According to a population analysis conducted by Swedish scientists, intrauterine infections are associated with an increased risk of developing autism spectrum disorders and intellectual disability.
These infections include TORCH infections, such as toxoplasmosis, rubella, cytomegalovirus, and herpesvirus infections, as well as other diseases.
The study results, published in the journal JAMA Pediatrics, are based on data collected from over 3.6 million children in Sweden.
Donald was a baby with atypical characteristics; he did not react to stimuli and rarely looked at his parents, the teacher Mary, and the lawyer Beamon Triplett. When he started talking, his communication was peculiar, limited to monosyllabic responses such as 'yes' or 'no,' while simultaneously showing great fascination with certain words, such as 'chrysanthemum,' which he repeated incessantly.
Although he presented clear developmental difficulties, Donald possessed remarkable intellectual abilities. At just one year old, he could already sing several songs, and at two years old, he had memorized a biblical psalm composed of 22 verses and 354 words, in addition to answering 25 questions and answers from the Presbyterian catechism. He had irregular eating habits, did not interact with other children, and exhibited repetitive behaviors, such as a fixation on spinning circular objects, seeming to live in a private world where he preferred solitude.
The family sought help, and the boy remained hospitalized in a clinic for a year. However, the parents decided to bring Don home. Five years later, they consulted the Austrian child psychiatrist Leo Kanner. While observing Don, Kanner noticed that other children presented similar traits. In 1943, he published a scientific article describing 11 children—three girls and eight boys—and coined the term 'early childhood autism.'
In the aforementioned article, Don was classified as 'Case 1,' becoming the first child to receive this diagnosis. Until then, the term held another meaning, as the word, derived from the Greek 'autos,' meaning 'by oneself,' was introduced in 1911 by the Swiss Eugen Bleuler to describe the tendency of schizophrenic adults to isolate themselves.
Donald completed elementary school and entered university, studying French and mathematics. Gradually, he managed to integrate into the community of small Forest, Mississippi (USA), where he lived and worked as a banker for 65 years. He practiced driving and golf daily and enjoyed traveling, having visited an impressive 40 countries. Although he never dated or married, he cultivated friendships, stating that 'he is not one for idle talk' in 2022. Donald passed away in June 2023, at the age of 89, proving that autism did not prevent a long, productive, and happy life.
This is the expected scenario for families and individuals who receive this diagnosis, given that its occurrence has increased drastically in recent years. In the 1970s, the rate was 1 in every 2,500 autistic individuals. In the 2000s, this number rose to 1 in every 150, and in 2010, it reached 1 in every 68. Currently, data from the United States Centers for Disease Control and Prevention (CDC) indicate that 1 in every 31 children is autistic.
In Brazil, the situation is analogous: the 2022 IBGE Census registered 1 in every 38 children with Autism Spectrum Disorder (ASD). Considering adults, who account for one-third of cases, it is estimated that the country has 2.4 million autistic people. The incidence of autism has quintupled in twenty years and grown by 8,000% in five decades. Science is intensifying efforts to find explanations for this phenomenon.
The database of the U.S. National Institutes of Health shows a significant increase in studies: in 2005, 938 articles on autism were published globally, whereas the previous year saw 9,045. Next, some of the most complex topics related to ASD diagnoses will be addressed.
On May 24, 2010, the career of English doctor Andrew Wakefield ended after the Council found him guilty of professional misconduct and ordered the removal of his name from the medical register. He was the author of a study published in 1998 in the scientific journal Lancet, which raised the controversial claim that the triple viral vaccine (protecting against measles, mumps, and rubella) caused autism.
This work reported cases of 12 children with ASD and suggested that, in eight of them, the disorder was triggered by the vaccine, as symptoms appeared after immunization and the children showed intestinal inflammation. However, such a report proves nothing. Later, it was discovered that Wakefield's study had been fraudulent: some parents contested the information provided.
The English doctor fabricated responses and manipulated data, and was even paid by Richard Barr, a lawyer preparing a multimillion-dollar lawsuit against vaccine manufacturers. It was, therefore, a scheme. There are countless studies, conducted with over 1.2 million children, that demonstrate that vaccines do not cause autism.
Paracetamol, or acetaminophen, is also not linked to autism. Last year, U.S. President Donald Trump accused this analgesic (marketed as Tylenol) of causing autism. Although the origin of this claim is uncertain, it may derive from a 2024 study that analyzed medical records of 2.5 million children in Sweden, pointing to 'marginally increased risks of autism and ADHD associated with acetaminophen use during pregnancy.'
However, as the study itself points out, after removing so-called 'confounding factors,' there was no increased risk of autism. An illustrative example is hot weather in the summer, which increases both ice cream consumption and drownings; ice cream does not cause drowning, but heat is the common factor. Brian Lee, an epidemiologist and co-author of the study, explained that in the case of paracetamol, the confounding factor lies in the fact that many pregnant women use the medication to treat other conditions that may be related to autism, such as fever or infections. Furthermore, there is the genetic predisposition of the parents and the use of other drugs during pregnancy.
Autism is a neurological condition associated with modifications in brain development. Its basis is genetic, and it can manifest on its own (if very strong) or be triggered by environmental elements. José Salomão Schwartzman, a neuropediatrician specializing in ASD, clarifies that 'in families where the genetic aspect is very strong, a trigger is not necessary. We see this in families with three, four, or even six autistic children.'
Environmental factors refer to influences in the intrauterine environment during fetal development. The use of certain medications during pregnancy, for example, can increase the risk of autism in children. Valproic acid (or valproate), an anticonvulsant also used for migraines, is the agent with the highest certainty. A study conducted with 655,000 children in Denmark concluded that 'the use of valproic acid during pregnancy was associated with a significantly higher risk of ASD.'
There are indications, although less definitive, involving other medications, such as 'sterol biosynthesis inhibitors' (SBIs), including sertraline and atorvastatin. Despite having different structures and indications (one antidepressant and another heart medication), both interfere with cholesterol production, a molecule essential for brain development. Scientists from the University of Nebraska, USA, investigated the link between 15 SBIs and autism in 6 million pregnancies. Women who used at least one SBI during pregnancy had a 47% higher risk of having an autistic child, and each additional prescribed SBI increased this risk by 33%. These data are worrying due to the increase in the use of these medications (in the US, it jumped from 4.6% of pregnancies in 2014 to 16.8% in 2023).
Some research has pointed to a correlation between autism and antidepressants during pregnancy, especially 'selective serotonin reuptake inhibitors' (SSRIs), the most common type. Lisa Croen, director of the Kaiser Permanente Autism Research Program, USA, analyzed data from 298 children with ASD (and their mothers) and a control group of 1,507 children without ASD. The result showed that the incidence of autism was 2.2 times higher among pregnant women who used SSRIs in the year before delivery.
British and Chinese researchers, reviewing observational studies from 1946 to 2014, also concluded a high risk of ASD in children exposed to antidepressants during pregnancy. However, two major reviews—one in 2017 by Indian psychiatrist Chittaranjan Andrade and another this year by scientists from the University of Hong Kong—reached opposite conclusions. They identified a small relationship, but it disappeared after excluding 'confounding factors,' such as maternal mental health and genetic predisposition.
Living near farms with pesticides appears to be a risk factor, as demonstrated by a study from the University of California. Of the 970 pregnant women examined, one-third lived less than 1.5 km from where pesticides were applied, and their children showed, on average, 60% more cases of ASD. A study from Nanjing Medical University, China, corroborated these findings: mothers exposed to pesticides during pregnancy had children with a 19% higher probability of developing autism. It is important to note that this is an association, not proof of direct causality, since observational studies cannot isolate variables like genetics.
Regarding parental age, the evidence is stronger. An analysis of various studies published by Chinese scientists indicated that every ten-year increase in the age of the mother and father raises the risk of ASD by 18% and 21%, respectively. A possible reason for this is the increased risk of genetic mutations in reproductive cells with advancing age.
The largest study conducted in the area included 5.7 million children (30,902 with ASD) in five countries (Australia, Denmark, Israel, Norway, and Sweden), along with their parents. Men aged 50 or older had a 66% higher risk of having an autistic child compared to parents aged 20 to 29. For women aged 40 to 49, the risk was 15% higher than for women in their 20s. The authors concluded that the risk was higher when both parents were older, but it also increased when there was a large age disparity between them. This may explain an interesting finding: adolescent mothers had an 18% higher risk compared to mothers in their 20s, due to the greater age difference relative to the father.
Research also correlates maternal overweight with a higher risk of ASD in children. Scientists from the University of South Australia analyzed data from 42 studies involving 3.7 million pregnant women. Children of obese mothers had a 42% higher chance of autism, which is attributed to inflammation and metabolic changes generated by maternal adiposity in the uterine environment, affecting fetal development. Premature birth also increases the risk of autism, as noted by a meta-analysis of 52 studies conducted by psychologists from the University of Birmingham, England, which found that autism diagnoses were 3.3 times more frequent in premature neonates.
