The timing of an autism diagnosis in children seems to be influenced by genetic factors, which may also affect how the condition progresses.

“This reinforces the notion that autism could be a potentially multifaceted condition,” states Natalie Sauerwald from the Flatiron Institute in New York, who was not involved in this particular research.

Autism is classified as a neurodevelopmental disorder, characterized by challenges with social interactions and restricted behaviors and interests. The World Health Organization estimates that 1 in 127 individuals are diagnosed with autism.

“Our key inquiry was why some individuals are diagnosed with autism later in life?” posits Varun Warrier from Cambridge University.

To explore this, he and his research team gathered data from individuals diagnosed with autism between the ages of 5 and 17. Caregivers filled out a survey regarding their social, emotional, and behavioral growth, which aided the researchers in determining the correlation between these factors and the age of diagnosis.

Previous studies have linked children’s gender and socioeconomic status to the age of diagnosis, with autism being more frequent in boys and those from affluent backgrounds. However, the team’s analysis indicated that these influences were minimal, with “Typically, no single factor accounts for more than 10% of the variance,” Warrier observes.

Contrarily, the researchers discovered that children with autism displayed different developmental trajectories. “Our findings indicate that individuals with autism can be categorized into two broad groups,” Warrier explained. One group faced challenges from an early age that remained relatively constant, while the other group encountered fewer issues during childhood, but faced increased difficulties in later childhood or early adolescence—this represents “anywhere between 10-25% of the diagnosis age for autism.”

Moreover, the study found that differences between these two groups were observable in previously collected DNA samples. Those diagnosed with autism were more prone to have common genetic variations different from those diagnosed later, which accounted for 11% of the variance in autism diagnosis age. However, the researchers lacked the necessary data to identify rare variants or spontaneous mutations beyond inherited ones.

Despite these distinct trajectories, there is no clear separation between them, says Sauerwald. “The overlap between groups likely occurs because they are not entirely distinct,” she remarks. Warrier agrees, describing the categories as “gradients.”

He stresses that neither group should be regarded as having milder or more severe forms of autism. In July, Sauerwald and her team released a study indicating evidence of four moderately different groups whose symptoms, behaviors, and genetics differ.

Warrier’s research team also identified a higher likelihood of genetic mutations linked to other disorders, such as ADHD and PTSD, in children diagnosed later in life. Similarly, Sauerwald’s study found a connection between late autism diagnosis and ADHD. However, the reason for this link remains unclear, says Sauerwald. “The findings related to ADHD are not unexpected,” she comments, particularly concerning specific symptoms.

A deeper understanding of the potential subtypes of autism could ultimately enhance diagnostic practices and offer more personalized support for children with autism and their families. “Improving our understanding of their condition and how to assist them can only lead to a better quality of life for individuals,” asserts Warrier.