Ten years ago, my research team found evidence of brain overgrowth in many toddlers who developed autism. Just last year, we published a study showing that the larger brains of young children with autism have an excess number of brain cells, or neurons, in the part of the brain known as the frontal cortex. In the study we published today, we found clues to how this excess occurs.
Our study found dysfunction in several gene networks that may affect the number of neurons that are generated during the second trimester of pregnancy, when about 40 billion neurons are produced in the developing brain. We also found abnormality in gene networks that affect the number of neurons that survive through the second and third trimesters. Not all early neurons are meant to survive. Some play temporary roles during brain development and are supposed to die off when their job is done. In fact, “apoptosis” or naturally occurring cell death, is a normal and important part of prenatal brain development. By way of analogy, consider the scaffolding set up when constructing a building and then taken down once the building is finished. With autism, one possibility is that some of these “scaffolding” neurons remain. This may contribute to the excess of neurons and abnormal brain wiring.
These findings are exciting. We’ve known that something happens very, very early in the development of the brain: There are too many neurons in frontal brain regions. Now, we also know some of the genetic basis for this: abnormal gene activity in specific networks. This appears to rule out many speculations about post-natal causes of autism. Instead, it points strongly to prenatal events, at least in a majority of cases.
Importantly, this gives us hope that, one day, research will find ways to normalize gene activity and related neural growth and function. Normally frontal brain circuits are not fully formed at birth. They develop slowly across childhood. This provides a wide window of opportunity for intervention.