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News

Large study finds ‘baby sibs’ at high risk of autism

by  /  15 August 2011

Close study: Children who have one or more older siblings with autism should be closely monitored in infancy for early signs of the disorder.

Children who have more than one older sibling with autism have a one in three chance of developing the disorder themselves, according to a study published today in Pediatrics1. The risk is higher for boys: Even if they have only one older sibling with autism, they are almost three times more likely than girls with the same family history to develop the disorder.

The numbers, which are significantly higher than most previous estimates of three to ten percent2,3, are based on the largest study to date of autism risk in siblings of children with the disorder.

“Families who already have a child with autism have a significant risk for having another one,” says lead investigator Sally Ozonoff, professor-in-residence of psychiatry and behavioral sciences at the University of California, Davis.

“These new babies in the family need careful developmental surveillance and special monitoring beyond what you would do for a child that doesn’t have autism in the family,” says Ozonoff.

The High Risk Baby Siblings Research Consortium, comprising 21 research institutions in the U.S., Canada, Israel and the U.K., pooled data on 664 high-risk infants — those who have one or more biological siblings already diagnosed with autism — at 12 sites.

Researchers began following these children at birth, and the children now range in age from 4.5 to 10 years of age. Overall, 18.7 percent of so-called baby sibs developed an autism spectrum disorder by age 3. The risk is much higher in boys, however, with 26.2 percent of boys versus 9.1 percent of girls diagnosed. Among boys and girls who have multiple older siblings with autism, an average of 32.2 percent of the infants developed an autism spectrum disorder themselves.

“With this study, it is possible to more adequately assess gender as a risk factor,” says Ami Klin, director of the Marcus Autism Center at Emory University in Atlanta. “We’ve all known for quite some time that being male is a very important risk factor, but now one has a nice assessment of risk liability for females as well.”

Risk analysis:

The new estimates aren’t surprising to clinicians who see many ‘multiplex’ families, which have more than one child with autism.

“The recurrence rates are in keeping with what we have been observing,” says Klin, who was formerly based at Yale University and is the principal investigator on a baby siblings study there. “But this is a very important study because these rates had not been documented in a publication before in quite a large sample.”

The study’s methodology is rigorous, say others not involved with the research, making the findings particularly compelling. For one thing, the researchers at all 12 institutions in the study followed the children from infancy, allowing experts to directly assess them at 36 months, notes Peter Szatmari, professor of psychiatry and behavioral neurosciences at McMaster University in Canada.

“The study also includes a more accurate assessment of the other children in the family,” Szatmari notes.

Earlier studies rarely accounted for the tendency of some families to stop having children after having one child diagnosed with autism4. This ‘stoppage’ phenomenon can skew estimates of risk for the younger siblings because some potential multiplex families might be mistakenly classified as simplex.

The new study avoided that problem by following later-born children who have older siblings diagnosed with autism. “This study is giving us the true sibling estimates,” Szatmari says.

One of the more interesting findings of the study is the large proportion of siblings — more than half — who were diagnosed at 36 months with pervasive developmental disorder-not otherwise specified (59.1 percent) as opposed to the more severe autistic disorder (40.9 percent).

This diagnosis may reflect characteristics of the broad autism phenotype in the baby sibs, says Helen Tager-Flusberg, professor of psychology at Boston University.

Researchers once thought that it might be possible to diagnose autism in siblings at 24 months, she says. But they’ve since learned differently. “In the siblings, we see a huge amount of kids coming into a diagnosis and going out of diagnosis in this 18-to-36 month period that you don’t necessarily see in a more standard population,” says Tager-Flusberg.

On the other hand, the study may have missed some children who will be diagnosed at a later age with Asperger syndrome or pervasive developmental disorders, Ozonoff says. “In fact, we are reevaluating the sample at our site at age 7, so we may pick up a few who were missed.” That may up the risk rate even more, she adds.

Although the new findings point to highly penetrant genetic risk factors for autism in multiplex families, the researchers have not yet carried out a genetic analysis of blood samples collected from family members at various sites.

The findings are likely to encourage many families with a child with autism to seek out genetic testing, says Tager-Flusberg. “It will also be a wake-up call to pediatricians that they may want to refer such a family to genetic counseling and genetic testing if they’d like to have another child.”

References:


  • Anonymous

    “One of the more interesting findings of the study is the large proportion of siblings — more than half — who were diagnosed at 36 months with pervasive developmental disorder-not otherwise specified (59.1 percent) as opposed to the more severe autistic disorder (40.9 percent).”
    ———————————————————————————————–
    The research is consistent with the fact that PDD-NOS is the most prevalent diagnosis of an ASD.
    ———————————————————————————————-
    “Researchers once thought that it might be possible to diagnose autism in siblings at 24 months, she says. But they’ve since learned differently. “In the siblings, we see a huge amount of kids coming into a diagnosis and going out of diagnosis in this 18-to-36 month period that you don’t necessarily see in a more standard population,” says Tager-Flusberg.”

    ———————————————————————————————–

    (1) The Tests used to detect Autism have greater reliability when children past the age of 30 months. The developmental milestones are more numerous and distinct at 30 months for typically developing children, and to a large degree for atypical children too. This is a period of time in which language skills, sense of self, and socialization greatly increases. The six month gap between 24 months and 30 months is why ABA therapy works so well. Basically, you’ve intuitively picked a point in time in which the child is most receptive to developmental growth.

    (2) IF children can regress along the spectrum, there may be a possibility that they can progress along the spectrum i.e move in and move out of a diagnosis. We have to take into consideration that some of these cases MAY NOT be misdiagnosed. What does a child diagnosed with autism at 18 months old suppose to look like at 36 months old ? IF he or she stays relatively the same(slow development over a period of time) or regresses, we’ve done our job BUT if he or she progresses, we tend to question the diagnosis. Why?

    (3) A small percentage of children(hopefully this number will grow larger) actually move OFF the spectrum. Controversial BUT we have to consider it because of the fluidity of this disorder.

  • Anonymous

    Ths older studies you cite include the 2010 Costantino et al study which included over ,1300 families and clearly states ‘RESULTS: A traditionally defined autism spectrum disorder in an additional child occurred in 10.9% of the families. An additional 20% of nonautism-affected siblings had a history of language delay’

    Thats entirely consistent with the 10% recurrance rate reported over many years. The new study included sibs diagnosed with PDD/NOS a catchall group that now is inclusive of children with a childhood language disorder and are not considered as having traditional autism. 60% of the baby sibs group had a PDD/NOS diagnosis leaving the baby sibs study with less than 10% who met the traditional diagnosis of autism.

    Autism is associated with birth complications so the recurrance risk shouldn’t be any great surprise. Autism is been shown in several studies to be associated with pre term birth and pre-eclampsia for example;

    Recurrance risks for pre-term delivery is highest (57%) in women with two prior pre term deliveries. Recurrence risk, which is affected by the frequency, order, and severity of prior preterm births with a 57% recurrance risk for women with 2 prior very preterm deliveries (21-31 weeks).

    The risk of recurrent preeclampsia in pregnancy is inversely related to gestational age at the first delivery: 38.6% for 28 weeks’ gestation or earlier, 29.1% for 29-32 weeks, 21.9% for 33-36 weeks, and 12.9% for 37 weeks or more.

    Familial autoimmune disorders which can be transmitted to the fetus in pregnancy is also associated with very high risk for autism and high recurrance risks. Pregnancy problems associated with maternal auto-immune disease include prenatal maternal urinary tract, upper respiratory, and vaginal infections and in the newborns asphyxia; prematurity, and seizures are common in the autistic group.

    http://jcn.sagepub.com/content/14/6/388.short

    http://www.ncbi.nlm.nih.gov/pubmed/17547902

    http://www.ncbi.nlm.nih.gov/pubmed/18280450

  • Anonymous

    LoL. I’m not gonna say one word. yes, i am. Come on, now.

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