Dopamine DRD2 polymorphism (DRD2/ANNK1-Taq1A) is not a significant risk factor in writer’s cramp

Dystonia and dopamine: From phenomenology to pathophysiology

A line of evidence suggests that the pathophysiology of dystonia involves the striatum, whose activity is modulated among other neurotransmitters, by the dopaminergic system. However, the link between dystonia and dopamine appears complex and remains unclear. Here, we propose a physiological approach to investigate the clinical and experimental data supporting a role of the dopaminergic system in the pathophysiology of dystonic syndromes. Because dystonia is a disorder of motor routines, we first focus on the role of dopamine and striatum in procedural learning. Second, we consider the phenomenology of dystonia from every angle in order to search for features giving food for thought regarding the pathophysiology of the disorder. Then, for each dystonic phenotype, we review, when available, the experimental and imaging data supporting a connection with the dopaminergic system. Finally, we propose a putative model in which the different phenotypes could be explained by changes in the balance between the direct and indirect striato-pallidal pathways, a process critically controlled by the level of dopamine within the striatum. Search strategy and selection criteria References for this article were identified through searches in PubMed with the search terms « dystonia », « dopamine", « striatum », « basal ganglia », « imaging data », « animal model », « procedural learning », « pathophysiology », and « plasticity » from 1998 until 2018. Articles were also identified through searches of the authors' own files. Only selected papers published in English were reviewed. The final reference list was generated on the basis of originality and relevance to the broad scope of this review.

Risk Factor Genes in Patients with Dystonia: A Comprehensive Review

Background

Dystonia is a movement disorder with high heterogeneity regarding phenotypic appearance and etiology that occurs in both sporadic and familial forms. The etiology of the disease remains unknown. However, there is increasing evidence suggesting that a small number of gene alterations may lead to dystonia. Although pathogenic variants to the familial type of dystonia have been extensively reviewed and discussed, relatively little is known about the contribution of single-nucleotide polymorphisms (SNPs) to dystonia. This review focuses on the potential role of SNPs and other variants in dystonia susceptibility.

Methods

We searched the PubMed database for peer-reviewed articles published in English, from its inception through January 2018, that concerned human studies of dystonia and genetic variants. The following search terms were included: “dystonia” in combination with the following terms: 1) “polymorphisms” and 2) “SNPs” as free words.

Results

A total of 43 published studies regarding TOR1A, BDNF, DRD5, APOE, ARSG, NALC, OR4X2, COL4A1, TH, DDC, DBH, MAO, COMT, DAT, GCH1, PRKRA, MR-1, SGCE, ATP1A3, TAF1, THAP1, GNAL, DRD2, HLA-DRB, CBS, MTHFR, and MS genes, were included in the current review.

Discussion

To date, a few variants, which are possibly involved in several molecular pathways, have been related to dystonia. Large cohort studies are needed to determine robust associations between variants and dystonia with adjustment for other potential cofounders, in order to elucidate the pathogenic mechanisms of dystonia and the net effect of the genes.

Association of expression of DRD2 rs1800497 polymorphism with migraine risk in Han Chinese individuals

Background

Previous studies suggested that single-nucleotide polymorphisms in dopamine receptor D2 (DRD2) are the susceptibility loci for migraine. This study was aimed at evaluating the contribution of DRD2 rs1800497 and its expression to migraine risk in Han Chinese subjects.

Methods

In total, 250 patients with migraine and 250 age- and sex-matched control subjects were included in this study. TaqMan allelic discrimination assay was used for DRD2 rs1800497 genotyping. Plasma DRD2 concentration was determined using enzyme-linked immunosorbent assay.

Results

Significant associations were observed for the rs1800497 genotype (c²=6.37, p=0.041) and allele (c²=4.69, p=0.03; odds ratio [OR]=1.33, 95% CI=1.03-1.72, power=58%) frequencies between the migraine and control groups. Sex analysis indicated a positive association for rs1800497 between female patients with migraine and control individuals (genotype: c²=7.84, p=0.019; allele: c²=6.60, p=0.010; OR=1.61, 95% CI=1.12-2.30, power=73.4%). Furthermore, a significant association was observed only in female patients with migraine without aura (MO) (genotype: c²=6.88, p=0.032; allele: c²=5.65, p=0.017; OR=1.59, 95% CI=1.08-2.36, power=65.1%). The mean plasma DRD2 levels in the control group (mean±SD: 24.20±2.78) were significantly lower than those in the migraine with aura (MA) (30.86±3.69, p<0.0001) and MO groups (31.88±4.99, p<0.0001). Additionally, there was a sex-based difference in DRD2 expression in the MA (male vs female: 29.46±3.59 vs 32.27±3.27, p<0.01) and MO groups (male vs female: 29.18±3.50 vs 34.58±4.84, p<0.0001). Moreover, plasma DRD2 levels in patients were significantly different among the three genotypes (CC vs CT vs TT: 24.76±3.76 vs 30.93±3.85 vs 37.06±3.95, p<0.0001). Similar results were observed both in the MA (CC vs CT vs TT: 25.09±3.84 vs 28.57±2.84 vs 33.37±1.58, p<0.0001) and MO groups (CC vs CT vs TT: 24.65±3.79 vs 31.65±3.86 vs 38.29±3.74, p<0.0001).

Conclusion

Our case-control study suggested that the DRD2 polymorphism rs1800497 was significantly associated with the risk of migraine in Han Chinese females. Additionally, the plasma DRD2 level was high in patients with migraine. Females with migraine had considerably higher DRD2 levels than males with migraine. DRD2 expression may be regulated by DRD2 rs1800497 genotype in patients with migraine.