Sex-dependent association between variability in infants’ OXTR methylation at birth and negative affectivity at 3 months

Background: Sex-specific differences in DNA methylation of the oxytocin receptor gene (OXTR) have been shown in adults and are related to several mental disorders. Negative affectivity early in life is a trans-diagnostic risk marker of later psychopathology and is partly under genetic control. However, sex-specific variations in OXTR methylation (OXTRm) in infants and their associations with negative affectivity are still unknown. Aims: Here, we explored sex differences in the association between infant OXTRm at birth and negative affec- tivity at 3 months of age. Methods: Infants and their mothers (N = 224) were recruited at delivery. Infants’ methylation status was assessed in 13 CpG sites within the OXTR gene intron 1 region (chr3: 8810654–8810919) in buccal cells at birth while 3- month-old infants’ negative affectivity was assessed by mothers using a well-validated temperament questionnaire. Results: OXTRm at 12 CpG sites was higher in females than in males. Moreover, higher infants’ OXTRm at 6 specific CpG sites was associated with greater negative affectivity in males, but not in females. Conclusions: These results provide new insights into the role of sex-dependent epigenetic mechanisms linking OXTRm with early infants’ emotional development. Understanding the degree to which epigenetic processes relate to early temperamental variations may help inform the etiology of later childhood psychopathological outcomes.