A number of rare inherited genetic variants have been identified in families with children diagnosed with autism.
Researchers from the University of Washington School of Medicine, Seattle, discovered that ultra-rare genetic variants affecting 163 genes were present in the genomes of children with autism and at least one of their unaffected parents. These genetic variants are so rare that each one appeared exclusively in the genetic sequence of only one family featuring an child with autism, and are called private variants. Previously, these genes had not been associated with autism, a developmental condition that influences a person's communication and social skills, affecting around one percent of people in the UK.
'While most autism studies focus on de novo mutations, this study focuses on rare inherited mutations, which are often understudied in autism' Dr Amy Wilfert, lead author of the study told News Medical Life Sciences.
De novo gene mutations are present only in the genomes of children with autism and not in their parents. They arise from random mutations in the parents' gametes or during early embryonic development. However, these de novo mutations do no explain why autism can be hereditary and why some families have multiple children with autism.
This study examined the genome sequences of 3474 families that had at least one child with autism and focused specifically on gene variations that were likely to disable the gene it was present on. These were termed as 'likely-gene disruptive' variants in the study. They then repeated this analysis on genomes from an existing dataset of 5879 families which brought the total number of genomes analysed to 34,880. Their results were published in Nature Genetics.
The presence of one of these ultra-rare inherited genetic variations was found to increase the risk of a child having autism by 4.5 percent but did not cause autism in any of the parents who had it. This suggests that other factors either genetic or environmental must also be present in order for the children to have autism.
The results of the study support the theory that autism develops due to multiple factors. 'Our study suggests that one inherited mutation is not enough, you need at least one other mutation to push a child over the threshold required to be diagnosed with autism.' said Dr Wilfert.
Further research is required to understand how the genes affected and the gene variations discovered could play a role in the development of autism.