Parents with autistic first child face one in five risk of sibling developing disorder
Parents of a child with autism face a risk of almost one in five that their next child will also develop the disorder, say researchers.
The risk is higher than previous estimates – and goes even higher if the second child is a boy.
In families where there is more than one older sibling with autism, there is a one in three risk the next child will be affected, according to an international study published online in the journal Pediatrics.
Previous estimates put the risk at between 3 and 10 per cent that an infant with an older sibling with autism would also develop the disorder, which affects the ability to interact socially and communicate.
But the new study found a ‘substantially higher’ risk rate of 18.7 per cent on average.
However, the risk rises to over 26 per cent if the second child is male – because the disorder is mostly found among boys – and over 32 per cent for infants with more than one older sibling with autism.
Sally Ozonoff, professor of psychiatry and behavioural sciences at the MIND Institute at the University of California-Davis, Sacramento, who led the study, said: ‘This is the largest study of the siblings of children with autism ever conducted.
‘There is no previous study that identified a risk of recurrence that is this high.’
Autism, or autistic spectrum disorder(ASD), including Asperger’s syndrome, is an umbrella term for a range of developmental disorders that have a lifelong effect on someone’s ability to interact socially and communicate.
Around one child in every 100 – 80 per cent are male – has autism and genetic factors play a role in its development.
Researchers in the U.S., Canada and Israel, included 664 infants whose average age was eight months at the start of the study, and who were tested for autism when they reached three years.
A total of 132 infants met the criteria for ASD, with 26 per cent of boys compared with nine per cent of girls diagnosed in the study as a whole.
The overall rate of autism among all study participants was 18.7 per cent.
In families with one older child with autism, or simplex families, the rate of incidence was 20.1 per cent.
In families with more than one sibling with autism, the recurrence rate was 32.2 per cent.
Dr Ozonoff said ‘It’s important to recognise that these are estimates that are averaged across all of the families. So, for some families, the risk will be greater than 18 per cent, and for other families it would be less than 18 per cent.
‘At the present time, unfortunately, we do not know how to estimate an individual family’s actual risk.’