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.