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Background: We describe a 4-generation Dutch pedigree with a unique dominantly inherited clinical phenotype of a combined progressive chorea and cervical dystonia carrying a novel heterozygous dopamine D2 receptor (DRD2) variant., Objectives: The objective of this study was to identify the genetic cause of the disease and to further investigate the functional consequences of the genetic variant., Methods: After detailed clinical and neurological examination, whole-exome sequencing was performed. Because a novel variant in the DRD2 gene was found as the likely causative gene defect in our pedigree, we sequenced the DRD2 gene in a cohort of 121 Huntington-like cases with unknown genetic cause (Germany). Moreover, functional characterization of the DRD2 variant included arrestin recruitment, G protein activation, and G protein-mediated inhibition of adenylyl cyclase determined in a cell model, and G protein-regulated inward-rectifying potassium channels measured in midbrain slices of mice., Result: We identified a novel heterozygous variant c.634A > T, p.Ile212Phe in exon 5 of DRD2 that cosegregated with the clinical phenotype. Screening of the German cohort did not reveal additional putative disease-causing variants. We demonstrated that the D2 S/L -I 212 F receptor exhibited increased agonist potency and constitutive activation of G proteins in human embryonic kidney 239 cells as well as significantly reduced arrestin3 recruitment. We further showed that the D2 S -I 212 F receptor exhibited aberrant receptor function in mouse midbrain slices., Conclusions: Our results support an association between the novel p.Ile212Phe variant in DRD2, its modified D2 receptor activity, and the hyperkinetic movement disorder reported in the 4-generation pedigree. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society., (© 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.)

Musician's dystonia and writer's cramp are examples of task-specific dystonia. Recently, the arylsulfatase G (ARSG) locus was suggested to be associated with musician's dystonia and writer's cramp by a genome-wide association study. To test for the presence of causal variants, the entire coding region and exon-intron boundaries of ARSG were sequenced in DNA samples from 158 musician's dystonia patients which were collected at the University of Music, Drama, and Media (Hanover, Germany), and 72 patients with writer's cramp which were recruited at the Academic Medical Centers in Amsterdam and Groningen, the Netherlands. The frequency of variants within ARSG was compared to publically available data at the exome variant server (EVS) from the NHLBI GO Exome Sequencing Project. We identified 11 single nucleotide variants (SNVs) in the patients including eight non-synonymous substitutions. All variants have previously been reported at EVS including two SNVs with a reported minor allele frequency <1%. One rare missense variant, rs61999318 (p.I493T), was significantly enriched in the group of writer's cramp patients compared to European Americans in EVS database (p = 0.0013). In patients with writer's cramp, there was an overall enrichment for rare, protein-changing variants compared to controls (p < 0.01). In conclusion, we did not detect any conclusive mutation in ARSG. However, we showed an association with rs61999318 in patients with writer's cramp that contributed to an overall enrichment for rare, protein-changing variants in these patients. Thus, our data provide further support for a role of ARSG variants in task-specific dystonia, especially writer's cramp.