Prematurity and Epigenetic Regulation of SLC6A4: Longitudinal Insights from Birth to the First Month of Life

<b>Background/Objectives:</b> Prematurity is a significant global health concern, often associated with neurodevelopmental challenges. Solute Carrier Family 6 Member 4 (<i>SLC6A4</i>), the gene encoding the serotonin transporter, a key component in serotonin reuptake in the synaptic cleft, plays a key role in stress response and neurodevelopment. Epigenetic regulation of stress-related genes, such as <i>SLC6A4</i>, influences neonatal stress adaptation and developmental outcomes. This study aimed to quantify and compare DNA methylation levels at 13 CpG sites in the promoter region of the <i>SLC6A4</i> gene between preterm and term neonates at three time points. <b>Methods:</b> A cohort of 46 preterm infants and a cohort of 49 full-term infants were analyzed. Blood samples collected at birth (D0), the fifth day (D5), and the thirtieth day (D30) were used to analyze DNA methylation, using bisulfite conversion and pyrosequencing. <b>Results:</b> Significant differences in <i>SLC6A4</i> methylation were observed. At D0, CpGs 12 and 13 showed higher methylation in preterm infants. CpG 9 showed lower methylation in preterm infants at D5. Extremely preterm infants had the highest values of methylation at the three time points. Longitudinal mixed-effects analysis revealed distinct temporal patterns between groups. Total and site-specific methylation at CpGs 2, 8, and 9 increased over time in full-term infants, while methylation remained stable over time in very preterm and extremely preterm infants. <b>Conclusions:</b> This study reveals significant differences in <i>SLC6A4</i> methylation between very preterm, extremely preterm, and full-term infants, highlighting the impact of prematurity and early-life stress on the epigenome. These findings contribute to improving our understanding of the epigenetic mechanisms shaping neurodevelopment and stress adaptation in neonates.