In our first post on gene-environment interactions, we introduced the idea that the environment can interact with genes to influence behaviors and traits. In this post, we discuss the concept of epigenetics and how epigenetic changes can alter DNA expression, that is, its ability to create proteins. We will discuss how some of these types of changes have been related to autism. Lastly, we point you to an interesting little video that offers an accessible explanation of how the environment interacts with genes to make “identical” twins increasingly different over the course of their lives.
Scientists talk about two types of variations in the underlying gene sequence – one is referred to as”single nucleotide polymorphisms.” These are variations in our DNA that are common in the general population. The second is referred to as “copy number variations” – these are deletions or duplications in our DNA. Both types of genetic variation can contribute to conditions such as autism, as well as many diseases. However, there are other ways in which gene expression can be changed without actually changing the underlying gene sequence. Any change in gene expression that does not result from the underlying amino acid sequence may be due to “epigenetics.”
What is “epigenetics”?The word epigenetics means “above the genome,” or changes in DNA expression that do not come from the underlying DNA sequence. How does this happen? Genes contain the instructions for building proteins that serve functions in cells at different times in life. Some modifications in the way genes are expressed can be made by adding a methyl group to a specific tag within the DNA. This typically turns off gene expression. Additionally, the way the two DNA strands wrap around each other may change. Again, the sequence of amino acids stays the same, but the histones – or proteins around which DNA strands wrap – change, then this can alter genetic expression.
How does this affect susceptibility to conditions such as autism?Epigenetic changes can occur within a lifetime, or across generations. These types of changes have been linked to asthma, cancer, obesity, and neurological disorders like Parkinson’s Disease or schizophrenia. Epigenetics are also responsible for many neurodevelopmental disorders with similarities to autism like Rett Syndrome and Angelman Syndrome.
Does the environment play a role?One of the first discoveries that epigenetics was environmentally mediated came from a study in the Netherlands after a period of intense famine. The famine not only produced problems in offspring born during the famine, but in their children. Recently, studies have shown that certain pesticides can alter DNA methylation. Nutritional factors, such as folic acid intake, may also target epigenetic markers. While these environmental factors may alter gene expression through epigenetic mechanisms, in most cases a clear path to disease has not been established.
What is being done to investigate the link between epigenetics and autism?The National Institute of Health is investing millions of dollars to study epigenetics and the role that the environment plays in altering genetic expression through this mechanism. In addition, Autism Speaks has funded research to examine how epigenetics might play a role in autism spectrum disorders. These studies are using both blood and brain tissue. Early studies have suggested some differences, especially in an area of the gene called the “MeCP2 promoter,” and newer studies will be targeting whether certain genes of interest in autism can be modified epigenetically. Animal models are very important in this regard. Researchers can examine the effects of specific chemicals on gene expression and how epigenetic tags such as methylation and histone modification are expressed.
And now for the promised video – the video, called The Epigenetics of Identical Twins, was produced by Harmony Starr, Molly Malone and Brendan Nicholson of the Genetic Science Learning Center at the University of Utah and won an award in the 2009 International Engineering and Science Visualization Challenge, sponsored by the National Science Foundation (NSF) and the journal Science. The creators produced a nice illustration of what happens to our DNA over the course of a lifetime of different exposures. The video is not about autism, but gets across the main point – environmental context matters. Scientists studying autism are beginning to understand some of the contexts in which the epigenome can differ and longitudinal studies that sample the environment, such as the National Children’s Study and studies of high risk infants that Autism Speaks is funding are more important than ever for helping us learn how these different contexts exert their effects.
There is nothing new here and nothing that gives families hope.
I am so disappointed that AS science has chosen a PhD in eye studies to work for AS science. It is the most grossly over funded are of autism research and one that done nothing to address causation factors or help children living today.
Of course environmental context matters but the National Children’s Study will take a decade to achieve any meaningful results.
AS science need to focus on real environmental issues that families want researched- and that does not include eye gazing.