When an individual develops a neurodevelopment disorder like autism, the severity of that disorder depends on genetic changes beyond a single supposedly disease-causing mutation.

The total amount of rare mutations - deletions, duplications, or other changes to the DNA sequence in a person's genome can explain why individuals with a disease-associated mutation can have vastly different symptoms. Senior author of the paper, Santhosh Girirajan said, "Genetic sequencing tools can reveal a large number of mutations in a person's genome, but diagnosis typically focuses on identifying one primary mutation as the cause of a disorder."

The research team considered genetic, cognitive, and developmental information from individuals who contained one of two known disease-associated mutations, and of their families. Individuals with one of the primary mutations who expressed clinical features had significantly more mutations in the genetic background than their parents or siblings who did not express clinical features.

They suggest that the primary mutation sensitizes an individual to a particular disorder and that the genetic background sets the trajectory for potential clinical features. This study focused solely on genetic changes that occurred in the protein-coding portions of the genome. The researchers plan to expand their investigation to the rest of the genome. The full findings are present in the journal- Genetics in medicine.