Williams syndrome: from genotype through to the cognitive phenotype

Atypical epigenesis

It is becoming increasingly clear that little in development is predetermined or permanently fixed. Rather, gene expression is activity dependent, and epigenesis is probabilistic. So, the study of genetic disorders needs to change from the still widely held view that developmental disorders can be accounted for in terms of intact versus impaired modules, to one which takes serious account of the fact that the infant cortex passes from an initial state of high regional interconnectivity to a subsequent state of increasing specialization and localization of function. With such early interconnectivity in mind, developmental neuroscientists must consider the possibility that an early deficit in one part of the brain may have subtle effects on other parts of the developing brain, even when scores fall 'in the normal range'. In studying developmental disorders, it is thus crucial to examine not only domains of clear-cut deficit, but also domains of behavioural proficiency. Atypical epigenesis may often involve a lack of specialization and localization of brain function over developmental time, even in cases of behavioural proficiency.

Autism and Williams syndrome: a case report

Williams syndrome (WS) is a neurodevelopmental disorder caused by a deletion in the 7q11.23 region which includes at least 17 genes. The presence of autistic features in WS is a controversial issue. While some authors describe WS as the opposite phenotype of autism, recent studies indicate that both share many common characteristics. We report a 12-year-old boy diagnosed as autistic disorder and WS with hemizygosity at the elastin locus and a karyotype of 46,XY,del(7)(q11.21q11.23). Molecular genetic studies have shown that deletion at the elastin gene may account for the cardiovascular abnormalities seen in WS, but autistic features are likely caused by other genes flanking elastin.

The tortuous route from genes to behavior: A neuroconstructivist approach

In their excitement at using the human genome project to uncover the functions of specific genes, researchers have often ignored one fundamental factor: the gradual process of ontogenetic development. The view that there might be a gene for spatial cognition or language has emanated from a focus on the structure of the adult brain in neuropsychological patients whose brains were fully and normally developed until their brain insult. The developing brain is very different. It starts out highly interconnected across regions and is neither localized nor specialized at birth, allowing interaction with the environment to play an important role in gene expression and the ultimate cognitive phenotype. This article takes a neuroconstructivist perspective, arguing that domain-specific end states can stem from more domain-general start states, that associations may turn out to be as informative as dissociations, and that genetic mutations that alter the trajectory of ontogenetic development can inform nature/nurture debates.

A new chromosome 17q21.31 microdeletion syndrome associated with a common inversion polymorphism

Submicroscopic genomic copy number changes have been identified only recently as an important cause of mental retardation. We describe the detection of three interstitial, overlapping 17q21.31 microdeletions in a cohort of 1,200 mentally retarded individuals associated with a clearly recognizable clinical phenotype of mental retardation, hypotonia and a characteristic face. The deletions encompass the MAPT and CRHR1 genes and are associated with a common inversion polymorphism.

Thoracolumbar syrinx in association with Williams syndrome

Williams syndrome is a genetic condition caused by a deletion on chromosome 7. Clinically it consists of multiple cardiovascular and craniofacial structural abnormalities as well as developmental delay, specific cognitive difficulties, and a characteristic personality. Although scoliosis is a noted manifestation of the disorder, syrinx in association with Williams syndrome has not been reported previously in the literature. Here we present the case of a child with Williams syndrome, scoliosis, and a thoracolumbar syrinx that was successfully treated surgically. We recommend that children with Williams syndrome and scoliosis undergo preoperative evaluation of the spinal cord, as well as the spinal column, so that correctable lesions such as a syrinx are not overlooked. Although syrinxes are often associated with scoliosis, the association in this case of syrinx and Williams syndrome could imply the existence of a genetic contribution to syrinx formation on chromosome 7.

Neural mechanisms in Williams syndrome: a unique window to genetic influences on cognition and behaviour

Williams syndrome, a rare disorder caused by hemizygous microdeletion of about 28 genes on chromosome 7q11.23, has long intrigued neuroscientists with its unique combination of striking behavioural abnormalities, such as hypersociability, and characteristic neurocognitive profile. Williams syndrome, therefore, raises fundamental questions about the neural mechanisms of social behaviour, the modularity of mind and brain development, and provides a privileged setting to understand genetic influences on complex brain functions in a 'bottom-up' way. We review recent advances in uncovering the functional and structural neural substrates of Williams syndrome that provide an emerging understanding of how these are related to dissociable genetic contributions characterized both in special participant populations and animal models.

Parieto-occipital grey matter abnormalities in children with Williams syndrome

Williams syndrome (WS) is a neurodevelopmental disorder resulting from a hemizygous deletion of chromosome 7q11.23. The phenotype of WS consists of typical dysmorphic features, supravalvular aortic stenosis, infantile hypercalcemia and growth retardation. While language and facial recognition seem to be relatively spared, visuospatial constructive disabilities are a hallmark of the neurobehavioral profile of WS. In order to search for actual structural abnormalities underlying this precisely defined neurodevelopmental disorder, we performed anatomical magnetic resonance imaging (MRI) in 9 WS children (11.6 +/- 3.1 years; age range: 5.5-15 years) and 11 normal age-matched control children (11.8 +/- 2.2 years; age range: 8-15 years) using voxel-based morphometry (VBM). VBM is a fully automated whole-brain technique that delivers a voxel-wise assessment of regional grey and white matter concentration. A significant decrease in grey matter concentration was detected in the left parieto-occipital region of WS children (P < 0.05 corrected height threshold). The location of this abnormality in WS children coincides with the location of the structural abnormality previously described using the same method in 13 WS adults. These parieto-occipital abnormalities are consistent with the cognitive profile of WS which includes severe visuospatial construction and numerical cognition deficits. The demonstration of identical structural abnormalities in both adults and children argues for their early origin. Additionally, our study provides support for the use of advanced structural imaging techniques in children, in order to improve our understanding of neurobehavioral phenotypes associated with well-defined genetic disorders.

Outcome in adult life for people with Williams syndrome-- results from a survey of 239 families

BACKGROUND

Although there has been considerable research into the genotype and phenotype of Williams syndrome, there have been relatively few studies of long-term prognosis. As a preliminary to a more detailed investigation of adults with Williams syndrome, a parental questionnaire was distributed to members of the UK Williams Syndrome Foundation, focusing on areas of skill and difficulties in adult life.

METHOD

A postal questionnaire was distributed to all members of the UK Williams Syndrome Foundation who had a son or daughter aged 18 years or over. The questionnaire covered issues related to the physical and mental health of the adults with Williams syndrome, together with questions about educational and employment status, self-help and independence skills.

RESULTS

Out of a total of 290 questionnaires distributed, 239 were returned (82% response rate). The data highlighted the continuing high rates of physical problems in this group and apparent increases in rates of mental health problems with age. Parents also expressed their concerns about the lack of adequate support and care. Educational and employment attainments were generally low and self-help skills were relatively poor.

DISCUSSION

The findings highlight the need for far better understanding of conditions such as Williams syndrome among professionals working in adult services and the need for more adequate support from educational, health and social services.

Are numerical impairments syndrome specific? Evidence from Williams syndrome and Down's syndrome

BACKGROUND

Several theorists maintain that exact number abilities rely on language-relevant processes whereas approximate number calls on visuo-spatial skills. We chose two genetic disorders, Williams syndrome and Down's syndrome, which differ in their relative abilities in verbal versus spatial skills, to examine this hypothesis. Five experiments assessed number skills in these two genetic syndromes and in their mental age (MA) and chronological age (CA) matched controls.

METHODS

Experiment 1 used a preferential looking paradigm with infants and toddlers to measure sensitivity to changes in numerosity. Experiment 2 measured reaction times in older children and adults in a numerosity comparison task with dots in a random pattern. Experiment 3 comprised a number battery that measured various forms of counting and simple arithmetic.

RESULTS

The WS infants displayed a level of performance equal to that of their CA-controls, whereas the DS infants failed to reach even the level of their MA-controls. By contrast, the older DS children and adults outstripped the older WS group in their numerosity abilities, with different patterns of errors in the two clinical groups.

CONCLUSIONS

Differences in the infant and adult number phenotypes between these two genetic disorders are discussed with reference to the processing styles used by each group and how these might impact on their developmental trajectories. Theoretically, we highlight our contention that one cannot infer the infant starting state from the adult end state. Rather, the development process itself must be taken into account.

GTF2IRD1 in craniofacial development of humans and mice

Craniofacial abnormalities account for about one-third of all human congenital defects, but our understanding of the genetic mechanisms governing craniofacial development is incomplete. We show that GTF2IRD1 is a genetic determinant of mammalian craniofacial and cognitive development, and we implicate another member of the TFII-I transcription factor family, GTF2I, in both aspects. Gtf2ird1-null mice exhibit phenotypic abnormalities reminiscent of the human microdeletion disorder Williams-Beuren syndrome (WBS); craniofacial imaging reveals abnormalities in both skull and jaws that may arise through misregulation of goosecoid, a downstream target of Gtf2ird1. In humans, a rare WBS individual with an atypical deletion, including GTF2IRD1, shows facial dysmorphism and cognitive deficits that differ from those of classic WBS cases. We propose a mechanism of cumulative dosage effects of duplicated and diverged genes applicable to other human chromosomal disorders.

Scaling of visuospatial attention undergoes differential longitudinal change as a function of APOE genotype prior to old age: Results from the NIMH BIOCARD Study

The effect of apolipoprotein E (APOE) genotype on longitudinal cognitive decline in midlife was investigated with attentional scaling. Healthy individuals (mean age 59.6 years) genotyped for APOE were tested at 3 12-month intervals on a cued visual search task. A random effects model revealed significant interaction in effect of precue size on search speed between APOE-epsilon4 gene dose and assessment, with longitudinal increases in noncarriers and heterozygotes but longitudinal decreases in homozygotes. Association of APOE-epsilon4 with cognitive decline in midlife is consistent with an Alzheimer's disease (AD) prodrome, albeit a decade or more before average age of AD diagnosis. However, cognitive decline in midlife associated with a gene modulating neuronal response to insult argues that the concept of an AD prodrome includes factors that allow as well as cause AD.

Williams-Beuren syndrome associated with caudal regression syndrome and coagulopathy--a case report

Williams-Beuren syndrome is a genetic disorder caused by a heterozygous deletion at 7q11.23. The present report describes a female patient with Williams-Beuren syndrome combined with caudal regression syndrome and two forms of coagulopathy. Besides the typical developmental abnormalities such as mental and growth retardation, a distinctive facial appearance, and cardiovascular anomalies, our patient showed fusion of fourth and fifth lumbar vertebra and a sacrococcygeal agenesis. Blood coagulation tests revealed a deficiency of coagulation factor XI and XII. Magnetic resonance imaging angiography showed multiple vascular stenoses mainly in the abdominal aorta and its major branches as a consequence of the insufficient elastin gene. Previous reports identified a deletion of HLXB9 as a possible genetic cause of the caudal regression syndrome, which could not be identified in the present case. This unusual combination of the above-mentioned genetic disorders has not been published so far.

In-depth analysis of spatial cognition in Williams syndrome: A critical assessment of the role of the LIMK1 gene

The LIM kinase1 protein (LIMK1) is thought to be involved in neuronal development and brain function. However, its role in spatial cognition in individuals with Williams syndrome (WS) is currently ambiguous, with conflicting reports on the cognitive phenotypes of individuals who do not have classic WS but harbour partial deletions including LIMK1. Two families with partial WS deletions have been described with deficits in visuospatial cognition (Frangiskakis, J. M., Ewart, A. K., Morris, C. A., Mervis, C. B., Bertrand, & J., Robinson, et al. (1996). LIM-kinase 1 hemizygosity implicated in impaired visuospatial constructive cognition. Cell, 86, 59-69), in contrast to others with similar partial deletions who did not display spatial impairments (Tassabehji, M., Metcalfe, K., Karmiloff-Smith, A., Carette, M. J., Grant, J., & Dennis, N., et al. (1999). Williams syndrome: Use of chromosomal microdeletions as a tool to dissect cognitive and physical phenotypes. American Journal of Human Genetics, 64, 118-125). To determine the role of LIMK1 in the highly penetrant visuospatial deficits associated with classic WS, it is essential to investigate the discrepancies between the two studies. Previous research used a standardised task to measure spatial cognition, which may not pick up subtle impairments. We therefore undertook more extensive testing of the spatial cognition of two adults with partial genetic deletions in the WS critical region (LIMK1 and ELN only), who had not displayed spatial impairments in the previous study, and compared them to two high-functioning adults with WS matched on verbal ability. All participants completed a broad battery of 16 perceptual and constructive spatial tests, and the clear-cut spatial difficulties observed in the WS group were not found in the partial deletion group. These findings rule out the claim that the deletion of one copy of LIMK1 is alone sufficient to result in spatial impairment, but leave open the possibility that LIMK1 contributes to the WS cognitive deficits if deleted in combination with other genes within the WS deletion. We conclude that a deeper assessment of WS at the genetic level is required before the contribution of specific genes to phenotypic outcomes can be fully understood.

MAPH: from gels to microarrays

The development of accurate and sensitive methodologies to detect small chromosomal imbalances (<3 Mb) is extremely important in clinical diagnostics and research in human genetics. The technique of array-comparative genomic hybridization (CGH) using BAC and PAC clones is very sensitive methodology and is rapidly becoming the method of choice for high-resolution screening of genomic copy-number changes. An alternative methodology to CGH is the multiplex amplifiable probe hybridization (MAPH) methodology, a DNA based method that allows the accurate and reliable determination of changes in copy number in "known" or "unknown locations" in the human genome. MAPH uses probes of 100-500 bp in size, that can be specifically designed for any gene or locus in the genome and cover any gene exons, the subtelomeric or subcentromeric regions, any chromosomal segment, a whole chromosome or the total human genome. MAPH can provide extremely high resolution and enable the sensitive detection of loss or gain of genomic DNA sequences as small as 150 bp. Very recently we succeeded in the advancement of MAPH from gel and capillary analyses to microarrays. The array-MAPH methodology offers an alternative methodology to array-CGH and provides a new sensitive microarray-based method including several advantages for the detection of copy number changes in the human genome.

Clinical manifestations and molecular investigation of 50 patients with Williams syndrome in the Greek population

Williams syndrome (WS) is a well-recognized neurodevelopmental disorder manifested by both connective tissue and CNS abnormalities. The study depicts the 8-y experience and follow-up of 50 Greek children with the clinical diagnosis of WS. Clinical data on the facial features and cardiovascular, endocrinologic, and neurodevelopmental evaluation are presented. The most consistent findings were dysmorphic features (100%), followed by dental anomalies (90%) and hyperacousis (90%). Only eight of 50 children had severe cardiovascular defects that required surgical intervention during the first year of life. Supravalvular aortic stenosis was less frequent (28%) than shown in the literature. Severe hypertension was noticed in 22% of our patients, and infantile hypercalcemia was noticed in 6%. Twelve percent of our patients showed an elevation of CPK. Most children presented with moderate to severe mental retardation with IQ ranging from 20 to 85. Elastin hemizygosity was detected by fluorescence in situ hybridization. Dinucleotide repeat polymorphism analysis was performed in an attempt to correlate phenotype with genotype. The origin of deletions was more frequently maternal (59%), and a more severe phenotype seemed to be associated with those deletions. This is the first report on WS patients in the Greek population.

Effects of apolipoprotein E genotype on spatial attention, working memory, and their interaction in healthy, middle-aged adults: results From the National Institute of Mental Health's BIOCARD study

The cognitive consequences of the apolipoprotein E-epsilon4 (APOE-epsilon4) allele were examined in middle age, before likely onset of symptoms of Alzheimer's disease. The authors identified 3 cognitive processes--visuospatial attention, spatial working memory, and the effect of visuospatial attention on working memory--and devised "behavioral assays" of the integrity of components of these processes. Redirecting visuospatial attention, retention of memory for location, and attentional modulation of memory of target location were affected by APOE genotype. Visuospatial attention showed additive effects of epsilon4 gene dose; each additional epsilon4 allele inherited further slowed disengagement from invalidly cued space. In contrast, working memory performance was affected only in epsilon4 homozygotes. Effect sizes for the APOE gene were moderate to large, ranging from 14% to 24%. Effects of APOE genotype on component processes of cognition in healthy, middle-aged adults is consistent with the emergence in adulthood of an APOE-epsilon4 cognitive phenotype.

Williams syndrome: pediatric, neurologic, and cognitive development

This study examines the developmental history of 32 Williams syndrome patients, positive to the fluorescence in situ hybridization (FISH) test. The information is intended to provide help for early diagnosis and appropriate stimulation of these patients. In the sample reported here, only about half of the patients referred with presumptive diagnosis were in fact FISH+, indicating that facial dysmorphism may not be the most reliable sign for diagnosis. Initial pediatric signs are developmental delay and nocturnal irritability. In consultation, facial dysmorphies and heart murmur are detected. There is also low birth weight, failure to thrive, unsuccessful breastfeeding, and gastroesophageal reflux. All these symptoms are strongly suggestive of Williams syndrome. Subsequent steps consist of cardiologic studies. Our results indicate that the triad of symptoms consisting of infantile hypercalcemia, dysmorphic facies, and supravalvular aortic stenosis, which until recently was considered fundamental for Williams syndrome diagnosis, is not usually present and does not lead to an early diagnosis. Cognitively, these children are characterized by hypersociability, hyperacusia, deficient visuoconstructive abilities, attentional deficit and hyperactivity, and in some cases, spontaneous musical interests. There are no special verbal skills. The results of this study indicate that the concept of Williams syndrome patients as language- and musically-gifted is not fully accurate.

Burkitt lymphoma and Williams syndrome: a model for children with a multisystem disorder and malignancy

The authors describe a child with Williams syndrome who developed Burkitt lymphoma with a t(8;14). Williams syndrome is a contiguous gene syndrome that is not associated with a predilection for cancer. However, the management of a child with Williams syndrome and a malignancy is complicated by underlying disease in multiple organs. In 2001, the American Academy of Pediatrics published health care guidelines for children with Williams syndrome. These guidelines were adopted in the treatment of this child. Disease-specific guidelines should be applied to other children with multisystem disorders such as Down syndrome that require treatment of a malignancy.

Chromosomal phenotypes and submicroscopic abnormalities

The finding, during the last decade, that several common, clinically delineated syndromes are caused by submicroscopic deletions or, more rarely, by duplications, has provided a powerful tool in the annotation of the human genome. Since most microdeletion/microduplication syndromes are defined by a common deleted/duplicated region, abnormal dosage of genes located within these regions can explain the phenotypic similarities among individuals with a specific syndrome. As such, they provide a unique resource towards the genetic dissection of complex phenotypes such as congenital heart defects, mental and growth retardation and abnormal behaviour. In addition, the study of phenotypic differences in individuals with the same microdeletion syndrome may also become a treasury for the identification of modifying factors for complex phenotypes. The molecular analysis of these chromosomal anomalies has led to a growing understanding of their mechanisms of origin. Novel tools to uncover additional submicroscopic chromosomal anomalies at a higher resolution and higher speed, as well as the novel tools at hand for deciphering the modifying factors and epistatic interactors, are 'on the doorstep' and will, besides their obvious diagnostic role, play a pivotal role in the genetic dissection of complex phenotypes.

Age-Associated Memory Changes in Adults With Williams Syndrome

Age-associated changes on measures of episodic and working memory were examined in 15 adults with Williams Syndrome (WS; M age = 48.3 years, SD = 14.7; M IQ = 62.9, SD = 8.5) and their performance was compared to that of 33 adults with mental retardation (MR) with unspecified etiologies (M age = 54.2 years, SD = 8.9; M IQ = 61.7, SD = 6.5). Among the group with WS, older adults were significantly poorer than younger adults on the free recall task, a measure of episodic memory. Although this finding is consistent with normal aging, it occurred at a chronologically early age in adults with WS and was not found in their peers with unspecified MR. Although both groups showed small declines with age on a backward digit span task, a measure of working memory, for the group with WS the rate of decline on backward digit span was slower as compared to their performance on the free recall task. The findings from this study indicate a chronologically early and precipitous age-associated decrease in long-term, episodic memory in adults with WS.

Comparison of TFII-I gene family members deleted in Williams-Beuren syndrome

Williams-Beuren syndrome (WBS) is a neurological disorder resulting from a microdeletion, typically 1.5 megabases in size, at 7q11.23. Atypical patients implicate genes at the telomeric end of this multigene deletion as the main candidates for the pathology of WBS in particular the unequal cognitive profile associated with the condition. We recently identified a gene (GTF2IRD2) that shares homology with other members of a unique family of transcription factors (TFII-I family), which reside in the critical telomeric region. Using bioinformatics tools this study focuses on the detailed assessment of this gene family, concentrating on their characteristic structural components such as the leucine zipper (LZ) and I-repeat elements, in an attempt to identify features that could aid functional predictions. Phylogenetic analysis identified distinct I-repeat clades shared between family members. Linking functional data to one such clade has implicated them in DNA binding. The identification of PEST, synergy control motifs, and sumoylation sites common to all family members suggest a shared mechanism regulating the stability and transcriptional activity of these factors. In addition, the identification/isolation of short truncated isoforms for each TFII-I family member implies a mode of self-regulation. The exceptionally high identity shared between GTF2I and GTF2IRD2, suggests that heterodimers as well as homodimers are possible, and indicates overlapping functions between their respective short isoforms. Such cross-reactivity between GTF2I and GTF2IRD2 short isoforms might have been the evolutionary driving force for the 7q11.23 chromosomal rearrangement not present in the syntenic region in mice.

Exploring the Williams syndrome face-processing debate: the importance of building developmental trajectories

BACKGROUND

Face processing in Williams syndrome (WS) has been a topic of heated debate over the past decade. Initial claims about a normally developing ('intact') face-processing module were challenged by data suggesting that individuals with WS used a different balance of cognitive processes from controls, even when their behavioural scores fell within the normal range. Measurement of evoked brain potentials also point to atypical processes. However, two recent studies have claimed that people with WS process faces exactly like normal controls.

METHOD

In this paper, we examine the details of this continuing debate on the basis of three new face-processing experiments. In particular, for two of our experiments we built task-specific full developmental trajectories from childhood to adolescence/adulthood and plotted the WS data on these trajectories.

RESULTS

The first experiment used photos of real faces. While it revealed broadly equivalent accuracy across groups, the WS participants were worse at configural processing when faces were upright and less sensitive than controls to face inversion. In Experiment 2, measuring face processing in a storybook context, the face inversion effect emerged clearly in controls but only weakly in the WS developmental trajectory. Unlike the controls, the Benton Face Recognition Test and the Pattern Construction results were not correlated in WS, highlighting the different developmental patterns in the two groups. Again in contrast to the controls, Experiment 3 with schematic faces and non-face stimuli revealed a configural-processing deficit in WS both with respect to their chronological age (CA) and to their level of performance on the Benton.

CONCLUSION

These findings point to both delay and deviance in WS face processing and illustrate how vital it is to build developmental trajectories for each specific task.

Annotation: Deconstructing the attention deficit in fragile X syndrome: a developmental neuropsychological approach

BACKGROUND

Fragile X syndrome is one of the world's leading hereditary causes of developmental delay in males. The past decade has witnessed an explosion of research that has begun to unravel the condition at its various levels: from the genetic and brain levels to the cognitive level, and then to the environmental and behavioural levels. Our aim in this review is to attempt to integrate some of the extensive body of knowledge to move the research a step closer to understanding how the dynamics of atypical development can influence the specific cognitive and behavioural end-states frequently observed in children and adolescents with fragile X syndrome.

METHODS

We conducted a review of the current neuropsychological and neuropsychiatric approaches that have attempted to delineate the pattern of 'spared' and 'impaired' functions associated with the phenotype.

RESULTS

The profile of findings suggests that fragile X syndrome should not be viewed merely as a catalogue of spared and impaired cognitive functions or modules. Instead, there appears to be a process of almost gradual modularisation whereby cognitive mechanisms become domain specific as a function of development itself (Karmiloff-Smith, 1992). The results of a decade of intense research point towards an early weakness in one or more components of executive control rather than single, static higher-level deficits (e.g., spatial cognition, speech processing). This weakness affects both the development of more complex functions and current performance.

CONCLUSIONS

The prevailing tendency to interpret developmental disorders in terms of fixed damage to distinct modular functions needs to be reconsidered. We offer this review as an example of an alternative approach, attempting to identify an initial deficit and its consequences for the course of development. Through better definition of the cognitive and behavioural phenotype, in combination with current progress in brain imaging techniques and molecular studies, the next decade should continue to hold exciting promise for fragile X syndrome and other neurodevelopmental disorders.

Postmortem findings in term neonates

Neonatal deaths in infants born at term are relatively rare in the USA, occurring in 0.9/1000 live births. Congenital malformations, perinatal asphyxia, infections and inborn errors of metabolism are the leading causes. Chromosomal malformation syndromes, congenital heart disease, pulmonary hypoplasia and severe neural tube defects comprise the majority of lethal malformations. Several skeletal dysplasias are lethal in the newborn infant. Group B Streptococcus still plays a major role in neonatal mortality while deaths due to other infectious agents have decreased. Hypoxic ischaemic encephalopathy is a significant cause of neonatal death. Inborn errors of metabolism have variable presentations but some, such as the fatty acid oxidation disorders, may present in neonates and cause sudden death.

"Everybody in the world is my friend" hypersociability in young children with Williams syndrome

Williams syndrome (WS) is a rare genetic disorder involving a characteristic cardiac defect, typical facial appearance, and an uneven profile of cognitive strengths and weaknesses. WS is caused by a hemizygous deletion in chromosome band 7q11.23, including the gene for elastin (ELN). Typically, individuals with WS seem driven to greet and interact with strangers. The goal of the present study was to investigate age-related changes in the expression of hypersociability in WS. Parents of 64 children with WS, 31 children with Down syndrome (DS), and 27 normal controls (NC) provided data concerning specific aspects of their children's social behavior using the Salk Institute Sociability Questionnaire (SISQ). Children ranged in age from 1 year, 1 month to 12 years, 10 months. Consistent with earlier findings, whole group analyses showed the WS group to be significantly higher on all aspects of sociability studied. Comparisons among the groups at different ages revealed that hypersociability is evident even among very young children with WS, and, significantly, children with WS exceed children with DS with respect to Global Sociability and Approach Strangers in every age group. The findings from children who have the typical deletion for WS are contrasted with data obtained from a young child with WS who has a smaller deletion and many physical features of WS, but who does not demonstrate hypersociability, providing intriguing clues to a genetic basis of social behavior in this syndrome. These data suggest the involvement of a genetic predisposition in the expression of hypersociability in WS.

Imaging of neurogenetic and neurometabolic disorders of childhood

Magnetic resonance imaging (MRI) has emerged as a powerful tool in the study of normal and abnormal brain structure, function, and biochemistry. In particular, functional MRI has come into its own as a tool to study normal and abnormal brain functions such as learning, memory, and motor learning, as well as delineation of neurogenetic cognitive phenotypes. White matter microstructure can be studied using diffusion tensor imaging, which may allow abnormal white matter to be visualized prior to abnormalities on anatomic MRI. Magnetic resonance spectroscopy, a noninvasive method to study brain biochemistry, may allow for the delineation of regional metabolic changes as a result of disease progression and/or therapeutic intervention. With MRI techniques, one can investigate the relationship between structure, function, genes, and behavior. This report discusses the research applications of MRI to the study of neurogenetic disorders of childhood.

Visual search in typically developing toddlers and toddlers with Fragile X or Williams syndrome

Visual selective attention is the ability to attend to relevant visual information and ignore irrelevant stimuli. Little is known about its typical and atypical development in early childhood Experiment 1 investigates typically developing toddlers' visual search for multiple targets on a touch-screen. Time to hit a target, distance between successively touched items, accuracy and error types revealed changes in 2- and 3-year-olds' vulnerability to manipulations of the search display. Experiment 2 examined search performance by toddlers with Fragile X syndrome (FXS) or Williams syndrome (WS). Both of these groups produced equivalent mean time and distance per touch as typically developing toddlers matched by chronological or mental age; but both produced a larger number of errors. Toddlers with WS confused distractors with targets more than the other groups; while toddlers with FXS perseverated on previously found targets. These findings provide information on how visual search typically develops in toddlers, and reveal distinct search deficits for atypically developing toddlers.

Saccade dysmetria in Williams–Beuren syndrome

Numerous studies have described the poor visuo-spatial processing capacities of subjects with Williams-Beuren syndrome (WBS), a genetically based developmental disorder. Since visual perception and eye movements are closely related we hypothesized that the poor visuo-spatial processing capacities of subjects with WBS might be related to a poor saccadic control. Thereto, we recorded horizontal and vertical saccadic eye movements to targets using infrared video-oculography in 27 subjects with WBS and eight healthy controls. In the WBS group saccadic gains were highly variable, both between and within individual subjects, and they often needed more than one correction saccade to reach the target. Ten (out of a subgroup of 22) WBS subjects showed a large number of hypometric and/or hypermetric saccades, and, also a left-right asymmetry in saccadic gains was observed in WBS. We conclude that the observed impairments in saccadic control are likely to affect the proper processing of visuo-spatial information.

Síndrome de Williams-Beuren: presentación de 82 casos

OBJECTIVE

We performed a retrospective review of a series of 82 cases of Williams-Beuren syndrome (WBS) and associated diseases.

MATERIAL AND METHODS

A series of 82 patients (47 males and 35 females) who consulted at the hospital because of mental retardation and/or congenital cardiopathy were included. The patients were studied mainly from a neurological and cardiological point of view, and secondarily because of endocrinological and nephrological problems. Since description of the chromosomal abnormalities provoking the syndrome, we perform karyotyping in all patients with suspected WBS.

RESULTS

Alterations mainly consisted of distinctive facial appearance (100 %), mental retardation with friendly behavior (90 %), congenital cardiopathy (85.4 %), mostly consisting of supravalvular aortic stenosis (72 %), with (12 %) or without (60 %) pulmonary stenosis, and behavior typical of attention deficit-hyperactivity disorder, which usually manifested at the age of 4 to 5 years in both boys and girls. Approximately 90 % started to walk and speak later than average. Birthweight was below 3000 g in 65 % of the patients in whom this datum was included in the medical record. Eleven of the 13 patients (84.5 %) studied showed the typical deletion of WBS.

CONCLUSION

Study of patients with WBS should be multidisciplinary. Most patients require help during schooling and subsequent vocational guidance.

Modeling language acquisition in atypical phenotypes

An increasing number of connectionist models have been proposed to explain behavioral deficits in developmental disorders. These simulations motivate serious consideration of the theoretical implications of the claim that a developmental disorder fits within the parameter space of a particular computational model of normal development. The authors examine these issues in depth with respect to a series of new simulations investigating past-tense formation in Williams syndrome. This syndrome and the past-tense domain are highly relevant because both have been used to make strong theoretical claims about the processes underlying normal language acquisition. The authors conclude that computational models have great potential to advance psychologists' understanding of developmental deficits because they focus on the developmental process itself as a pivotal causal factor in producing atypical phenotypic outcomes.

Williams-Beuren syndrome: a model of recurrent genomic mutation

Williams-Beuren syndrome is a segmental aneusomy syndrome with manifestations affecting the vascular, connective tissue, endocrine and central nervous systems. Most patients show a similar heterozygous approximately 1.5 Mb deletion at 7q11.23 that contains a number of reported genes. Deletion mapping in the few atypical patients with smaller deletions suggested that additive effects of haploinsufficiency for two or more genes might be necessary for the phenotype. Vascular stenoses are caused by haploinsufficiency at the elastin gene, while the genes responsible for the cognitive deficits are likely located at the telomeric edge of the deletion, including CYLN2 and GTF2I. Large region-specific segmental duplications predispose to misalignment and inter- or intrachromosomal unequal crossing-over causing the deletions. Atypical alleles at 7q11.23 such as inversions and deletions/insertions of large repeats, also generated through aberrant recombination between the local segmental duplications, are found in approximately 35% of transmitting parents. Genomic instability at 7q11.23 is directly related to the genomic structure of the region.

ERP abnormalities of illusory contour perception in Williams Syndrome

Williams syndrome is a genetic disorder in which visuo-spatial performance is poor. Theorists have claimed that the deficit lies in high-level processing, leaving low-level visual processes intact. We investigated this claim by examining an aspect of low-level processing, perceptual completion, i.e. the ability of this clinical group to perceive illusory Kanizsa squares. We then used event-related potentials to examine neural correlates of perceptual completion. While participants were able to perceive illusory contours, the neural correlates of this apparently normal perception were different from controls. Such differences in low-level visual processes may significantly impact on the development of higher-level visual processes. We conclude that, contrary to earlier claims, there is atypical neural processing during low-level visual perception in Williams syndrome.

How clinicians add to knowledge of development

Studies of human birth defects and developmental disorders have made major contributions to our understanding of development. Rare human syndromes have allowed identification of important developmental genes, and revealed mechanisms such as uniparental disomy and unstable trinucleotide repeats that were not suspected from animal studies. Some aspects of development, in particular cognitive development, can only be studied in human beings. Basic developmental mechanisms are very highly conserved across a very wide range of animals, making for a rich interplay between animal and human studies. Often, clinical studies identify a gene, or suggest a hypothesis, that can then be investigated in animals.

Spatial representation and attention in toddlers with Williams syndrome and Down syndrome

The nature of the spatial representations that underlie simple visually guided actions early in life was investigated in toddlers with Williams syndrome (WS), Down syndrome (DS), and healthy chronological age- and mental age-matched controls, through the use of a "double-step" saccade paradigm. The experiment tested the hypothesis that, compared to typically developing infants and toddlers, and toddlers with DS, those with WS display a deficit in using spatial representations to guide actions. Levels of sustained attention were also measured within these groups, to establish whether differences in levels of engagement influenced performance on the double-step saccade task. The results showed that toddlers with WS were unable to combine extra-retinal information with retinal information to the same extent as the other groups, and displayed evidence of other deficits in saccade planning, suggesting a greater reliance on sub-cortical mechanisms than the other populations. Results also indicated that their exploration of the visual environment is less developed. The sustained attention task revealed shorter and fewer periods of sustained attention in toddlers with DS, but not those with WS, suggesting that WS performance on the double-step saccade task is not explained by poorer engagement. The findings are also discussed in relation to a possible attention disengagement deficit in WS toddlers. Our study highlights the importance of studying genetic disorders early in development.

What makes counting count? Verbal and visuo-spatial contributions to typical and atypical number development

Williams Syndrome (WS) is marked by a relative strength in verbal cognition coupled with a serious impairment in non-verbal cognition. A strong deficit in numerical cognition has been anecdotally reported in this disorder; however, its nature has not been systematically investigated. Here, we tested 14 children with WS (mean age=7 years 2 months), 14 typically developing controls individually matched on visuo-spatial ability (mean age=3 years 5 months) as well as a larger group of typically developing controls (mean age=3 years 4 months) on two tasks to assess their understanding that counting determines the exact quantity of sets (cardinality principle). The understanding of the cardinality principle in children with WS is extremely delayed and only at the level predicted by their visuo-spatial MA. In this clinical group, only language accounted for a significant amount of the variance in cardinality understanding, whereas in the normal comparison group only visuo-spatial competence predicted the variance. The present findings suggest that visuo-spatial ability plays a greater role than language ability in the actual development of cardinality understanding in typically developing children, whereas the opposite obtains for the clinical group.

Regulation of growth cone actin dynamics by ADF/cofilin

Nervous system development is reliant on neuronal pathfinding, the process in which axons are guided to their target cells by specific extracellular cues. The ability of neurons to extend over long distances in response to environmental guidance signals is made possible by the growth cone, a highly motile structure found at the end of neuronal processes. Growth cones detect directional cues and respond with either attractive or repulsive movements. The motility of growth cones is dependent on rapid reorganization of the actin cytoskeleton, presumably mediated by actin-associated proteins under the control of incoming guidance signals. This article reviews how one such family of proteins, the ADF/cofilins, are emerging as key regulators of growth cone actin dynamics. These proteins are essential for rapid actin turnover in a variety of different cell types. ADF/cofilins are heavily co-localized with actin in growth cones and are necessary for neurite outgrowth. ADF/cofilin activities are regulated through reversible phosphorylation by LIM kinases and slingshot phosphatases. LIM kinases are downstream effectors of the Rho GTPases Rho, Rac, and Cdc42. Growing evidence suggests that extracellular guidance cues may locally alter actin dynamics by regulating the activity of LIM kinase and ADF/cofilin phosphatases via the Rho GTPases. In this way, ADF/cofilins and their upstream effectors may be pivotal to our understanding of how guidance information is translated into physical alterations of the growth cone actin cytoskeleton.

Signaling mechanisms that regulate actin-based motility processes in the nervous system

Actin-based motility is critical for nervous system development. Both the migration of neurons and the extension of neurites require organized actin polymerization to push the cell membrane forward. Numerous extracellular stimulants of motility and axon guidance cues regulate actin-based motility through the rho GTPases (rho, rac, and cdc42). The rho GTPases reorganize the actin cytoskeleton, leading to stress fiber, filopodium, or lamellipodium formation. The activity of the rho GTPases is regulated by a variety of proteins that either stimulate GTP uptake (activation) or hydrolysis (inactivation). These proteins potentially link extracellular signals to the activation state of rho GTPases. Effectors downstream of the rho GTPases that directly influence actin polymerization have been identified and are involved in neurite development. The Arp2/3 complex nucleates the formation of new actin branches that extend the membrane forward. Ena/VASP proteins can cause the formation of longer actin filaments, characteristic of growth cone actin morphology, by preventing the capping of barbed ends. Actin-depolymerizing factor (ADF)/cofilin depolymerizes and severs actin branches in older parts of the actin meshwork, freeing monomers to be re-incorporated into actively growing filaments. The signaling mechanisms by which extracellular cues that guide axons to their targets lead to direct effects on actin filament dynamics are becoming better understood.

Visual information process in Williams syndrome: intact motion detection accompanied by typical visuospatial dysfunctions

It has been suggested that visuospatial cognitive disabilities seen in children with Williams syndrome (WMS) are related to a dysfunction of the dorsal stream in the visual information analysis system. We investigated whether visual motion detection is also impaired in WMS because it is one of the main functions of the dorsal stream. Using various psychophysical examinations and magnetoencephalography, we studied a child with WMS who had the typical features of the syndrome. We found profound impairments in the visuospatial cognitions, as previously reported in WMS. In contrast, he had normal ability for the direction discrimination of coherent motion on a background of randomly moving dots, and he perceived apparent motion as do normal children. Furthermore, the latencies of both responses to the coherent and incoherent motions as measured by magnetoencephalography were within the mean +/- 2 SD among normal adults and the estimated origins were near the human homologue of V5/MT (visual area 5/middle temporal area). The results indicate that the visuospatial cognitive deficits in WMS can occur without impairment of the visual motion detection. We consider that the deficits are caused by a restricted dysfunction of the neural groups for position and three-dimensional form perceptions in the dorsal stream of the visual system, though other possibilities are not excluded.

Early categorization abilities in young children with Williams syndrome

The present study investigated whether 2- to 6-year-old children with Williams syndrome can form new object categories based on either visual or verbal information alone. Children were presented with six triads of objects. In each triad, two objects either shared visual properties, or were given the same name. Following the presentation of each triad, categorization based on the shared visual or verbal property was evaluated through object manipulation. While the children categorized the objects according to visual cues, they failed to use the verbal cues. These results contrast with previous research showing that typically developing toddlers, who were much younger than the children with Williams syndrome and much less advanced in their vocabulary development, could perform both types of categorization. The present study hence supports the claim that vocabulary acquisition in Williams syndrome develops atypically.

Face and place processing in Williams syndrome: evidence for a dorsal-ventral dissociation

Individuals with Williams syndrome (WMS) show an interesting dissociation of ability within the visuospatial domain, particularly between face perception and other visuospatial tasks. In this population, using tasks matched for stimuli, required response, and difficulty (for controls) is critical when comparing performance across these areas. We compared WMS individuals with a sample of typically developing 8- and 9-year-old children, and with a sample of adults, closer to the WMS participants in chronological age, in order to investigate performance across two precisely matched perceptual tasks, one assessing face processing and the other assessing proficiency in processing stimuli location. The pattern of performance seen in WMS, but not in controls, implicates a specific deficit of dorsal stream functioning in this syndrome.

The role of Rho GTPases and associated kinases in regulating neurite outgrowth

Neurones are highly specialised cells that can extend over great distances, enabling the complex networking of the nervous system. We are beginning to understand in detail the molecular mechanisms that control the shape of neurones during development. One family of proteins that are clearly essential are the Rho GTPases which have a pivotal role in regulating the actin cytoskeleton in all cell types. The Rho GTPases are responsible for the activation and downregulation of many downstream kinases. This review discusses individual kinases that are regulated by three members of the Rho GTPases, Rac, Rho and Cdc42 and their function during neurite outgrowth and remodelling.

High-throughput analysis of subtelomeric chromosome rearrangements by use of array-based comparative genomic hybridization

Telomeric chromosome rearrangements may cause mental retardation, congenital anomalies, and miscarriages. Automated detection of subtle deletions or duplications involving telomeres is essential for high-throughput diagnosis, but impossible when conventional cytogenetic methods are used. Array-based comparative genomic hybridization (CGH) allows high-resolution screening of copy number abnormalities by hybridizing differentially labeled test and reference genomes to arrays of robotically spotted clones. To assess the applicability of this technique in the diagnosis of (sub)telomeric imbalances, we here describe a blinded study, in which DNA from 20 patients with known cytogenetic abnormalities involving one or more telomeres was hybridized to an array containing a validated set of human-chromosome-specific (sub)telomere probes. Single-copy-number gains and losses were accurately detected on these arrays, and an excellent concordance between the original cytogenetic diagnosis and the array-based CGH diagnosis was obtained by use of a single hybridization. In addition to the previously identified cytogenetic changes, array-based CGH revealed additional telomere rearrangements in 3 of the 20 patients studied. The robustness and simplicity of this array-based telomere copy-number screening make it highly suited for introduction into the clinic as a rapid and sensitive automated diagnostic procedure.

Different approaches to relating genotype to phenotype in developmental disorders

In this article, we discuss the complex problem of relating genotype to phenotype and challenge the simple mapping of genes to higher level cognitive modules. We examine various methods that have been used to investigate this relation including quantitative genetics, molecular genetics, animal models, and in-depth psychological and computational studies of developmental disorders. Both single gene and multiple gene disorders indicate that the relationship between genotype and phenotype is very indirect and that, rather than identifying mere snapshots of developmental outcomes, the process of ontogenetic development itself must be taken into account.

Prevalence estimation of Williams syndrome

There are limited population-based data on the occurrence of Williams syndrome. We estimated its prevalence combining data from two investigations. One was an epidemiologic study originally designed to assess the prevalence and etiology of mental retardation among 30,037 Norwegian children born between 1980 and 1985 and living in Akershus County on January 1, 1993. The other investigation was a national survey of Williams syndrome. In the first study, 213 children were referred for evaluation, whereas the second study comprised 57 cases with Williams syndrome born between 1970 and 1992, who were referred for evaluation from all Norwegian counties. The epidemiologic study revealed three children with Williams syndrome, whereas one additional case complying with our demographic criteria was identified in the national survey, thus giving a prevalence of 1 in 7500. In all cases, a typical chromosome 7q11.23 deletion was detected. We also conclude that Williams syndrome is not an uncommon cause of mental retardation, with a prevalence of approximately 6% of patients with genetic etiology.

Generation and comparative analysis of approximately 3.3 Mb of mouse genomic sequence orthologous to the region of human chromosome 7q11.23 implicated in Williams syndrome

Williams syndrome is a complex developmental disorder that results from the heterozygous deletion of a approximately 1.6-Mb segment of human chromosome 7q11.23. These deletions are mediated by large (approximately 300 kb) duplicated blocks of DNA of near-identical sequence. Previously, we showed that the orthologous region of the mouse genome is devoid of such duplicated segments. Here, we extend our studies to include the generation of approximately 3.3 Mb of genomic sequence from the mouse Williams syndrome region, of which just over 1.4 Mb is finished to high accuracy. Comparative analyses of the mouse and human sequences within and immediately flanking the interval commonly deleted in Williams syndrome have facilitated the identification of nine previously unreported genes, provided detailed sequence-based information regarding 30 genes residing in the region, and revealed a number of potentially interesting conserved noncoding sequences. Finally, to facilitate comparative sequence analysis, we implemented several enhancements to the program, including the addition of links from annotated features within a generated percent-identity plot to specific records in public databases. Taken together, the results reported here provide an important comparative sequence resource that should catalyze additional studies of Williams syndrome, including those that aim to characterize genes within the commonly deleted interval and to develop mouse models of the disorder.