Muscleblind-Like 1 Knockout Mice Reveal Novel Splicing Defects in the Myotonic Dystrophy Brain

Myotonic dystrophy type 1 (DM1) is a multi-systemic disorder caused by a CTG trinucleotide repeat expansion (CTGexp) in the DMPK gene. In skeletal muscle, nuclear sequestration of the alternative splicing factor muscleblind-like 1 (MBNL1) explains the majority of the alternative splicing defects observed in the HSALR transgenic mouse model which expresses a pathogenic range CTGexp. In the present study, we addressed the possibility that MBNL1 sequestration by CUGexp RNA also contributes to splicing defects in the mammalian brain. We examined RNA from the brains of homozygous Mbnl1ΔE3/ΔE3 knockout mice using splicing-sensitive microarrays. We used RT-PCR to validate a subset of alternative cassette exons identified by microarray analysis with brain tissues from Mbnl1ΔE3/ΔE3 knockout mice and post-mortem DM1 patients. Surprisingly, splicing-sensitive microarray analysis of Mbnl1ΔE3/ΔE3 brains yielded only 14 candidates for mis-spliced exons. While we confirmed that several of these splicing events are perturbed in both Mbnl1 knockout and DM1 brains, the extent of splicing mis-regulation in the mouse model was significantly less than observed in DM1. Additionally, several alternative exons, including Grin1 exon 4, App exon 7 and Mapt exons 3 and 9, which have previously been reported to be aberrantly spliced in human DM1 brain, were spliced normally in the Mbnl1 knockout brain. The sequestration of MBNL1 by CUGexp RNA results in some of the aberrant splicing events in the DM1 brain. However, we conclude that other factors, possibly other MBNL proteins, likely contribute to splicing mis-regulation in the DM1 brain

RNA Gain-of-Function in Spinocerebellar Ataxia Type 8

Microsatellite expansions cause a number of dominantly-inherited neurological diseases. Expansions in coding-regions cause protein gain-of-function effects, while non-coding expansions produce toxic RNAs that alter RNA splicing activities of MBNL and CELF proteins. Bi-directional expression of the spinocerebellar ataxia type 8 (SCA8) CTG CAG expansion produces CUG expansion RNAs (CUGexp) from the ATXN8OS gene and a nearly pure polyglutamine expansion protein encoded by ATXN8 CAGexp transcripts expressed in the opposite direction. Here, we present three lines of evidence that RNA gain-of-function plays a significant role in SCA8: 1) CUGexp transcripts accumulate as ribonuclear inclusions that co-localize with MBNL1 in selected neurons in the brain; 2) loss of Mbnl1 enhances motor deficits in SCA8 mice; 3) SCA8 CUGexp transcripts trigger splicing changes and increased expression of the CUGBP1-MBNL1 regulated CNS target, GABA-A transporter 4 (GAT4/Gabt4). In vivo optical imaging studies in SCA8 mice confirm that Gabt4 upregulation is associated with the predicted loss of GABAergic inhibition within the granular cell layer. These data demonstrate that CUGexp transcripts dysregulate MBNL/CELF regulated pathways in the brain and provide mechanistic insight into the CNS effects of other CUGexp disorders. Moreover, our demonstration that relatively short CUGexp transcripts cause RNA gain-of-function effects and the growing number of antisense transcripts recently reported in mammalian genomes suggest unrecognized toxic RNAs contribute to the pathophysiology of polyglutamine CAG CTG disorders

High-throughput mutational analysis of TOR1A in primary dystonia

<p>Abstract</p> <p>Background</p> <p>Although the c.904_906delGAG mutation in Exon 5 of <it>TOR1A </it>typically manifests as early-onset generalized dystonia, DYT1 dystonia is genetically and clinically heterogeneous. Recently, another Exon 5 mutation (c.863G>A) has been associated with early-onset generalized dystonia and some ΔGAG mutation carriers present with late-onset focal dystonia. The aim of this study was to identify <it>TOR1A </it>Exon 5 mutations in a large cohort of subjects with mainly non-generalized primary dystonia.</p> <p>Methods</p> <p>High resolution melting (HRM) was used to examine the entire <it>TOR1A </it>Exon 5 coding sequence in 1014 subjects with primary dystonia (422 spasmodic dysphonia, 285 cervical dystonia, 67 blepharospasm, 41 writer's cramp, 16 oromandibular dystonia, 38 other primary focal dystonia, 112 segmental dystonia, 16 multifocal dystonia, and 17 generalized dystonia) and 250 controls (150 neurologically normal and 100 with other movement disorders). Diagnostic sensitivity and specificity were evaluated in an additional 8 subjects with known ΔGAG DYT1 dystonia and 88 subjects with ΔGAG-negative dystonia.</p> <p>Results</p> <p>HRM of <it>TOR1A </it>Exon 5 showed high (100%) diagnostic sensitivity and specificity. HRM was rapid and economical. HRM reliably differentiated the <it>TOR1A </it>ΔGAG and c.863G>A mutations. Melting curves were normal in 250/250 controls and 1012/1014 subjects with primary dystonia. The two subjects with shifted melting curves were found to harbor the classic ΔGAG deletion: 1) a non-Jewish Caucasian female with childhood-onset multifocal dystonia and 2) an Ashkenazi Jewish female with adolescent-onset spasmodic dysphonia.</p> <p>Conclusion</p> <p>First, HRM is an inexpensive, diagnostically sensitive and specific, high-throughput method for mutation discovery. Second, Exon 5 mutations in <it>TOR1A </it>are rarely associated with non-generalized primary dystonia.</p

Unique noncoding variants upstream of PRDM13 are associated with a spectrum of developmental retinal dystrophies including progressive bifocal chorioretinal atrophy

The autosomal dominant progressive bifocal chorioretinal atrophy (PBCRA) disease locus has been mapped to chromosome 6q14–16.2 which overlaps the North Carolina Macular Dystrophy (NCMD) locus MCDR1. NCMD is a non‐progressive developmental macular dystrophy, in which variants upstream of PRDM13 have been implicated. Whole genome sequencing was performed to interrogate structural variants (SVs) and single nucleotide variants (SNVs) in eight individuals, six affected individuals from two families with PBCRA and two individuals from an additional family with a related developmental macular dystrophy. A SNV (chr6:100,046,804 T > C), located 7.8 kb upstream of the PRDM13 gene, was shared by all PBCRA‐affected individuals in the disease locus. Haplotype analysis suggested that the variant arose independently in the two families. The two affected individuals from family 3, were screened for rare variants in the PBCRA and NCMD loci. This revealed a de novo variant in the proband, 21 bp from the first SNV (chr6:100,046,783 A > C). This study expands the non‐coding variant spectrum upstream of PRDM13 and suggests altered spatio‐temporal expression of PRDM13 as a candidate disease mechanism in the phenotypically distinct but related conditions, NCMD and PBCRA

Cardiac Outcomes in Adults With Mitochondrial Diseases

Background: Patients with mitochondrial diseases are at risk of heart failure (HF) and arrhythmic major adverse cardiac events (MACE). Objectives: We developed prediction models to estimate the risk of HF and arrhythmic MACE in this population. Methods: We determined the incidence and searched for predictors of HF and arrhythmic MACE using Cox regression in 600 adult patients from a multicenter registry with genetically confirmed mitochondrial diseases. Results: Over a median follow-up time of 6.67 years, 29 patients (4.9%) reached the HF endpoint, including 19 hospitalizations for nonterminal HF, 2 cardiac transplantations, and 8 deaths from HF. Thirty others (5.1%) reached the arrhythmic MACE, including 21 with third-degree or type II second-degree atrioventricular blocks, 4 with sinus node dysfunction, and 5 sudden cardiac deaths. Predictors of HF were the m.3243A>G variant (HR: 4.3; 95% CI: 1.8-10.1), conduction defects (HR: 3.0; 95% CI: 1.3-6.9), left ventricular (LV) hypertrophy (HR: 2.6; 95% CI: 1.1-5.8), LV ejection fraction <50% (HR: 10.2; 95% CI: 4.6-22.3), and premature ventricular beats (HR: 4.1; 95% CI: 1.7-9.9). Independent predictors for arrhythmia were single, large-scale mtDNA deletions (HR: 4.3; 95% CI: 1.7-10.4), conduction defects (HR: 6.8; 95% CI: 3.0-15.4), and LV ejection fraction <50% (HR: 2.7; 95% CI: 1.1-7.1). C-indexes of the Cox regression models were 0.91 (95% CI: 0.88-0.95) and 0.80 (95% CI: 0.70-0.90) for the HF and arrhythmic MACE, respectively. Conclusions: We developed the first prediction models for HF and arrhythmic MACE in patients with mitochondrial diseases using genetic variant type and simple cardiac assessments