the parental alleles or their preferential X inactivation was not associated with psychotic symptoms.

The structural brain correlates of cognitive deficits in adults with Klinefelter's syndrome

CONTEXT

Adults with Klinefelter's syndrome (KS) are known to present disturbances of language skills and delayed learning abilities.

OBJECTIVES

The aim of this study was to assess brain morphometry in KS and to correlate eventual volumetric changes with performance on neuropsychological tests.

PATIENTS

Patients included 18 KS adults and 20 age-matched controls.

METHODS

All participants underwent prospectively double-spin-echo brain magnetic resonance imaging and neuropsychological testing of verbal and nonverbal domains. On the axial stack of magnetic resonance imaging slices, regional brain volumes were measured either by automated segmentation (full brain, total cerebrospinal fluid, and ventricular volume) or manual drawing with help of a neuroanatomy atlas (frontal, temporal, and parietal lobes, gray matter component of the lobes, cerebellar hemispheres, and hippocampal complexes).

RESULTS

KS patients performed significantly lower than controls on language-related tasks exploring verbal processing speed and verbal executive function. They were diagnosed with significant enlargement of ventricular volume and bilateral reduction of cerebellar hemispheres. Furthermore, after separation of participants according to handedness and after correction of regional brain volumes for atrophy, a significant reduction of left temporal lobe volume was found in KS compared with controls. Ventricular volume was inversely correlated with cognitive function, whereas left temporal lobe volume was positively correlated with language-related tasks.

CONCLUSION

This study hypothesizes that supernumerary X-chromosome and/or congenital hypogonadism provoke structural alterations in the subcortical pathways involved in language processing, thus providing a neurobiological substrate for cognitive deficits in KS.

Differences in the pattern of X-linked gene expression between fetal bovine muscle and fibroblast cultures derived from the same muscle biopsies

The sex determination system in mammals creates an imbalance between males and females in the number of X chromosomes. This imbalance is compensated through transcriptional silencing of one of the two X chromosomes in female diploid cells by epigenetic modifications. Although common for mammals, X inactivation shows marked species-specific differences in mechanisms and end results, and provides a unique opportunity to study epigenetic regulation of gene expression. The aim of the present study was to establish the expression pattern of selected X-linked genes in bovine fetal muscle tissue and muscle fibroblast cultures in order to follow possible modifications at the transcriptional level attributable to in vitro culture. We used heterologous cDNA microarray hybridization and quantitative real-time PCR to study the pattern of expression of X-linked genes including SLC25A6, GAB3, MECP2, RPS4X, JARID1C, UBE1, BIRC4 and SLC16A2. Quantitative real-time PCR analysis in fetal bovine muscle showed higher transcript levels in females for all X-linked genes tested with the exception of SLC25A6, with differences being significant for RPS4X, JARID1C and UBE1. The expression in fibroblast cultures derived from the same samples differed, with significantly higher levels for UBE1, GAB3 and BIRC4, while the rest of the panel of X-linked genes remained unchanged. The changed expression pattern in vitro, probably reflecting modifications in the epigenetic mechanisms that regulate transcriptional activity and gene silencing in X inactivation, has important implications for the advancement of new biotechnologies such as somatic cell nuclear transfer and stem cell therapy.

Klinefelter's syndrome (XXY) as a genetic model for psychotic disorders

Males with an extra-X chromosome (Klinefelter's syndrome) frequently, although not always, have an increased prevalence of psychiatric disturbances that range from attention deficit disorder in childhood to schizophrenia or severe affective disorders during adulthood. In addition, they frequently have characteristic verbal deficits. Thus, examining brain magnetic resonance imaging (MRI) scans of these individuals may yield clues to the influence of X chromosome genes on brain structural variation corresponding to psychiatric and cognitive disorders. Eleven adult XXY and 11 age matched XY male controls were examined with a structured psychiatric interview, battery of cognitive tests, and an MRI scan. Ten of eleven of the XXY men had some form of psychiatric disturbance, four of whom had auditory hallucinations compared with none of the XY controls. Significantly smaller frontal lobe, temporal lobe, and superior temporal gyrus (STG) cortical volumes were observed bilaterally in the XXY men. In addition, diffusion tensor imaging (DTI) of white matter integrity resulted in four regions of reduced fractional anisotropy (FA) in XXY men compared with controls, three in the left hemisphere, and one on the right. These correspond to the left posterior limb of the internal capsule, bilateral anterior cingulate, and left arcuate bundle. Specific cognitive deficits in executive functioning attributable to frontal lobe integrity and verbal comprehension were noted. Thus, excess expression of one or more X chromosome genes influences both gray and white matter development in frontal and temporal lobes, as well as white matter tracts leading to them, and may in this way contribute to the executive and language deficits observed in these adults. Future prospective studies are needed to determine which gene or genes are involved and whether their expression could be modified with appropriate treatments early in life. Brain expressed genes that are known to escape inactivation on extra-X chromosomes would be prime candidates.

Genomic microarrays in the spotlight

Microarray-based comparative genomic hybridization (array-CGH) has emerged as a revolutionary platform, enabling the high-resolution detection of DNA copy number aberrations. In this article we outline the use and limitations of genomic clones, cDNA clones and PCR products as targets for genomic microarray construction. Furthermore, the applications and future aspects of these arrays for DNA copy number analysis in research and diagnostics, epigenetic profiling and gene annotation are discussed. These recent developments of genomic microarrays mark only the beginning of a new generation of high-resolution and high-throughput tools for genetic analysis.

Functional neuroimaging provides evidence of anomalous cerebral laterality in adults with Klinefelter's syndrome

This study aimed to characterize cerebral perfusion in men with Klinefelter's syndrome, known to present specific deficits in language, using (99m)Tc- hexamethylpropylene-amine-oxime scintigraphy and Talairach normalization. While a perfusion asymmetry toward the left hemisphere was found in controls, perfusion was mostly symmetrical in Klinefelter patients in the upper temporal and lower parietal areas. Scores on verbal tests were inversely correlated with perfusion changes, providing neurobiological substrate of anomalous cerebral laterality.

DNA microarrays: translation of the genome from laboratory to clinic

As the complete sequences of human and other mammalian genomes become available we are faced with the challenge of understanding how variation in sequence and gene expression contributes to neurological and psychiatric disorders. DNA microarrays, or DNA chips, provide the means to measure simultaneously where and when thousands of genes are expressed. Microarrays are changing the way that researchers approach work at the bench and have already yielded new insights into brain tumours, multiple sclerosis, acute neurological insults such as stroke and seizures, and schizophrenia. The study of disease-related changes in gene expression is the first step in the long process in translation of genome research to the clinic. Eventually, the changes observed in microarray studies will need to be independently confirmed and we wil need to understand how gene expression changes translate into functional effects at the cellular level in the nervous system. Progress in these studies will translate into array-based disease classification schemes and help optimise therapy for individual patients based on gene expression patterns or their genetic background.

High-Resolution Analysis of Genetic Events in Cancer Cells Using Bacterial Artificial Chromosome Arrays and Comparative Genome Hybridization

Chromosome analysis of cancer cells has been one of the primary means of identifying key genetic events in the development of cancer. The relatively low resolution of metaphase chromosomes, however, only allows characterization of major genetic events that are defined at the megabase level. The development of the human genome-wide bacterial artificial chromosome (BAC) libraries that were used as templates for the human genome project made it possible to design microarrays containing these BACs that can theoretically span the genome uninterrupted. Competitive hybridization to these arrays using tumor and normal DNA samples reveals numerical chromosome abnormalities (deletions and amplifications) that can be accurately defined depending on the density of the arrays. At present, we are using arrays with 6,000 BACs, which provide an average resolution of less than 700 kb. Analysis of tumor DNA samples using these arrays reveals small deletions and amplifications that were not detectable by chromosome analysis and provides a global view of these genetic changes in a single hybridization experiment in 24 hours. The extent of the genetic changes can then be determined precisely and the gene content of the affected regions established. These arrays have widespread application to the analysis of cancer patients and their tumors and can detect constitutional abnormalities as well. The availability of these high-density arrays now provides the opportunity to classify tumors based on their genetic fingerprints, which will assist in staging, diagnosis, and even prediction of response to therapy. Importantly, subtle genetic changes that occur consistently in tumor cell types may eventually be used to stratify patients for clinical trials and to predict their response to custom therapies.

Characterizing the physical genome

The genome of an organism is a dynamic physical entity, comprising genomic DNA bound to many different proteins and organized into chromosomes. A thorough characterization of the physical genome is relevant to our understanding of processes such as the regulation of gene expression, DNA replication and repair, recombination, chromosome segregation, epigenetic inheritance and genomic instability. Methods based on microarrays are beginning to provide a detailed picture of this physical genome, and they complement the genome-wide studies of mRNA expression profiling that have previously been so successful.

Gene expression profiling with DNA microarrays: advancing our understanding of psychiatric disorders

DNA microarray transcriptome profiling of the postmortem brain opens novel horizons in understanding molecular changes associated with complex psychiatric disorders. With careful analysis and interpretation of microarray data we are uncovering previously unknown, expression patterns that maybe subject-specific and pivotal in understanding the disease process. In our recent studies, analyses of the prefrontal cortex of subjects with schizophrenia and matched controls uncovered complex changes in the expression of genes related to presynaptic secretory release, GABAergic and glutamatergic transmission, metabolic pathways, myelination, as well as cAMP and phosphoinositol second messenger systems. Our goal will be to integrate this expression data within the context of the relevant anatomical, biochemical, molecular, imaging and clinical findings.

Structural brain abnormalities in adult males with clefts of the lip and/or palate

PURPOSE

To evaluate brain morphology of adult males with nonsyndromic clefts of the lip and/or palate (NSCLP) in comparison to a matched healthy control group.

METHODS

Brain structure was measured using quantitative analysis of magnetic resonance images.

RESULTS

Subjects with NSCLP had significant abnormalities in brain morphology consisting of abnormally enlarged anterior regions of the cerebrum, and decreased volumes of the posterior cerebrum and cerebellum. Overall, the most severely affected region was the left temporal lobe. Furthermore, these structural abnormalities were directly related to cognitive dysfunction.

CONCLUSIONS

These findings highlight the important relationship and interplay between face and brain development.

Physical mapping of genes in somatic cell radiation hybrids by comparative genomic hybridization to cDNA microarrays

BACKGROUND

Somatic cell mutants can be informative in the analysis of a wide variety of cellular processes. The use of map-based positional cloning strategies in somatic cell hybrids to analyze genes responsible for recessive mutant phenotypes is often tedious, however, and remains a major obstacle in somatic cell genetics. To fulfill the need for more efficient gene mapping in somatic cell mutants, we have developed a new DNA microarray comparative genomic hybridization (array-CGH) method that can rapidly and efficiently map the physical location of genes complementing somatic cell mutants to a small candidate genomic region. Here we report experiments that establish the validity and efficacy of the methodology.

RESULTS

CHO cells deficient for hypoxanthine:guanine phosphoribosyl transferase (HPRT) were fused with irradiated normal human fibroblasts and subjected to HAT selection. Cy5-labeled genomic DNA from the surviving hybrids containing the HPRT gene was mixed with Cy3-labeled genomic DNA from normal CHO cells and hybridized to a microarray containing 40,185 cDNAs, representing 29,399 genes (UniGene clusters). The DNA spots with the highest Cy5:Cy3 fluorescence ratios corresponded to a group of genes mapping within a 1 Mb interval centered near position 142.7 Mb on the X chromosome, the genomic location of HPRT.

CONCLUSION

The results indicate that our physical mapping method based on radiation hybrids and array-CGH should significantly enhance the speed and efficiency of positional cloning in somatic cell genetics.

Assembly of microarrays for genome-wide measurement of DNA copy number

We have assembled arrays of approximately 2,400 BAC clones for measurement of DNA copy number across the human genome. The arrays provide precise measurement (s.d. of log2 ratios=0.05-0.10) in cell lines and clinical material, so that we can reliably detect and quantify high-level amplifications and single-copy alterations in diploid, polyploid and heterogeneous backgrounds.

Analysis of complex brain disorders with gene expression microarrays: schizophrenia as a disease of the synapse

The level of cellular and molecular complexity of the nervous system creates unique problems for the neuroscientist in the design and implementation of functional genomic studies. Microarray technologies can be powerful, with limitations, when applied to the analysis of human brain disorders. Recently, using cDNA microarrays, altered gene expression patterns between subjects with schizophrenia and controls were shown. Functional data mining led to two novel discoveries: a consistent decrease in the group of transcripts encoding proteins that regulate presynaptic function; and the most changed gene, which has never been previously associated with schizophrenia, regulator of G-protein signaling 4. From these and other findings, a hypothesis has been formulated to suggest that schizophrenia is a disease of the synapse. In the context of a neurodevelopmental model, it is proposed that impaired mechanics of synaptic transmission in specific neural circuits during childhood and adolescence ultimately results in altered synapse formation or pruning, or both, which manifest in the clinical onset of the disease.

XXY male mice: an experimental model for Klinefelter syndrome

Klinefelter syndrome (47,XXY) is the most common sex chromosome aneuploidy in men. Thus, it is important to establish an experimental animal model to explore its underlying molecular mechanisms. Mice with a 41,XXY karyotype were produced by mating wild-type male mice with chimeric female mice carrying male embryonic stem cells. The objectives of the present study were to characterize the testicular phenotype of adult XXY mice and to examine the ontogeny of loss of germ cells in juvenile XXY mice. In the first experiment the testicular phenotypes of four adult XXY mice and four littermate controls (40,XY) were studied. XXY mice were identified by either Southern hybridization or karyotyping and were further confirmed by fluorescence in situ hybridization. The results showed that the testis weights of adult XXY mice (0.02 +/- 0.01 g) were dramatically decreased compared with those of the controls (0.11 +/- 0.01 g). Although no significant differences were apparent in plasma testosterone levels, the mean plasma LH and FSH levels were elevated in adult XXY mice compared with controls. The testicular histology of adult XXY mice showed small seminiferous tubules with varying degrees of intraepithelial vacuolization and a complete absence of germ cells. Hypertrophy and hyperplasia of Leydig cells were observed in the interstitium. Electron microscopic examination showed Sertoli cells containing scanty amounts of cytoplasm and irregular nuclei with prominent nucleoli. The junctional region between Sertoli cells appeared normal. In some tubules, nests of apparently degenerating Sertoli cells were found. In the second experiment the ontogeny of germ cell loss in juvenile XXY mice and their littermate controls was studied. Spermatogonia were found and appeared to be morphologically normal in juvenile XXY mice. Progressive loss of germ cells occurred within 10 days after birth. This resulted in the absence of germ cells in the adult XXY mice. We conclude that a progressive loss of germ cells occurring in early postnatal life results in the complete absence of germ cells in adult XXY mice. The XXY mouse provides an experimental model for its human XXY counterpart, Klinefelter syndrome.

Microarray applications in neuroscience

Advances in all facets of technology from molecular biology to imaging and computational biology offer unprecedented opportunities for improving our understanding of the brain in health and disease. Oligonucleotide and cDNA microarray analysis, using a variety of "DNA chips," is a recently developed high-throughput technique that allows for tour-de-force analysis of gene expression. We review this powerful technique, developed in genetics laboratories, with reference to applications in neurologic diseases in humans and the use of animal models. The typical microarray experiment is multistaged and includes preparation or purchase of arrays, preparation of target DNA and probe, target DNA hybridization, microarray scanning, and image analysis. The power and pitfalls of this technology are discussed in the context of neuroscience paradigms. Since unprecedented amounts of data are produced from microarray experiments, bioinformatics and modeling expertise are increasingly becoming critical components of this approach.