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Autism is diagnosed more frequently in boys, who also tend to receive their diagnosis earlier than girls. A new study published in Behavior Genetics suggests that the genetic signal for early-diagnosed autism carries links to educational and cognitive traits that cannot be explained by biological sex. Whether the stronger ties between late-diagnosed autism and conditions like depression reflect diagnosis timing or sex, however, could not yet be untangled.
Autism is a neurodevelopmental disorder that typically appears in childhood. It is characterized by difficulties with verbal and nonverbal communication, challenges in social interactions, and the presence of repetitive behaviors or highly restricted interests. Historically, autism has been diagnosed roughly four times more often in boys than in girls.
Along with this difference in diagnosis rates, boys and girls often differ in when they are identified. A 2012 study demonstrated that males typically receive autism diagnoses at a younger age than females. Because girls are frequently diagnosed later in life, scientists have wondered if outward traits associated with biological sex might be masking or confusing the traits associated with the timing of a diagnosis.
Recently, a 2025 study provided evidence that early-diagnosed autism and late-diagnosed autism possess distinctly different underlying genetic profiles. The authors of that earlier study concluded that sex differences were unlikely to account for these diverging pathways. To directly test this claim and untangle these overlapping categories, a team of researchers conducted a new investigation.
“Because boys are typically diagnosed earlier, we wanted to know whether those early-versus-late differences were partly explained by sex differences,” lead author Sophie Breunig, a PhD candidate in the Department of Psychology and Neuroscience and the Institute for Behavioral Genetics at the University of Colorado at Boulder, told PsyPost. “If certain interpersonal, cognitive, and behavioral traits are more typical of autism in females, that knowledge could eventually help clinicians recognize autism in girls sooner and get them support earlier.”
The research team set out to determine whether the unique genetic profile of late-diagnosed autism is simply a byproduct of the fact that late-diagnosed individuals are more likely to be female, or if the age of diagnosis points to a genuinely different genetic pathway. They utilized a statistical approach known as genomic structural equation modeling. This technique allows scientists to analyze large sets of genetic data to identify how different traits and conditions share underlying genetic risk factors.
The authors analyzed genome-wide association study data, which scans the complete set of DNA across many people to find tiny genetic variations associated with a particular condition. They used genetic summary statistics for autism divided into four categories: early-diagnosed, late-diagnosed, male, and female. In the contributing studies, early diagnosis generally meant before about age 6 to 9, depending on the cohort, while late diagnosis meant age 10 or older.
The sample sizes comprised individuals of European genetic ancestry, including an effective sample size (a statistical estimate of how much data each group contributes) of 33,608 for early-diagnosed autism and 21,775 for late-diagnosed autism. The sex-specific data included 15,025 male cases and 4,845 female cases, each compared against more than 19,000 controls.
To explore how these four categories relate to other areas of human health and behavior, the researchers compared them against 68 external traits. These traits included psychiatric conditions like depression and post-traumatic stress disorder (PTSD), cognitive abilities like memory and general intelligence, and social outcomes like loneliness and family satisfaction. The researchers first tested which of these traits were linked differently to male versus female autism, and to early- versus late-diagnosed autism. They then used multiple regression models to check whether differences tied to diagnosis timing could be explained by sex, and vice versa.
“In this study, we measured genetic correlations, which range from −1 to 1 and describe how much the genetic influences on two traits overlap across large groups of people,” Breunig explained. “These are population-level patterns and therefore can’t be used to diagnose or predict anything about an individual person. Their value is in showing that people who share a diagnosis, such as autism, aren’t all the same. Paying attention to subgroups, like biological sex or whether they were diagnosed earlier or later in life, may eventually help clinicians know what to look for and how to tailor support.”
When looking at biological sex, the researchers found that the genetic profiles of male and female autism were highly similar, sharing a genetic correlation of 0.81. Out of the 68 external traits tested, only two showed distinctly different associations based on sex. Anorexia nervosa shared a stronger genetic overlap with female autism, while a tendency toward speeding in traffic was negatively associated with female autism but not male autism.
The finding that common genetic variants for autism are highly similar between sexes adds nuance to other recent research. For example, a study covered by PsyPost in 2024 found that the overall heritability of autism was higher in boys (about 87 percent) than in girls (about 76 percent). However, higher heritability in boys is a different question from whether the exact same genetic influences are involved, and that earlier study analyzed family-based registry data rather than common genetic variants across the broader population.
In contrast to the strong similarities between sexes, early- and late-diagnosed autism showed much less genetic overlap in the new study, with a genetic correlation of 0.42. Thirty-one of the tested external traits displayed diverging genetic associations depending on when the autism diagnosis occurred. Late-diagnosed autism was more strongly linked to an increased psychiatric burden, showing greater genetic overlap with major depressive disorder, PTSD, and attention-deficit/hyperactivity disorder (ADHD).
Late diagnosis was also linked to adverse social outcomes, such as higher levels of loneliness and lower satisfaction with friendships and family relationships. Early-diagnosed autism, on the other hand, showed stronger genetic links to education and certain cognitive tests, though in different directions. It shared more genetic overlap with higher educational attainment than late-diagnosed autism did, but it was also genetically linked to lower performance on a memory test and a symbol-matching task that measures processing speed. Both subtypes showed similar positive genetic overlap with general intelligence.
When the researchers adjusted for biological sex, the most distinctive associations of early-diagnosed autism held up and even grew stronger, including its links to the parts of educational attainment not explained by cognitive ability and to a symbol-matching task. This suggests the early-diagnosed profile is not simply a byproduct of the large number of boys diagnosed early. Similarly, when the models were adjusted to account for early diagnosis, the two female-specific links to anorexia and a lower tendency for speeding also remained robust. The same test could not be run for late-diagnosed autism, whose genetic signal was almost identical to that of male autism (a correlation of 0.99) and very similar to that of female autism (0.91).
“Because girls tend to be diagnosed later, we checked whether these early-versus-late differences were explained by sex differences,” Breunig noted. “For the early-diagnosed group, they weren’t and we can’t tell yet for the late-diagnosed group. The late-diagnosed genetic signal overlapped so much with both male and female autism that our analyses couldn’t separate them.”
The team also ran follow-up analyses grouping major depressive disorder, anxiety, and PTSD into a single general category representing internal emotional distress. They found that female autism and late-diagnosed autism both shared stronger genetic overlap with this distress factor, though the gap between female and male autism was slight and only just met the study’s statistical threshold, so it awaits confirmation.
When the researchers factored this general emotional distress into their models, the genetic link between late-diagnosed autism and adult ADHD dropped from 0.42 to near zero; early-diagnosed autism had shown almost no link to begin with. This indicates that the connection between autism and adult ADHD might actually be driven by general psychiatric distress rather than overlapping pathways specific to autism.
Accounting for this distress factor also shrank autism’s genetic overlap with ADHD far more for female autism (from 0.39 to 0.07) than for male autism (from 0.51 to 0.23). “The surprising part was that when we statistically removed that shared signal, we saw that in females, much more of the genetic overlap between autism and ADHD was explained by internalizing problems than in males,” Breunig said. “This suggests that the link between autism and ADHD in girls and women may operate through broader emotional distress.”
As with all research, there are a few things to keep in mind regarding these findings. The study relied exclusively on genetic data from individuals of European ancestry. Because genetic frequencies and environmental interactions can vary across populations, these findings might not fully apply to people of other ancestral backgrounds. The researchers also note that “male” and “female” in this dataset refer to sex assigned at birth.
In addition, because late-diagnosed autism was so genetically similar to both male and female autism, the researchers could not test whether its stronger links to depression, PTSD, and other psychiatric conditions reflect diagnosis timing or sex. The authors advise treating claims that late-diagnosed autism carries its own distinct psychiatric overlap as tentative until larger studies are available.
“It is also worth noting that late-diagnosed autism is still autism,” Breunig pointed out. “While it was genetically not very related to earlier diagnosed autism, it was about as closely related to autism overall as early-diagnosed autism was. Some of its extra overlap with other conditions may reflect the challenges of diagnosing autism in adulthood, when other conditions can mask or mimic it.”
Looking ahead, the researchers hope to build on this framework. “We would like to repeat these analyses as larger datasets become available to fully separate the effects of sex and age at diagnosis,” Breunig added. “We also want to study other traits, like depression or ADHD, separately in males and females, since sex differences can be missed in large genomic studies where everyone is combined.”
The study, “Uncovering the Role of Biological Sex in the Divergent Genetic Profiles of Early and Late-Diagnosed Autism,” was authored by Sophie Breunig, Lukas Schaffer, Jeremy Lawrence, Alexander Sheppard, and Andrew Grotzinger.