Background
Heterozygous KMT2B variants are a common cause of dystonia. A novel synonymous KMT2B variant, c.5073C>T (p.Gly1691=) was identified in an individual with childhood‐onset progressive ...dystonia.
Methods
The splicing impact of c.5073C>T was assessed using an in vitro exon‐trapping assay. The genomic region of KMT2B exons 23–26 was cloned into the pSpliceExpress plasmid between exon 2 and 3 of the rat Ins2 gene. The c.5073C>T variant was then introduced through site‐directed mutagenesis. The KMT2B wild‐type and c.5073C>T plasmids were transfected separately into HeLa cells and RNA was extracted 48 hours after transfection. The RNA was reverse transcribed to produce cDNA, which was PCR amplified using primers annealing to the flanking rat Ins2 sequences.
Results
Sanger sequencing of the PCR products revealed that c.5073C>T caused a novel splice donor site and therefore a 5‐bp deletion of KMT2B exon 23 in mature mRNA, leading to a coding frameshift and premature stop codon (p.Lys1692AsnfsTer7).
Conclusion
To our knowledge, this is the first report of a KMT2B synonymous variant associated with dystonia. Reassessment of synonymous variants may increase diagnostic yield for inherited disorders including monogenic dystonia. This is of clinical importance, given the generally favourable response to deep brain stimulation for KMT2B‐related dystonia.
We report a synonymous variant in the KMT2B gene identified on dystonia panel screening. While the variant was predicted to disturb splicing, it was formally reported as a variant of uncertain significance. The patient was reluctant to provide further tissue, however, we were able to confirm aberrant splicing on an exon‐trapping assay, thus changing the classification of the variant to pathogenic.
Abstract Dystonia is a hyperkinetic movement disorder that can be highly stigmatizing and disabling. Substantial evidence from animal models, neuropathological, neurophysiological, neuroimaging and ...clinical studies emphasizes the role of dopaminergic dysfunction in the pathophysiology of dystonia, illustrating possible pathophysiological overlap with parkinsonism. Furthermore, basal ganglia dysfunction has been implicated in the pathogenesis of dystonia, and is well established to underlie the manifestations of Parkinson's disease. Clinically, parkinsonian features are a key characteristic of some combined dystonias, including dopa-responsive dystonia, and Parkinson's disease often presents with dystonia. Moreover, many treatments effective in Parkinson's disease, both medical and surgical, also offer some benefit in dystonia. Therefore, mild parkinsonian features might logically accompany idiopathic and inherited isolated dystonias. However, as the current literature is particularly scant, the present review aimed to investigate mild parkinsonism in idiopathic and inherited dystonia. We found limited evidence alluding to the presence of mildly reduced arm-swing, increased tone, and non-decremental bradykinesia in adult-onset focal dystonia. Tremor, with postures, action and rest, also occurs commonly in idiopathic isolated dystonia, and can simulate Parkinson's disease tremor and be a cause of ‘scans without evidence of dopaminergic deficit’. Parkinsonian features in monogenic isolated dystonias have been less well investigated, despite the potential benefit of correlating pathophysiological and clinical findings. The recognition and improved clinical characterization of parkinsonian features in idiopathic and inherited isolated dystonia extends the clinical spectrum of motor features in dystonia, which may help avoid incorrect diagnosis and inform therapeutic research.
Objectives
The majority of people with suspected genetic dystonia remain undiagnosed after maximal investigation, implying that a number of causative genes have not yet been recognized. We aimed to ...investigate this paucity of diagnoses.
Methods
We undertook weighted burden analysis of whole‐exome sequencing (WES) data from 138 individuals with unresolved generalized dystonia of suspected genetic etiology, followed by additional case‐finding from international databases, first for the gene implicated by the burden analysis (VPS16), and then for other functionally related genes. Electron microscopy was performed on patient‐derived cells.
Results
Analysis revealed a significant burden for VPS16 (Fisher's exact test p value, 6.9 × 109). VPS16 encodes a subunit of the homotypic fusion and vacuole protein sorting (HOPS) complex, which plays a key role in autophagosome‐lysosome fusion. A total of 18 individuals harboring heterozygous loss‐of‐function VPS16 variants, and one with a microdeletion, were identified. These individuals experienced early onset progressive dystonia with predominant cervical, bulbar, orofacial, and upper limb involvement. Some patients had a more complex phenotype with additional neuropsychiatric and/or developmental comorbidities. We also identified biallelic loss‐of‐function variants in VPS41, another HOPS‐complex encoding gene, in an individual with infantile‐onset generalized dystonia. Electron microscopy of patient‐derived lymphocytes and fibroblasts from both patients with VPS16 and VPS41 showed vacuolar abnormalities suggestive of impaired lysosomal function.
Interpretation
Our study strongly supports a role for HOPS complex dysfunction in the pathogenesis of dystonia, although variants in different subunits display different phenotypic and inheritance characteristics. ANN NEUROL 2020;88:867–877
Dystonia is a clinically and genetically heterogeneous disorder and a genetic cause is often difficult to elucidate. This is the first study to use whole genome sequencing (WGS) to investigate ...dystonia in a large sample of affected individuals.
WGS was performed on 111 probands with heterogenous dystonia phenotypes. We performed analysis for coding and non-coding variants, copy number variants (CNVs), and structural variants (SVs). We assessed for an association between dystonia and 10 known dystonia risk variants.
A genetic diagnosis was obtained for 11.7% (13/111) of individuals. We found that a genetic diagnosis was more likely in those with an earlier age at onset, younger age at testing, and a combined dystonia phenotype. We identified pathogenic/likely-pathogenic variants in ADCY5 (n = 1), ATM (n = 1), GNAL (n = 2), GLB1 (n = 1), KMT2B (n = 2), PRKN (n = 2), PRRT2 (n = 1), SGCE (n = 2), and THAP1 (n = 1). CNVs were detected in 3 individuals. We found an association between the known risk variant ARSG rs11655081 and dystonia (p = 0.003).
A genetic diagnosis was found in 11.7% of individuals with dystonia. The diagnostic yield was higher in those with an earlier age of onset, younger age at testing, and a combined dystonia phenotype. WGS may be particularly relevant for dystonia given that it allows for the detection of CNVs, which accounted for 23% of the genetically diagnosed cases.
•Whole genome sequencing (WGS) offers potential advantages over whole exome sequencing or gene panels for testing in dystonia.•A genetic diagnosis was found in 13/111 (11.7%) of individuals with dystonia in this study using WGS.•The diagnostic yield was higher with an earlier age of onset, younger age at testing, and combined dystonia phenotype.•WGS is better at detecting clinically relevant sequencing variants in dystonia genes in comparison to WES.•WGS can detect copy number variants in dystonia genes, which accounted for 3/13 (23%) individuals with a genetic diagnosis.
We investigated the contribution of genomic data reanalysis to the diagnostic yield of dystonia patients who remained undiagnosed after prior genome sequencing.
Probands with heterogeneous dystonia ...phenotypes who underwent initial genome sequencing (GS) analysis in 2019 were included in the reanalysis, which was performed through gene-specific discovery collaborations and systematic genomic data reanalysis.
Initial GS analysis in 2019 (n = 111) identified a molecular diagnosis in 11.7 % (13/111) of cases. Reanalysis between 2020 and 2023 increased the diagnostic yield by 7.2 % (8/111); 3.6 % (4/111) through focused gene-specific clinical correlation collaborative efforts VPS16 (two probands), AOPEP and POLG, and 3.6 % (4/111) by systematic reanalysis completed in 2023 NUS1 (two probands) and DDX3X variants, and a microdeletion encompassing VPS16. Seven of these patients had a high phenotype-based dystonia score ≥3. Notable unverified findings in four additional cases included suspicious variants of uncertain significance in FBXL4 and EIF2AK2, and potential phenotypic expansion associated with SLC2A1 and TREX1 variants.
GS data reanalysis increased the diagnostic yield from 11.7 % to 18.9 %, with potential extension up to 22.5 %. While optimal timing for diagnostic reanalysis remains to be determined, this study demonstrates that periodic re-interrogation of dystonia GS datasets can provide additional genetic diagnoses, which may have significant implications for patients and their families.
•Genome sequencing reanalysis increased the diagnostic yield from 11.7 % to 18.9 %.•Phenotype-based dystonia score ≥3 was associated with a higher diagnostic yield.•Periodic genomic data reanalysis can provide additional diagnoses in dystonia.
Summary Objectives/Hypothesis The objective of this study was to better define the relationship of laryngeal electromyography and video laryngostroboscopy in the diagnosis of vocal fold paralysis. ...Study Design Retrospective diagnostic cohort study with cross-sectional data analysis Methods Data were obtained from 57 patients with unilateral vocal fold paralysis who attended a large tertiary voice referral center. Electromyographic findings were classified according to recurrent laryngeal nerve, superior laryngeal nerve, and high vagal/combined lesions. Video laryngostroboscopy recordings were classified according to the position of the immobile fold into median, paramedian, lateral, and a foreshortened/hooded vocal fold. The position of the paralyzed vocal fold was then analyzed according to the lesion as determined by electromyography. Results The recurrent laryngeal nerve was affected in the majority of cases with left-sided lesions more common than right. Vocal fold position differed between recurrent laryngeal and combined vagal lesions. Recurrent laryngeal nerve lesions were more commonly associated with a laterally displaced immobile fold. No fold position was suggestive of a combined vagal lesion. The inter-rater reliability for determining fold position was high. Conclusion Laryngeal electromyography is useful in diagnosing neuromuscular dysfunction of the larynx and best practice recommends its continued implementation along with laryngostroboscopy. While recurrent laryngeal nerve lesions are more likely to present with a lateral vocal fold, this does not occur in all cases. Such findings indicate that further unknown mechanisms contribute to fold position in unilateral paralysis.
Functional Popliteal Entrapment Syndrome (FPES) is caused by compression of neurovascular structures in the popliteal fossa by hypertrophic muscles, provoking severe leg pain with exercise. Treatment ...is limited to myotomy of hypertrophic musculature. 8 FPES patients underwent imaging and exercise studies, before receiving botulinum toxin A injections (BTX-A) into the gastrocnemius and plantaris muscles. 81.3 % of patients reported clinical improvement on follow-up, and pathological ankle–brachial indices were normalized. BTX-A injection may present a new, safe, effective and non-invasive approach to FPES.
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