Autism 101

How is autism diagnosed? What explains the rise in autism’s prevalence? How much do genes contribute to the condition? What about the environment?

In this section of Spectrum, dubbed Autism 101, we answer these and other questions about autism. Each article pulls together the latest science to reflect what we know.

Autism 101 is designed to both provide information and highlight knowledge gaps, indicating where data on a subject are absent or contradictory. Like our understanding of autism, this section is evolving, so please check back often.

Read more here. 

Inheritance plays different roles in autism with and without intellectual disability

 Autism with intellectual disability is less heritable than autism alone, according to a new study of how the conditions run in extended families.

About a third of autistic people have intellectual disability (ID) — an intelligence quotient (IQ) of 70 or less. Autistic people with lower IQs are more likely to have spontaneous, or de novo, gene mutations than autistic people with higher IQs, studies show, suggesting that the genetic underpinnings of autism with ID differ from those of autism alone.

Read more here at Spectrum. 

New study links autism traits and eating disorders in moms of autistic children

 A July 2020 study in the journal Autism Research found that mothers with eating disorders and a child with autism showed more autistic traits than mothers without an eating disorder, leading researchers to suggest that overlap between disordered eating and autism could contribute to underdiagnosis of autism in females. 

Read more here at Autism Speaks. 

Researchers urge caution over study linking marijuana to autism

Women who use marijuana while pregnant may be more likely to give birth to an autistic child, according to a study published last week in Nature Medicine1.

The findings generated widespread press coverage, but researchers are calling for a cautious interpretation of the results — in part because the association surfaced through an analysis of birth records, not a controlled study.

Read more here at Spectrum. 

Early screen exposure associated with increased ASD-like symptoms

An analysis of 2,152 children showed that screen viewing at age 12 months was associated with a “modest [but] notable” increase in autism spectrum disorder-like symptoms at age 2 years, though not an increase in ASD risk, researchers reported in JAMA Pediatrics.

Additionally, the study showed that daily parent-child play also was modestly associated with fewer ASD-like symptoms at age 2 years compared with less than daily parent-child play, according to David S. Bennett, PhD, a professor of psychiatry at Drexel University College of Medicine, and colleagues.

Read more here. 

Common pregnancy complication linked to increased autism odds

High blood pressure during pregnancy may raise a woman’s chances of having an autistic child, according to a new analysis1.

The onset of high blood pressure during pregnancy, a condition known as preeclampsia, also increases the odds of other neurodevelopmental conditions, the study found.

“The effects of preeclampsia on fetal development may be broad-ranging, affecting a range of disabilities,” says lead researcher Allen Wilcox, scientist emeritus at the U.S. National Institute of Environmental Health Sciences in Durham, North Carolina.

This work adds to a growing body of evidence that preeclampsia and related conditions, such as gestational diabetes, increase the chances of autism in a woman’s children, although the mechanisms remain unknown. Genetic factors could account for the associations.

Read more here at Spectrum. 

Environmental factors unlikely to account for rise in autism prevalence

The relative contributions of genetic and environmental factors to autism and traits of the condition have held steady over multiple decades, according to a large twin study 1.

Among tens of thousands of Swedish twins born over the span of 26 years, genetic factors have consistently had a larger impact on the occurrence of autism and autism traits than environmental factors have. The study suggests that genetics account for about 93 percent of the chance that a person has autism, and 61 to 73 percent of the odds she shows autism traits.

Some experts question whether twin studies — even large ones like this — can offer definitive answers.

The origins of autism may involve an interaction between genetics and the environment, which twin studies do not capture, says Brian Lee, associate professor of epidemiology and biostatistics at Drexel University in Philadelphia, Pennsylvania, who was not involved in the study.

“Asking whether genetics or environment is more important is the wrong question,” Lee says. “To me, it’s sort of like asking whether it’s more important to put on your left shoe or your right shoe to go out in public.”

Read more here at Spectrum. 

Largest-Ever Study Ties Over 100 Genes to Autism

The study, involving over 50 centers around the globe, identified 102 genes associated with ASD -- including a few dozen that had not been recognized before.

Some of the genes are also associated with intellectual disabilities and developmental delays, the researchers said. But others are unique to ASD, and appear related to the social difficulties that mark the disorder.

Read more here. 

Severity of autism symptoms varies greatly among identical twins

Identical twins with autism spectrum disorder (ASD) often experience large differences in symptom severity even though they share the same DNA, according to an analysis funded by the National Institutes of Health.

The researchers determined a 96% chance that if one twin has ASD, the other has it, too. However, symptom scores varied greatly between twins diagnosed with ASD. The researchers estimated that genetic factors contributed to only 9% of the cause of trait variation among these twins. In contrast, among pairs of identical twins without ASD, the scores for traits were very similar.

Read more here.

Extreme male brain theory of autism rests on shaky ground

This hypothesis, called the ‘extreme male brain’ theory, postulates that males are at higher risk for autism as a result of in-utero exposure to steroid hormones called androgens. This exposure, the theory goes, accentuates the male-like tendency to recognize patterns in the world (systemizing behavior) and diminishes the female-like capacity to perceive social cues (socializing behavior). Put simply, boys are already part way along the spectrum, and if they are exposed to excessive androgens in the womb, these hormones can push them into the diagnostic range.

Read more here at Spectrum. 

Study challenges idea that autism is caused by an overly masculine brain

Of the many proposed triggers for autism, one of the most controversial is the “extreme male brain” hypothesis. The idea posits that exposure to excess testosterone in the womb wires both men and women to have a hypermasculine view of the world, prioritizing stereotypically male behaviors like building machines over stereotypically female behaviors like empathizing with a friend. Now, a study is raising new doubts about this theory, finding no effect of testosterone on empathy in adult men.

The work does not directly address whether high levels of prenatal testosterone cause autism or lack of empathy. That would require directly sampling the hormone in utero, which can endanger a developing fetus. But the new study’s large size—more than 600 men—makes it more convincing than similar research in the past, which included no more than a few dozen participants, experts say.

The extreme male brain hypothesis was first proposed by psychologist Simon Baron-Cohen at the University of Cambridge in the United Kingdom. In 2011, he and colleagues found that women given a single hefty dose of testosterone fared significantly worse at the Reading the Mind in the Eyes test (RMET), which asked them to gauge the emotional states of others based on their facial expressions. The women’s performance seemed to track with a controversial metric called the 2D:4D ratio, the relative lengths of the second and fourth fingers. Men—and people with autism—tend to have a longer ring finger than index finger, and some researchers believe that is due to higher prenatal exposure to testosterone. 

Read more here at Science. 

Having smart father raises child’s risk of autism

Children whose fathers are highly intelligent are at a 32 percent higher risk of autism than those whose fathers are of average intelligence, according to research published 23 April in the Journal of the American Academy of Child & Adolescent Psychiatry1.

The work supports observations that date back to the 1940s, when Leo Kannerand Hans Asperger noted in separate reports that the fathers of children with autism tended to be highly intelligent and in several cases worked in technical fields. A 2012 study also showed that children from regions in the Netherlands where high-tech jobs are prevalent are more likely to have autism than those who live in other regions.

Read more here at Spectrum. 

The Quest For the Roots of Autism — and What It Says About Us All

As clinicians view it, autism involves communication deficits and formulaic, repetitive behaviors that present obstacles to establishing conventional relationships. The soft borders of that definition — where does communication difficulty cross over into communication deficit? — suggest blurred margins between people who are diagnosed with autism and those who approach, but never quite cross, the line into diagnostic territory.

Those who do have diagnoses display behaviors on a continuum of intensity. Their use of spoken language ranges from not speaking at all to being hyperverbal. They can have a unique interest in the finer details of window blinds or an intense but more socially tolerated fascination with dinosaurs. As with many human behaviors, each feature exists on a spectrum, and these spectra blend in a person to create what clinicians call autism.

By pinpointing risk-associated genes and uncovering their roles, studying the roots of autism also is providing new insights into the development of all human brains, autistic or not. Here is a taste of what we now know, and what we don’t, about autism’s causes — and what that search is teaching us about everybody’s neurology.

They Know It When They See It

Read more here at Discover.

Autism runs in families with history of brain conditions

Children in families with a history of brain conditions are at increased odds of being autistic, a large study in Sweden suggests1. The more closely related the family members with these conditions, the greater the child’s chances of having autism.

Other studies have reported similar trends: A child’s odds of having autism increase if she has a sibling with autism, attention deficit hyperactivity disorder (ADHD) or intellectual disability, or a parent with schizophrenia, depression, bipolar disorder or anxiety2,3,4.

The new study looked at family history of these conditions, as well as epilepsyand more than a dozen others, and included grandparents, aunts, uncles and cousins.

Read more here at Spectrum. 

Birth seasonality and risk of autism spectrum disorder

There was a modest increase in risk for children born in the fall and a modest decrease in risk for children born in the spring. Solar radiation levels around conception and the postnatal period were inversely correlated with seasonal trends in ASD risk. In the first multinational study of birth seasonality of ASD, there was evidence supporting the presence of seasonal trends in Finland and Sweden. The observations that risk was highest for fall births (i.e., conceived in the winter) and lowest for spring births (i.e., conceived in the summer), and sunlight levels during critical neurodevelopmental periods explained much of the seasonal trends, are consistent with the hypothesis that a seasonally fluctuating risk factor may influence risk of ASD.

Read more here at Springerlink.

A Mother's Exposure to Pesticides During Pregnancy May Raise Children's Autism Risk

The scientists found that women who were pregnant and who lived within a 2,000 meter radius of a highly sprayed area were anywhere from 10% to 16% more likely to have children diagnosed with autism than women who lived in places farther away from sprayed areas. The researchers reviewed spraying of 11 popular pesticides, including chlorpyrifos, diazinon and permethrin (often used to control ticks). When they looked at diagnoses of autism spectrum disorder that also came with intellectual disabilities, they found on average 30% higher rates among children who were exposed to the pesticides while in utero. Exposure in the first year of life increased the risk of autism by up to 50% compared to those not exposed to certain pesticides.

Read more here at Time. 

Archived Webinar: Ivan Iossifov discusses genotype, phenotype in autism

View the archived webinar here.

Significant association detected between food allergies, ASD

This artilce also appeared in the 2018, Volume 32, No. 3 issue of ARI's Autism Research Review International newsletter. 

Children with food, respiratory, or skin allergies are significantly more likely to have an autism spectrum disorder (ASD) than children without allergies, according to a new study that adds to evidence implicating immune dysfunction in autism.

In the study, Guifeng Xu and colleagues reviewed data collected by the U.S. National Health Interview Survey between 1997 and 2016. Their analysis included nearly 200,000 children between 3 years and 17 years of age. Of these, 1,868 had an ASD diagnosis.

The researchers report that children with ASD were more likely to have food allergies (11.25% vs. 4.25%), respiratory allergies (18.73% vs. 12.08%), and skin allergies (16.81% vs. 9.84%) than children without ASD. The likelihood of having ASD more than doubled among children with food allergies compared to those without food allergies. Skin and respiratory allergies were also associated with elevated odds of having an ASD diagnosis, although to a lesser degree.

The researchers note, “The association between food allergy and ASD was consistent and significant in all age, sex, and racial/ ethnic subgroups.” However, boys with ASD were more likely than girls with ASD to have respiratory and skin allergies.

Read more here at theAutism Research Institute. 

Sex differences in brain hint at roots of ‘camouflaging’ in autism

Autistic women’s activity in a ‘social’ brain region tracks with the extent to which they mask their autism, according to a new study1.

Their activity in this and another social brain region when they reflect on themselves or others resembles that of their typical peers. Men with autism, by contrast, show less activity in these regions than typical men do.

The new findings reinforce the idea that autism manifests differently in women than it does in men.

“Maybe the idea of a hypoactivated social brain doesn’t apply universally to everyone on the spectrum,” says co-lead investigator Meng-Chuan Lai, assistant professor of psychiatry at the University of Toronto in Canada.

The findings represent the first attempt to pinpoint brain areas that may be involved when autistic women ‘camouflage,’ or mask their autism traits.

Read more here at Spectrum. 

Slow onset may explain late autism diagnosis in some children

Some autistic children don’t show traits of the condition until age 5 or later, new research suggests1. Others show a few mild features at age 3 but only later meet the criteria for diagnosis.

The findings suggest that autism traits are not always apparent by 24 months, the typical age for screening. As a result, efforts to bring down the average age of diagnosis, now at 4 years, can only go so far.

“There are some children who do get evaluated, sometimes multiple times, only to get diagnosed later,” says lead researcher Sally Ozonoff, endowed professor of psychiatry and behavioral sciences at the University of California, Davis. “This research is explanatory for those children.”

The results are based on following ‘baby sibs,’ or younger siblings of children with autism, who are at increased risk for the condition. But they should remind clinicians not to rule out autism in older children, even among the general population, experts say.

Read more here.