A homozygous mutation of VWA3B causes cerebellar ataxia with intellectual disability

Identification of DNA methylation episignature for the intellectual developmental disorder, autosomal dominant 21 syndrome, caused by variants in the CTCF gene

PURPOSE

The main objective of this study was to assess clinical features and genome-wide DNA methylation profiles in individuals affected by intellectual developmental disorder, autosomal dominant 21 (IDD21) syndrome, caused by variants in the CCCTC-binding factor (CTCF) gene.

METHODS

DNA samples were extracted from peripheral blood of 16 individuals with clinical features and genetic findings consistent with IDD21. DNA methylation analysis was performed using the Illumina Infinium Methylation EPIC Bead Chip microarrays. The methylation levels were fitted in a multivariate linear regression model to identify the differentially methylated probes. A binary support vector machine classification model was constructed to differentiate IDD21 samples from controls.

RESULTS

We identified a highly specific, reproducible, and sensitive episignature associated with CTCF variants. Six variants of uncertain significance were tested, of which 2 mapped to the IDD21 episignature and clustered alongside IDD21 cases in both heatmap and multidimensional scaling plots. Comparison of the genomic DNA methylation profile of IDD21 with that of 56 other neurodevelopmental disorders provided insights into the underlying molecular pathophysiology of this disorder.

CONCLUSION

The robust and specific CTCF/IDD21 episignature expands the growing list of neurodevelopmental disorders with distinct DNA methylation profiles, which can be applied as supporting evidence in variant classification.

Single-nucleus RNA-sequencing of autosomal dominant Alzheimer disease and risk variant carriers

Genetic studies of Alzheimer disease (AD) have prioritized variants in genes related to the amyloid cascade, lipid metabolism, and neuroimmune modulation. However, the cell-specific effect of variants in these genes is not fully understood. Here, we perform single-nucleus RNA-sequencing (snRNA-seq) on nearly 300,000 nuclei from the parietal cortex of AD autosomal dominant (APP and PSEN1) and risk-modifying variant (APOE, TREM2 and MS4A) carriers. Within individual cell types, we capture genes commonly dysregulated across variant groups. However, specific transcriptional states are more prevalent within variant carriers. TREM2 oligodendrocytes show a dysregulated autophagy-lysosomal pathway, MS4A microglia have dysregulated complement cascade genes, and APOEε4 inhibitory neurons display signs of ferroptosis. All cell types have enriched states in autosomal dominant carriers. We leverage differential expression and single-nucleus ATAC-seq to map GWAS signals to effector cell types including the NCK2 signal to neurons in addition to the initially proposed microglia. Overall, our results provide insights into the transcriptional diversity resulting from AD genetic architecture and cellular heterogeneity. The data can be explored on the online browser ( http://web.hararilab.org/SNARE/ ).

Applying whole exome sequencing in a consanguineous population with autism spectrum disorder

This study aimed to systematically assess the impact of clinical and demographic variables on the diagnostic yield of Whole Exome Sequencing (WES) when applied to children with Autism Spectrum Disorder (ASD) from a consanguineous population. Ninety-seven children were included in the analysis, 63% were male and 37% were females. 77.3% had a suspected syndromic aetiology of which 68% had co-existent central nervous system (CNS) clinical features, while 69% had other systems involved. The diagnostic yield of WES in our cohort with ASD was 34%. Children with seizures were more likely to have positive WES results (46% vs. 31%, p = 0.042). Probands with suspected syndromic ASD aetiology showed no significant differential impact on the diagnostic yield of WES.

Systematic Analysis of Actively Transcribed Core Matrisome Genes Across Tissues and Cell Phenotypes

The extracellular matrix (ECM) is a highly dynamic, well-organized acellular network of tissue-specific biomolecules, that can be divided into structural or core ECM proteins and ECM-associated proteins. The ECM serves as a blueprint for organ development and function and, when structurally altered through mutation, altered expression, or degradation, can lead to debilitating syndromes that often affect one tissue more than another. Cross-referencing the FANTOM5 SSTAR (Semantic catalog of Samples, Transcription initiation And Regulators) and the defined catalog of core matrisome ECM (glyco)proteins, we conducted a comprehensive analysis of 511 different human samples to annotate the context-specific transcription of the individual components of the defined matrisome. Relative log expression normalized SSTAR cap analysis gene expression peak data files were downloaded from the FANTOM5 online database and filtered to exclude all cell lines and diseased tissues. Promoter-level expression values were categorized further into eight core tissue systems and three major ECM categories: proteoglycans, glycoproteins, and collagens. Hierarchical clustering and correlation analyses were conducted to identify complex relationships in promoter-driven gene expression activity. Integration of the core matrisome and curated FANTOM5 SSTAR data creates a unique tool that provides insight into the promoter-level expression of ECM-encoding genes in a tissue- and cell-specific manner. Unbiased clustering of cap analysis gene expression peak data reveals unique ECM signatures within defined tissue systems. Correlation analysis among tissue systems exposes both positive and negative correlation of ECM promoters with varying levels of significance. This tool can be used to provide new insight into the relationships between ECM components and tissues and can inform future research on the ECM in human disease and development. We invite the matrix biology community to continue to explore and discuss this dataset as part of a larger and continuing conversation about the human ECM. An interactive web tool can be found at matrixpromoterome.github.io along with additional resources that can be found at dx.doi.org/10.6084/m9.figshare.19794481 (figures) and https://figshare.com/s/e18ecbc3ae5aaf919b78 (python notebook).

Autosomal recessive adult onset ataxia

Autosomal recessive ataxias (ARCA) represent a complex group of diseases ranging from primary ataxias to rare and complex metabolic disorders in which ataxia is a part of the clinical picture. Small number of ARCA manifest exclusively in adulthood, while majority of typical childhood onset ARCA may also start later with atypical clinical presentation. We have systematically searched the literature for ARCA with adult onset, both in the group of primary ataxias including those that are less frequently described in isolated or in a small number of families, and also in the group of complex and metabolic diseases in which ataxia is only part of the clinical picture. We propose an algorithm that could be used when encountering a patient with adult onset sporadic or recessive ataxia in whom the acquired causes are excluded. ARCA are frequently neglected in the differential diagnosis of adult-onset ataxias. Rising awareness of their clinical significance is important, not only because some of these disorders may be potentially treatable, but also for prognostic implications and inclusion of patients to future clinical trials with disease modifying agents.

Association of a Variant in VWA3A with Response to Anti-Vascular Endothelial Growth Factor Treatment in Neovascular AMD

Purpose

Anti–vascular endothelial growth factor (VEGF) therapy for neovascular AMD (nvAMD) obtains a variable outcome. We performed a genome-wide association study for anti-VEGF treatment response in nvAMD to identify variants potentially underlying such a variable outcome.

Methods

Israeli patients with nvAMD who underwent anti-VEGF treatment (n = 187) were genotyped on a whole exome chip containing approximately 500,000 variants. Genotyping was correlated with delta visual acuity (deltaVA) between baseline and after three injections of anti-VEGF. Top principal components, age, and baseline VA were included in the analysis. Two lead associated variants were genotyped in an independent validation set of patients with nvAMD (n = 108).

Results

Linear regression analysis on 5,353,842 variants revealed five exonic variants with an association P value of less than 6 × 10⁻⁵. The top variant in the gene VWA3A (P = 1.77 × 10⁻⁶) was tested in the validation cohort. The minor allele of the VWA3A variant was associated with worse response to treatment (P = 0.02). The average deltaVA of discovery plus validation was –0.214 logMAR (≈ a gain of 10.7 Early Treatment Diabetic Retinopathy Study letters) for homozygote for the major allele, 0.172 logMAR for heterozygotes (≈ a loss of 8.6 Early Treatment Diabetic Retinopathy Study letters), and 0.21 logMAR for homozygote for the minor allele (≈ a loss of 10.5 Early Treatment Diabetic Retinopathy Study letters). Minor allele carriers had a higher frequency of macular hemorrhage at baseline.

Conclusions

An VWA3A gene variant was associated with worse response to anti-VEGF treatment in Israeli patients with nvAMD. The VWA3A protein is a precursor of the multimeric von Willebrand factor which is involved in blood coagulation, a system previously associated with nvAMD.

De novo variants in CAMTA1 cause a syndrome variably associated with spasticity, ataxia, and intellectual disability

Previously, intragenic CAMTA1 copy number variants (CNVs) have been shown to cause non-progressive, congenital ataxia with or without intellectual disability (OMIM#614756). However, ataxia, intellectual disability, and dysmorphic features were all incompletely penetrant, even within families. Here, we describe four patients with de novo nonsense, frameshift or missense CAMTA1 variants. All four patients predominantly manifested features of ataxia and/or spasticity. Borderline intellectual disability and dysmorphic features were both present in one patient only, and other neurological and behavioural symptoms were variably present. Neurodevelopmental delay was found to be mild. Our findings indicate that also nonsense, frameshift and missense variants in CAMTA1 can cause a spastic ataxia syndrome as the main phenotype.

Copy Number Variation Pattern for Discriminating MACROD2 States of Colorectal Cancer Subtypes

Copy number variation (CNV) is a common structural variation pattern of DNA, and it features a higher mutation rate than single-nucleotide polymorphisms (SNPs) and affects a larger fragment of genomes. CNV is related with the genesis of complex diseases and can thus be used as a strategy to identify novel cancer-predisposing markers or mechanisms. In particular, the frequent deletions of mono-ADP-ribosylhydrolase 2 (MACROD2) locus in human colorectal cancer (CRC) alters DNA repair and the sensitivity to DNA damage and results in chromosomal instability. The relationship between CNV and cancer has not been explained. In this study, on the basis of the genome variation profiling by the SNP array from 651 CRC primary tumors, we computationally analyzed the CNV data to select crucial SNP sites with the most relevance to three different states of MACROD2 (heterozygous deletion, homozygous deletion, and normal state), suggesting that these CNVs may play functional roles in CRC tumorigenesis. Our study can shed new insights into the genesis of cancer based on CNV, providing reference for clinical diagnosis, and treatment prognosis of CRC.

Homozygosity mapping and whole exome sequencing reveal a novel ERCC8 mutation in a Chinese consanguineous family with unique cerebellar ataxia

BACKGROUND

A consanguineous Chinese family was affected by an apparently novel autosomal recessive disorder characterized by cerebellar ataxia, cutaneous photosensitivity, and mild intellectual disability.

METHODS

The family was evaluated by homozygosity mapping, haplotype analysis, whole exome sequencing, and candidate gene mutation screening to identify the disease-associated gene and mutation. Bioinformatics methods were used to predict the functional significance of the mutated gene product. ERCC8 mutations and phenotypes were examined.

RESULTS

All three patients presented cerebellar ataxia, cutaneous photosensitivity, and mild intellectual disability. Whole genome and candidate region linkage analysis in the consanguineous family revealed a maximum logarithm of the odds score at 5q12.1. This homozygous region was confirmed by homozygosity mapping. The pathogenic missense mutation p.Gly257Arg affecting an evolutionary highly conserved amino acid was identified in ERCC8 at 5q12.1. Integrated application of whole exome sequencing and homozygosity mapping is an efficient approach for gene mapping and mutation identification in consanguineous families.

CONCLUSIONS

We identified a novel ERCC8 mutation and new unique disease phenotype. These results also confirmed the genotype-phenotype relationship between mutations in ERCC8 and clinical findings.

Autosomal-recessive cerebellar ataxias

The autosomal-recessive cerebellar ataxias comprise more than half of the known genetic forms of ataxia and represent an extensive group of clinically heterogeneous disorders that can occur at any age but whose onset is typically prior to adulthood. In addition to ataxia, patients often present with polyneuropathy and clinical symptoms outside the nervous system. The most common of these diseases is Friedreich ataxia, caused by mutation of the frataxin gene, but recent advances in genetic analysis have greatly broadened the ever-expanding number of causative genes to over 50. In this review, the clinical neurogenetics of the recessive cerebellar ataxias will be discussed, including updates on recently identified novel ataxia genes, advancements in unraveling disease-specific molecular pathogenesis leading to ataxia, potential treatments under development, technologic improvements in diagnostic testing such as clinical exome sequencing, and what the future holds for clinicians and geneticists.

Spastic paraplegia type 4: A novel SPAST splice site donor mutation and expansion of the phenotype variability

Mutations in SPG4/SPAST are the most frequent molecular aetiology in the autosomal dominant form of hereditary spastic paraplegia (HSP). Loss-of-function and haploinsufficiency in SPAST have been demonstrated and the pure form of spastic paraplegia is a main clinical manifestation. This study is to explore the novel SPAST splice site donor variant, c.1004+3A>C, in seven patients from two families, one from Italy and the other from Japan. Exon 6 is skipped out by the variant, leading to a premature termination of translation, p.Gly290Trpfs*5. Measurement of SPAST transcripts in lymphocytes demonstrated a reduction through nonsense-mediated mRNA decay (NMD). Intra- and inter-familial phenotypic variations were observed, including age-at-onset, severity of spasticity, and scoliosis. Our study demonstrated further evidence of allelic heterogeneity in SPG4, dosage effects through NMD, and broad clinical features of the SPAST mutation.

Overcoming the divide between ataxias and spastic paraplegias: Shared phenotypes, genes, and pathways

Autosomal-dominant spinocerebellar ataxias, autosomal-recessive spinocerebellar ataxias, and hereditary spastic paraplegias have traditionally been designated in separate clinicogenetic disease classifications. This classification system still largely frames clinical thinking and genetic workup in clinical practice. Yet, with the advent of next-generation sequencing, phenotypically unbiased studies have revealed the limitations of this classification system. Various genes (eg, SPG7, SYNE1, PNPLA6) traditionally rooted in either the ataxia or hereditary spastic paraplegia classification system have now been shown to cause ataxia on the one end of the disease continuum and hereditary spastic paraplegia on the other. Other genes such as GBA2 and KIF1C were almost simultaneously published as both a hereditary spastic paraplegia and an ataxia gene. The variability and fluidity of observed phenotypes along the ataxia-spasticity spectrum warrants a rethinking of the traditional classification system. We propose to replace this divisive diagnosis-driven ataxia and hereditary spastic paraplegia classification system by a descriptive, unbiased approach of modular phenotyping. This approach is also open to expansion of the phenotype beyond ataxia and spasticity, which often occur as part of broader multisystem neuronal dysfunction. The concept of a continuous ataxia-spasticity disease spectrum is further supported by ataxias and hereditary spastic paraplegias sharing not only overlapping phenotypes and underlying genes, but also common cellular pathways and disease mechanisms. This suggests a shared vulnerability of cerebellar and corticospinal neurons for common pathophysiological processes. It might be this mechanistic overlap that drives their clinical overlap. A mechanistically inspired classification system will help to pave the way for mechanism-based strategies for drug development. © 2017 International Parkinson and Movement Disorder Society.

Systematic review of autosomal recessive ataxias and proposal for a classification

Background

The classification of autosomal recessive ataxias represents a significant challenge because of high genetic heterogeneity and complex phenotypes. We conducted a comprehensive systematic review of the literature to examine all recessive ataxias in order to propose a new classification and properly circumscribe this field as new technologies are emerging for comprehensive targeted gene testing.

Methods

We searched Pubmed and Embase to identify original articles on recessive forms of ataxia in humans for which a causative gene had been identified. Reference lists and public databases, including OMIM and GeneReviews, were also reviewed. We evaluated the clinical descriptions to determine if ataxia was a core feature of the phenotype and assessed the available evidence on the genotype-phenotype association. Included disorders were classified as primary recessive ataxias, as other complex movement or multisystem disorders with prominent ataxia, or as disorders that may occasionally present with ataxia.

Results

After removal of duplicates, 2354 references were reviewed and assessed for inclusion. A total of 130 articles were completely reviewed and included in this qualitative analysis. The proposed new list of autosomal recessive ataxias includes 45 gene-defined disorders for which ataxia is a core presenting feature. We propose a clinical algorithm based on the associated symptoms.

Conclusion

We present a new classification for autosomal recessive ataxias that brings awareness to their complex phenotypes while providing a unified categorization of this group of disorders. This review should assist in the development of a consensus nomenclature useful in both clinical and research applications.

Electronic supplementary material

The online version of this article (doi:10.1186/s40673-017-0061-y) contains supplementary material, which is available to authorized users.

Impaired Axonal Na(+) Current by Hindlimb Unloading: Implication for Disuse Neuromuscular Atrophy

This study aimed to characterize the excitability changes in peripheral motor axons caused by hindlimb unloading (HLU), which is a model of disuse neuromuscular atrophy. HLU was performed in normal 8-week-old male mice by fixing the proximal tail by a clip connected to the top of the animal's cage for 3 weeks. Axonal excitability studies were performed by stimulating the sciatic nerve at the ankle and recording the compound muscle action potential (CMAP) from the foot. The amplitudes of the motor responses of the unloading group were 51% of the control amplitudes [2.2 ± 1.3 mV (HLU) vs. 4.3 ± 1.2 mV (Control), P = 0.03]. Multiple axonal excitability analysis showed that the unloading group had a smaller strength-duration time constant (SDTC) and late subexcitability (recovery cycle) than the controls [0.075 ± 0.01 (HLU) vs. 0.12 ± 0.01 (Control), P < 0.01; 5.4 ± 1.0 (HLU) vs. 10.0 ± 1.3 % (Control), P = 0.01, respectively]. Three weeks after releasing from HLU, the SDTC became comparable to the control range. Using a modeling study, the observed differences in the waveforms could be explained by reduced persistent Na⁺ currents along with parameters related to current leakage. Quantification of RNA of a SCA1A gene coding a voltage-gated Na⁺ channel tended to be decreased in the sciatic nerve in HLU. The present study suggested that axonal ion currents are altered in vivo by HLU. It is still undetermined whether the dysfunctional axonal ion currents have any pathogenicity on neuromuscular atrophy or are the results of neural plasticity by atrophy.