For years, researchers have grappled with one of autism’s enduring mysteries: why males receive diagnoses at more than four times the rate of females. While many theories have suggested that biological or social differences play a role, a new study from the UC San Diego School of Medicine challenges that assumption.
It finds no clinical differences in autistic traits between males and females at the time of early diagnosis, suggesting gender disparities in diagnoses may emerge later in life.
The study analyzed more than 2,500 toddlers between 12 and 48 months of age, making it the most extensive investigation.
Researchers examined a spectrum of developmental markers—language abilities, social engagement, motor skills, cognitive function, and repetitive behaviors—in male and female autistic children. The results?
Social brain networks are altered at a young age in autism, study finds
They were virtually identical across the sexes, except for a slight advantage for females in daily living skills such as self-feeding and dressing.
“This was unexpected,” says Karen Pierce, Ph.D., senior author of the study and director of the Autism Center of Excellence at UC San Diego. “Based on previous small studies, we had anticipated some sex differences. Instead, we found nothing at all.”
Surprisingly, while autistic toddlers showed no sex differences, typically developing females consistently outperformed males in more than half the assessments. These gaps were most pronounced in social and language skills, aligning with previous research that suggests young girls develop these abilities slightly faster than boys.
So, where does this leave the longstanding assumption that autism manifests differently in males and females? Pierce and her team propose two possibilities: Either past studies have overstated sex differences due to small sample sizes and methodological biases, or these distinctions emerge later in life, shaped by socialization, biological development, or other external influences.
If the latter holds, researchers would need long-term studies following autistic children beyond toddlerhood to pinpoint when and how these differences evolve.
Beyond reshaping our understanding of autism’s gender gap, the findings also highlight a critical shift in early intervention. Rather than focusing on presumed sex-based distinctions, Pierce suggests clinicians should prioritize autism’s core subtypes—patterns of development that might offer better insights into tailoring interventions.
“If you can improve a toddler’s communication at the youngest age possible, they’ll be better equipped to express their needs and thrive in society,” Pierce says. “It’s really about helping every child reach their full potential.”
With growing interest in refining autism diagnosis and intervention strategies, this study signals a new direction—one where early detection focuses less on gender and more on individual developmental trajectories.
Journal Reference:
- Nazari, S., Ramos Cabo, S., Nalabolu, S. et al. Large-scale examination of early-age sex differences in neurotypical toddlers and those with autism spectrum disorder or other developmental conditions. Nat Hum Behav (2025).DOI: 10.1038/s41562-025-02132-6
