Predictors of Alcohol Misuse : Role of MAOA Genotype, Methylation, Transcription, and Negative and Positive Environmental factors

Alcohol misuse is a risk factor for alcohol use disorder (AUD). Gene-environment interactions contribute to the risk or resilience for AUD. A functional polymorphism in the promoter of the monoamine oxidase A gene (MAOA-uVNTR), in interaction with negative environment (Eneg), is associated with alcohol misuse and AUD. Men carrying short (MAOA-S), and women carrying long (MAOA-L), MAOA-uVNTR alleles who experienced maltreatment or poor parent-child relationships are at increased susceptibility to alcohol misuse and AUD. This thesis assessed whether the association of MAOAxEneg with the risk of AUD is moderated by MAOA methylation or positive environment and whether MAOA methylation-associated changes in MAOA expression in the stress- and reward-related brain regions is an underlying mechanism. The thesis reveals that the association of MAOAxEneg with alcohol misuse is moderated by MAOA methylation in men, but not in women. In the clinical sample, men carrying MAOA-S allele who experienced maltreatment and had low MAOA methylation displayed higher alcohol-related problems than those without maltreatment or MAOA-L carriers with and without maltreatment. Furthermore, the quality of the parent–child relationship moderated the association of MAOAxEneg with alcohol misuse in a sex- and AUD stage-dependent manner. In the non-clinical sample of adolescents, girls carrying MAOA-L allele who experienced maltreatment and poor parent–child relationship displayed higher alcohol consumption, whereas those with average or good parent–child relationship had lower alcohol consumption. In the clinical sample of adolescents, however, no such association was observed. These results suggest that a good parent–child relationship protects MAOA susceptibility genotype carriers exposed to maltreatment during the early stages of alcohol use. The preclinical studies revealed that the male rats exposed to Eneg and alcohol had higher CpG-specific Maoa promoter methylation, which was associated with lower Maoa expression in the nucleus accumbens than the control rats. Thus, MAOA methylation-associated changes in MAOA expression in the nucleus accumbens might mediate the effect of environment on alcohol use. The thesis contributes to the understanding of biological mechanisms underlying MAOAxEnvironment effect and the critical role of MAOA methylation and positive environment in moderating risk and resilience for AUD. Also, the identification of subgroups may benefit from personalised interventions for AUD