Having an older sibling with either disorder greatly raises risks

Autism and ADHD do run in families: Having an older sibling with autism raises a child’s risk 30-fold – and ADHD risk increases 13-fold

  • Doctors have suspected ADHD and autism share genetic roots 
  • A new University of California, Davis, study found that having an older sibling with either disorder greatly increases a younger child’s risks 
  • Risks for autism are 30 times higher among children whose older siblings have it
  • ADHD in a sibling increases risks for younger kids by 13-fold  

Having an older sibling with autism raises a younger sibling’s risks by 30-fold, and ADHD in an older sibling is liked to a 13-fold greater risk, a new study found.  

The exact causes of both autism and ADHD elude scientists, but we know that both genetic and environmental factors play roles in the development of the disorders. 

Experts estimate that as many as 1,000 genes can contribute to autism risks, accounting for as much as 83 percent of the disorder, and ADHD is considered ‘highly heritable.’   

Studies done on twins and conducted in Scandinavia have suggested close sibling risks, a new University of California, Davis study established clear evidence that having one child with either disorder raises the risks that younger siblings will too. 

In fact, children whose older siblings are either on the autism spectrum or have ADHD are at far greater risks of having either disorder themselves, the new study reveals.

Having an older sibling with autism or ADHD greatly increases the risks that younger children in the same family will have one or both disorders, new research reveals 

An estimated one in 68 children are on the autism spectrum, which may moderately or massively affect their behavior. 

But even the Centers for Disease Control and Prevention (CDC) struggle to get an accurate count of kids affected because the symptoms associated with the behavioral disorder vary so widely.  

Attention-deficit/hyperactivity disorder’s severity ranges similarly and disrupts the focus and calm of abut five percent of kids in the US. 

Their symptoms are distinct, but it is not uncommon for the two disorders to co-occur, which raised scientists’ suspicions that some of their underlying causes might be related. 

Environmentally, research has shown that exposure in the womb to a number of chemicals – especially household cleaning products – may interfere with genes and brain development to raise both risks. 

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And in May of last year, three interrelated studies provided the best genetic evidence for the presence of ADHD in as many as 80 percent of children on the autism spectrum.  

Parents and adult children who suspect they might have either ADHD or autism often look to who their siblings and family histories for signs of the disorder.

But prior to the new study, no one had really looked at the relationship between autism or ADHD risks in younger siblings of children known to have either disorder.

Researchers at the UC Davis found that that instinct to look to family is correct. 

They analyzed data on over 15,000 children born at a California hospital between 1995 and 2018. 

About three percent of those children were eventually diagnosed with ADHD. About 0.8 percent were found to be on the autism spectrum. 

Children who had an older sibling with ADHD were at 13 times greater risks of being diagnosed with the disorder themselves. 

When an older sibling had autism spectrum disorder, a younger child was estimated to be 30 times more likely to fall on the spectrum as well. 

And a sibling’s diagnosis for with either disorder raised risks for the other. 

So those with an older brother or sister with autism spectrum disorder were at a 3.5 times greater risk of ADHD.  

If an older sibling had ADHD, a yougner one was about four times more likely to have autism. 

The study authors rather cautiously suggest that doctors may want to discuss these findings with patients who are family planning and already have a child with autism or ADHD so that they can begin watching for social signs and symptoms early in the lives of any future children. 

But in accompanying commentary, Dr Tony Charman and Dr Emily Jones, psychologists from King’s College and University of London, respectively, in the UK warn that doctors should be careful in deciding if and when to disclose this information to families. 

‘Often, parents seeking a diagnosis have known for some time that something is different about their child, and the developmental and behavioral difficulties their children are experiencing motivate the clinical consultation, they wrote 

‘A diagnosis can help parents to recognize and understand some of the challenges their child is experiencing and should provide a gateway to information and services that can help families support their child and anticipate their needs. Proactive monitoring of younger children for signs of ASD and ADHD could remove significant sources of stress in the process of seeking a diagnosis.’

On the other hand, ‘we suspect that there is wide variation in clinical practice in how information about the potential likelihood of another diagnosis in their younger child is presented,’ Dr Charman and Dr Jones wrote. 

‘It may be best not to impart this information at the initial feedback from the diagnostic consultation but instead at a later review meeting when parents have had the opportunity to find out more about ASD or ADHD and adjust to their new understanding of their child and family.’    

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