While specific genes may be intrinsically programmed to be switched on or off as part of an organism’s development (epigenesis), external conditions may also contribute to the pattern of expression

• Environmental factors may regulate DNA methylation by moderating the activity of the enzyme DNMT (DNA methyltransferase)

Air pollutants are an example of factors that can affect the methylation of DNA within an individual 

• Several traffic-related air pollutants have been associated with a change in DNA methylation – including nitrogen oxides and polyaromatic hydrocarbons (PAH)

In general, air pollution mediates a decrease in DNA methylation across the genome, although methylation at some sites may be increased

• Air pollution is specifically linked to the methylation of immunoregulatory genes, leading to increased inflammation and an altered immune profile

• These methylation patterns result in the manifestation of cardiopulmonary complications – including high blood pressure and various respiratory conditions (such as asthma)

• A change in normal gene expression is also a common cause for various forms of cancer

The epigenetic consequences of exposure to air pollution is influenced by a range of other factors, including age, diet and general health