British scientists have found that people who develop a psychotic disorder by age 18 had, on average, a slightly smaller head circumference in childhood than their peers. The work was published in the journal Psychological Medicine. Psychosis is a condition in which a person loses contact with reality: they may have hallucinations (perceiving things that are not there) and delusions (beliefs that do not correspond to reality).
The researchers analyzed data from the Avon Longitudinal Study of Parents and Children. It followed children born in south-west England between April 1991 and December 1992. The analysis included 3,866 people (2,177 girls and 1,689 boys) who had complete data and at least one head circumference measurement before age 15. On average, there were about eight such measurements per child.
When the participants were 17-18 years old, psychologists conducted structured interviews with them to assess whether they had experienced hallucinations, delusions or a sense of interference with thoughts since age 12. In 339 people (8.8% of the sample), a definite psychotic experience was identified. Of these, 62 (1.6%) met the criteria for a psychotic disorder: symptoms occurred at least once a month for six months and caused severe distress or disrupted social or working life. The remaining 3,527 participants formed the control group.
It turned out that adolescents with psychotic disorder had a head circumference on average 0.26 cm smaller than the control group throughout the period from birth to age 15. The gap did not increase or decrease with age. After adjustment for the mother's education and her body mass index before pregnancy, the difference persisted. When gestational age and birth weight were additionally taken into account, the difference shrank to 0.20 cm and was no longer statistically significant.
Among girls with milder psychotic experience (without a full disorder), head circumference was also smaller than among peers without such experience, on average by 0.27 cm. Among boys with psychotic experience, the picture was the opposite: overall their heads were on average 0.35 cm larger than those of boys in the control group. However, at birth they were smaller, and by ages 7 and 15 they were larger.
However, when the child's height at different periods was added to the statistical model, the differences in head circumference between the psychotic disorder group and the control group smoothed out and ceased to be significant. The same happened among girls with psychotic experience. This suggests that the smaller head circumference in these cases reflects a general slowing of physical growth rather than a problem specifically with brain growth.
The authors emphasize that these are differences between groups, not a prediction for an individual person. "We would not want a smaller head circumference to be perceived as a sign that a person will develop psychosis," said co-author Kate Merritt. According to her, the risk of psychosis is influenced by many factors, and head circumference must be considered together with other indicators.
The study has limitations. Measurements were not taken for all children at every age, so growth trajectories were modeled statistically. Psychotic disorder was determined by research interviews, not by a doctor's clinical diagnosis. In addition, there were only 62 people in the disorder group, of whom only 13 were boys, so conclusions about sex differences in this group require caution.