A new study focused on families with two or more autistic children and found several previously unrecognized genes that increase the risk of developing autism.
Previous research has shown that autism spectrum disorder (ASD) is heritable through common gene variations, gene mutations, or inheritance patterns.
However, most of this research focused on families with one autistic child, and some even excluded families with two or more children on the spectrum.
But in a new study published on July 28 in PNAS, researchers recruited 1,004 families with two or more children with ASD and conducted whole genome sequencing in 4,551 participants in total. The study also included 418 non-autistic children.
After the sequencing was complete, the scientists uncovered seven previously unidentified autism risk genes. These included PLEKHA8, PRR25, FBXL13, VPS54, SLFN5, SNCAIP, and TGM1.
The research team also looked at combinations of common genetic variations that can increase the likelihood of developing autism — also known as polygenic risk. The analysis revealed that children with polygenic risks that inherit rare genetic mutations from non-autistic parents are more likely to receive an autism diagnosis.
Scientists say this finding might explain why parents with a single rare gene mutation don't have autistic characteristics even when their child has ASD.
In addition, the team found that common genetic risks for ASD are over-transmitted to autistic children with rare inherited variants from their non-autistic parents, and this is linked to language delays and social challenges.
Moreover, children with language delays were more likely to have inherited a polygenic pattern associated with ASD. But the scientists did not find this association in children without a language delay.
What's more, the team did not observe this genetic pattern in other traits like educational talent, bipolar disorder, or schizophrenia. Therefore, the researchers suggest there's an association between language delay and genetic risk for ASD.
"This association of general risk for ASD that was strongest in those with language delay suggests that language is actually a core component of ASD. This finding needs to be replicated in larger cohorts, especially those recruited more recently under DSM-5," says lead study author Dr. Daniel Geschwind, the Gordon and Virginia MacDonald Distinguished Professor of Human Genetics, Neurology, and Psychiatry at UCLA, in a news release.
Currently, the DSM-5 considers language impairment an accompanying feature of ASD, not a primary symptom.
However, the study authors say the link they found between over-inheritance of autism risk genes and delays in language provides genetic evidence that current criteria used to diagnose autism should include language delay as a core symptom of the condition.