Meghan Miller, PhD CREDIT UC Davis Health

Later-born siblings of children with autism spectrum disorder (ASD) or attention-deficit/hyperactivity disorder (ADHD) are at elevated risk for both disorders, a new study led by Meghan Miller, assistant professor in the Department of Psychiatry and Behavioral Sciences and at the UC Davis MIND Institute, has concluded. The findings appear in JAMA Pediatrics.

The study suggests that families who already have a child diagnosed with ASD or ADHD may wish to monitor younger siblings for symptoms of both conditions.

Symptoms of ADHD include difficulty focusing, nonstop talking or blurting things out, increased activity, and trouble sitting still. ASD, on the other hand, involves significant challenges with social interaction and communication, as well as the presence of unusual interests or repetitive behaviors like hand flapping or lining up objects.

“We’ve known for a long time that younger siblings of children with autism are at higher-than-average risk for autism, but the field didn’t have adequate data to tell whether they were at increased risk for ADHD,” said Miller. “Despite the fact that autism and ADHD appear very different in their descriptions, this work highlights the overlapping risk; younger siblings of children with ASD are at elevated risk of both ADHD and autism, and younger siblings of children with ADHD are at elevated risk not only for ADHD, but also for autism.”

Miller’s research team looked at medical records of 730 later-born siblings of children with ADHD, 158 later-born siblings of children with ASD, and 14,287 later-born siblings of children with no known diagnosis. Only families who had at least one younger child after a diagnosed child were included in the study.

“Evaluating recurrence risk in samples that include only families who have had an additional child after a diagnosed child is important because recurrence may be underestimated if researchers include families who decided to stop having children after a child was diagnosed with ASD or ADHD,” explained Miller.

Researchers found in the study that compared to later-born siblings of non-diagnosed children, the odds of an ASD diagnosis were 30 times higher in later-born siblings of children with ASD, and 3.7 times higher for a diagnosis of ADHD. Alternatively, compared to later-born siblings of non-diagnosed children, the odds of an ADHD diagnosis were 13 times higher in later-born siblings of children with ADHD whereas the odds of an ASD diagnosis were 4.4 times higher.

ADHD and ASD are believed to share some genetic risk factors and biological influences. This study supports the conclusion that ASD and ADHD are highly heritable and may share underlying causes and genetics.

Reliable recurrence risk estimates of diagnoses within the same disorder and across other disorders can aid screening and early-detection efforts and enhance understanding of potential shared causes of the disorders. The ability to diagnose ASD and ADHD early could improve both treatment and quality of life.

“There are reliable screening measures and practices for the diagnosis of autism in very young children,” Miller said. “Unfortunately, we don’t have any clinical standards or adequate tools for screening for ADHD at such young ages. We are currently working on identifying early markers of autism and ADHD in infants and toddlers who have an older diagnosed sibling, since these younger siblings are at elevated risk for ASD and ADHD.”

Neurodivergent Imposter Syndrome (Autism & ADHD) Imposter syndrome can hit harder when you are neurodivergent because of the impact of neurodivergent related trauma on autistic people and people with ADHD’s self esteem.

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ADHD and/or Autism…I’ve always been interested in looking into the similarities and differences and finally feel like I have a better understanding of the topic

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An epidemiological study of more than 70,000 children in six European cohorts has linked symptoms of attention-deficit/hyperactivity disorder (ADHD) and autism spectrum conditions (ASC) to the mothers’ use of paracetamol (acetaminophen) during pregnancy. The study, published in the European Journal of Epidemiology, was led by the Barcelona Institute for Global Health (ISGlobal), a centre supported by the “la Caixa” Foundation.

In total, the researchers analysed 73,881 children for whom data were available on prenatal or postnatal exposure to paracetamol, at least one symptom of ASC or ADHD, and main covariates. Depending on the cohort, 14% to 56% of the mothers reported taking paracetamol while pregnant.

The study found that children exposed to paracetamol before birth were 19% more likely to develop ASC symptoms and 21% more likely to develop ADHD symptoms than children who were not exposed.

“Our findings are consistent with previous research,” explained ISGlobal researcher Sílvia Alemany, lead author of the study. “We also found that prenatal exposure to paracetamol affects boys and girls in a similar way, as we observed practically no differences.”

“Our results address some of the weaknesses of previous meta-analyses,” commented Jordi Sunyer, researcher at ISGlobal and last author of the study. “Considering all the evidence on the use of paracetamol and neurological development, we agree with previous recommendations indicating that while paracetamol should not be suppressed in pregnant women or children, it should be used only when necessary.”

At some point during pregnancy, an estimated 46%-56% of pregnant women in developed countries use paracetamol, which is considered the safest analgesic/antipyretic for pregnant women and children. However, mounting evidence has linked prenatal paracetamol exposure to poorer cognitive performance, more behavioural problems, and ASC and ADHD symptoms.

Those previous studies have been criticised for their heterogeneity. In the new study, therefore, “an effort was made to harmonise the assessment of ADHD and ASC symptoms and the definition of paracetamol exposure,” explained Alemany. “The sample is large,” she added, “and it includes cohorts from multiple European countries: the United Kingdom, Denmark, the Netherlands, Italy, Greece and Spain. We also used the same criteria for all of the cohorts, thereby reducing the heterogeneity of criteria that has hampered previous studies.”

The study also analysed postnatal exposure to paracetamol and found no association between paracetamol use during childhood and ASC symptoms. Nevertheless, the research team concluded that further studies are needed, given the heterogeneity of postnatal paracetamol exposure among the various cohorts, which ranged from 6% to 92.8%.

The six cohorts included the study were as follows: