BALTIMORE — A new Kennedy Krieger Institute study supports the findings of an earlier report that children are much more likely to have autism if they have an older sibling who was also diagnosed with it.
Autism recurrence is seven times higher in families with an autistic child, versus the general population.
This is a much more comprehensive report on autism in families, said Kennedy Krieger today. A more preliminary report was done about 13 years ago.
Overall, the prevalence of autism has increased to 1 in 36 children over the past 10 years. The rise is attributed to more awareness of autistic girls and verbal (versus non-verbal) children - not an actual rise in autism rates.
The new research showed that 20 percent of children - that's one in five - with an older sibling who has autism spectrum disorder are likely to be diagnosed with the disorder as well.
That rate rises to more than 36 percent when a child has multiple autistic siblings.
Researchers say this shows the importance of closely monitoring babies born into families that already have an autistic child.
Dr. Rebecca Landa, vice-president and executive director for Kennedy Krieger's Center for Autism Services, Science, and Innovation, said in a statement:
Pediatricians and family members have to keep a diligent eye on infants born into families with an already diagnosed autistic child... The scale and diversity of this group of infants [in the study], compared to our prior recurrence rate study published over a decade ago, gives strong evidence that these recurrence rates are reliable.
The child's sex is also a major factor.
Children with an older sister who has autism were 34.7 percent more likely to develop autism, versus 22.5 percent of those who have a brother.
Also, younger siblings who are boys are more likely to be autistic than younger siblings who are girls.
The recurrence rate was also affected by race and the mother's education.
Autism had a 25 percent recurrence rate among non-white families - compared to a 17.8 percent recurrence rate in white families.
Mothers with a high school education or less had a higher recurrence rate, at 32.6 percent. (The effect was only significant for mothers, not fathers.)
The Kennedy Krieger study analyzed data from 1,605 babies who have an older autistic sibling. The babies were evaluated from age 6 months to 36 months.
Landa said the results show how factors like race, sex, education and access to healthcare can affect the timeliness of diagnosis and support for autism.
Genetics and environmental factors both play a major part in autism; certain genes associated with the autism can be passed down.
A Kennedy Krieger spokesperson added:
Researchers at Kennedy Krieger are continuing their research to learn more about these genetic factors. This emphasizes the importance of genetic research and early intervention strategies in families with an autistic child.”
