The study, led by the Barcelona Institute for Global Health (ISGlobal), a centre supported by the “la Caixa” Foundation, and Aarhus University, found that young people diagnosed with ADHD or ASD in Denmark now more closely resemble the broader population than those who received the same diagnoses 10 years earlier.

The findings suggest that the increase in ADHD and ASD diagnoses may partly reflect changes in who is being identified and diagnosed, alongside any possible changes in the underlying likelihood of developing these conditions. The research was published in JAMA Psychiatry.

Tracking changes in ADHD and autism diagnoses

Previous studies have identified several characteristics that occur more often among people diagnosed with ADHD or ASD than among the general population. These include being born prematurely or at a low birth weight, having parents with lower levels of education or lower household income, having a parent with a history of psychiatric disorders, and making greater use of healthcare services before receiving a diagnosis.

Researchers wanted to know whether those patterns had changed as ADHD and ASD diagnoses became more common.

To investigate, the team analyzed information from more than 2.1 million children and adolescents in Denmark. The researchers compared more than 71,000 young people diagnosed with ADHD or ASD between 2012 and 2022 with more than 713,000 individuals who had not received either diagnosis.

Differences narrowed over 10 years

Young people diagnosed with ADHD or ASD were still more likely than their peers to have many of the characteristics previously linked with these conditions. However, the size of those differences steadily declined during the study period.

Low birth weight provides one example. At the beginning of the study period, children born with low birth weight were 54% more likely to later receive an ADHD or ASD diagnosis than children born at a normal weight. By the end of the study, the difference had dropped to 17%.

Researchers found comparable declines in the associations involving premature birth and several measures of socioeconomic disadvantage.

“The key message is not that these risk factors are no longer important,” says Magnus Elias Tarp, PhD student at Aarhus University and first author of the study. “What we found is that people diagnosed in recent years resemble the general population more closely than those who received the same diagnoses a decade ago.”

A different way to understand rising diagnoses

Much of the research surrounding ADHD and ASD has examined why diagnosis rates are increasing or which factors are associated with a greater likelihood of developing these conditions. The new study approaches the trend from another direction by asking whether the population receiving diagnoses has itself changed.

The researchers say several developments could potentially contribute to the shift. Awareness of ADHD and ASD has increased, healthcare and education systems may be identifying cases more effectively, access to diagnostic evaluations may have expanded, and the point at which neurodevelopmental characteristics are considered clinically impairing may have changed.

The study cannot determine how much each of these factors contributed. However, the findings indicate that rising diagnosis rates should not automatically be interpreted as evidence that the underlying occurrence of ADHD or ASD has increased by the same amount.

“Our findings help us better understand why ADHD and autism diagnoses have increased so markedly in recent years,” says Oleguer Plana-Ripoll, researcher at ISGlobal and Aarhus University and senior author of the study. “They do not show that these conditions are being overdiagnosed or that they have become less severe. Rather, they indicate that the population receiving these diagnoses has changed over time, and this needs to be taken into account when interpreting current trends. Further research in other countries would be needed to determine whether these findings can be replicated elsewhere,” he adds.

What the findings could mean

Researchers say the results could affect how scientists interpret changes in the prevalence of ADHD and ASD. They may also be important for planning healthcare, education, and social services for people with these diagnoses.

The findings could also influence how researchers interpret reports of improving outcomes among people with ADHD or ASD. Some apparent improvements may result partly from changes in the characteristics of the population now receiving diagnoses, rather than from an improvement in the prognosis of the conditions themselves.

Neither species has an English common name yet. Both are small, with cone-shaped shells measuring about 6 mm in length, and they live on limestone rocks where they feed on algae and lichens.

They also have several unusual features. Unlike most land snails, their eyes are positioned along the sides of the head rather than at the tips of eye stalks. They also carry a circular disk attached to the tail that can seal the shell opening like a door when the animal retreats inside.

New Species Found in Montenegro’s Mountains

The snails were discovered during expeditions organized by Taxon Expeditions, an initiative that allows members of the public to take part in genuine scientific fieldwork.

Between 2018 and 2025, expeditions in Montenegro were carried out through a partnership involving Taxon Expeditions, the non-profit Taxon Foundation, and local collaborators from the Montenegrin Ecologists Society.

The field teams brought together international researchers, citizen scientists, local students, and conservationists to investigate the biodiversity of Durmitor National Park and Komarnica Canyon.

Researchers encountered the snails at several locations while working in the region’s rugged mountain terrain. However, it was not immediately clear that they represented species unknown to science. That became evident only after the animals were dissected and genetically analysed in the field laboratory.

Named After the Places Where They Were Found

The expedition team chose the names during a vote held at camp.

“Cochlostoma dobrido,” was named after the Dobri Do Plateau, located among the peaks of Durmitor National Park. “Cochlostoma komarnica,” takes its name from the stunning but unprotected Komarnica Canyon, which lies south of Durmitor.

“I was amazed that it is still possible to discover new animal species in Europe,” says musician Janine Buisman from The Netherlands, who participated in one of the expeditions and later became a co-author of the paper.

Biologist Jovana Đokić of the Montenegrin Ecologists Society (MES), another author of the study, says the canyons, mountains, and gorges of this part of the Balkans contain extensive biodiversity that remains poorly explored, with many species potentially still waiting to be documented.

Komarnica Canyon Faces a Hydropower Threat

Đokić says that makes plans affecting Komarnica Canyon especially concerning.

“It is all the more worrying that the Komarnica Canyon is targeted to be flooded by a hydropower dam and reservoir. This will destroy this wild river canyon and all the biodiversity in it, including many species still unknown to science.”

– Jovana Đokić

The proposed development has helped make Komarnica Canyon a major focus of organized biodiversity surveys. Researchers and conservation groups are documenting its wildlife in an effort to build a scientific case for protecting the area.

MES is calling for Komarnica Canyon to become part of the UNESCO World Heritage site of Durmitor and for plans for the hydropower project to be abandoned.

“Hydropower is neither green nor sustainable energy when it destroys a unique ecosystem like this,” says Đokić.

“Ariel is pretty unique in terms of icy moons,” said paper co-author Alex Patthoff, a Planetary Science Institute senior scientist.

A Moon With a Surprisingly Violent Past

Ariel is the brightest of Uranus’ moons and the second closest to the planet. At only 720 miles (1,159 km) across (the distance from PSI in Tucson to Salt Lake City, Utah), it ranks as the fourth-largest moon in the Uranian system.

Despite its relatively small size, Ariel has an unusually complex surface. According to the paper’s first author, Caleb Strom, a recent graduate of the University of North Dakota, ancient features such as impact craters sit alongside much younger terrain. Some smooth regions may even have formed through cryovolcanism, a process in which water, ice, or other volatile materials erupt from an icy world rather than molten rock.

Ariel is also covered in fractures, ridges, and grabens, areas where sections of the crust have dropped below the surrounding terrain. Some of these structures occur on scales larger than those found almost anywhere else in the Solar System.

Reconstructing Ariel’s Hidden Interior

Those enormous surface features are what motivated the new investigation. The researchers wanted to determine what Ariel’s interior and orbit may have looked like in the past to produce the fractures visible today.

One key factor is orbital eccentricity, which describes how much an orbit differs from a perfect circle. Changes in Ariel’s interior structure and orbital eccentricity could both influence the amount of tidal stress acting on its icy crust. As the moon travels around Uranus, gravitational forces repeatedly stretch and squeeze it, potentially placing enough stress on the surface to cause large fractures.

“First, we mapped out the larger structures that we see on the surface, then we used a computer program to model the tidal stresses on the surface, which result from distortion of Ariel from soccer ball-shaped to slight football-shaped and back as it moves closer and farther from Uranus during its orbit,” Patthoff said. “By combining the model with what we see on the surface, we can make inferences about Ariel’s past eccentricity and how thick the ocean might have been.”

A Much More Eccentric Orbit

The researchers found that Ariel may once have had an orbital eccentricity of about 0.04, roughly 40 times greater than its value today.

Although 0.04 still represents an orbit that would look nearly circular, that difference would have greatly amplified the tidal forces acting on Ariel. Its orbit would have been about four times more eccentric than that of Jupiter’s moon Europa, whose icy shell is heavily fractured by the continual gravitational stretching and squeezing it experiences.

Those forces may have played a major role in shaping Ariel’s dramatic landscape.

“In order to create those fractures, you have to have either a really thin ice on a really big ocean, or a higher eccentricity and a smaller ocean,” Patthoff said. “But either way, we need an ocean to be able to create the fractures that we are seeing on Ariel’s surface.”

Uranus May Have Had Twin Ocean Worlds

The Ariel study is the second in a series examining what may once have existed beneath the surfaces of Uranus’ moons. Last year, the same research team reported similar results for Miranda, another icy moon orbiting Uranus.

Together, the findings raise the possibility that more than one moon in the Uranian system may have contained a substantial subsurface ocean.

“We are finding evidence that the Uranus system may harbor twin ocean worlds,” said coauthor, Tom Nordheim of Johns Hopkins University Applied Physics Laboratory and principal investigator of the NASA Solar System Workings grant that funded the Miranda and Ariel studies. “Unfortunately, we’ve only seen the southern hemispheres of Ariel and Miranda. But our results can give us predictions of what a future spacecraft might see on the moons’ unimaged northern hemispheres, such as the location of fractures and ridges there. Ultimately, we just need to go back to the Uranus system and see for ourselves.”

What a Future Uranus Mission Could Reveal

Scientists still do not know exactly when Ariel’s deep ocean may have existed, or how long it lasted. However, the new results offer an important foundation for future studies investigating how subsurface oceans on distant icy worlds form, evolve, and potentially disappear over time.

A future spacecraft mission to Uranus could also test the researchers’ predictions by imaging the unexplored northern hemispheres of Ariel and Miranda and searching for the fractures and ridges expected from their models.

This research was also funded by the North Dakota Space Grant Consortium.