Development of a Social Communication Questionnaire (QSC-ID) for People With Intellectual Disability in a Deaf Sample: A Pilot and Feasibility Study.

Background: Social communication (SC) includes the use and interpretation of verbal and non-verbal messages within a social context and thus requires more than knowledge of language. Social communication skills are essential for connecting and engaging with others, and SC deficits are often associated with emotional and behavioral problems. There is a lack of feasible instruments for assessing SC skills in individuals with intellectual disability (ID). Methods: A questionnaire on social communication in adults with ID (QSC-ID) comprising 20 Likert-scaled items was developed and completed on behalf of participants (n = 52) from three Austrian therapeutic living communities for people with ID and deafness by their living- and working-facility key caregivers. The sample of adults with hearing loss was considered ideal for the development of a measure of SC that is not restricted to a specific communication mode or overly related with language skills. Results: The preliminary results showed high construct validity. Correlations were high between SC and language, social skills, and severity of autism spectrum disorder (ASD), moderate between SC and adaptive skills, and non-verbal intelligence and, as expected, low between SC and motor skills. Interrater reliability was found to be good or at least acceptable for all items. Total raw scores were well-distributed over the whole range-Cut-offs based on the 10th and 20th percentile are suggested to identify atypical and borderline SC skills. Caregiver feedback and completeness of data suggest that the questionnaire is highly feasible. Conclusion: Questionnaire on social communication in adults with ID is an easy-to-use caregiver-reported questionnaire for use with individuals with mild to severe forms of ID. Initial testing of validity looks promising. Further validation in populations with typical hearing is required. Due to substantial correlations between SC and structural language skills the calculation of specific SC cut-offs for different levels of linguistic skills should be considered when sufficient data is available.

SCA7 Mouse Cerebellar Pathology Reveals Preferential Downregulation of Key Purkinje Cell-Identity Genes and Shared Disease Signature with SCA1 and SCA2.

Spinocerebellar ataxia type 7 (SCA7) is an inherited neurodegenerative disease mainly characterized by motor incoordination because of progressive cerebellar degeneration. SCA7 is caused by polyglutamine expansion in ATXN7, a subunit of the transcriptional coactivator SAGA, which harbors histone modification activities. Polyglutamine expansions in specific proteins are also responsible for SCA1-SCA3, SCA6, and SCA17; however, the converging and diverging pathomechanisms remain poorly understood. Using a new SCA7 knock-in mouse, SCA7140Q/5Q, we analyzed gene expression in the cerebellum and assigned gene deregulation to specific cell types using published datasets. Gene deregulation affects all cerebellar cell types, although at variable degree, and correlates with alterations of SAGA-dependent epigenetic marks. Purkinje cells (PCs) are by far the most affected neurons and show reduced expression of 83 cell-type identity genes, including these critical for their spontaneous firing activity and synaptic functions. PC gene downregulation precedes morphologic alterations, pacemaker dysfunction, and motor incoordination. Strikingly, most PC genes downregulated in SCA7 have also decreased expression in SCA1 and SCA2 mice, revealing converging pathomechanisms and a common disease signature involving cGMP-PKG and phosphatidylinositol signaling pathways and LTD. Our study thus points out molecular targets for therapeutic development, which may prove beneficial for several SCAs. Furthermore, we show that SCA7140Q/5Q males and females exhibit the major disease features observed in patients, including cerebellar damage, cerebral atrophy, peripheral nerves pathology, and photoreceptor dystrophy, which account for progressive impairment of behavior, motor, and visual functions. SCA7140Q/5Q mice represent an accurate model for the investigation of different aspects of SCA7 pathogenesis.SIGNIFICANCE STATEMENT Spinocerebellar ataxia 7 (SCA7) is one of the several forms of inherited SCAs characterized by cerebellar degeneration because of polyglutamine expansion in specific proteins. The ATXN7 involved in SCA7 is a subunit of SAGA transcriptional coactivator complex. To understand the pathomechanisms of SCA7, we determined the cell type-specific gene deregulation in SCA7 mouse cerebellum. We found that the Purkinje cells are the most affected cerebellar cell type and show downregulation of a large subset of neuronal identity genes, critical for their spontaneous firing and synaptic functions. Strikingly, the same Purkinje cell genes are downregulated in mouse models of two other SCAs. Thus, our work reveals a disease signature shared among several SCAs and uncovers potential molecular targets for their treatment.

Mutations in the KIF21B kinesin gene cause neurodevelopmental disorders through imbalanced canonical motor activity.

KIF21B is a kinesin protein that promotes intracellular transport and controls microtubule dynamics. We report three missense variants and one duplication in KIF21B in individuals with neurodevelopmental disorders associated with brain malformations, including corpus callosum agenesis (ACC) and microcephaly. We demonstrate, in vivo, that the expression of KIF21B missense variants specifically recapitulates patients' neurodevelopmental abnormalities, including microcephaly and reduced intra- and inter-hemispheric connectivity. We establish that missense KIF21B variants impede neuronal migration through attenuation of kinesin autoinhibition leading to aberrant KIF21B motility activity. We also show that the ACC-related KIF21B variant independently perturbs axonal growth and ipsilateral axon branching through two distinct mechanisms, both leading to deregulation of canonical kinesin motor activity. The duplication introduces a premature termination codon leading to nonsense-mediated mRNA decay. Although we demonstrate that Kif21b haploinsufficiency leads to an impaired neuronal positioning, the duplication variant might not be pathogenic. Altogether, our data indicate that impaired KIF21B autoregulation and function play a critical role in the pathogenicity of human neurodevelopmental disorder.

Loss of zebrafish Ataxin-7, a SAGA subunit responsible for SCA7 retinopathy, causes ocular coloboma and malformation of photoreceptors.

Polyglutamine (polyQ) expansion in Ataxin-7 (ATXN7) results in spinocerebellar ataxia type 7 (SCA7) and causes visual impairment. SCA7 photoreceptors progressively lose their outer segments (OSs), a structure essential for their visual function. ATXN7 is a subunit of the transcriptional coactivator Spt-Ada-Gcn5 Acetyltransferase complex, implicated in the development of the visual system in flies. To determine the function of ATXN7 in the vertebrate eye, we have inactivated ATXN7 in zebrafish. While ATXN7 depletion in flies led to gross retinal degeneration, in zebrafish, it primarily results in ocular coloboma, a structural malformation responsible for pediatric visual impairment in humans. ATXN7 inactivation leads to elevated Hedgehog signaling in the forebrain, causing an alteration of proximo-distal patterning of the optic vesicle during early eye development and coloboma. At later developmental stages, malformations of photoreceptors due to incomplete formation of their OSs are observed and correlate with altered expression of crx, a key transcription factor involved in the formation of photoreceptor OS. Therefore, we propose that a primary toxic effect of polyQ expansion is the alteration of ATXN7 function in the daily renewal of OS in SCA7. Together, our data indicate that ATXN7 plays an essential role in vertebrate eye morphogenesis and photoreceptor differentiation, and its loss of function may contribute to the development of human coloboma.

A novel function of Huntingtin in the cilium and retinal ciliopathy in Huntington's disease mice.

Huntington's disease (HD) is a neurodegenerative disorder caused by the toxic expansion of polyglutamine in the Huntingtin (HTT) protein. The pathomechanism is complex and not fully understood. Increasing evidence indicates that the loss of normal protein function also contributes to the pathogenesis, pointing out the importance of understanding the physiological roles of HTT. We provide evidence for a novel function of HTT in the cilium. HTT localizes in diverse types of cilia--including 9 + 0 non-motile sensory cilia of neurons and 9 + 2 motile multicilia of trachea and ependymal cells--which exert various functions during tissue development and homeostasis. In the photoreceptor cilium, HTT is present in all subciliary compartments from the base of the cilium and adjacent centriole to the tip of the axoneme. In HD mice, photoreceptor cilia are abnormally elongated, have hyperacetylated alpha-tubulin and show mislocalization of the intraflagellar transport proteins IFT57 and IFT88. As a consequence, intraflagellar transport function is perturbed and leads to aberrant accumulation of outer segment proteins in the photoreceptor cell bodies and disruption of outer segment integrity, all of which precede overt cell death. Strikingly, endogenous mouse HTT is strongly reduced in cilia and accumulates in photoreceptor cell bodies, suggesting that HTT loss function contributes to structural and functional defects of photoreceptor cilia in HD mouse. Our results indicate that cilia pathology participates in HD physiopathology and may represent a therapeutic target.

Transcriptional activation of REST by Sp1 in Huntington's disease models.

In Huntington's disease (HD), mutant huntingtin (mHtt) disrupts the normal transcriptional program of disease neurons by altering the function of several gene expression regulators such as Sp1. REST (Repressor Element-1 Silencing Transcription Factor), a key regulator of neuronal differentiation, is also aberrantly activated in HD by a mechanism that remains unclear. Here, we show that the level of REST mRNA is increased in HD mice and in NG108 cells differentiated into neuronal-like cells and expressing a toxic mHtt fragment. Using luciferase reporter gene assay, we delimited the REST promoter regions essential for mHtt-mediated REST upregulation and found that they contain Sp factor binding sites. We provide evidence that Sp1 and Sp3 bind REST promoter and interplay to fine-tune REST transcription. In undifferentiated NG108 cells, Sp1 and Sp3 have antagonistic effect, Sp1 acting as an activator and Sp3 as a repressor. Upon neuronal differentiation, we show that the amount and ratio of Sp1/Sp3 proteins decline, as does REST expression, and that the transcriptional role of Sp3 shifts toward a weak activator. Therefore, our results provide new molecular information to the transcriptional regulation of REST during neuronal differentiation. Importantly, specific knockdown of Sp1 abolishes REST upregulation in NG108 neuronal-like cells expressing mHtt. Our data together with earlier reports suggest that mHtt triggers a pathogenic cascade involving Sp1 activation, which leads to REST upregulation and repression of neuronal genes.

Polyglutamine toxicity induces rod photoreceptor division, morphological transformation or death in spinocerebellar ataxia 7 mouse retina.

In neurodegenerative disorders caused by polyglutamine (polyQ) expansion, polyQ toxicity is thought to trigger a linear cascade of successive degenerative events leading to neuronal death. To understand how neurons cope with polyQ toxicity, we studied a Spinocerebellar ataxia 7 (SCA7) mouse which expresses polyQ-expanded ATXN7 only in rod photoreceptors. We show that in response to polyQ toxicity, SCA7 rods go through a range of radically different cell fates, including apoptotic and non-apoptotic cell death, cell migration, morphological transformation into a round cell or, most remarkably, cell division. The temporal profile of retinal remodeling indicates that some degenerative pathways are triggered early in the disease but decline later on, while others worsen progressively. Retinal remodeling results in a relative maintenance of photoreceptor population, but does not preserve the retinal function. Rod responses to proteotoxicity correlate with the nature, level and ratio of mutant ATXN7 species. The multifaceted response of neurons to polyQ toxicity is an important concept for the design of therapeutic strategies.

Mapping of the epitope of monoclonal antibody 2B4 to the proline-rich region of human Huntingtin, a region critical for aggregation and toxicity.

Huntington's disease is a neurodegenerative disease caused by a polyglutamine (polyQ) expansion in Huntingtin, which provokes aggregation of a proteolytic amino-terminal fragment of the affected protein encompassing the polyQ expansion. Accumulation of mutant Huntingtin somehow triggers cellular dysfunction and leads to a progressive degeneration of striatal neurons. Despite considerable efforts, the function of Huntingtin as well as the precise molecular mechanisms by which the expanded polyQ elicits cellular dysfunction remain unclear. In addition, no treatment is available to prevent, cure, or even slow down the progression of this devastating disorder. Antibodies are valuable tools to understand protein function and disease mechanisms. Here, we have identified the epitope recognized by the mAb 2B4, a broadly used antibody generated against the amino-terminal region of Huntingtin, which detects both aggregated and soluble Huntingtin. The 2B4 antibody specifically recognizes amino acids 50-64 of human Huntingtin but not the murine homologous region. Furthermore, the 2B4 epitope resides within the proline-rich region of Huntingtin, which is critical for polyQ aggregation and toxicity. These properties suggest that the 2B4 antibody might be useful in antibody-based therapeutic strategies.

Preventing polyglutamine-induced activation of c-Jun delays neuronal dysfunction in a mouse model of SCA7 retinopathy.

We have approached the role of cellular stress in neurodegenerative diseases caused by polyglutamine expansion (polyQ) in the context of Spinocerebellar ataxia type 7 (SCA7) that includes retinal degeneration. Using the R7E mouse, in which polyQ-ataxin-7 is specifically over-expressed in rod photoreceptors, we previously showed that rod dysfunction correlated to moderate and prolonged activation of the JNK/c-Jun stress pathway. SCA7 retinopathy was also associated with reduced expression of rod-specific genes, including the transcription factor Nrl, which is essential for rod differentiation and function. Here, we report that R7E retinopathy is improved upon breeding with the JunAA knock-in mice, in which JNK-mediated activation of c-Jun is compromised. Expression of Nrl and its downstream targets, which are involved in phototranduction, are partially restored in the JunAA-R7E mice. We further show that c-Jun can directly repress the transcription of Nrl. Our studies suggest that polyQ-induced cellular stress leads to repression of genes necessary for neuronal fate and function.

Polyglutamine expansion causes neurodegeneration by altering the neuronal differentiation program.

Huntington's disease (HD) and spinocerebellar ataxia type 7 (SCA7) belong to a group of inherited neurodegenerative diseases caused by polyglutamine (polyQ) expansion in corresponding proteins. Transcriptional alteration is a unifying feature of polyQ disorders; however, the relationship between polyQ-induced gene expression deregulation and degenerative processes remains unclear. R6/2 and R7E mouse models of HD and SCA7, respectively, present a comparable retinal degeneration characterized by progressive reduction of electroretinograph activity and important morphological changes of rod photoreceptors. The retina, which is a simple central nervous system tissue, allows correlating functional, morphological and molecular defects. Taking advantage of comparing polyQ-induced degeneration in two retina models, we combined gene expression profiling and molecular biology techniques to decipher the molecular pathways underlying polyQ expansion toxicity. We show that R7E and R6/2 retinal phenotype strongly correlates with loss of expression of a large cohort of genes specifically involved in phototransduction function and morphogenesis of differentiated rod photoreceptors. Accordingly, three key transcription factors (Nrl, Crx and Nr2e3) controlling rod differentiation genes, hence expression of photoreceptor specific traits, are down-regulated. Interestingly, other transcription factors known to cause inhibitory effects on photoreceptor differentiation when mis-expressed, such as Stat3, are aberrantly re-activated. Thus, our results suggest that independently from the protein context, polyQ expansion overrides the control of neuronal differentiation and maintenance, thereby causing dysfunction and degeneration.

Ataxin-7 is a subunit of GCN5 histone acetyltransferase-containing complexes.

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder caused by a CAG repeat expansion in the SCA7 gene leading to elongation of a polyglutamine tract in ataxin-7, a protein of unknown function. A putative ataxin-7 yeast orthologue (SGF73) has been identified recently as a new component of the SAGA (Spt/Ada/Gcn5 acetylase) multisubunit complex, a coactivator required for transcription of a subset of RNA polymerase II-dependent genes. We show here that ataxin-7 is an integral component of the mammalian SAGA-like complexes, the TATA-binding protein-free TAF-containing complex (TFTC) and the SPT3/TAF9/GCN5 acetyltransferase complex (STAGA). In agreement, immunoprecipitation of ataxin-7 retained a histone acetyltransferase activity, characteristic for TFTC-like complexes. We further identified a minimal domain in ataxin-7 that is required for interaction with TFTC/STAGA subunits and is conserved highly through evolution, allowing the identification of a SCA7 gene family. We showed that this domain contains a conserved Cys(3)His motif that binds zinc, forming a new zinc-binding domain. Finally, polyglutamine expansion in ataxin-7 did not affect its incorporation into TFTC/STAGA complexes purified from SCA7 patient cells. We demonstrate here that ataxin-7 is the human orthologue of the yeast SAGA SGF73 subunit and is a bona fide subunit of the human TFTC-like transcriptional complexes.

Disease progression despite early loss of polyglutamine protein expression in SCA7 mouse model.

Nine neurodegenerative diseases including Huntington's disease (HD) and spinocerebellar ataxia type 7 (SCA7) are caused by an expansion of a polyglutamine (polyQ) stretch in the respective proteins. Aggregation of expanded polyQ-containing proteins into the nucleus is a hallmark of these diseases. Recent evidence indicates that transcriptional dysregulation may contribute to the molecular pathogenesis of these diseases. Using SCA7 and HD mouse models in which we recently described a retinal phenotype, we investigated whether altered gene expression underlies photoreceptor dysfunction. In both models, rhodopsin promoter activity was early and dramatically repressed, suggesting that downregulation of photoreceptor-specific genes plays a major role in polyQ-induced retinal dysfunction. Because the rhodopsin promoter drives mutant ataxin-7 expression in our SCA7 mice, we also assessed whether downregulation of mutant SCA7 transgene would reverse retinopathy progression and aggregate formation. Although residual expression of mutant ataxin-7 was found negligible from 9 weeks of age, SCA7 transgenic mice showed a progressive decline of photoreceptor activity leading to a complete loss of electroretinographic responses from 1 year of age. At this age, aggregates were cleared in only half of the photoreceptors, indicating that their formation is not fully reversible in this model. We demonstrate here that abolishing full-length mutant ataxin-7 expression did not reverse retinopathy progression in SCA7 mice, raising the possibility that some polyQ-induced pathological events might be irreversible.

Proteases acting on mutant huntingtin generate cleaved products that differentially build up cytoplasmic and nuclear inclusions.

Proteolytic processing of mutant huntingtin (mhtt) is regarded as a key event in the pathogenesis of Huntington's disease (HD). Mhtt fragments containing a polyglutamine expansion form intracellular inclusions and are more cytotoxic than full-length mhtt. Here, we report that two distinct mhtt fragments, termed cp-A and cp-B, differentially build up nuclear and cytoplasmic inclusions in HD brain and in a cellular model for HD. Cp-A is released by cleavage of htt in a 10 amino acid domain and is the major fragment that aggregates in the nucleus. Furthermore, we provide evidence that cp-A and cp-B are most likely generated by aspartic endopeptidases acting in concert with the proteasome to ensure the normal turnover of htt. These proteolytic processes are thus potential targets for therapeutic intervention in HD.