The neurodevelopmental nature of attention-deficit hyperacti
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Population studies have suggested that most adults with attention-deficit hyperactivity disorder (ADHD) did not have the disorder in childhood, challenging the neurodevelopmental conceptualisation of ADHD. Arbitrary definitions of age at onset and lack of defined trajectories were accounted for the findings.

The objective of this study was to assess the proportion of individuals presenting with either a neurodevelopmental trajectory or late-onset disorder, and to assess risk factors associated with them.

Data of 4676 individuals from the 1993 Pelotas birth cohort at 11, 15, 18 and 22 years of age were used. Polythetic and latent class mixed model analysis were performed to define ADHD trajectories from childhood to adulthood, and characterise the neurodevelopmental or late-onset courses. Regression models were applied to assess factors associated with different trajectories.

Classical polythetic analysis showed that 67% of those with ADHD at 22 years of age had a neurodevelopmental course of the disorder. Latent class mixed model analysis indicated that 78% of adults with ADHD had a trajectory of persistent symptoms, more common in males. The remaining adults with ADHD had an ascending symptom trajectory that occurred after puberty, with late-onset ADHD associated with female gender and higher IQ.

Conclusively, both polythetic and latent trajectories analysis provided empirical evidence supporting that the large majority of adults with ADHD had a neurodevelopmental disorder.