Recent studies are uncovering more about genes contributing to developing the disorder. An article in Nature Genetics identified numerous genes associated with ADHD, many of which are active when the brain is developing. “The most recent studies on the genetics of ADHD have identified 27 common genetic variants that are associated with having ADHD,” says Sandra K. Loo, director of pediatric neuropsychology and professor of psychiatry at UCLA’s David Geffen School of Medicine. “Having more of these gene variants is likely to confer a higher risk for having ADHD.”

The combination of elements contributing to an individual case of the disorder might be different depending on the person. “Genetic expression is highly influenced by the environment, as well as its interaction with other genes,” Javier says. “So things like physical, chemical, social, and nutritional influences can vary widely, and that can affect the manifestation of ADHD.”

(Why rates of adult ADHD are rising)

The most recent studies on the genetics of ADHD have identified 27 common genetic variants that are associated with having ADHD. Having more of these gene variants is likely to confer a higher risk for having ADHD.

Sandra K. Loo, director of pediatric neuropsychology and professor of psychiatry at UCLA’s David Geffen School of Medicine

While Chandler seems to have passed down a paternal link to the condition, researchers are learning that, for some people, what happens during pregnancy or shortly after birth may contribute to the condition. “There are strong associations with maternal smoking, maternal obesity, preeclampsia during pregnancy, and the use of acetaminophen,” Rush says, although the evidence surrounding acetaminophen use is still mixed.

Research published in the Journal of Child Psychology and Psychiatry suggests that an infection during pregnancy, especially one that causes a fever, is a risk factor because the mother’s immune response to an infection could disrupt the brain development of the fetus. “There’s also literature that suggests that September is a peak birth month for children diagnosed with ADHD,” Javier says, “and the idea is that there is a higher risk of prenatal exposure to infection during the first trimester, in the winter months, when infections are more common.” (Another theory suggests that the September peak isn’t solely correlated with prenatal infection. It may be affected by school enrollment cutoff dates, where children who are young for their grade may be more likely to be diagnosed because of developmental immaturity.)

While there isn’t enough research yet to understand the exact influence certain environmental factors have on developing the disorder, there are some strong associations. For example, studies have shown a connection between lead exposure in young children and the emergence of ADHD symptoms. Research has also associated the prevalence of phthalates or bisphenol A (BPA)—chemicals found in plastic consumer products—with the condition. “Of the toxins, exposure to high levels of lead has been strongly associated with ADHD risk,” Loo says.

(Dust isn’t just dirt—it’s full of ‘forever chemicals’ that can harm your health.)

But associations between genetics and our environment still aren’t fully understood. “There’s a whole lot of things that contribute to these brain changes,” Rush says, “and we call them ADHD because of the symptoms that they cause.”

While doctors and researchers still aren’t sure of the exact cause of the disorder, the predominant theory ‘is primarily genetics and the biology of what’s going on in the brain that seems to be associated with it.’

Stephen Rush, professor of psychiatry, University of Cincinnati

For Chandler, understanding the condition has helped his family better navigate their daily life. He currently applies his hands-on skills in his job as a technician and enjoys motorcycling. After their daughter’s diagnosis and years of keeping her in the school system, he and his wife chose homeschooling for their family. Their daughter flourished, as it allowed her to go at her own pace.

Today, she’s a teenager, and her favorite subjects are anatomy and biology. She is preparing to begin a welding program, and she shows signs of following in her father’s footsteps. She just bought a motorcycle. “Whatever culture we’re in, we can help to move it forward,” Chandler says, “to be more accepting of the realities of human nature.”

A version of this story appears in the November 2025 issue of National Geographic magazine.