Tulin Ozkaragoz

D2 and D4 dopamine receptor polymorphisms and personality

The relationship of various dimensions of temperament, measured by the Tridimensional Personality Questionnaire (TPQ), to polymorphisms of the D2 dopamine receptor (DRD2) and D4 dopamine receptor (DRD4) genes was determined in 119 healthy Caucasian boys who had not yet begun to consume alcohol and other drugs of abuse. Total Novelty Seeking score of the TPQ was significantly higher in boys having, in common, all three minor (A1, B1, and Intron 6 1) alleles of the DRD2 compared to boys without any of these alleles. Boys with the DRD4 7 repeat (7R) allele also had a significantly higher Novelty Seeking score than those without this allele. However, the greatest difference in Novelty Seeking score was found when boys having all three minor DRD2 alleles and the DRD4 7R allele were contrasted to those without any of these alleles. Neither the DRD2 nor the DRD4 polymorphisms differentiated total Harm Avoidance score. Whereas subjects having all three minor DRD2 alleles had a significantly higher Reward Dependence 2 (Persistence) score than subjects without any of these alleles, no significant difference in this personality score was found between subjects with and without the DRD4 7R allele. In conclusion, DRD2 and DRD4 polymorphisms individually associate with Novelty Seeking behavior. However, the combined DRD2 and DRD4 polymorphisms contribute more markedly to this behavior than when these two gene polymorphisms are individually considered.

Association of the A1 allele of the D2 dopamine receptor gene with severe alcoholism.

In a blinded study, 159 subjects composed of nonalcoholics (N = 43), less severe alcoholics (N = 44), severe alcoholics (N = 52) and young children of alcoholics (CoAs, N = 20) were studied for their allelic association with the D2 dopamine receptor (D2DR) gene utilizing peripheral lymphocytes as the DNA source. The combined alcoholic group compared to the nonalcoholic group showed a significantly greater association with the A1 allele of the D2DR gene. Furthermore, an even more robust association was found when severe alcoholics were compared to nonalcoholics. CoAs also showed a significantly greater association with the A1 allele than nonalcoholics but not when compared to alcoholics. Analysis of risk of alcoholism severity suggests that it comprises of two independent components: family history of alcoholism and presence of the A1 allele. Genotype and allelic frequency of the D2DR gene were also analyzed with respect to race. A higher percentage of blacks compared to whites had the A1/A1 genotype, and A1 allelic frequency in the total sample of blacks was significantly greater than in the total sample of whites. Moreover, frequency of the A1 allele was significantly greater in severe alcoholics compared to nonalcoholics in both whites and blacks. However, due to the small sample size of blacks, these racial differences need to be further studied. This study, of the largest sample of alcoholics to date, strongly affirms association of severe alcoholism with the A1 allele of the D2DR gene.

D2 dopamine receptor gene polymorphism discriminates two kinds of novelty seeking

Cloningers psychobiological model of personality as applied to substance misuse has received mixed support. Contrary to the model, recent data suggest that a combination of high novelty seeking (NS) and high harm avoidance (HA) represents a significant risk for the development of severe substance misuse. A genetic polymorphism previously implicated in severe substance dependence, the A1 allele of the D2 dopamine receptor (DRD2) gene, was examined in relation to NS and HA amongst 203 adolescent boys. Specifically, we hypothesized that subjects with the A1 + allele (A1/A1 and A1/A2 genotypes) would report stronger NS and would exhibit a more positive relationship between NS and HA than those with the A1-allele (A2/A2 genotypes). These predictions were supported. The correlation between NS and HA in 81 A1 + allelic boys (r = 0.27, P = 0.02), and that in the 122 A1- allelic boys (r = -0.15, P = 0.09), indicated that this relationship differed according to allelic status (F = 8.52, P < 0:004). Among those with the A1-allele, the present results are consistent with the traditional view that novelty seeking provides positive reinforcement, or the fulfillment of appetitive drives. In contrast, novelty seeking in those with the A1 + allele appears to include a negative reinforcement or self-medicating function

Neuropsychological functioning in sons of active alcoholic, recovering alcoholic, and social drinking fathers

Sons of active alcoholic, recovering alcoholic, and social drinking fathers were administered neuropsychological tests to assess whether they differ in their cognitive functioning. Multivariate analyses of variance showed that sons of active alcoholic sons perform significantly worse on visuospatial, memory, and attentional tasks as well as general intellectual functioning than sons of social drinking fathers. The sons of recovering alcoholic fathers showed no significant difference from social drinking fathers in their cognitive functioning. These results suggest that the clinical type of the alcoholic father (i.e., inability to abstain, more severe alcoholic vs. ability to abstain, less severe alcoholic) may be an important factor that determines whether offspring of alcoholics have neuropsychological deficits.

Extraversion. Interaction between D2 dopamine receptor polymorphisms and parental alcoholism.

Both molecular genetic factors (the D2 dopamine receptor (DRD2) and the D4 dopamine receptor (DRD4) polymorphisms) and environmental influences of living in an alcoholic or nonalcoholic home on the personality traits of Extraversion and Neuroticism were assessed in drug-naive, young adolescent boys. There were no significant main effects of genetic or environmental factors on either Neuroticism or Extraversion as measured by the Junior Eysenck Personality Inventory (JEPI). However, a significant interaction between DRD2 (but not DRD4) alleles and environmental variables was observed on Extraversion. Specifically, children with the minor alleles of the DRD2 gene showed a significantly greater Extraversion score when living in an alcoholic than in a nonalcoholic home. In contrast, children with the major alleles of the DRD2 gene showed a trend in the opposite direction. Although the results are preliminary and pending replication, they nevertheless provide the first report of a specific gene-environment interaction involving a human personality trait.

D2 dopamine receptor (DRD2) gene, P300, and personality in children of alcoholics

The D2 dopamine receptor (DRD2) gene has been associated with alcoholism and other drug use disorders. Reduced P300 amplitude has been noted in individuals with psychiatric disorders. Personality variables are also associated with reduced P300 amplitude. The current study was conducted to determine whether variants of the DRD2 would show differential relationships among P300 amplitude and personality traits. The study consisted of 101 adolescent children of alcoholics; 39 carried the A1(+) genotype (A1A1, A1A2) and 62 carried the A1(-) genotype (A2A2). The A1(+) genotype group had higher IQ and Self-Directedness scores than the A1(-) genotype group. As predicted, the negative relationship between Novelty Seeking and Harm Avoidance was present in A1(-) but not A1(+) participants. Additionally, in A1(+) but not in A1(-) participants, there was a negative relationship between Novelty Seeking and Self-Directedness and a positive relationship between P300 amplitude and Cooperativeness. The results suggest that in adolescent children of alcoholics, dopaminergic genetic determinants are critical modifiers of the relationship between neurocognitive and personality endophenotypes proposed as vulnerability markers for substance use disorders.