Exploring functional polymorphisms in the dopamine receptor D2 gene using prolactin concentration in healthy subjects

Cumulative Genetic Score of DRD2 Polymorphisms Is Associated with Impulsivity and Masked Semantic Priming

Individual differences in the magnitude of semantic priming effects are associated with executive functions (EF). Striatal dopamine has been shown to be associated with EF as well as impulsivity and could therefore be associated with differences in the magnitude of semantic priming. We investigated n = 155 individuals in an unmasked as well as in a masked semantic priming paradigm. We additionally assessed self-reported impulsivity and a cumulative genetic score (CGS) comprising six polymorphisms that have been found to be functionally relevant for the expression of the DRD2 gene. We found a significantly negative association between the DRD2 CGS and reaction time priming in the masked semantic priming paradigm. In addition, the DRD2 CGS was positively associated with self-reported impulsivity. Our findings complement previous research by showing a role of the DRD2 gene for masked semantic priming. Therefore, the investigation of genes within the dopamine system might improve our understanding of the genetic basis of impulsivity and semantic processing. Thus, the DRD2 CGS is of interest for clinical as well as experimental psychological research.

Effects of aripiprazole, quetiapine and ziprasidone on plasma prolactin levels in individuals with first episode nonaffective psychosis: Analysis of a randomized open-label 1year study

RATIONALE

Hyperprolactinemia is considered a troubling adverse effect of antipsychotics. Direct comparisons among second generation antipsychotics are scant in clinical practice. We hypothesize prolactin-sparing second-generation antipsychotics may have differential effects on prolactin levels and that they may be influenced by sex.

OBJECTIVES

To explore the differential effect of three widely used prolactin-sparing antipsychotics, aripiprazole, quetiapine and ziprasidone, on prolactin plasma levels in first episode non-affective psychosis during a 1year of treatment.

METHOD

From October 2005 to January 2011 a prospective, randomized, open-label study was undertaken. 141 patients who were randomly allocated to aripiprazole (N=56), quetiapine (N=36) or ziprasidone (N=49) were analyzed. The main outcome was differences in prolactin plasma levels over 1year follow-up among the three antipsychotics. Prolactin levels had a skewed distribution and therefore they were log-transformed before statistical analyses.

RESULTS

Male patients on aripiprazole had a lower risk of suffering an increase on prolactin plasma levels (N=71; F=12.645; p<0.001). There was a gender effect with smaller changes in mean prolactin values only in males. Aripiprazole had a reduced risk of hyperprolactinemia (aripiprazole 19.6%) compared to quetiapine (44.4%) and ziprasidone (32.7%) (p=0.038); and quite similar findings were found when investigating males (p=0.040). No significant differences were found in females. The percentages of mild prolactin excess were: 14.3% on aripiprazole, 36.1% on quetiapine and 18.4% on ziprasidone (χ²=6.611 p=0.037).

CONCLUSIONS

Our findings provide additional evidence of differential effects of three sparing-prolactin antipsychotics on prolactin release and may help clinicians to decide among therapeutic options.

Affiliation with substance-using peers: Examining gene-environment correlations among parent monitoring, polygenic risk, and children's impulsivity

Parental monitoring can buffer the effect of deviant peers on adolescents' substance use by reducing affiliation with substance-using peers. However, children's genetic predispositions may evoke poorer monitoring, contributing to negative child outcomes. We examined evocative genotype-environment correlations underlying children's genetic predisposition for behavioral undercontrol and parental monitoring in early adolescence via children's impulsivity in middle childhood, and the influence of parental monitoring on affiliation with substance-using peers a year and a half later (n = 359). Genetic predisposition for behavioral undercontrol was captured using a polygenic risk score, and a portion of passive rGE was controlled by including parents' polygenic risk scores. Children's polygenic risk predicted poorer parental monitoring via greater children's impulsivity, indicating evocative rGE, controlling for a portion of passive rGE. Poorer parental monitoring predicted greater children's affiliation with substance-using peers a year and a half later. Results are discussed with respect to gene-environment correlations within developmental cascades.

Aggression, DRD1 polymorphism, and lesion location in penetrating traumatic brain injury

OBJECTIVE

This study evaluated whether structural brain lesions modulate the relationship between pathological aggression and the dopaminergic system in traumatic brain injury (TBI). While converging evidence suggests that different areas of the prefrontal cortex modulate dopaminergic activity, to date no evidence exists of a modulation of endogenous dopaminergic tone by lesion localization in penetrating TBI (pTBI).

METHODS

This study included 141 male Caucasian veterans who suffered penetrating pTBI during their service in Vietnam and 29 healthy male Caucasian Vietnam veterans. Participants were genotyped for 3 functional single nucleotide polymorphisms (SNPs): dopamine receptor D1 (DRD1) rs686, dopamine receptor D2 (DRD2) rs4648317, and catechol-O-methyltransferase (COMT) Val158Met. Patients underwent brain CT scans and were divided into medial prefrontal cortex, lateral prefrontal cortex, and posterior cortex lesion groups. Long-term aggression levels were evaluated with the agitation/aggression subscale of the Neuropsychiatric Inventory.

RESULTS

Our data showed that carriers of more transcriptionally active DRD1 alleles compared to noncarriers demonstrated greater aggression levels due to medial prefrontal cortex lesions but reduced aggression levels due to lateral prefrontal cortex lesions independently of DRD2 rs4648317 or COMT Val158Met genotypes.

CONCLUSIONS

Our results suggest that the relationship between pTBI-related aggression and the dopaminergic system is modulated by lesion location. Potentially lesion location could represent an easy-to-use, widely available, para-clinical marker to help in the development of an individualized therapeutic approach to pTBI-related pathological aggression.

Sensorimotor gating and D2 receptor signalling: evidence from a molecular genetic approach

Converging evidence from pharmacological investigations, genetic association studies and schizophrenia research indicates an important influence of the dopamine system on sensorimotor gating as measured by prepulse inhibition (PPI) of the acoustic startle response. In particular, D2 receptor agonists have been shown to disrupt PPI in humans and rodents. In the present study, we investigated the associations of two functional DRD2 related single nucleotide polymorphisms (rs4648317 and rs1800497, the latter also known as DRD2/ANKK1 Taq1A) with PPI in two independent healthy human samples (overall n=197; Munich n=101; London n=96). Taq1A is a prominent marker of striatal D2 receptor signalling and was therefore hypothesized to impact on PPI. In line with our hypothesis, we report here reduced PPI levels in individuals with higher striatal D2 receptor signalling as indicated by the Taq1A genotype. Meta-analysis across both samples confirmed this finding. In contrast, an association between rs4648317 and PPI found in the Munich sample could not be confirmed in the London sample. Overall, the present study helps to bridge the gap between pharmacological manipulations of PPI and molecular genetics of the dopaminergic system.