Subjects: male children (n = 117) with CU traits, aged 3–16 years. Subjects were grouped by CU traits (see text). Comorbidity: ODD/CD n = 57), ADHD (n = 33), anxiety/depression (n = 11), ASD (n = 15). Diagnostic: DSM-IV, DISCAP, APSD, SDQ, QFE. Methods: DNA sequencing of HTR1B SNP rs11568817genotype by PCR and mass spectrometry analysis. Selected methylation quantification by quantitative mass spectroscopy of three CpG rich regions surrounding the SNP (19 CpG). This evidence concerns the gene HTR1B and major depressive disorder.