Infants have higher risk of developing autism if they have siblings with the disorder, according to a US study.
The risk that an infant with an older sibling with autism also will develop the disorder, previously estimated at three to 10 per cent, is 19 per cent, according to the study by researchers at the University of California Davis.
For male infants the risk was even higher, at 26 per cent, and for infants with more than one older sibling with autism the risk of recurrence jumped to 32 per cent, according to the study.
Autism, a complex disorder that affects a child’s ability to think, learn, communicate and interact socially, occurs in one out of 110 children born in the United States, according to the US Centre for Disease Control.
Males account for 80 per cent of diagnosed cases, researchers said.
“This is the largest study of the siblings of children with autism ever conducted,” said Sally Ozonoff, professor of psychiatry and behavioural sciences at UC Davis’s MIND Institute and the study’s lead author.
“There is no previous study that identified a risk of recurrence that is this high.”
The study involved 664 infants whose average age was eight months, with two-thirds recruited younger than six months. The researchers followed their development until 36 months, when they were tested for autism.
What is autism
Autism is a lifelong developmental disability that affects how a person communicates with, and relates to, other people. It also affects how they make sense of the world around them.
It is a spectrum condition, which means that, while all people with autism share certain difficulties, their condition will affect them in different ways.
Some people with autism are able to live relatively independent lives but others may have accompanying learning disabilities and need a lifetime of specialist support.
People with autism may also experience over- or under-sensitivity to sounds, touch, tastes, smells, light or colours.
Asperger syndrome is a form of autism. People with Asperger syndrome are often of average or above average intelligence.
They have fewer problems with speech but may still have difficulties with understanding and processing language.