In today’s Academic Minute, Dr. Molly Losh of Northwestern University examines what studies of identical twins have to say about the causes of autism.
Molly Losh is the Jane and Michael Hoffman Associate Professor of Communication Sciences and Disorders at Northwestern University. Her research focuses on delineating the nature and basis of language impairment in autism and other related neurogenetic disorders. She holds at Ph.D. from the University of California Berkeley.
Dr. Molly Losh – Birth Weight and Autism
Autism is a neurodevelopmental disorder occurring in approximately 1% of individuals. There is strong evidence that genetic factors play a large role in causing autism –A number of genes that can cause autism have now been identified. Twins studies also support the role of genetic factors. Monozygotic twins who share all of their genes show high concordance rates, which means that if one twin has autism the other is very likely to have it as well. However, not all cases of autism can be explained entirely by genes. For instance, not all identical twins are concordant for autism, which suggests that environmental factors may play a role in the development of autism. We don’t know exactly
The study of twins represents an valuable opportunity to study environmental factors that could play a role in risk for autism. That is, bc these twins share all their genes, if they differ in clinical expression, we can reasonably assume that environmental factors are playing a role in clinical outcome. A number of environmental factors have been associated with autism, including maternal and paternal age, low birth weight, and several others. In this study we examined birth weight as a potential environmental risk factor in autism.
The study was a collaboration with scientists at the Karolinska Institute who lead the Swedish Twin Registry, which is a population register of all twins born in Sweden. We studied twins between the ages of 9 and 12 years old, where one twin had autism and the other did not, and used medical birth records to examine birth weight in these discordant twin pairs. We found that lighter twins in discordant twin-pairs were more than twice as likely to meet criteria for autism than heavier twins. Because these twins were identical genetically, this finding is good evidence that lower birth weight can increase risk of autism.