BACKGROUND: Research in mammals has demonstrated the involvement of oxytocin (OT) in social bond formation; yet, its role in human bonding remains unclear. Plasma OT has been used as a proxy for central activity and studies indicate its association with human affiliative behaviors. Molecular genetic studies also reveal a role for OT neuropathways in shaping the social brain. However, the links between peripheral OT, genetic markers, and their combined contribution to human parenting are unknown.

METHODS: Participants included 352 individuals: 272 mothers and fathers and their 4- to 6-month-old-infants and 80 nonparents. Plasma OT was assayed from adults who were genotyped for oxytocin receptor (OXTR) and CD38 risk alleles associated with social dysfunctions. CD38 is an ectoenzyme that mediates the release of brain OT. Parent-infant interactions were microcoded for parental touch and gaze synchrony and participants reported on parental care in childhood.

RESULTS: OXTR (rs2254298 and rs1042778) and CD38 (rs3796863) risk alleles were each associated with lower plasma OT. Reduced plasma OT and both OXTR and CD38 risk alleles were related to less parental touch. The interaction of high plasma OT and low-risk CD38 alleles predicted longer durations of parent-infant gaze synchrony. Parents reporting greater parental care showed higher plasma OT, low-risk CD38 alleles, and more touch toward their infants.

CONCLUSIONS: Results indicate that peripheral and genetic markers of the extended OT pathway are interrelated and underpin core behaviors associated with human parenting and social engagement. These findings may have important implications for understanding neuropsychiatric disorders marked by early social dysfunctions.