While genetic and genomic research is a critical part of understanding ASD, genes alone do not tell the whole story. Environment also plays an important role; by “environment”, scientists generally mean any influence other than inherited genes. Therefore, as well as looking inside our DNA for potential causes of the condition, researchers are also looking outwards, sorting through the various environmental factors that may be linked to the development of ASD.
To date, the environmental factors that research has linked most strongly to ASD are primarily physical factors concerning pregnancy and birth. These include advanced parental age, of either mother or father, at the time of conception; periods of less than a year between pregnancies; fevers or infections contracted by the mother during pregnancy; and complications during birth, especially those that deprive the baby of oxygen. For all these factors, various studies have made reasonably clear connections between the appearance of a particular factor, such as a mother contracting rubella during pregnancy, and a child’s chances of developing ASD.
In addition, there are a number of other factors that research suggests may be linked with ASD, but we still need more information to determine whether these links are direct or simply coincidental. Many of these factors involve a pregnant woman’s exposure to particular chemicals or drugs, such as pesticides, substances commonly found in plastics like phthalates, and the seizure-controlling medication valproic acid, all of which have molecules that have the potential to alter fetal development.
And approaching things from another angle, some research has also been done into environmental factors that can reduce the chances of ASD development. Of these factors, the best-known is pre-natal vitamin consumption: studies have shown that when women take pre-natal vitamins before conceiving, it is less likely that their children will develop ASD.
But do all these environmental factors actually cause autism? Here, scientists are quick to distinguish between “cause” and “risk”, emphasizing that at present, any single “cause” of ASD is not in fact known. The current belief is that ASD likely results from genetic factors, but that environmental factors act as additional pressures, or “risk factors”, which can slightly increase the likelihood of ASD development in someone already genetically predisposed to the condition. In other words, environmental factors don’t “cause” ASD on their own, but can perhaps “trigger” it under certain genetic conditions. This idea also helps account for the fact that countless fetuses and babies are exposed to these same environmental factors without ever developing ASD.
As the prevalence of ASD increases, ongoing research into connected environmental factors is of vital importance, as unlike many genetic factors, environmental elements are more within our power to control. Understanding as much as possible about their influence on ASD development will therefore enable scientists and health care professionals to better help those individuals and families affected by or predisposed to ASD, and to provide more accurate diagnoses and treatments.