A large Danish study has found that widening diagnostic criteria explain much of the sharp increase in autism and ADHD diagnoses over recent decades. Researchers examined genetic data from 140,000 people and concluded there is no evidence of overdiagnosis.
The research, published in JAMA Psychiatry, analyzed polygenic risk scores for 37,000 individuals diagnosed with autism or ADHD between 1994 and 2016. Those diagnosed more recently showed significantly lower genetic risk scores than earlier groups, indicating that milder cases are now being identified.
Sonja LaBianca of Copenhagen University Hospital said the findings point to a lowered diagnostic threshold rather than environmental changes or overdiagnosis. Even the lowest-risk individuals still carried more variants than neurotypical controls.
The study also ruled out shifts from other mental health diagnoses as a primary factor. Tinca Polderman of Vrije University Amsterdam noted that genetics alone cannot fully separate from environmental influences.
Diagnoses of both conditions have increased up to tenfold worldwide in the past 20 years, especially among girls and adults.
