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)-(IF)-F-212 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)-(IF)-F-212 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. (c) 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.