Infants undergo extensive developments during their frst year of life. Although the biological mechanisms involved are not yet fully understood, changes in the DNA methylation in mammals are believed to play a key role. This study was designed to investigate changes in infant DNA methylation that occurs between 6 and 52 weeks. A total of 214 infant saliva samples from 6 or 52 weeks were assessed using principal component analyses and t-distributed stochastic neighbor-embedding algorithms. Between the two time points, there were clear diferences in DNA methylation. To further investigate these fndings, paired two-sided student’s t-tests were performed. Diferently methylated regions were defned as at least two consecutive probes that showed signifcant diferences, with a q-value<0.01 and a mean diference>0.2. After correcting for false discovery rates, changes in the DNA methylation levels were found in 42 genes. Of these, 36 genes showed increased and six decreased DNA methylation. The overall DNA methylation changes indicated decreased gene expression. This was surprising because infants undergo such profound developments during their frst year of life. The results were evaluated by taking into consideration the extensive development that occurs during pregnancy. During the frst year of life, infants have an overall three-fold increase in weight, while the fetus develops from a single cell into a viable infant in 9 months, with an 875-million-fold increase in weight. It is possible that the fndings represent a biological slowing mechanism in response to extensive fetal development. In conclusion, our study provides evidence of DNA methylation changes during the frst year of life, representing a possible biological slowing mechanism. We encourage future studies of DNA methylation changes in infants to replicate the fndings by using a repeated measures model and less stringent criteria to see if the same genes can be found, as well as investigating whether other genes are involved in development during this period.
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