Williams-Beuren syndrome: a model of recurrent genomic mutation

Late phonological development in Williams syndrome

Williams syndrome is a neurodevelopmental genetic disorder characterized by a unique phenotype, including mild to moderate intellectual disability and an uneven neuropsychological profile of relative strengths and weaknesses. Language structure components (i.e., phonology, morphosyntax, and vocabulary) have been considered an area of specific ability compared to pragmatic language use. However, research on phonological development in Williams syndrome is very scarce, and it suggests atypical patterns. Therefore, the aim of the present study was to explore the profiles of late phonological development in Spanish-speaking children, adolescents, and adults with Williams syndrome, based on the analysis of five classes of processes (Syllable Structure, Substitution, Omission, Assimilation, and Addition) in spontaneous speech. The phonological profiles of seven children (aged 3-8 years), and seven adolescents and young adults (aged 14-25 years) with Williams syndrome were compared with two normative groups of typically developing (TD) children at different stages of late phonological development (aged 3 and 5 years). The frequency of phonological processes in the group of children with Williams syndrome was similar to that of 3-year-old TD children, which suggests that they would be in the first stage of late phonological development (expansion stage). The group of older individuals with Williams syndrome showed a much lower frequency of processes, similar to that of 5-year-old TD children in the last stage of phonological development (resolution stage). However, their phonological processes appeared to be persistent and independent of chronological age. Furthermore, asynchronies in quantitative and qualitative profiles (relative frequency) indicated atypical and complex trajectories in late phonological development, which cannot be described as simply delayed or protracted. Remarkable individual differences were observed, especially in the group of adolescents and adults with Williams syndrome, although the majority of cases conformed to the modal profiles of their groups. A major tendency for Omission, including final consonant deletion, may be considered atypical and specific to Williams syndrome at all ages. The results of the present study raise the need for continued and appropriate phonological assessment and treatment for people with Williams syndrome across the lifespan.

Cannabinoid signaling modulation through JZL184 restores key phenotypes of a mouse model for Williams-Beuren syndrome

Williams–Beuren syndrome (WBS) is a rare genetic multisystemic disorder characterized by mild-to-moderate intellectual disability and hypersocial phenotype, while the most life-threatening features are cardiovascular abnormalities. Nowadays, there are no pharmacological treatments to directly ameliorate the main traits of WBS. The endocannabinoid system (ECS), given its relevance for both cognitive and cardiovascular function, could be a potential druggable target in this syndrome. We analyzed the components of the ECS in the complete deletion (CD) mouse model of WBS and assessed the impact of its pharmacological modulation in key phenotypes relevant for WBS. CD mice showed the characteristic hypersociable phenotype with no preference for social novelty and poor short-term object-recognition performance. Brain cannabinoid type-1 receptor (CB1R) in CD male mice showed alterations in density and coupling with no detectable change in main endocannabinoids. Endocannabinoid signaling modulation with subchronic (10 days) JZL184, a selective inhibitor of monoacylglycerol lipase, specifically normalized the social and cognitive phenotype of CD mice. Notably, JZL184 treatment improved cardiovascular function and restored gene expression patterns in cardiac tissue. These results reveal the modulation of the ECS as a promising novel therapeutic approach to improve key phenotypic alterations in WBS.

Williams-Beuren syndrome (WBS) is a rare disorder that causes hyper-social behavior, intellectual disability, memory problems, and life-threatening overgrowth of the heart. Behavioral therapies can help improve the cognitive and social aspects of the syndrome and surgery is sometimes used to treat the effects on the heart, although often with limited success. However, there are currently no medications available to treat WBS.

The endocannabinoid system – which consists of cannabis-like chemical messengers that bind to specific cannabinoid receptor proteins – has been shown to influence cognitive and social behaviors, as well as certain functions of the heart. This has led scientists to suspect that the endocannabinoid system may play a role in WBS, and drugs modifying this network of chemical messengers could help treat the rare condition.

To investigate, Navarro-Romero, Galera-López et al. studied mice which had the same genetic deletion found in patients with WBS. Similar to humans, the male mice displayed hyper-social behaviors, had memory deficits and enlarged hearts. Navarro-Romero, Galera-López et al. found that these mutant mice also had differences in the function of the receptor protein cannabinoid type-1 (CB1).

The genetically modified mice were then treated with an experimental drug called JZL184 that blocks the breakdown of endocannabinoids which bind to the CB1 receptor. This normalized the number and function of receptors in the brains of the WBS mice, and reduced their social and memory symptoms. The treatment also restored the animals’ heart cells to a more normal size, improved the function of their heart tissue, and led to lower blood pressure. Further experiments revealed that the drug caused the mutant mice to activate many genes in their heart muscle cells to the same level as normal, healthy mice.

These findings suggest that JZL184 or other drugs targeting the endocannabinoid system may help ease the symptoms associated with WBS. More studies are needed to test the drug’s effectiveness in humans with this syndrome. Furthermore, the dramatic effect JZL184 has on the heart suggests that it might also help treat high blood pressure or conditions that cause the overgrowth of heart cells.

Clinical and genetic characteristics of two cases with Williams-Beuren syndrome

Herein, we describe 2 cases of Williams-Beuren syndrome (WBS). In both cases, the patients exhibited mental retardation, characteristic facial features, and indirect inguinal hernia. Case 1, a girl aged 2 years and 5 months old, presented with hypercalcemia, and in case 2, a boy aged 4 years and 11 months old, the disorder manifested as infantile spasms, supravalvular aortic stenosis, and pulmonary stenosis. Brain MRI revealed no abnormalities in either case. The electroencephalogram of case 2 showed hypsarrhythmia. Case 1 was treated with bisphosphonates and somatropin for hypercalcemia and short stature. Case 2 received antiepileptic drug and ketogenic diet therapy. In both cases, a 7q11.23 deletion including fragment deletion of the GTF21 gene was found, which may be associated with mental retardation. Notably, in case 2, a 921.1kb deletion in Yq11.23 was detected, which has not been reported in WBS before. The deletion of Yq11.23 is located in the AZFc region, which is an important factor in male infertility with primary azoospermia and oligozoospermia. The occurrence of hypercalcemia in case 1 may be related to the deletion of BAZ1B, while the supravalvular aortic stenosis and pulmonary stenosis were associated with deletion of the ELN gene. We explored the clinical and genetic characteristics of WBS to better understand disease.

Evaluating quality of life in families with Williams Syndrome patients

Background

Williams Syndrome is a developmental disorder characterized by a variable intellectual disability. People with Williams Syndrome need the intervention of several clinical and educational specialists throughout their life. However, little is known about the impact produced by this disability in their immediate environment, especially in families. The purpose was to know the level of quality of life described by families with Williams Syndrome.

Methods

The sample was made up of 33 families belong to Spanish Williams Syndrome Association who were evaluated using the Kidslife Scale. Their children and adolescents were between 4 and 20 years old. Eight main quality of life domains were evaluated: emotional well-being, physical well-being, material well-being, personal development, interpersonal relations, social inclusion, self-determination and rights

Results

The obtained data indicated that the degree and presence of intellectual disability did not homogeneously influence people’s quality of life, but many variables could alter their quality of life to a greater or lesser extent. There are no significant differences between quality of life areas but significant differences appeared for level of dependence in the self-determination subarea (p < .05).

Conclusions

These results led us to analyse the social and emotional implications for families and their environment.

Drosophila Model for the Analysis of Genesis of LIM-kinase 1-Dependent Williams-Beuren Syndrome Cognitive Phenotypes: INDELs, Transposable Elements of the Tc1/Mariner Superfamily and MicroRNAs

Genomic disorders, the syndromes with multiple manifestations, may occur sporadically due to unequal recombination in chromosomal regions with specific architecture. Therefore, each patient may carry an individual structural variant of DNA sequence (SV) with small insertions and deletions (INDELs) sometimes less than 10 bp. The transposable elements of the Tc1/mariner superfamily are often associated with hotspots for homologous recombination involved in human genetic disorders, such as Williams Beuren Syndromes (WBS) with LIM-kinase 1-dependent cognitive defects. The Drosophila melanogaster mutant agnts3 has unusual architecture of the agnostic locus harboring LIMK1: it is a hotspot of chromosome breaks, ectopic contacts, underreplication, and recombination. Here, we present the analysis of LIMK1-containing locus sequencing data in agnts3 and three D. melanogaster wild-type strains-Canton-S, Berlin, and Oregon-R. We found multiple strain-specific SVs, namely, single base changes and small INDEls. The specific feature of agnts3 is 28 bp A/T-rich insertion in intron 1 of LIMK1 and the insertion of mobile S-element from Tc1/mariner superfamily residing ~460 bp downstream LIMK1 3'UTR. Neither of SVs leads to amino acid substitutions in agnts3 LIMK1. However, they apparently affect the nucleosome distribution, non-canonical DNA structure formation and transcriptional factors binding. Interestingly, the overall expression of miRNAs including the biomarkers for human neurological diseases, is drastically reduced in agnts3 relative to the wild-type strains. Thus, LIMK1 DNA structure per se, as well as the pronounced changes in total miRNAs profile, probably lead to LIMK1 dysregulation and complex behavioral dysfunctions observed in agnts3 making this mutant a simple plausible Drosophila model for WBS.

A Role for the Chromatin-Remodeling Factor BAZ1A in Neurodevelopment

Chromatin‐remodeling factors are required for a wide range of cellular and biological processes including development and cognition, mainly by regulating gene expression. As these functions would predict, deregulation of chromatin‐remodeling factors causes various disease syndromes, including neurodevelopmental disorders. Recent reports have linked mutations in several genes coding for chromatin‐remodeling factors to intellectual disability (ID). Here, we used exome sequencing and identified a nonsynonymous de novo mutation in BAZ1A (NM_182648.2:c.4043T > G, p.Phe1348Cys), encoding the ATP‐utilizing chromatin assembly and remodeling factor 1 (ACF1), in a patient with unexplained ID. ACF1 has been previously reported to bind to the promoter of the vitamin D receptor (VDR)‐regulated genes and suppress their expression. Our results show that the patient displays decreased binding of ACF1 to the promoter of the VDR‐regulated gene CYP24A1. Using RNA sequencing, we find that the mutation affects the expression of genes involved in several pathways including vitamin D metabolism, Wnt signaling and synaptic formation. RNA sequencing of BAZ1A knockdown cells and Baz1a knockout mice revealed that BAZ1A carry out distinctive functions in different tissues. We also demonstrate that BAZ1A depletion influence the expression of genes important for nervous system development and function. Our data point to an important role for BAZ1A in neurodevelopment, and highlight a possible link for BAZ1A to ID.

Facial emotion processing in patients with social anxiety disorder and Williams-Beuren syndrome: an fMRI study

BACKGROUND

Social anxiety disorder (SAD) and Williams-Beuren syndrome (WBS) are 2 conditions with major differences in terms of genetics, development and cognitive profiles. Both conditions are associated with compromised abilities in overlapping areas, including social approach, processing of social emotional cues and gaze behaviour, and to some extent they are associated with opposite behaviours in these domains. We examined common and distinct patterns of brain activation during a facial emotion processing paradigm in patients with SAD and WBS.

METHODS

We examined patients with SAD and WBS and healthy controls matched by age and laterality using functional MRI during the processing of happy, fearful and angry faces.

RESULTS

We included 20 patients with SAD and 20 with WBS as well as 20 matched controls in our study. Patients with SAD and WBS did not differ in the pattern of limbic activation. We observed differences in early visual areas of the face processing network in patients with WBS and differences in the cortical prefrontal regions involved in the top-down regulation of anxiety and in the fusiform gyrus for patients with SAD. Compared with those in the SAD and control groups, participants in the WBS group did not activate the right lateral inferior occipital cortex. In addition, compared with controls, patients with WBS hypoactivated the posterior primary visual cortex and showed significantly less deactivation in the right temporal operculum. Participants in the SAD group showed decreased prefrontal activation compared with those in the WBS and control groups. In addition, compared with controls, participants with SAD showed decreased fusiform activation. Participants with SAD and WBS also differed in the pattern of activation in the superior temporal gyrus, a region that has been linked to gaze processing.

LIMITATIONS

The results observed in the WBS group are limited by the IQ of the WBS sample; however, the specificity of findings suggests that the pattern of brain activation observed for WBS is more likely to reflect a neurobiological substrate rather than intellectual impairment per se.

CONCLUSION

Patients with SAD and WBS showed common and specific patterns of brain activation. Our results highlight the role of cortical regions during facial emotion processing in individuals with SAD and WBS.

Intracisternal Gtf2i Gene Therapy Ameliorates Deficits in Cognition and Synaptic Plasticity of a Mouse Model of Williams-Beuren Syndrome

Williams-Beuren syndrome (WBS) is a neurodevelopmental disorder caused by a heterozygous deletion of 26-28 genes at chromosome band 7q11.23. Haploinsufficiency at GTF2I has been shown to play a major role in the neurobehavioral phenotype. By characterizing the neuronal architecture in four animal models with intragenic, partial, and complete deletions of the WBS critical interval (ΔGtf2i(+/-), ΔGtf2i( -/-), PD, and CD), we clarify the involvement of Gtf2i in neurocognitive features. All mutant mice showed hypersociability, impaired motor learning and coordination, and altered anxiety-like behavior. Dendritic length was decreased in the CA1 of ΔGtf2i(+/-), ΔGtf2i ( -/-), and CD mice. Spine density was reduced, and spines were shorter in ΔGtf2i ( -/-), PD, and CD mice. Overexpression of Pik3r1 and downregulation of Bdnf were observed in ΔGtf2i(+/-), PD, and CD mice. Intracisternal Gtf2i-gene therapy in CD mice using adeno-associated virus resulted in increased mGtf2i expression and normalization of Bdnf levels, along with beneficial effects in motor coordination, sociability, and anxiety, despite no significant changes in neuronal architecture. Our findings further indicate that Gtf2i haploinsufficiency plays an important role in the neurodevelopmental and cognitive abnormalities of WBS and that it is possible to rescue part of this neurocognitive phenotype by restoring Gtf2i expression levels in specific brain areas.

Metabolic abnormalities in Williams-Beuren syndrome

BACKGROUND

Williams-Beuren syndrome (WBS, OMIM-194050) is a neurodevelopmental disorder with multisystemic manifestations caused by a 1.55-1.83 Mb deletion at 7q11.23 including 26-28 genes. Reported endocrine and metabolic abnormalities include transient hypercalcaemia of infancy, subclinical hypothyroidism in ∼ 30% of children and impaired glucose tolerance in ∼ 75% of adult individuals. The purpose of this study was to further study metabolic alterations in patients with WBS, as well as in several mouse models, to establish potential candidate genes.

METHODS

We analysed several metabolic parameters in a cohort of 154 individuals with WBS (data available from 69 to 151 cases per parameter), as well as in several mouse models with complete and partial deletions of the orthologous WBS locus, and searched for causative genes and potential modifiers.

RESULTS

Triglyceride plasma levels were significantly decreased in individuals with WBS while cholesterol levels were slightly decreased compared with controls. Hyperbilirubinemia, mostly unconjugated, was found in 18.3% of WBS cases and correlated with subclinical hypothyroidism and hypotriglyceridemia, suggesting common pathogenic mechanisms. Haploinsufficiency at MLXIPL and increased penetrance for hypomorphic alleles at the UGT1A1 gene promoter might underlie the lipid and bilirubin alterations. Other disturbances included increased protein and iron levels, as well as the known subclinical hypothyroidism and glucose intolerance.

CONCLUSIONS

Our results show that several unreported biochemical alterations, related to haploinsufficiency for specific genes at 7q11.23, are relatively common in WBS. The early diagnosis, follow-up and management of these metabolic disturbances could prevent long-term complications in this disorder.

Coeliac disease and risk for other autoimmune diseases in patients with Williams-Beuren syndrome

BACKGROUND

A higher prevalence of coeliac disease (CD) has been reported in patients with Williams-Beuren syndrome (WBS), though coexistence with other autoimmune diseases has not been evaluated.

OBJECTIVE

The aim of this study was to examine the prevalence of the more frequent autoimmune diseases and organ- and non-organ specific autoantibodies in WBS.

METHODS

We longitudinally analysed 46 WBS patients to evaluate the prevalence and co-occurrence of the major autoantibodies and HLA typing for CD diagnosis. These data were compared with healthy age- and sex-matched controls and Down (DS) and Turner (TS) syndrome patients.

RESULTS

CD was diagnosed in one (2.2%) WBS patient; this differed significantly from DS and TS (respectively, 10.5% and 9.4%; P < 0.005) but not from healthy controls (0.6%; P = NS). However, no patients with WBS showed anti-thyroid antibodies or other organ- and non-organ specific autoantibodies, which differed significantly from DS (respectively, 10.5% and 7.0%; P < 0.005) and TS (respectively, 9.4% and 9.3%; P < 0.005) patients but not from healthy controls (1.1% and 2.3%). The frequencies of CD-specific HLA-DQ heterodimers were not significantly higher than controls, even though the WBS patients more frequently carried the DQA1*0505 allele (57% vs. 39%; P < 0.05).

CONCLUSIONS

CD may not be more frequent in patients with WBS. In fact, no evidence of a significantly higher prevalence of other autoimmune diseases or positivity of the main organ and non-organ specific autoantibodies was found in WBS, such as showed in the healthy controls and unlike by the patients with Turner or Down syndrome. This should prompt us to better understand the occurrence of CD in WBS. Other studies or longer follow-up might be useful to clarify this issue.

Development of neurodevelopmental disorders: a regulatory mechanism involving bromodomain-containing proteins

Neurodevelopmental disorders are classified as diseases that cause abnormal functions of the brain or central nervous system. Children with neurodevelopmental disorders show impaired language and speech abilities, learning and memory damage, and poor motor skills. However, we still know very little about the molecular etiology of these disorders. Recent evidence implicates the bromodomain-containing proteins (BCPs) in the initiation and development of neurodevelopmental disorders. BCPs have a particular domain, the bromodomain (Brd), which was originally identified as specifically binding acetyl-lysine residues at the N-terminus of histone proteins in vitro and in vivo. Other domains of BCPs are responsible for binding partner proteins to form regulatory complexes. Once these complexes are assembled, BCPs alter chromosomal states and regulate gene expression. Some BCP complexes bind nucleosomes, are involved in basal transcription regulation, and influence the transcription of many genes. However, most BCPs are involved in targeting. For example, some BCPs function as a recruitment platform or scaffold through their Brds-binding targeting sites. Others are recruited to form a complex to bind the targeting sites of their partners. The regulation mediated by these proteins is especially critical during normal and abnormal development. Mutant BCPs or dysfunctional BCP-containing complexes are implicated in the initiation and development of neurodevelopmental disorders. However, the pathogenic molecular mechanisms are not fully understood. In this review, we focus on the roles of regulatory BCPs associated with neurodevelopmental disorders, including mental retardation, Fragile X syndrome (FRX), Williams syndrome (WS), Rett syndrome and Rubinstein-Taybi syndrome (RTS). A better understanding of the molecular pathogenesis, based upon the roles of BCPs, will lead to screening of targets for the treatment of neurodevelopmental disorders.

Functional and genetic characterization of two extremely rare cases of Williams-Beuren syndrome associated with chronic granulomatous disease

Williams-Beuren syndrome (WBS) is a neurodevelopmental disorder with multi-systemic manifestations, caused by a heterozygous segmental deletion of 1.55-1.83 Mb at chromosomal band 7q11.23. The deletion can include the NCF1 gene that encodes the p47(phox) protein, a component of the leukocyte NADPH oxidase enzyme, which is essential for the defense against microbial pathogens. It has been postulated that WBS patients with two functional NCF1 genes are more susceptible to occurrence of hypertension than WBS patients with only one functional NCF1 gene. We now describe two extremely rare WBS patients without any functional NCF1 gene, because of a mutation in NCF1 on the allele not carrying the NCF1-removing WBS deletion. These two patients suffer from chronic granulomatous disease with increased microbial infections in addition to WBS. Interestingly, one of these patients did suffer from hypertension, indicating that other factors than NADPH oxidase in vascular tissue may be involved in causing hypertension.

Epigenetic modulation by TFII-I during embryonic stem cell differentiation

TFII-I transcription factors play an essential role during early vertebrate embryogenesis. Genome-wide mapping studies by ChIP-seq and ChIP-chip revealed that TFII-I primes multiple genomic loci in mouse embryonic stem cells and embryonic tissues. Moreover, many TFII-I-bound regions co-localize with H3K4me3/K27me3 bivalent chromatin within the promoters of lineage-specific genes. This minireview provides a summary of current knowledge regarding the function of TFII-I in epigenetic control of stem cell differentiation.

A role for transcription factor GTF2IRD2 in executive function in Williams-Beuren syndrome

Executive functions are amongst the most heritable cognitive traits with twin studies indicating a strong genetic origin. However genes associated with this domain are unknown. Our research into the neurodevelopmental disorder Williams-Beuren syndrome (WBS) has identified a gene within the causative recurrent 1.5/1.6 Mb heterozygous microdeletion on chromosome 7q11.23, which may be involved in executive functioning. Comparative genome array screening of 55 WBS patients revealed a larger ∼1.8 Mb microdeletion in 18% of cases, which results in the loss of an additional gene, the transcription factor GTF2IRD2. The GTF gene family of transcription factors (GTF2I, GTF2IRD1 and GTF2IRD2) are all highly expressed in the brain, and GTF2I and GTF2IRD1 are involved in the pathogenesis of the cognitive and behavioural phenotypes associated with WBS. A multi-level analysis of cognitive, behavioural and psychological functioning in WBS patients showed that those with slightly larger deletions encompassing GTF2IRD2 were significantly more cognitively impaired in the areas of spatial functioning, social reasoning, and cognitive flexibility (a form of executive functioning). They also displayed significantly more obsessions and externalizing behaviours, a likely manifestation of poor cognitive flexibility and executive dysfunction. We provide the first evidence for a role for GTF2IRD2 in higher-level (executive functioning) abilities and highlight the importance of integrating detailed molecular characterisation of patients with comprehensive neuropsychological profiling to uncover additional genotype-phenotype correlations. The identification of specific genes which contribute to executive function has important neuropsychological implications in the treatment of patients with conditions like WBS, and will allow further studies into their mechanism of action.

Essential role of the N-terminal region of TFII-I in viability and behavior

Background

GTF2I codes for a general intrinsic transcription factor and calcium channel regulator TFII-I, with high and ubiquitous expression, and a strong candidate for involvement in the morphological and neuro-developmental anomalies of the Williams-Beuren syndrome (WBS). WBS is a genetic disorder due to a recurring deletion of about 1,55-1,83 Mb containing 25-28 genes in chromosome band 7q11.23 including GTF2I. Completed homozygous loss of either the Gtf2i or Gtf2ird1 function in mice provided additional evidence for the involvement of both genes in the craniofacial and cognitive phenotype. Unfortunately nothing is now about the behavioral characterization of heterozygous mice.

Methods

By gene targeting we have generated a mutant mice with a deletion of the first 140 amino-acids of TFII-I. mRNA and protein expression analysis were used to document the effect of the study deletion. We performed behavioral characterization of heterozygous mutant mice to document in vivo implications of TFII-I in the cognitive profile of WBS patients.

Results

Homozygous and heterozygous mutant mice exhibit craniofacial alterations, most clearly represented in homozygous condition. Behavioral test demonstrate that heterozygous mutant mice exhibit some neurobehavioral alterations and hyperacusis or odynacusis that could be associated with specific features of WBS phenotype. Homozygous mutant mice present highly compromised embryonic viability and fertility. Regarding cellular model, we documented a retarded growth in heterozygous MEFs respect to homozygous or wild-type MEFs.

Conclusion

Our data confirm that, although additive effects of haploinsufficiency at several genes may contribute to the full craniofacial or neurocognitive features of WBS, correct expression of GTF2I is one of the main players. In addition, these findings show that the deletion of the fist 140 amino-acids of TFII-I altered it correct function leading to a clear phenotype, at both levels, at the cellular model and at the in vivo model.

A genome-wide screen for modifiers of transgene variegation identifies genes with critical roles in development

An extended ENU screen for modifiers of transgene variegation identified four new modifiers, MommeD7-D10.

Background

Some years ago we established an N-ethyl-N-nitrosourea screen for modifiers of transgene variegation in the mouse and a preliminary description of the first six mutant lines, named MommeD1-D6, has been published. We have reported the underlying genes in three cases: MommeD1 is a mutation in SMC hinge domain containing 1 (Smchd1), a novel modifier of epigenetic gene silencing; MommeD2 is a mutation in DNA methyltransferase 1 (Dnmt1); and MommeD4 is a mutation in Smarca 5 (Snf2h), a known chromatin remodeler. The identification of Dnmt1 and Smarca5 attest to the effectiveness of the screen design.

Results

We have now extended the screen and have identified four new modifiers, MommeD7-D10. Here we show that all ten MommeDs link to unique sites in the genome, that homozygosity for the mutations is associated with severe developmental abnormalities and that heterozygosity results in phenotypic abnormalities and reduced reproductive fitness in some cases. In addition, we have now identified the underlying genes for MommeD5 and MommeD10. MommeD5 is a mutation in Hdac1, which encodes histone deacetylase 1, and MommeD10 is a mutation in Baz1b (also known as Williams syndrome transcription factor), which encodes a transcription factor containing a PHD-type zinc finger and a bromodomain. We show that reduction in the level of Baz1b in the mouse results in craniofacial features reminiscent of Williams syndrome.

Conclusions

These results demonstrate the importance of dosage-dependent epigenetic reprogramming in the development of the embryo and the power of the screen to provide mouse models to study this process.

Copy number variation at the 7q11.23 segmental duplications is a susceptibility factor for the Williams-Beuren syndrome deletion

Large copy number variants (CNVs) have been recently found as structural polymorphisms of the human genome of still unknown biological significance. CNVs are significantly enriched in regions with segmental duplications or low-copy repeats (LCRs). Williams-Beuren syndrome (WBS) is a neurodevelopmental disorder caused by a heterozygous deletion of contiguous genes at 7q11.23 mediated by nonallelic homologous recombination (NAHR) between large flanking LCRs and facilitated by a structural variant of the region, a approximately 2-Mb paracentric inversion present in 20%-25% of WBS-transmitting progenitors. We now report that eight out of 180 (4.44%) WBS-transmitting progenitors are carriers of a CNV, displaying a chromosome with large deletion of LCRs. The prevalence of this CNV among control individuals and non-transmitting progenitors is much lower (1%, n=600), thus indicating that it is a predisposing factor for the WBS deletion (odds ratio 4.6-fold, P= 0.002). LCR duplications were found in 2.22% of WBS-transmitting progenitors but also in 1.16% of controls, which implies a non-statistically significant increase in WBS-transmitting progenitors. We have characterized the organization and breakpoints of these CNVs, encompassing approximately 100-300 kb of genomic DNA and containing several pseudogenes but no functional genes. Additional structural variants of the region have also been defined, all generated by NAHR between different blocks of segmental duplications. Our data further illustrate the highly dynamic structure of regions rich in segmental duplications, such as the WBS locus, and indicate that large CNVs can act as susceptibility alleles for disease-associated genomic rearrangements in the progeny.

Solution structure of the general transcription factor 2I domain in mouse TFII-I protein

The general transcription factor TFII-I, with the corresponding gene name GTF2I, is an unusual transcriptional regulator that associates with both basal and signal-induced transcription factors. TFII-I consists of six GTF2I repeat domains, called I-repeats R1-R6. The structure and function of the GTF2I domain are not clearly understood, even though it contains a helix-loop-helix motif, which is considered to be the protein-protein interaction area, based on biochemical analyses. Here, we report the solution structure of the fifth repeat of the six GTF2I repeat domains from murine TFII-I, which was determined by heteronuclear multidimensional NMR spectroscopy (PDB code 1Q60). The three-dimensional structure of the GTF2I domain is classified as a new fold, consisting of four helices (residues 8-24, 34-39, 63-71, and 83-91), two antiparallel beta strands (residues 44-47 and 77-80), and a well-defined loop containing two beta-turns between sheet 1 and helix 3. All of the repeats probably have similar folds to that of repeat 5, because the conserved residues in the GTF2I repeat domains are assembled on the hydrophobic core, turns, and secondary structure elements, as revealed by a comparison of the sequences of the first through the sixth GTF2I repeats in TFII-I.

Expression of Gtf2ird1, the Williams syndrome-associated gene, during mouse development

The gene GTF2IRD1 is localized within the critical region on chromosome 7 that is deleted in Williams syndrome patients. Genotype-phenotype comparisons of patients carrying variable deletions within this region have implicated GTF2IRD1 and a closely related homolog, GTF2I, as prime candidates for the causation of the principal symptoms of Williams syndrome. We have generated mice with an nls-LacZ knockin mutation of the Gtf2ird1 allele to study its functional role and examine its expression profile. In adults, expression is most prominent in neurons of the central and peripheral nervous system, the retina of the eye, the olfactory epithelium, the spiral ganglion of the cochlea, brown fat adipocytes and to a lesser degree myocytes of the heart and smooth muscle. During development, a dynamic pattern of expression is found predominantly in musculoskeletal tissues, the pituitary, craniofacial tissues, the eyes and tooth buds. Expression of Gtf2ird1 in these tissues correlates with the manifestation of some of the clinical features of Williams syndrome.

Hemizygosity at the NCF1 gene in patients with Williams-Beuren syndrome decreases their risk of hypertension

Williams-Beuren syndrome (WBS), caused by a heterozygous deletion at 7q11.23, represents a model for studying hypertension, the leading risk factor for mortality worldwide, in a genetically determined disorder. Haploinsufficiency at the elastin gene is known to lead to the vascular stenoses in WBS and is also thought to predispose to hypertension, present in approximately 50% of patients. Detailed clinical and molecular characterization of 96 patients with WBS was performed to explore clinical-molecular correlations. Deletion breakpoints were precisely defined and were found to result in variability at two genes, NCF1 and GTF2IRD2. Hypertension was significantly less prevalent in patients with WBS who had the deletion that included NCF1 (P=.02), a gene coding for the p47(phox) subunit of the NADPH oxidase. Decreased p47(phox) protein levels, decreased superoxide anion production, and lower protein nitrotyrosination were all observed in cell lines from patients hemizygous at NCF1. Our results indicate that the loss of a functional copy of NCF1 protects a proportion of patients with WBS against hypertension, likely through a lifelong reduced angiotensin II-mediated oxidative stress. Therefore, antioxidant therapy that reduces NADPH oxidase activity might have a potential benefit in identifiable patients with WBS in whom serious complications related to hypertension have been reported, as well as in forms of essential hypertension mediated by a similar pathogenic mechanism.

Direct duplication 12p11.21-p13.31 mediated by segmental duplications: a new recurrent rearrangement?

We describe the characterization of an interstitial duplication of 12p, dup(12)(p11.21p13.31), by array-CGH and FISH in a patient with mental retardation and dysmorphic features. The sequence analysis of the breakpoints revealed the presence of homologous low copy repeats (LCRs) flanking the duplication region, thus suggesting that they have mediated the rearrangement. Pip-maker analysis showed that a third cluster of homologous LCRs lie distally to the two mediating the 12p duplication. We hypothesize that this duplication might be a new recurrent rearrangement and that, thanks to the different orientations of the homologous regions lying within each cluster, the three clusters are responsible for at least some of the several 12p aneuploidies reported in the literature such as direct and inverted duplications, deletions and supernumerary analphoid chromosomes. Moreover, we excluded that polymorphic inversions between these three clusters are present in the normal population.

Thyroid function and morphology in patients affected by Williams syndrome

OBJECTIVE

To evaluate the prevalence of abnormalities of thyroid function and morphology in a cohort of patients with Williams syndrome (WS).

METHODS

Serum concentrations of free-T3, free-T4, TSH, thyroperoxidase antibodies (TPOA) and thyroglobulin antibodies (TgA), as well as ultrasonographic data, of 20 patients with WS (12 females and eight males), aged 1.7-34.9 years, were evaluated.

RESULTS

Three cases (15%) of subclinical hypothyroidism were identified. Overt hypothyroidism was diagnosed in two cases (10%). Thyroid antibodies were negative in all patients. Fourteen patients (70%) showed thyroid hypoplasia involving the entire gland. In these patients, the left thyroid lobe appeared usually, but not significantly, reduced compared with the right thyroid lobe. One patient (5%) showed thyroid hemiagenesis. Only five patients (25%) showed a thyroid with normal volume, and of these five, one patient showed marked thyroid hypoplasia of the left lobe. In all WS patients with diagnosis of subclinical or overt hypothyroidism, thyroid hypoplasia was detected. No cases of subclinical or overt hypothyroidism were found in WS with normal thyroid volume.

CONCLUSIONS

This study confirms the presence of alterations of thyroid function in WS and also suggests the frequent occurrence of abnormalities of thyroid morphology in these patients. Patients with WS should be monitored for thyroid function and a thyroid ultrasound screening should be considered, especially in those patients with changes in thyroid function.

Relative sparing of primary auditory cortex in Williams Syndrome

Williams Syndrome (WS) is a neurodevelopment disorder associated with a hemizygous deletion on chromosome 7. WS is characterized with mental retardation, severe visual-spatial deficits, relative language preservation, and excellent facial recognition. Distinctive auditory features include musical ability, heightened sound sensitivity, and specific patterns of auditory evoked potentials. These features have led to the hypothesis that the dorsal forebrain is more affected than the ventral. Previously, we reported primary visual area 17 abnormalities in rostral striate cortex, a region contributing to the dorsal visual pathway. Based on the dorsal-ventral hypothesis, and language and auditory findings, we predicted a more normal histometric picture in auditory area 41. We used an optical dissector method to measure neurons in layers II-VI of area 41 in right and left hemispheres of the same 3 WS and 3 control brains used in the area 17 study. There was a hemisphere by diagnosis interaction in cell packing density (CPD) in layer IV and in cell size in layer III between WS and control brains. Post hoc analysis disclosed in control brains, but not WS, a layer IV left > right asymmetry in CPD, and a layer III left < right asymmetry in cell size. WS brains showed more large neurons bilaterally in layer II and in left layer VI. Histometric alterations in area 41 were less widespread than rostral visual cortex. Also, there was less asymmetry in the WS brain. We interpret layers II and VI differences as reflecting increased limbic connectivity in primary auditory cortex of WS.

GTF2IRD2 is located in the Williams-Beuren syndrome critical region 7q11.23 and encodes a protein with two TFII-I-like helix-loop-helix repeats

Williams-Beuren syndrome (also known as Williams syndrome) is caused by a deletion of a 1.55- to 1.84-megabase region from chromosome band 7q11.23. GTF2IRD1 and GTF2I, located within this critical region, encode proteins of the TFII-I family with multiple helix-loop-helix domains known as I repeats. In the present work, we characterize a third member, GTF2IRD2, which has sequence and structural similarity to the GTF2I and GTF2IRD1 paralogs. The ORF encodes a protein with several features characteristic of regulatory factors, including two I repeats, two leucine zippers, and a single Cys-2/His-2 zinc finger. The genomic organization of human, baboon, rat, and mouse genes is well conserved. Our exon-by-exon comparison has revealed that GTF2IRD2 is more closely related to GTF2I than to GTF2IRD1 and apparently is derived from the GTF2I sequence. The comparison of GTF2I and GTF2IRD2 genes revealed two distinct regions of homology, indicating that the helix-loop-helix domain structure of the GTF2IRD2 gene has been generated by two independent genomic duplications. We speculate that GTF2I is derived from GTF2IRD1 as a result of local duplication and the further evolution of its structure was associated with its functional specialization. Comparison of genomic sequences surrounding GTF2IRD2 genes in mice and humans allows refinement of the centromeric breakpoint position of the primate-specific inversion within the Williams-Beuren syndrome critical region.

The subcellular localization of the ChoRE-binding protein, encoded by the Williams–Beuren syndrome critical region gene 14, is regulated by 14-3-3

The Williams-Beuren syndrome (WBS) is a contiguous gene syndrome caused by chromosomal rearrangements at chromosome band 7q11.23. Several endocrine phenotypes, in particular impaired glucose tolerance and silent diabetes, have been described for this clinically complex disorder. The WBSCR14 gene, one of the genes mapping to the WBS critical region, encodes a member of the basic-helix-loop-helix leucine zipper family of transcription factors, which dimerizes with the Max-like protein, Mlx. This heterodimeric complex binds and activates, in a glucose-dependent manner, carbohydrate response element (ChoRE) motifs in the promoter of lipogenic enzymes. We identified five novel WBSCR14-interacting proteins, four 14-3-3 isotypes and NIF3L1, which form a single polypeptide complex in mammalian cells. Phosphatase treatment abrogates the association between WBSCR14 and 14-3-3, as shown previously for multiple 14-3-3 interactors. WBSCR14 is exported actively from the nucleus through a CRM1-dependent mechanism. This translocation is contingent upon the ability to bind 14-3-3. Through this mechanism the 14-3-3 isotypes directly affect the WBSCR14:Mlx complexes, which activate the transcription of lipogenic genes.

Mutational mechanisms of Williams-Beuren syndrome deletions

Williams-Beuren syndrome (WBS) is a segmental aneusomy syndrome that results from a heterozygous deletion of contiguous genes at 7q11.23. Three large region-specific low-copy repeat elements (LCRs), composed of different blocks (A, B, and C), flank the WBS deletion interval and are thought to predispose to misalignment and unequal crossing-over, causing the deletions. In this study, we have determined the exact deletion size and LCR copy number in 74 patients with WBS, as well as precisely defined deletion breakpoints in 30 of them, using LCR-specific nucleotide differences. Most patients (95%) exhibit a 1.55-Mb deletion caused by recombination between centromeric and medial block B copies, which share approximately 99.6% sequence identity along 105-143 kb. In these cases, deletion breakpoints were mapped at several sites within the recombinant block B, with a cluster (>27%) occurring at a 12 kb region within the GTF2I/GTF2IP1 gene. Almost one-third (28%) of the transmitting progenitors were found to be heterozygous for an inversion between centromeric and telomeric LCRs. All deletion breakpoints in the patients with the inversion occurred in the distal 38-kb block B region only present in the telomeric and medial copies. Finally, only four patients (5%) displayed a larger deletion ( approximately 1.84 Mb) caused by recombination between centromeric and medial block A copies. We propose models for the specific pairing and precise aberrant recombination leading to each of the different germline rearrangements that occur in this region, including inversions and deletions associated with WBS. Chromosomal instability at 7q11.23 is directly related to the genomic structure of the region.