[Show abstract][Hide abstract] ABSTRACT: Genome wide association studies (GWAS) have revolutionized the study of complex diseases and have uncovered common genetic variants associated with an increased risk for major psychiatric disorders. A recently published schizophrenia GWAS replicated earlier findings implicating common variants in Transcription factor 4 (TCF4) as susceptibility loci for schizophrenia. By contrast, loss of function TCF4 mutations, although rare, cause Pitt-Hopkins syndrome (PTHS); a disorder characterized by intellectual disability (ID), developmental delay and behavioral abnormalities. TCF4 mutations have also been described in individuals with ID and non-syndromic neurodevelopmental disorders. TCF4 is a member of the basic helix-loop-helix (bHLH) family of transcription factors that regulate gene expression at E-box-containing promoters and enhancers. Accordingly, TCF4 has an important role during brain development and can interact with a wide array of transcriptional regulators including some proneural factors. TCF4 may, therefore, participate in the transcriptional networks that regulate the maintenance and differentiation of distinct cell types during brain development. Here, we review the role of TCF4 variants in the context of several distinct brain disorders associated with impaired cognition.
[Show abstract][Hide abstract] ABSTRACT: Myoclonus dystonia syndrome (MDS) is a young-onset movement disorder. A proportion of cases are due to mutations in the maternally imprinted SGCE gene. We assembled the largest cohort of MDS patients to date, and determined the frequency and type of SGCE mutations. The aim was to establish the motor phenotype in mutation carriers and utility of current diagnostic criteria. Eighty-nine probands with clinical features compatible with MDS were recruited from the UK and Ireland. Patients were phenotypically classified as "definite", "probable" or "possible" MDS according to previous guidelines. SGCE was analyzed using direct sequencing and copy number variant analysis. In those where no mutation was found, DYT1 (GAG deletion), GCH1, THAP1 and NKX2.1 genes were also sequenced. Nineteen (21.3 %) probands had an SGCE mutation. Three patterns of motor symptoms emerged: (1) early childhood onset upper body myoclonus and dystonia, (2) early childhood onset lower limb dystonia, progressing later to more pronounced myoclonus and upper body involvement, and (3) later childhood onset upper body myoclonus and dystonia with evident cervical involvement. Five probands had large contiguous gene deletions ranging from 0.7 to 2.3 Mb in size with distinctive clinical features, including short stature, joint laxity and microcephaly. Our data confirms that SGCE mutations are most commonly identified in MDS patients with (1) age at onset ≤10 years and (2) predominant upper body involvement of a pure myoclonus-dystonia. Cases with whole SGCE gene deletions had additional clinical characteristics, which are not always predicted by deletion size or gene involvement.
No preview · Article · Sep 2014 · Journal of Neurology
[Show abstract][Hide abstract] ABSTRACT: Background
Myoclonus dystonia syndrome (MDS) is a hyperkinetic movement disorder caused, in a proportion of cases, by mutations of the maternally imprinted epsilon-sarcoglycan gene (SGCE). SGCE mutation rates vary between cohorts, suggesting genetic heterogeneity. E- and ζ-sarcoglycan are both expressed in brain tissue. In this study we tested whether zeta-sarcoglycan gene (SGCZ) mutations also contribute to this disorder.
Patients with clinically suspected MDS and no SGCE mutation were recruited and classified, according to previously published criteria, as to their likelihood of the movement disorder. All SGCZ exons and intron/exon boundaries were screened by direct sequencing.
Fifty-four SGCE mutation-negative patients were recruited from the UK and the Netherlands. Subdivided according to the likelihood of the movement disorder resulted in 17 ‘definite’, 16 ‘probable’ and 21 ‘possible’ cases. No pathogenic SGCZ mutations were identified.
SGCZ mutations are unlikely to contribute to the genetic heterogeneity in MDS.
[Show abstract][Hide abstract] ABSTRACT: Genome-wide association studies have identified common variants in transcription factor 4 (TCF4) as susceptibility loci for schizophrenia, Fuchs' endothelial corneal dystrophy, and primary sclerosing cholangitis. By contrast, rare TCF4 mutations cause Pitt-Hopkins syndrome, a disorder characterized by intellectual disability and developmental delay, and have also been described in patients with other neurodevelopmental disorders. TCF4 therefore sits at the nexus between common and rare disorders. TCF4 interacts with other basic helix-loop-helix proteins, forming transcriptional networks that regulate the differentiation of several distinct cell types. Here, we review the role of TCF4 in these seemingly diverse disorders and discuss recent data implicating TCF4 as an important regulator of neurodevelopment and epithelial-mesenchymal transition.
Full-text · Article · Mar 2014 · Trends in Molecular Medicine
[Show abstract][Hide abstract] ABSTRACT: An intronic G4C2 hexanucleotide repeat expansion in C9ORF72 is a major cause of amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Several mechanisms including RNA toxicity, repeat-associated non-AUG translation mediated dipeptide protein aggregates, and haploinsufficiency of C9orf72 have been implicated in the molecular pathogenesis of this disorder. The aims of this study were to compare the use of two different Southern blot probes for detection of repeat expansions in an amyotrophic lateral sclerosis and frontotemporal lobar degeneration pathological cohort and to determine the levels of C9orf72 transcript variants and protein isoforms in patients versus control subjects. Our Southern blot studies identified smaller repeat expansions (250-1800 bp) that were only detectable with the flanking probe highlighting the potential for divergent results using different Southern blotting protocols that could complicate genotype-phenotype correlation studies. Further, we characterize a new C9orf72 antibody and show for the first time decreased C9orf72 protein levels in the frontal cortex from patients with a pathological hexanucleotide repeat expansion. These data suggest that a reduction in C9orf72 protein may be a consequence of the disease.
Full-text · Article · Jan 2014 · Neurobiology of aging
[Show abstract][Hide abstract] ABSTRACT: Background / Purpose:
To analyse the differential TDP-43 and non-TDP-43 pathology as well as C9orf72 transcript levels in C9orf72 hexanucleotide expansion carriers.
Different brain regions show distinct ratios of TDP-43 vs non-TDP-43 pathology. C9orf72 transcript levels are reduced in expansion carriers compared with controls.
[Show abstract][Hide abstract] ABSTRACT: Haploinsufficiency of TCF4 causes Pitt-Hopkins syndrome (PTHS): a severe form of mental retardation with phenotypic similarities to Angelman, Mowat-Wilson and Rett syndromes. Genome-wide association studies have also found that common variants in TCF4 are associated with an increased risk of schizophrenia. Although TCF4 is transcription factor, little is known about TCF4-regulated processes in the brain. In this study we used genome-wide expression profiling to determine the effects of acute TCF4 knockdown on gene expression in SH-SY5Y neuroblastoma cells. We identified 1204 gene expression changes (494 upregulated, 710 downregulated) in TCF4 knockdown cells. Pathway and enrichment analysis on the differentially expressed genes in TCF4-knockdown cells identified an over-representation of genes involved in TGF-β signaling, epithelial to mesenchymal transition (EMT) and apoptosis. Among the most significantly differentially expressed genes were the EMT regulators, SNAI2 and DEC1 and the proneural genes, NEUROG2 and ASCL1. Altered expression of several mental retardation genes such as UBE3A (Angelman Syndrome), ZEB2 (Mowat-Wilson Syndrome) and MEF2C was also found in TCF4-depleted cells. These data suggest that TCF4 regulates a number of convergent signaling pathways involved in cell differentiation and survival in addition to a subset of clinically important mental retardation genes.
[Show abstract][Hide abstract] ABSTRACT: Mutations in FKRP gene are associated with a wide range of muscular dystrophies from mild limb-girdle muscular dystrophy (LGMD) 2I to severe Walker-Warburg syndrome (WWS) and muscle-eye-brain disease (MEB). The characteristic biochemical feature of these diseases is the hypoglycosylation of α-dystroglycan (α-DG). Currently there is no effective treatment available. In this study we examined the Adeno-associated virus serotype 9 vector (AAV9)-mediated gene therapy in the FKRP mutant mouse model with a proline to leucine missense mutation (P448L). Our results showed that intraperitoneal administration of AAV9-FKRP resulted in systemic FKRP expression in all striated muscles examined with the highest levels in cardiac muscle. Consistent with our previous observations, FKRP protein is localized in the Golgi apparatus in myofibers. Expression of FKRP consequently restored functional glycosylation of α-DG in the skeletal and cardiac muscles. Significant improvement in dystrophic pathology, serum creatine kinase levels and muscle function was observed. Only limited FKRP transgene expression was detected in kidney and liver with no detectable toxicity. Our results provided evidence for the utility of AAV-mediated gene replacement therapy for FKRP-related muscular dystrophies.Molecular Therapy (2013); doi:10.1038/mt.2013.156.
No preview · Article · Jul 2013 · Molecular Therapy
[Show abstract][Hide abstract] ABSTRACT: Myoclonus dystonia syndrome is a childhood onset hyperkinetic movement disorder characterized by predominant alcohol responsive upper body myoclonus and dystonia. A proportion of cases are due to mutations in the maternally imprinted SGCE gene. Previous studies have suggested that patients with SGCE mutations may have an increased rate of psychiatric disorders. We established a cohort of patients with myoclonus dystonia syndrome and SGCE mutations to determine the extent to which psychiatric disorders form part of the disease phenotype. In all, 89 patients with clinically suspected myoclonus dystonia syndrome were recruited from the UK and Ireland. SGCE was analysed using direct sequencing and for copy number variants. In those patients where no mutation was found TOR1A (GAG deletion), GCH1, THAP1 and NKX2-1 were also sequenced. SGCE mutation positive cases were systematically assessed using standardized psychiatric interviews and questionnaires and compared with a disability-matched control group of patients with alcohol responsive tremor. Nineteen (21%) probands had a SGCE mutation, five of which were novel. Recruitment of family members increased the affected SGCE mutation positive group to 27 of whom 21 (77%) had psychiatric symptoms. Obsessive-compulsive disorder was eight times more likely (P < 0.001) in mutation positive cases, compulsivity being the predominant feature (P < 0.001). Generalized anxiety disorder (P = 0.003) and alcohol dependence (P = 0.02) were five times more likely in mutation positive cases than tremor controls. SGCE mutations are associated with a specific psychiatric phenotype consisting of compulsivity, anxiety and alcoholism in addition to the characteristic motor phenotype. SGCE mutations are likely to have a pleiotropic effect in causing both motor and specific psychiatric symptoms.
[Show abstract][Hide abstract] ABSTRACT: Pitt-Hopkins syndrome (PTHS) is a rare developmental disorder associated with severe mental retardation, facial abnormalities, and intermittent hyperventilation. Autosomal dominant PTHS is caused by mutations in the transcription factor 4 (TCF4) gene, whereas NRXN1 and CNTNAP2 mutations are associated with autosomal recessive PTHS. To determine the impact of missense mutations on TCF4 function, we tested a panel of PTHS-associated mutations using a range of quantitative techniques. Mutations in the basic helix-loop-helix (bHLH) domain of TCF4 alter the subnuclear localization of the mutant protein and can attenuate homo- and heterodimer formation in homogenous time-resolved fluorescence (HTRF) assays. By contrast, mutations proximal to the bHLH domain do not alter the location of TCF4 or impair heterodimer formation. In addition, we show that TCF4 can transactivate the NRXN1β and CNTNAP2 promoters in luciferase assays. Here we find variable, context-specific deficits in the ability of the different PTHS-associated TCF4 mutants to transactivate these promoters when coexpressed with different bHLH transcription factors. These data demonstrate that PTHS-associated missense mutations can have multiple effects on the function of the protein, and suggest that TCF4 may modulate the expression of NRXN1 and CNTNAP2 thereby defining a regulatory network in PTHS.
[Show abstract][Hide abstract] ABSTRACT: In addition to muscle disease, defects in processing and assembly of the dystrophin-glycoprotein complex (DGC) are associated with a spectrum of brain abnormalities ranging from mild cognitive impairment (MCI) to neuronal migration disorders. In brain, the DGC is involved in the organisation of GABA(A) receptors (GABA(A)Rs) and aquaporin-4 (AQP4)-containing protein complexes in neurons and glia, respectively. During development, defects in the glycosylation of α-dystroglycan that impair its ability to interact with the extracellular matrix (ECM) are frequently associated with cobblestone lissencephaly and mental retardation. Furthermore, mutations in the gene encoding ɛ-sarcoglycan (SGCE) cause the neurogenic movement disorder myoclonus dystonia syndrome. In this review, we describe recent progress in defining distinct roles for the DGC in neurons and glia.
No preview · Article · May 2012 · Trends in Neurosciences
[Show abstract][Hide abstract] ABSTRACT: There is a clinical and pathological overlap between amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). A number of autosomal-dominant genes have been described that primarily cause ALS or FTLD such as progranulin (GRN), valosin-containing protein (VCP), and TAR DNA-Binding Protein (TARDBP), and for each of these conditions there are a small number of cases with both ALS and FTLD. Two major genes were described in 2011, which cause FTLD and/or ALS within extended kindreds. Ubiquilin2 (UBQLN2) is responsible for X-linked FTLD/ALS. A hexanucleotide repeat expansion in C9ORF72 causes chromosome 9p linked FTLD/ALS and is the most common cause of familial ALS accounting for about 40 % of familial cases. Both UBQLN2 and C9ORF72 mutations lead to TDP-43 positive neuropathology, and C9ORF72-positive cases have p62/ubiquitin-positive pathology, which is not stained by TDP-43 antibodies. Ubiquilin2 is one of a family of proteins thought to be important in targeting abnormal proteins for degradation via lysosomal and proteasomal routes. The pathogenic mechanism of the C9ORF72 expansion is unknown but may involve partial haploinsufficiency of C9ORF72 and/or the formations of toxic RNA inclusions. The identification of mutations in these genes represents an important step forward in our understanding of the clinical, pathological, and genetic spectrum of ALS/FTLD diseases.
No preview · Article · Apr 2012 · Current Neurology and Neuroscience Reports
[Show abstract][Hide abstract] ABSTRACT: Missense mutations in the SGCE gene encoding ε-sarcoglycan account for approximately 15% of SGCE-positive cases of myoclonus-dystonia syndrome (MDS) in humans. In this study, we show that while the majority of MDS-associated missense mutants modeled with a murine ε-sarcoglycan cDNA are substrates for endoplasmic reticulum-associated degradation, one mutant, M68T (analogous to human c.275T>C, p.M92T), located in the Ig-like domain of ε-sarcoglycan, results in a gain-of-glycosylation mutation producing a protein that is targeted to the plasma membrane, albeit at reduced levels compared to wild-type ε-sarcoglycan. Removal of the ectopic N-linked glycan failed to restore efficient plasma membrane targeting of M68T demonstrating that the substitution rather than the glycan was responsible for the trafficking defect of this mutant. M68T also colocalized with CD63-positive vesicles in the endosomal-lysosomal system and was found to be more susceptible to lysosomal proteolysis than wild-type ε-sarcoglycan. Finally, we demonstrate impaired ectodomain shedding of M68T, a process that occurs physiologically for ε-sarcoglycan resulting in the lysosomal trafficking of the intracellular C-terminal domain of the protein. Our findings show that functional analysis of rare missense mutations can provide a mechanistic insight into the pathogenesis of MDS and the physiological role of ε-sarcoglycan.
[Show abstract][Hide abstract] ABSTRACT: The chromosome 9p21 amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) locus contains one of the last major unidentified autosomal-dominant genes underlying these common neurodegenerative diseases. We have previously shown that a founder haplotype, covering the MOBKL2b, IFNK, and C9ORF72 genes, is present in the majority of cases linked to this region. Here we show that there is a large hexanucleotide (GGGGCC) repeat expansion in the first intron of C9ORF72 on the affected haplotype. This repeat expansion segregates perfectly with disease in the Finnish population, underlying 46.0% of familial ALS and 21.1% of sporadic ALS in that population. Taken together with the D90A SOD1 mutation, 87% of familial ALS in Finland is now explained by a simple monogenic cause. The repeat expansion is also present in one-third of familial ALS cases of outbred European descent, making it the most common genetic cause of these fatal neurodegenerative diseases identified to date.