ASD and ADHD symptoms in 18-year-olds - A population-based study of twins born 1993 to 2001.

Researchers studied whether autism and ADHD symptoms have actually increased in young people, despite more diagnoses being made. They looked at parent reports of 18-year-olds born from 1993-2001. They found no increase in autism symptoms over time. For ADHD, only girls showed a small increase in symptoms, while boys stayed the same. This suggests the rise in diagnoses might not reflect more severe symptoms in the community.

This population-based twin study examined parent-reported ASD and ADHD symptoms in 18-year-olds born between 1993-2001 to determine if increasing diagnostic rates correspond to increasing symptom levels. The study found no increase in ASD symptoms across birth years at either population mean or high percentile levels. For ADHD, girls showed a small but statistically significant increase in mean symptom scores and prevalence above the 90th percentile, while boys showed no change. These findings suggest that rising clinical diagnoses of ASD and ADHD in adolescents and young adults may not reflect corresponding increases in underlying symptom severity in the general population.

Rising diagnostic rates of ASD and ADHD may reflect improved awareness, diagnostic practices, or help-seeking rather than increased symptom prevalence. Gender differences in ADHD trends warrant attention. Clinicians should consider multiple factors when interpreting diagnostic trends beyond symptom severity alone.

Sample size not reported. Study relies on parent reports which may be subject to bias. Limited to 18-year-olds, may not generalize to other ages. Birth cohort limited to 1993-2001. Unclear methodology details affect interpretation of findings.

The diagnostic prevalences of Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) have increased dramatically over the past two decades in the western world, particularly among teenagers and young adults. Here, we aimed to investigate whether there had been a corresponding increase in parent reported symptoms of ASD and ADHD in a population-based sample of 18-year-old twins born between 1993-2001. Data were collected in the Child and Adolescent Twin Study in Sweden (CATSS), in which parents report on symptoms of ASD and ADHD in connection with their children´s 18birthday. Trends across 9 consecutive birth years in reported symptoms were analyzed as population mean scores and with percentile-based cut-offs using linear and logistic regression methods.

For ASD, there was no increase in the symptom phenotype across the examined birth years, neither at the population mean level nor at or above the 95percentile of the ASD symptom score. For ADHD, there was a small - but statistically significant - increase over time of the population mean ADHD symptom score in girls (regression coefficient: 0.046 (95 % Confidence interval 0.025 - 0.066). p < 0.001), but not in boys. The prevalence at or above the 90percentile of the ADHD symptom score was stable in boys but increased statistically significantly in girls (Odds Ratio: 1.053 (95 % Confidence interval 1.016-1.094). p = 0.005). The rise in clinical diagnoses of ASD and ADHD in the adolescent/young adult population does not seem to be parallelled by a similar increase in ASD and ADHD symptoms.