Assessing peripheral oxytocin and cortisol levels and epigenetic variations of oxytocin receptor and glucocorticoid receptor genes in school-aged preterm-born children.

BACKGROUND: Preterm birth is a life-changing event, followed by hospitalization in the Neonatal Intensive Care Unit. During this critical period of biological immaturity, preterm infants encounter atypical sensory stimulation and (painful and stressful) medical interventions. Such early environmental factors can alter the development of the hypothalamic-pituitary-adrenal (HPA) axis and the oxytocinergic system, potentially leading to long-term effects on neurodevelopment. The research on these physiological markers in preterm individuals remains inconclusive, partly due to variability in study designs, sample collection, and participant selection. Studies later in life, during childhood or adulthood, are particularly scarce.

METHODS: Oxytocin and cortisol levels, and DNA methylation of the oxytocin receptor gene (OXTR) and the glucocorticoid receptor gene (NR3C1) were assessed in 39 preterm and 38 full-term school-aged children. Salivary samples were collected at two timepoints: one sample after awakening, and two samples at the end of the study visit.

RESULTS: Preterm children had lower morning oxytocin levels but similar afternoon oxytocin levels compared to full-term children. Both groups showed elevated cortisol levels in the morning compared to the afternoon. Preterm children exhibited a steeper decline in cortisol, with lower afternoon cortisol levels compared to full-term children. DNA methylation of NR3C1 was lower in preterm children, whereas no group differences were observed for OXTR.

CONCLUSION: These findings suggest differences in salivary measures of the HPA axis and oxytocinergic system in preterm school-aged children compared to full-term children, highlighting the importance of further research into the long-term impact of preterm birth and early life stressors.