An individual is composed of trillions of cells with the same DNA that are differentially regulated to produce various cell types. This DNA regulation is through genetic predisposition inherited from our parents. However, this regulation is also greatly impacted by our environment, known as epigenetics. One of the most commonly studied forms of epigenetic regulation is DNA methylation. This can either activate or repress gene expression via addition of methyl groups to the DNA (figure 1).
Previous studies have shown that prenatal period is the time most vulnerable to environmental impacts and can essentially shape a child’s life including which diseases they’ll develop in later life. Studies have shown that maternal smoking is considered as one of the most hazardous exposure that could potentially lead to latent development of lung diseases, obesity, and cancer. A study by Bauer and colleagues looked at the genome of smoking vs. non-smoking mothers and their new-borns up to the age of four, to determine how maternal smoking altered DNA methylation patterns of genes in both the mother and child.
Genome-wide sequencing data revealed global changes in DNA methylation and gene expression for the mothers who smoked during their pregnancy and their children. The main changes occurred in the enhancer regions of genes which act as an ON/OFF switch in allowing gene expression. It is interesting to note that these changes in the maternal DNA methylation patterns has also been observed in their newborns, of which changes are stably maintained for several years.
Figure 1. Methylation of cytosine, one of the four bases that makes up DNA, involves replacement of hydrogen H5 of a cytosine with a methyl group (image from http://www.ks.uiuc.edu/Research/methylation/).
Most people would agree that smoking during pregnancy is a dangerous choice that a mother can make, due to visible newborn complications such as premature birth and lower birth weight. However, this investigation also shed light on how a mother’s choice during pregnancy can be imprinted in the children’s genome. So, you and your children will always be what you eat during pregnancy and more importantly, what you smoke.