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For Siblings of Autistic Children, Risk is Higher Than Thought

Autism does run in families more than researchers previously believed, a new study shows.

Scientists have suspected for a long time that autism runs in families, but a new study on autism is a little startling, as it reveals that it occurs more frequently in families who already have an autistic child than originally believed. While this news is a little unsettling, it is news that parents of autistic children need to be aware of when planning to extend their family.

Let me start by explaining some basic facts about what autism is and what causes it. First, as reported on the website Autism Speaks, “Autism is a general term used to describe a group of complex developmental brain disorders known as Pervasive Developmental Disorders.” It is more common than childhood cancer, juvenile diabetes, and pediatric AIDS combined because it is estimated that one in every 110 children are diagnosed with autism.

With an estimated 1.5 million people in the United States, and tens of millions worldwide diagnosed with autism, it is alarming to learn that, according to government statistics, the prevalence rate is increasing as much as 10% to 17% annually. At this time, it is unclear what is causing this increase, but two possible explanations have been given: the improvements made in diagnosing the disease and environmental influences.

Autism study

Additionally, studies point to a higher incidence of autism in boys than in girls. In fact, boys are diagnosed three to four times more frequently than girls, and current estimates are that one out of 70 boys is diagnosed with this disease in the United States alone.

Unfortunately, there is no simple answer as to what causes autism. Autism Speaks reports: “The best scientific evidence available to us today points toward a potential for various combinations of factors causing autism-multiple genetic components that may cause autism on their own or possibly when combined with exposure to as yet undetermined environmental factors. Timing of exposure during the child’s development (before, during or after birth) may also play a role in the development or final presentation of the disorder.”

Now, a recent comprehensive study, performed at UC Davis MIND Institute, has revealed that parents who have a child with autism have a 19% chance that their next child will also have autism. Most previous estimates of the risk of recurrence ranged from 3% to 10%.

In this study, researchers in twelve different locations across the United States and Canada tracked 664 infants who had at least one older sibling with autism. On average, the infants were 8 months old when they were enrolled in the study, since autism is usually not apparent at that age.

Most of the sites where babies were observed saw each baby four to seven times until they turned three years old. If, however, at any point along the way, children showed any signs of autism they could be diagnosed without waiting till they turned three.

All children who were not yet diagnosed were then evaluated at the age of three, and the results were significant. In male children, 26% had some form of autism, while in female children, the rate was only 9%. The rates were not affected by either the gender of the older sibling or the severity of the older child’s case.

A rather disturbing finding was that when there was more than one child in a family with autism, the chance of other siblings having autism increased to 32%.

Experts explained that the calculations are averages, based on the study, and could be higher or lower in any given family.

In the study, scientists collected DNA samples from many of the children to look for genetic differences between the sibling pairs who had autism and those who didn’t. The goal is to better comprehend the genes involved in autism in the hope of developing tests which would measure the risk in individual families.

Dr. Daniel Geschwind, an expert on autism genetics at UCLA who wasn’t involved in the study said, “To a limited extent, scientists can already predict risk from DNA.”

Up to 15% of these cases have already been linked to specific genetic mutations, and if one of those mutations is present in the parent as well as the autistic child, the risk for the next child to have autism is even higher than the rate found in the study. Whereas, if the mutation occurs only in the autistic child and not a parent, that would indicate that it arose spontaneously, and it is unlikely that there would be any risk to future siblings.

Scientists have known that when twins are identical, the risk of both twins having autism is much higher than it would be for fraternal twins. But this new study discovered that the autism risk for regular siblings is comparable to the risk for fraternal twins. Since fraternal twins and regular siblings share about half their DNA, this is what scientists would expect for a genetic disorder.

According to Sally Ozonoff, the lead author of the journal Pediatrics, which published the results of this study online Monday, the information gleaned from the study is not intended to frighten parents, but rather to inform them. She explained, “If a family has a child with autism, it’s the first question they ask. But even now with better estimates, it’s important to convey this was the average risk.”

Ozonoff recommends that parents who decide to have more children should be in contact with a pediatrician who will begin early developmental surveillance of future children.

“These babies should potentially be treated differently than other infants,” says Ozonoff. Pediatricians should be asking questions about their baby’s eye contact, babbling, smiling at people, and playing peek-a-boo, because these are developmental milestones. If babies aren’t doing these things, pediatricians or parents should be looking into early intervention services.

I want to conclude this blog on a positive note because, according to Ozonoff, the research, as a whole, should give families of autistic children hope. “These findings are much higher than any of us anticipated, but the flip side is that over 80% of these children did not develop autism,” says Ozonoff. “That is really important for these families to hang on to. The glass is still more than half full.”