Children normally experience flights of fancy, including imaginary friends and conversations with stuffed animals, but some of them are also having hallucinations and delusions which might be the early signs of psychosis.
A study of British 12-year-olds that asked whether they had ever seen things or heard voices that weren't really there, and then asked careful follow-up questions, has found that nearly 6 percent may be showing at least one definite symptom of psychosis.
The children who exhibited these symptoms had many of the same risk factors that are known to correlate with adult schizophrenia, including genetic, social, neurodevelopmental, home-rearing and behavioural risks.
"We don't want to be unduly alarmist, but this is also not something to dismiss," said co-author Terrie Moffitt.
The children were participants in the long-term Environmental Risk Longitudinal Twin Study in Britain, which includes 2,232 children who have been tracked since age 5 and reassessed at 7, 10 and 12.
The British study is an outgrowth of research that the same group did earlier with a long-term cohort in Dunedin, New Zealand. At age 11, those children were asked about psychotic symptoms, but the researchers waited 15 years to see how, as adults, their symptoms matched what they reported at 11. By age 26, half of the people who self-reported symptoms at age 11 were found to be psychotic as adults.
"It looks like a non-trivial minority of children report these symptoms," said co-author Avshalom Caspi.
The findings provide more clues to the development of schizophrenia, but don't solve any questions by themselves, said co-author Richard Keefe.
Schizophrenia often goes undetected until adolescence, when the first overt symptoms - antisocial behaviour, self-harm, delusions - begin to manifest in an obvious way. But nobody knows whether the disease is triggered by the process of adolescence itself, or brain development or hormone changes. "It's my impression that all of those things interact," Keefe said.
Psychotic symptoms in childhood also can be a marker of impaired developmental processes, and are something caregivers should look for, Moffitt said. "There is not much you can do except monitoring and surveillance," Moffitt said. "But we feel we should be alerting clinicians that there's a minority to pay attention to."
While the incidence of psychotic symptoms in this study was around 5 or 6 percent, the adult incidence of schizophrenia is believed to be about 1 percent, Keefe added. There are some recent findings however, that many more people experience hallucinations and delusions without being diagnosed as psychotic, he said.
Polanczyk G, Moffitt TE, Arseneault L, Cannon M, Ambler A, Keefe RS, Houts
R, Odgers CL, Caspi A.
Etiological and clinical features of childhood psychotic symptoms: results
from a birth cohort.
Arch Gen Psychiatry. 2010 Apr;67(4):328-38.