A Different Brain: Anomalies of Functional and Structural Connections in Williams Syndrome

Internalising and Externalising Symptoms and Their Association with the Family Environment in Young Children with Williams Syndrome: A Longitudinal Study

Williams Syndrome (WS) involves high rates of psychopathology across the lifespan. However, little is known about the early, longitudinal trajectory of internalising/externalising symptoms or the association between these and the family environment in WS. WS (n = 16; aged 2 years, 2 months to 9 years, 5 months) and typically developing or TD (n = 46; aged 2 years, 2 months to 11 years, 1 month) children were assessed on two occasions over 2.5 years utilising parent report questionnaires-the Child Behaviour Checklist and the Family Environment Scale. No statistically significant changes were found in CBCL/psychopathology profiles across timepoints, on average, for either WS or TD children. However, reliable change scores showed WS children had considerable variability in CBCL scores over time. Cross-sectionally, the WS group showed higher scores (reflecting more psychopathology) compared to TD controls at both time points across most CBCL subscales, with elevated overall psychopathology problems identified in 56-68% of WS children (versus 8% in TD controls). Psychopathology was not associated with sex, chronological age, or cognitive ability in WS. Conflict in the family environment was positively associated with higher Attention Problems at Time 1 in the WS group, whilst the TD group showed associations between family conflict and total psychopathology problems at both time points and between family cohesion and total psychopathology problems at Time 2. Family environment did not differ between groups, except for lower engagement in intellectual and cultural activities in WS. Findings highlight variable Internalising and Externalising Problems in young WS children over time, with greater biological than environmental contributions to psychopathology in WS.

Cognitive predictors of Social processing in congenital atypical development

According to current accounts of social cognition, the emergence of verbal and non-verbal components of social perception might rely on the acquisition of different cognitive abilities. These components might be differently sensitive to the pattern of neuropsychological impairments in congenital neurodevelopmental disorders. Here, we explored the association between social and non-social cognitive domains by administering subtests of the NEPSY-II battery to 92 patients with Intellectual and Developmental Disability (IDD). Regardless the level of intellectual functioning and presence of congenital brain malformations, results revealed that visuospatial skills predicted emotion recognition and verbal component of Theory of Mind, whereas imitation predicted the non-verbal one. Future interventions might focus on spatial and sensorimotor abilities to boost the development of social cognition in IDD.

Dorsal visual stream and LIMK1: hemideletion, haplotype, and enduring effects in children with Williams syndrome

BACKGROUND

Williams syndrome (WS), a rare neurodevelopmental disorder caused by hemizygous deletion of ~ 25 genes from chromosomal band 7q11.23, affords an exceptional opportunity to study associations between a well-delineated genetic abnormality and a well-characterized neurobehavioral profile. Clinically, WS is typified by increased social drive (often termed "hypersociability") and severe visuospatial construction deficits. Previous studies have linked visuospatial problems in WS with alterations in the dorsal visual processing stream. We investigated the impacts of hemideletion and haplotype variation of LIMK1, a gene hemideleted in WS and linked to neuronal maturation and migration, on the structure and function of the dorsal stream, specifically the intraparietal sulcus (IPS), a region known to be altered in adults with WS.

METHODS

We tested for IPS structural and functional changes using longitudinal MRI in a developing cohort of children with WS (76 visits from 33 participants, compared to 280 visits from 94 typically developing age- and sex-matched participants) over the age range of 5-22. We also performed MRI studies of 12 individuals with rare, shorter hemideletions at 7q11.23, all of which included LIMK1. Finally, we tested for effects of LIMK1 variation on IPS structure and imputed LIMK1 expression in two independent cohorts of healthy individuals from the general population.

RESULTS

IPS structural (p < 10-4 FDR corrected) and functional (p < .05 FDR corrected) anomalies previously reported in adults were confirmed in children with WS, and, consistent with an enduring genetic mechanism, were stable from early childhood into adulthood. In the short hemideletion cohort, IPS deficits similar to those in WS were found, although effect sizes were smaller than those found in WS for both structural and functional findings. Finally, in each of the two general population cohorts stratified by LIMK1 haplotype, IPS gray matter volume (pdiscovery < 0.05 SVC, preplication = 0.0015) and imputed LIMK1 expression (pdiscovery = 10-15, preplication = 10-23) varied according to LIMK1 haplotype.

CONCLUSIONS

This work offers insight into neurobiological and genetic mechanisms responsible for the WS phenotype and also more generally provides a striking example of the mechanisms by which genetic variation, acting by means of molecular effects on a neural intermediary, can influence human cognition and, in some cases, lead to neurocognitive disorders.

Neuroimaging Findings in Neurodevelopmental Copy Number Variants: Identifying Molecular Pathways to Convergent Phenotypes

Genomic copy number variants (CNVs) are associated with a high risk of neurodevelopmental disorders. A growing body of genetic studies suggests that these high-risk genetic variants converge in common molecular pathways and that common pathways also exist across clinically distinct disorders, such as schizophrenia and autism spectrum disorder. A key question is how common molecular mechanisms converge into similar clinical outcomes. We review emerging evidence for convergent cognitive and brain phenotypes across distinct CNVs. Multiple CNVs were shown to have similar effects on core sensory, cognitive, and motor traits. Emerging data from multisite neuroimaging studies have provided valuable information on how these CNVs affect brain structure and function. However, most of these studies examined one CNV at a time, making it difficult to fully understand the proportion of shared brain effects. Recent studies have started to combine neuroimaging data from multiple CNV carriers and identified similar brain effects across CNVs. Some early findings also support convergence in CNV animal models. Systems biology, through integration of multilevel data, provides new insights into convergent molecular mechanisms across genetic risk variants (e.g., altered synaptic activity). However, the link between such key molecular mechanisms and convergent psychiatric phenotypes is still unknown. To better understand this link, we need new approaches that integrate human molecular data with neuroimaging, cognitive, and animal model data, while taking into account critical developmental time points. Identifying risk mechanisms across genetic loci can elucidate the pathophysiology of neurodevelopmental disorders and identify new therapeutic targets for cross-disorder applications.

Altered White Matter and microRNA Expression in a Murine Model Related to Williams Syndrome Suggests That miR-34b/c Affects Brain Development via Ptpru and Dcx Modulation

Williams syndrome (WS) is a multisystem neurodevelopmental disorder caused by a de novo hemizygous deletion of ~26 genes from chromosome 7q11.23, among them the general transcription factor II-I (GTF2I). By studying a novel murine model for the hypersociability phenotype associated with WS, we previously revealed surprising aberrations in myelination and cell differentiation properties in the cortices of mutant mice compared to controls. These mutant mice had selective deletion of Gtf2i in the excitatory neurons of the forebrain. Here, we applied diffusion magnetic resonance imaging and fiber tracking, which showed a reduction in the number of streamlines in limbic outputs such as the fimbria/fornix fibers and the stria terminalis, as well as the corpus callosum of these mutant mice compared to controls. Furthermore, we utilized next-generation sequencing (NGS) analysis of cortical small RNAs' expression (RNA-Seq) levels to identify altered expression of microRNAs (miRNAs), including two from the miR-34 cluster, known to be involved in prominent processes in the developing nervous system. Luciferase reporter assay confirmed the direct binding of miR-34c-5p to the 3'UTR of PTPRU-a gene involved in neural development that was elevated in the cortices of mutant mice relative to controls. Moreover, we found an age-dependent variation in the expression levels of doublecortin (Dcx)-a verified miR-34 target. Thus, we demonstrate the substantial effect a single gene deletion can exert on miRNA regulation and brain structure, and advance our understanding and, hopefully, treatment of WS.

White matter alterations in Williams syndrome related to behavioral and motor impairments

Myelin is the electrical insulator surrounding the neuronal axon that makes up the white matter (WM) of the brain. It helps increase axonal conduction velocity (CV) by inducing saltatory conduction. Damage to the myelin sheath and WM is associated with many neurological and psychiatric disorders. Decreasing myelin deficits, and thus improving axonal conduction, has the potential to serve as a therapeutic mechanism for reducing the severity of some of these disorders. Myelin deficits have been previously linked to abnormalities in social behavior, suggesting an interplay between brain connectivity and sociability. This review focuses on Williams syndrome (WS), a genetic disorder characterized by neurocognitive characteristics and motor abnormalities, mainly known for its hypersociability characteristic. We discuss fundamental aspects of WM in WS and how its alterations can affect motor abilities and social behavior. Overall, findings regarding changes in myelin genes and alterations in WM structure in WS suggest new targets for drug therapy aimed at improving conduction properties and altering brain-activity synchronization in this disorder.

Williams syndrome hemideletion and LIMK1 variation both affect dorsal stream functional connectivity

Williams syndrome is a rare genetic disorder caused by hemizygous deletion of ∼1.6 Mb affecting 26 genes on chromosome 7 (7q11.23) and is clinically typified by two cognitive/behavioural hallmarks: marked visuospatial deficits relative to verbal and non-verbal reasoning abilities and hypersocial personality. Clear knowledge of the circumscribed set of genes that are affected in Williams syndrome, along with the well-characterized neurobehavioural phenotype, offers the potential to elucidate neurogenetic principles that may apply in genetically and clinically more complex settings. The intraparietal sulcus, in the dorsal visual processing stream, has been shown to be structurally and functionally altered in Williams syndrome, providing a target for investigating resting-state functional connectivity and effects of specific genes hemideleted in Williams syndrome. Here, we tested for effects of the LIMK1 gene, deleted in Williams syndrome and important for neuronal maturation and migration, on intraparietal sulcus functional connectivity. We first defined a target brain phenotype by comparing intraparietal sulcus resting functional connectivity in individuals with Williams syndrome, in whom LIMK1 is hemideleted, with typically developing children. Then in two separate cohorts from the general population, we asked whether intraparietal sulcus functional connectivity patterns similar to those found in Williams syndrome were associated with sequence variation of the LIMK1 gene. Four independent between-group comparisons of resting-state functional MRI data (total n = 510) were performed: (i) 20 children with Williams syndrome compared to 20 age- and sex-matched typically developing children; (ii) a discovery cohort of 99 healthy adults stratified by LIMK1 haplotype; (iii) a replication cohort of 32 healthy adults also stratified by LIMK1 haplotype; and (iv) 339 healthy adolescent children stratified by LIMK1 haplotype. For between-group analyses, differences in intraparietal sulcus resting-state functional connectivity were calculated comparing children with Williams syndrome to matched typically developing children and comparing LIMK1 haplotype groups in each of the three general population cohorts separately. Consistent with the visuospatial construction impairment and hypersocial personality that typify Williams syndrome, the Williams syndrome cohort exhibited opposite patterns of intraparietal sulcus functional connectivity with visual processing regions and social processing regions: decreased circuit function in the former and increased circuit function in the latter. All three general population groups also showed LIMK1 haplotype-related differences in intraparietal sulcus functional connectivity localized to the fusiform gyrus, a visual processing region also identified in the Williams syndrome-typically developing comparison. These results suggest a neurogenetic mechanism, in part involving LIMK1, that may bias neural circuit function in both the general population and individuals with Williams syndrome.

Williams syndrome: recent advances in our understanding of cognitive, social and psychological functioning

PURPOSE OF REVIEW

Since the last review of Williams syndrome in Current Opinion (2001) there have been many advances in knowledge about the cognitive, social and psychological impairments that characterize the disorder. The present review focuses on current research in these areas.

RECENT FINDINGS

Williams syndrome is associated with a wide range of cognitive, linguistic, social and other difficulties. When young, these deficits may appear relatively mild - for example, many children are highly sociable and talkative - but with age the impact of these difficulties becomes more evident. Thus, inappropriate social behaviours can significantly increase the risk of social exclusion and vulnerability to abuse. Their superficially good speech can lead to educational and other services failing to understand the true extent of impairments or the need for specialist support. Mental health problems, especially related to anxiety, often become an increasing challenge from adolescence onwards.

SUMMARY

The core difficulties associated with Williams syndrome have a cascading effect on many areas of development over time. However, specialist provision is rare and intervention trials are almost nonexistent. Longitudinal research is needed to identify factors associated with cognitive, social and emotional problems and to develop more effective ways of minimizing and treating difficulties.