What is epigenetics? Does this new field hold promise for understanding the causes of ASD?
“Got Questions?” is a new weekly feature on our blog to address the desire for scientific understanding in our community. We received over 3000 responses when we asked what science questions were on your mind. We answered a few here and the Autism Speaks Science staff will address the other themes we received in this weekly post.
Scientists have long wondered how experiences during a person’s lifetime can alter behavior and body functioning. In the early 1800’s Jean Batiste Lamarck suggested that giraffes’ necks grew long through many generations of stretching to reach distant leaves. That theory eventually fell to evolution–pressures from the environment selectively amplify or quiet certain traits that are variably present within a population. Later, the DNA code was found to be the mechanism for inheritance and the level at which selective pressure acts.
Today’s scientists see hints of Lamark as they peer into the molecular biology of inheritance.
Consider DNA to be a library of books that encode genes. These “genetic books” must be read so that proteins can be formed from the code. Some genetic books are open and available for reading by the cell’s molecular machinery. Others maybe temporarily unavailable and still others are in the restricted section—essentially permanently unreadable.
Experiences throughout an individual’s life create tags on the genetic code, marking it as available or not for reading. The molecular methods that control the availability of the genetic code are collectively referred to as epigenetic mechanisms. Literally meaning “above the genome”, epigenetic mechanisms tag DNA with different chemical marks, such as methyl or acetyl groups. Certain tags can increase the reading frequency, resulting in more protein building-blocks transcribed from the DNA code, and more of that gene “expressed”. Other tags result in a particular piece of the genetic code to be skipped during reading.
A host of environmental agents and interactions may leave epigenetic marks on the genome. Early life stress, smoking, exposure to toxins may all leave epigenetic marks either creating or removing barriers for protein creation.
Here is where Lamark comes in. Most epigenetic marks are removed before the sperm and egg meet to form an embryo, but sometimes, epigenetic marks remain. This is one mechanism by which environmental exposures can be passed along from parent to child.
The study of epigenetics and gene expression in autism is underway and early findings are exciting. Some of the genetic syndromes associated with autism, such as Angelman and Prader-Willi syndrome, result from epigenetic marks that render one parent’s genetic contributions unreadable. Recently, gene expression studies from the blood and even brain tissue of individuals with autism have shown differences in the activity of patterns of genes that are involved in brain development and function.
This is an exciting area of research and we look forward to sharing more details as we learn more from the science.
Read more about epigenetics on or blog.