Lay Summary

We explored differences in head circumference in those with autism, subclinical autism, and psychotic experience groups to a control group over 13 timepoints. Autism was associated with increased head circumference at birth compared to controls, whereas psychotic experiences were associated with reduced volume at age 7 years. Head circumference measures offer a proxy of typical vs atypical brain development and such trajectories have not previously been studied in psychotic experience groups.

Background

Early brain overgrowth is a replicated neurophenotype associated with autism while psychotic disorders are more commonly associated with attenuated volumes. Head circumference, which can be used as a proxy measure for brain development, may offer insights into distinct neurobiological trajectories in these two disorders which have previously shown overlap in genetics and negative symptomology. We hypothesize that autism will be associated with increased head circumference, particularly during early childhood, while the presence of psychotic experiences will be associated with reduced head circumference compared to controls.

Methods

Head circumference measurements were collected in the ALSPAC birth cohort at birth and ages 7 and 15 years in over 3000 participants, as well as smaller focus groups of ~ 700 participants at an additional 10 timepoints. Autism diagnosis was assessed using maternal questionnaires at age 9 years and NHS linkage data. Psychotic experiences were assessed using the Psychosis Like Experiences Semi-Structured Interview at age 18 years. Analyses of covariances assessed group differences in head circumference.

Results

Autism was associated with significantly larger head circumference compared to controls at birth (F(1:5929) = 4.8, p = 0.03) and a similar trend at age 7 years (p = 0.07), with no difference at age 15 (p = 0.29). In contrast, psychotic experiences were associated with a trend towards reduced head circumference at birth (p = 0.06) and a significant reduction at age 7 compared to controls in a dose-dependent manner of severity (F(3:4027) = 3.58, p = 0.01). Post-hoc tests revealed significantly smaller head circumference in females with psychotic experiences compared to female controls (p < 0.001), with no significant group differences in males. Additional longitudinal analyses are currently underway.

Conclusion

Differences in childhood head circumference in both autism and schizophrenia compared to healthy volunteers indicates the presence of atypical neurodevelopment. The finding of divergent trajectories across the two disorders suggest that head circumference may act as an early biomarker to distinguish autism from psychotic experiences.