Pregnant women [illustrative]_311.
(photo credit: Reuters)
Parents who have one child with autism have a risk two to six times greater than
previously thought of having a second baby with the developmental disorder,
according to researchers from the Hebrew University of Jerusalem.
spectrum disorders (ASD) affect the brain’s normal development of social and
The exact cause is still unknown, but defective
genes are believed to be involved. What is described as “revolutionary research”
by HU psychology department Prof. Nurit Yirmiya and her team was published on
Monday in the prestigious journal Pediatrics.
In this study – the most
comprehensive conducted to date – the risk of a child developing ASD in a family
with one sibling who already has ASD was examined using the largest sample
collected so far and state-of-the-art diagnostic methods.
The sample was
made up of 664 infants, all of whom had at least one older biological sibling
with a verified diagnosis of ASD (6 percent had more than one sibling diagnosed
with autism). Infant siblings were included in the story at a very young age,
before signs of autism are readily apparent and parents typically have concerns
The babies’ average age was eight months, and
two-thirds of them were enrolled in the study before six months of
Infant siblings were followed until the age of 36 months, when
symptoms of ASD are present and reliably identified.
The main finding of
the study was that recurrence risk among siblings is 18.7%, which is
substantially higher than the results of previous studies, which found a 3% to
10% risk of recurrence. Furthermore, the researchers report even higher
recurrence rates for infants who fell into certain subcategories – for male
infants, a recurrence rate of 26.2% was found, compared to 9.1% for female
Remarkably, this means that almost one in three brothers of
children with autism will eventually develop ASD. In addition, the recurrence
risk for infants (boys and girls together) with more than one older affected
sibling was 32.2% – almost twice the rate of those having just one older sibling
Twelve research groups from North America took part in the
study, and all the participants were part of the Autism Speaks Baby Siblings
Research Consortium, an international network of funded studies examining
infants in families of children with autism. Yirmiya is part of this network and
one of the pioneering researchers in this field.
“The higher recurrence
rates found in this study in comparison with previous reports resulted from the
fact that previous studies were conducted in the 1980s and 1990s, when different
and more narrow diagnostic criteria were used to evaluate children with autism,
and there is an overall increase in the number of children who are diagnosed
with ASD,” Yirmiya said.
“In addition, previous studies used different
assessment methods. For example, in some studies, children were not assessed
directly, and other studies did not control for Estoppage [the tendency of
parents to limit reproduction after the birth of a child with a
She explained why this study was stronger than previous
ones on the subject.
“Only families that had a younger sibling
participated; gold standard diagnostic methods as well as comprehensive
developmental assessments were used and administered by experts; and this is by
far the largest sample to date, pooled across sites so it is a geographically
diverse sample. The improved methodology assures that the results of the current
study reflect the true population recurrence rates better than previous
reports,” Yirmiya explained.
“It should be emphasized that this study is
not an epidemiological one but rather a community- based sample of families who
voluntarily chose to participate.
The fact that families volunteered to
participate may explain the higher rates found in the current study.”
results suggest the development of young siblings of a child with ASD should be
monitored in a rigorous, careful, structured and routine fashion, the HU
“The study also indicates that sibling status
constitutes a significant risk factor for ASD.”
She advised professionals
in the field to work actively and cooperatively with parents to monitor specific
developmental milestones and make appropriate intervention plans as needed.