ABSTRACT
Detection of structural variants (SVs) is currently biased toward those that alter copy number. The relative contribution of inversions toward genetic disease is unclear. In this study, we analyzed genome sequencing data for 33,924 families with rare disease from the 100,000 Genomes Project. From a database hosting >500 million SVs, we focused on 351 genes where haploinsufficiency is a confirmed disease mechanism and identified 47 ultra-rare rearrangements that included an inversion (24 bp to 36.4 Mb, 20/47 de novo). Validation utilized a number of orthogonal approaches, including retrospective exome analysis. RNA-seq data supported the respective diagnoses for six participants. Phenotypic blending was apparent in four probands. Diagnostic odysseys were a common theme (>50 years for one individual), and targeted analysis for the specific gene had already been performed for 30% of these individuals but with no findings. We provide formal confirmation of a European founder origin for an intragenic MSH2 inversion. For two individuals with complex SVs involving the MECP2 mutational hotspot, ambiguous SV structures were resolved using long-read sequencing, influencing clinical interpretation. A de novo inversion of HOXD11-13 was uncovered in a family with Kantaputra-type mesomelic dysplasia. Lastly, a complex translocation disrupting APC and involving nine rearranged segments confirmed a clinical diagnosis for three family members and resolved a conundrum for a sibling with a single polyp. Overall, inversions play a small but notable role in rare disease, likely explaining the etiology in around 1/750 families across heterogeneous clinical cohorts.
Subject(s)
Chromosome Inversion , Rare Diseases , Humans , Rare Diseases/genetics , Male , Female , Chromosome Inversion/genetics , Pedigree , Genome, Human , Whole Genome Sequencing , Methyl-CpG-Binding Protein 2/genetics , Mutation , Homeodomain Proteins/genetics , Middle AgedABSTRACT
Loss-of-function mutations in SGCE, which encodes ε-sarcoglycan (ε-SG), cause myoclonus-dystonia syndrome (OMIM159900, DYT11). A "major" ε-SG protein derived from CCDS5637.1 (NM_003919.2) and a "brain-specific" protein, that includes sequence derived from alternative exon 11b (CCDS47642.1, NM_001099400.1), are reportedly localized in post- and pre-synaptic membrane fractions, respectively. Moreover, deficiency of the "brain-specific" isoform and other isoforms derived from exon 11b may be central to the pathogenesis of DYT11. However, no animal model supports this hypothesis. Gene-trapped ES cells (CMHD-GT_148G1-3, intron 9 of NM_011360) were used to generate a novel Sgce mouse model (C57BL/6J background) with markedly reduced expression of isoforms derived from exons 3' to exon 9 of NM_011360. Among those brain regions analyzed in adult (2month-old) wild-type (WT) mice, cerebellum showed the highest relative expression of isoforms incorporating exon 11b. Homozygotes (SgceGt(148G1)Cmhd/Gt(148G1)Cmhd or SgceGt/Gt) and paternal heterozygotes (Sgcem+/pGt, m-maternal, p-paternal) showed 60 to 70% reductions in expression of total Sgce. Although expression of the major (NM_011360) and brain-specific (NM_001130189) isoforms was markedly reduced, expression of short isoforms was preserved and relatively small amounts of chimeric ε-SG/ß-galactosidase fusion protein was produced by the Sgce gene-trap locus. Immunoaffinity purification followed by mass spectrometry assessments of Sgcem+/pGt mouse brain using pan- or brain-specific ε-SG antibodies revealed significant reductions of ε-SG and other interacting sarcoglycans. Genome-wide gene-expression data using RNA derived from adult Sgcem+/pGt mouse cerebellum showed that the top up-regulated genes were involved in cell cycle, cellular development, cell death and survival, while the top down-regulated genes were associated with protein synthesis, cellular development, and cell death and survival. In comparison to WT littermates, Sgcem+/pGt mice exhibited "tiptoe" gait and stimulus-induced appendicular posturing between Postnatal Days 14 to 16. Abnormalities noted in older Sgcem+/pGt mice included reduced body weight, altered gait dynamics, and reduced open-field activity. Overt spontaneous or stimulus-sensitive myoclonus was not apparent on the C57BL/6J background or mixed C57BL/6J-BALB/c and C57BL/6J-129S2 backgrounds. Our data confirm that mouse Sgce is a maternally imprinted gene and suggests that short Sgce isoforms may compensate, in part, for deficiency of major and brain-specific Sgce isoforms.
Subject(s)
Brain/metabolism , Dystonic Disorders/metabolism , Sarcoglycans/metabolism , Animals , Anxiety/metabolism , Disease Models, Animal , Exploratory Behavior/physiology , Female , Gait/physiology , Gene Expression Regulation, Developmental , Male , Mice, 129 Strain , Mice, Inbred BALB C , Mice, Inbred C57BL , Motor Activity/physiology , Phenotype , Protein Isoforms/metabolismABSTRACT
OBJECTIVE: How hexanucleotide (GGGGCC) repeat expansions in C9ORF72 cause amyotrophic lateral sclerosis (ALS) remains poorly understood. Both gain- and loss-of-function mechanisms have been proposed. Evidence supporting these mechanisms in vivo is, however, incomplete. Here we determined the effect of C9orf72 loss-of-function in mice. METHODS: We generated and analyzed a conditional C9orf72 knockout mouse model. C9orf72(fl/fl) mice were crossed with Nestin-Cre mice to selectively remove C9orf72 from neurons and glial cells. Immunohistochemistry was performed to study motor neurons and neuromuscular integrity, as well as several pathological hallmarks of ALS, such as gliosis and TDP-43 mislocalization. In addition, motor function and survival were assessed. RESULTS: Neural-specific ablation of C9orf72 in conditional C9orf72 knockout mice resulted in significantly reduced body weight but did not induce motor neuron degeneration, defects in motor function, or altered survival. INTERPRETATION: Our data suggest that C9orf72 loss-of-function, by itself, is insufficient to cause motor neuron disease. These results may have important implications for the development of therapeutic strategies for C9orf72-associated ALS.
Subject(s)
Motor Neuron Disease/genetics , Motor Neuron Disease/pathology , Nerve Degeneration/genetics , Nerve Degeneration/pathology , Proteins/genetics , Amino Acid Sequence , Animals , C9orf72 Protein , Gene Knockout Techniques , HEK293 Cells , Humans , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Transgenic , Molecular Sequence Data , Motor Neurons/pathologyABSTRACT
BACKGROUND: Myoclonus-dystonia is a neurogenic movement disorder caused by mutations in the gene encoding É-sarcoglycan. By contrast, mutations in the α-, ß-, γ-, and δ-sarcoglycan genes cause limb girdle muscular dystrophies. The sarcoglycans are part of the dystrophin-associated protein complex in muscle that is disrupted in several types of muscular dystrophy. Intriguingly, patients with myoclonus-dystonia have no muscle pathology; conversely, limb-girdle muscular dystrophy patients have not been reported to have dystonia-associated features. To gain further insight into the molecular mechanisms underlying these differences, we searched for evidence of a sarcoglycan complex in the brain. METHODS: Immunoaffinity chromatography and mass spectrometry were used to purify ubiquitous and brain-specific É-sarcoglycan directly from tissue. Cell models were used to determine the effect of mutations on the trafficking and assembly of the brain sarcoglycan complex. RESULTS: Ubiquitous and brain-specific É-sarcoglycan isoforms copurify with ß-, δ-, and ζ-sarcoglycan, ß-dystroglycan, and dystrophin Dp71 from brain. Incorporation of a muscular dystrophy-associated ß-sarcoglycan mutant into the brain sarcoglycan complex impairs the formation of the ßδ-sarcoglycan core but fails to abrogate the association and membrane trafficking of É- and ζ-sarcoglycan. CONCLUSIONS: É-Sarcoglycan is part of the dystrophin-associated protein complex in brain. Partial preservation of É- and ζ-sarcoglycan in brain may explain the absence of myoclonus dystonia-like features in muscular dystrophy patients. © 2016 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.
Subject(s)
Brain/metabolism , Dystonic Disorders/metabolism , Muscular Dystrophies/metabolism , Sarcoglycans/metabolism , Animals , HEK293 Cells , Humans , RatsABSTRACT
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.
Subject(s)
Alcoholism/genetics , Anxiety Disorders/genetics , Dystonic Disorders/genetics , Myoclonus/genetics , Obsessive-Compulsive Disorder/genetics , Sarcoglycans/genetics , Adolescent , Adult , Aged , Alcoholism/diagnosis , Anxiety Disorders/diagnosis , Child , Child, Preschool , Female , Genetic Predisposition to Disease , Humans , Male , Middle Aged , Mutation , Obsessive-Compulsive Disorder/diagnosis , Phenotype , Quality of LifeABSTRACT
An expanded hexanucleotide repeat in the C9orf72 gene is the most common genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis (c9FTD/ALS). We now report the first description of a homozygous patient and compare it to a series of heterozygous cases. The patient developed early-onset frontotemporal dementia without additional features. Neuropathological analysis showed c9FTD/ALS characteristics, with abundant p62-positive inclusions in the frontal and temporal cortices, hippocampus and cerebellum, as well as less abundant TDP-43-positive inclusions. Overall, the clinical and pathological features were severe, but did not fall outside the usual disease spectrum. Quantification of C9orf72 transcript levels in post-mortem brain demonstrated expression of all known C9orf72 transcript variants, but at a reduced level. The pathogenic mechanisms by which the hexanucleotide repeat expansion causes disease are unclear and both gain- and loss-of-function mechanisms may play a role. Our data support a gain-of-function mechanism as pure homozygous loss of function would be expected to lead to a more severe, or completely different clinical phenotype to the one described here, which falls within the usual range. Our findings have implications for genetic counselling, highlighting the need to use genetic tests that distinguish C9orf72 homozygosity.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Brain/pathology , DNA Repeat Expansion/genetics , Frontotemporal Dementia/genetics , Mutation/genetics , Proteins/genetics , Age of Onset , Amyotrophic Lateral Sclerosis/pathology , C9orf72 Protein , DNA-Binding Proteins/metabolism , Frontotemporal Dementia/pathology , Homozygote , Humans , Male , Middle Aged , Neuropsychological Tests , Pedigree , Proteins/metabolismABSTRACT
Fukutin-related protein (FKRP, MIM ID 606596) variants cause a range of muscular dystrophies associated with hypo-glycosylation of the matrix receptor, α-dystroglycan. These disorders are almost exclusively caused by homozygous or compound heterozygous missense variants in the FKRP gene that encodes a ribitol phosphotransferase. To understand how seemingly diverse FKRP missense mutations may contribute to disease, we examined the synthesis, intracellular dynamics, and structural consequences of a panel of missense mutations that encompass the disease spectrum. Under non-reducing electrophoresis conditions, wild type FKRP appears to be monomeric whereas disease-causing FKRP mutants migrate as high molecular weight, disulfide-bonded aggregates. These results were recapitulated using cysteine-scanning mutagenesis suggesting that abnormal disulfide bonding may perturb FKRP folding. Using fluorescence recovery after photobleaching, we found that the intracellular mobility of most FKRP mutants in ATP-depleted cells is dramatically reduced but can, in most cases, be rescued with reducing agents. Mass spectrometry showed that wild type and mutant FKRP differentially associate with several endoplasmic reticulum (ER)-resident chaperones. Finally, structural modelling revealed that disease-associated FKRP missense variants affected the local environment of the protein in small but significant ways. These data demonstrate that protein misfolding contributes to the molecular pathophysiology of FKRP-deficient muscular dystrophies and suggest that molecules that rescue this folding defect could be used to treat these disorders.
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 NRXN1ß 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.
Subject(s)
Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/genetics , Hyperventilation/genetics , Intellectual Disability/genetics , Mutation, Missense , Transcription Factors/genetics , Animals , Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/metabolism , COS Cells , Calcium-Binding Proteins , Cell Adhesion Molecules, Neuronal/genetics , Cell Nucleus/metabolism , Chlorocebus aethiops , Facies , Genes, Reporter , HEK293 Cells , Humans , Luciferases, Renilla/biosynthesis , Luciferases, Renilla/genetics , Membrane Proteins/genetics , Nerve Tissue Proteins/genetics , Neural Cell Adhesion Molecules , Promoter Regions, Genetic , Protein Multimerization , Protein Structure, Tertiary , Protein Transport , Transcription Factor 4 , Transcription Factors/metabolism , Transcriptional ActivationABSTRACT
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.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Frontotemporal Lobar Degeneration/genetics , Genetic Predisposition to Disease , Mutation/genetics , Adenosine Triphosphatases/genetics , Amyotrophic Lateral Sclerosis/pathology , C9orf72 Protein , Cell Cycle Proteins/genetics , Chromosomes, Human, Pair 9 , Frontotemporal Lobar Degeneration/pathology , Humans , Intercellular Signaling Peptides and Proteins/genetics , Progranulins , Proteins/genetics , RNA-Binding Proteins , Valosin Containing ProteinABSTRACT
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.
Subject(s)
Dystonic Disorders/genetics , Sarcoglycans/metabolism , Animals , Dystonic Disorders/metabolism , Glycosylation , HEK293 Cells , Humans , Lysosomes/metabolism , Mice , Mutation, Missense , Protein Transport , Proteolysis , Rats , Sarcoglycans/genetics , Secretory PathwayABSTRACT
BACKGROUND: Mutations in the maternally imprinted epsilon-sarcoglycan gene occur in 30%-50% of myoclonus-dystonia cases. Psychiatric symptoms, particularly obsessive-compulsive disorder, have been described in some patients. METHODS: We systematically reviewed 22 reports of psychiatric symptoms in myoclonus-dystonia, dividing individuals according to clinical and mutation status. RESULTS: Clinically manifesting mutation carriers demonstrated an excess of psychiatric disorders compared with nonmutation carriers (P < .001). No differences were seen between non-motor-manifesting carriers and nonmutation carriers with the exception of alcohol excess/dependence, higher in non-motor-manifesting carriers. CONCLUSIONS: The results confirm the association of epsilon-sarcoglycan gene mutations with psychiatric disease and suggest a possible separation of the motor and psychiatric effects.
Subject(s)
Dystonic Disorders/genetics , Genetic Predisposition to Disease , Mental Disorders/genetics , Mutation/genetics , Sarcoglycans/genetics , HumansABSTRACT
FOXG1 syndrome is a neurodevelopmental disorder caused by mutations in the FOXG1 gene. Here, an induced pluripotent stem cell (iPSC) line was generated from human dermal fibroblasts of an individual with the c.490dupG (p.Glu154fs) mutation in the FOXG1 gene. Fibroblasts were reprogrammed using non-integrating episomal plasmids and pluripotency marker expression was confirmed by both immunocytochemistry and quantitative PCR in the resultant iPSC line. There were no karyotypic abnormalities and the cell line successfully differentiated into all three germ layers. This cell line may prove useful in the study of the pathogenic mechanisms that underpin FOXG1 syndrome.
Subject(s)
Induced Pluripotent Stem Cells , Cell Differentiation , Cell Line , Fibroblasts , Forkhead Transcription Factors/genetics , Humans , Mutation , Nerve Tissue ProteinsABSTRACT
Mutations in the TANK-binding kinase 1 (TBK1) gene have recently been shown to cause frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). The phenotype is highly variable and has been associated with behavioral variant FTD, primary progressive aphasia, and pure ALS. We describe the clinical, anatomical, and pathological features of a patient who developed corticobasal syndrome (CBS)/progressive nonfluent aphasia (PNFA) overlap. The patient presented with progressive speech difficulties and later developed an asymmetric akinetic-rigid syndrome. Neuroimaging showed asymmetrical frontal atrophy, predominantly affecting the right side. There was a strong family history of neurodegenerative disease with four out of seven siblings developing either dementia or ALS in their 50s and 60s. The patient died at the age of 71 and the brain was donated for postmortem analysis. Histopathological examination showed frontotemporal lobar degeneration TDP-43 type A pathology. Genetic screening did not reveal a mutation in the GRN, MAPT, or C9orf72 genes, but exome sequencing revealed a novel p.E703X mutation in the TBK1 gene. Although segregation data were not available, this loss-of-function mutation is highly likely to be pathogenic because it is predicted to disrupt TBK1/optineurin interaction and impair cellular autophagy. In conclusion, we show that TBK1 mutations can be a cause of an atypical parkinsonian syndrome and screening should be considered in CBS patients with a family history of dementia or ALS.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Cell Cycle Proteins/genetics , Frontotemporal Dementia/genetics , Membrane Transport Proteins/genetics , Neurodegenerative Diseases/genetics , Protein Serine-Threonine Kinases/genetics , Amyotrophic Lateral Sclerosis/diagnostic imaging , Amyotrophic Lateral Sclerosis/pathology , Female , Frontotemporal Dementia/diagnostic imaging , Frontotemporal Dementia/pathology , Genetic Testing , Humans , Middle Aged , Mutation , Neurodegenerative Diseases/diagnostic imaging , Neurodegenerative Diseases/pathology , Phenotype , Exome SequencingABSTRACT
Background: Common genetic variants in and around the gene encoding transcription factor 4 (TCF4) are associated with an increased risk of schizophrenia. Conversely, rare damaging TCF4 mutations cause Pitt-Hopkins syndrome and have also been found in individuals with intellectual disability (ID) and autism spectrum disorder (ASD). Methods: Chromatin immunoprecipitation and next generation sequencing were used to identify the genomic targets of TCF4. These data were integrated with expression, epigenetic and disease gene sets using a range of computational tools. Results: We identify 10604 TCF4 binding sites in the genome that were assigned to 5437 genes. De novo motif enrichment found that most TCF4 binding sites contained at least one E-box (5'-CAtcTG). Approximately 77% of TCF4 binding sites overlapped with the H3K27ac histone modification for active enhancers. Enrichment analysis on the set of TCF4 targets identified numerous, highly significant functional clusters for pathways including nervous system development, ion transport and signal transduction, and co-expression modules for genes associated with synaptic function and brain development. Importantly, we found that genes harboring de novo mutations in schizophrenia (P = 5.3 × 10-7), ASD (P = 2.5 × 10-4), and ID (P = 7.6 × 10-3) were also enriched among TCF4 targets. TCF4 binding sites were also found at other schizophrenia risk loci including the nicotinic acetylcholine receptor cluster, CHRNA5/CHRNA3/CHRNB4 and SETD1A. Conclusions: These data demonstrate that TCF4 binding sites are found in a large number of neuronal genes that include many genetic risk factors for common neurodevelopmental disorders.
Subject(s)
Autism Spectrum Disorder/genetics , Gene Expression Regulation, Developmental/genetics , Gene Expression/genetics , Genetic Predisposition to Disease/genetics , Intellectual Disability/genetics , Schizophrenia/genetics , Transcription Factor 4/genetics , Chromatin Immunoprecipitation , High-Throughput Nucleotide Sequencing , HumansSubject(s)
Amyotrophic Lateral Sclerosis/genetics , Frontotemporal Dementia/genetics , Parkinson Disease/genetics , Proteins/genetics , Brain/pathology , C9orf72 Protein , Chromosomes, Human, Pair 9/genetics , DNA Repeat Expansion , Dopamine Plasma Membrane Transport Proteins/metabolism , Electromyography , Humans , Magnetic Resonance Imaging , Male , Middle Aged , PedigreeABSTRACT
The Cardiomyopathy-associated gene 5 (Cmya5) encodes myospryn, a large tripartite motif (TRIM)-related protein found predominantly in cardiac and skeletal muscle. Cmya5 is an expression biomarker for a number of diseases affecting striated muscle and may also be a schizophrenia risk gene. To further understand the function of myospryn in striated muscle, we searched for additional myospryn paralogs. Here we identify a novel muscle-expressed TRIM-related protein minispryn, encoded by Fsd2, that has extensive sequence similarity with the C-terminus of myospryn. Cmya5 and Fsd2 appear to have originated by a chromosomal duplication and are found within evolutionarily-conserved gene clusters on different chromosomes. Using immunoaffinity purification and mass spectrometry we show that minispryn co-purifies with myospryn and the major cardiac ryanodine receptor (RyR2) from heart. Accordingly, myospryn, minispryn and RyR2 co-localise at the junctional sarcoplasmic reticulum of isolated cardiomyocytes. Myospryn redistributes RyR2 into clusters when co-expressed in heterologous cells whereas minispryn lacks this activity. Together these data suggest a novel role for the myospryn complex in the assembly of ryanodine receptor clusters in striated muscle.
Subject(s)
Carrier Proteins/genetics , Cloning, Molecular/methods , Muscle Proteins/genetics , Ryanodine Receptor Calcium Release Channel/metabolism , Animals , COS Cells , Carrier Proteins/metabolism , Chlorocebus aethiops , Chromatography, Affinity , Chromosome Duplication , HEK293 Cells , Humans , Intracellular Signaling Peptides and Proteins , Mass Spectrometry , Mice , Muscle Proteins/metabolism , Sarcoplasmic Reticulum/metabolismABSTRACT
BACKGROUND: A CAG repeat expansion in HTT has been known to cause Huntington's disease for over 20 years. The genomic sequence of the 67 exon HTT is clear but few reports have detailed alternative splicing or alternative transcripts. Most eukaryotic genes with multiple exons show alternative splicing that increases the diversity of the transcriptome and proteome: it would be surprising if a gene with 67 known exons in its two major transcripts did not present some alternative transcripts. OBJECTIVE: To investigate the presence of alternative transcripts directly in human HTT. METHODS: An overlapping RT-PCR based approach was used to determine novel HTT splice variants in human brain from HD patients and controls and 3D protein homology modelling employed to investigate their significance on the function of the HTT protein. RESULTS: Here we show multiple previously unreported novel transcripts of HTT. Of the 22 splice variants found, eight were in-frame with the potential to encode novel HTT protein isoforms. Two splice variants were selected for further study; HTT Δex4,5,6 which results in the skipping of exons 4, 5 and 6 and HTTex41b which includes a novel exon created via partial retention of intron 41. 3D protein homology modelling showed that both splice variants are of potential functional significance leading to the loss of a karyopherin nuclear localisation signal and alterations to sites of posttranslational modification. CONCLUSIONS: The identification of novel HTT transcripts has implications for HTT protein isoform expression and function. Understanding the functional significance of HTT alternative splicing would be critical to guide the design of potential therapeutics in HD that aim to reduce the toxic HTT transcript or protein product including RNA silencing and correction of mis-splicing in disease.
Subject(s)
Alternative Splicing , Brain/metabolism , Exons , Nerve Tissue Proteins/genetics , HeLa Cells , Humans , Huntingtin Protein , Models, Molecular , Nerve Tissue Proteins/metabolismABSTRACT
An intronic G(4)C(2) 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.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , DNA Repeat Expansion/genetics , Frontotemporal Lobar Degeneration/genetics , Genetic Association Studies , Proteins/genetics , Proteins/metabolism , C9orf72 Protein , Cohort Studies , Frontal Lobe/metabolism , Genetic Association Studies/methods , Genetic Variation , Genotype , Humans , PhenotypeABSTRACT
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.
Subject(s)
Dystonia/genetics , Dystonic Disorders/diagnosis , Dystonic Disorders/genetics , Sarcoglycans/genetics , Adolescent , Adult , Age of Onset , Aged , Child , Child, Preschool , Cohort Studies , Dystonic Disorders/epidemiology , Dystonic Disorders/physiopathology , Female , Gene Deletion , Genotype , Humans , Ireland/epidemiology , Male , Middle Aged , Phenotype , United Kingdom/epidemiology , Young AdultABSTRACT
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-ß 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.