Researchers of the Cincinnati Children's Hospital Medical Center found that regions of two chromosomes are linked to susceptibility for a type of autism characterized by regression in development.
Developmental regression can include the loss of previously acquired language, social skills or both.
Moreover, the study is the first to identify involvement of chromosome 21 in this type of autism.
This may explain the increased prevalence of autism spectrum disorders ( ASD ) among children with Down syndrome, who have an extra copy of chromosome 21 and are 10 times more likely to have an ASD than the general population.
The findings represent " the important first step in identifying genetic variants that may contribute to susceptibility to this specific type of ASD, " says Cindy Molloy, lead author of the study.
The study is published in the Molecular Psychiatry.
Molloy and colleagues examined a U.S. database and DNA bank of hundreds of families with autism spectrum disorders.
They identified 32 pairs of siblings, one trio of siblings and one pair of cousins who showed definite evidence of regression at the age of approximately 18 to 24 months.
Researchers confirmed previous evidence for linkage with ASD on chromosome 7 and found new evidence for susceptibility on chromosome 21 in this subset of ASD families.
The research team is now sequencing genes in those regions to find the specific genetic variant that either contributes to susceptibility or modifies the disease.
"Among children with autism or autism spectrum disorders, 20 to 30 percent have a history of regression," says Molloy. " We think this represents a genetically distinct subgroup."
Autism is a complex developmental disability that affects an individual in the areas of social interaction and communication.
Autism is a spectrum disorder that affects each individual differently and to varying degrees of severity.
As many as 1.5 million Americans - children and adults - are thought to have autism today, according to the Autism Society of America.
Source: Cincinnati Children's Hospital Medical Center, 2005