Statistical analysis
All quantitative variables were tested for the normality using the skewness/kurtosis test, all of which were nonnormally distributed and expressed as the median (interquartile range) [M(IQR)]. χ2 tests were used to compare genotypic differences in SNPs between MAUD patients with/without MA-induced psychotic symptoms. The nonparametric Mann‒Whitney U test was used to compare the differences in total impulsivity scores, total aggression scores, and their scores on each dimension among participants in the MAUD group with different genotypes at the 8 SNPs. In the analysis of the degree of methylation in the promoter regions of the two genes, the following statistical methods were used. The nonparametric Mann‒Whitney U test was used to compare the differences in the methylation of each CpG unit of the promoter regions of the two genes between patients in the MAUD group with and without MA-induced paranoid symptoms; Spearman correlation analysis was used to explore the correlation between the methylation levels and psychotic symptoms.