Study reveals genetic and developmental differences in people with earlier versus later autism diagnosis

Good news! Autism is more complicated and dependent on age!

"... The scientists say that the findings challenge the long-held assumption that autism is a single condition with a unified underlying cause. ...

study analysed behavioural data across childhood and adolescence from the UK and Australia, and genetic data from over 45,000 autistic individuals across several large cohorts in Europe and the US. ...

Scientists ... found that children diagnosed as autistic earlier in life (typically before six years old) were more likely to show behavioural difficulties from early childhood, such as problems with social interaction.

However, those diagnosed with autism later on in life (in late childhood or beyond) were more likely to experience social and behavioural difficulties during adolescence. They also had an increased likelihood of mental health conditions such as depression. ...

They found that the underlying genetic profiles differed between those diagnosed with autism earlier and later in life, with only a modest overlap. In fact, the average genetic profile of later-diagnosed autism is closer to that of ADHD, as well as to mental health conditions like depression and PTSD, than it is to autism diagnosed in early childhood. ...

“The term ‘autism’ likely describes multiple conditions,” ..."

From the abstract:

"Although autism has historically been conceptualized as a condition that emerges in early childhood, many autistic people are diagnosed later in life. It is unknown whether earlier- and later-diagnosed autism have different developmental trajectories and genetic profiles.

Using longitudinal data from four independent birth cohorts, we demonstrate that two different socioemotional and behavioural trajectories are associated with age at diagnosis.

In independent cohorts of autistic individuals, common genetic variants account for approximately 11% of the variance in age at autism diagnosis, similar to the contribution of individual sociodemographic and clinical factors, which typically explain less than 15% of this variance. We further demonstrate that the polygenic architecture of autism can be broken down into two modestly genetically correlated (rg = 0.38, s.e. = 0.07) autism polygenic factors. One of these factors is associated with earlier autism diagnosis and lower social and communication abilities in early childhood, but is only moderately genetically correlated with attention deficit–hyperactivity disorder (ADHD) and mental-health conditions.

Conversely, the second factor is associated with later autism diagnosis and increased socioemotional and behavioural difficulties in adolescence, and has moderate to high positive genetic correlations with ADHD and mental-health conditions.

These findings indicate that earlier- and later-diagnosed autism have different developmental trajectories and genetic profiles. Our findings have important implications for how we conceptualize autism and provide a model to explain some of the diversity found in autism."

Study reveals genetic and developmental differences in people with earlier versus later autism diagnosis | University of Cambridge "Researchers find different genetic profiles related to two trajectories that autistic children tend to follow. One linked to early diagnosis, and communication difficulties in infancy. The other linked to later diagnosis, increased social and behavioural difficulties in adolescence, and higher rates of conditions like ADHD, depression, and PTSD."

Polygenic and developmental profiles of autism differ by age at diagnosis (open access)

Fig. 4: Two genetic latent factors in autism.