Children as young as four, who show a continuous decline in their intelligent quotient (IQ) levels could be at higher risk of developing psychotic disorders such as schizophrenia and other mental illnesses in adulthood, finds a study.

The researchers found that those who developed psychotic disorders as adults had normal IQ scores in infancy, but by age of four, their IQ levels had started to decline. It continued to drop throughout childhood, adolescence and early adulthood until they were an average of 15 points lower than their healthy peers. Besides low IQ level, these kids also lag behind their peers in cognitive abilities such as working memory, processing speed and attention along with abnormalities in perception and thinking.

"For individuals with psychotic disorders, cognitive decline does not just begin in adulthood, when individuals start to experience symptoms such as hallucinations and delusions, but rather many years prior -- when difficulties with intellectual tasks first emerge -- and worsen over time," said Josephine Mollon, researcher at the King's College in London.

"Our results suggest that among adults with a psychotic disorder, the first signs of cognitive decline are apparent as early as age four," Mollon added. However, not all children struggling at school are at risk of developing serious psychiatric disorders, the researchers said in a paper, published in the journal JAMA Psychiatry.

Early interventions to improve cognitive abilities may potentially help stave off psychotic symptoms from developing in later life. "There are early interventions offered to adolescents and young adults with psychosis," said Abraham Reichenberg, Professor at the varsity.

"Our results show the potential importance of interventions happening much earlier in life. Intervening in childhood or early adolescence may prevent cognitive abilities from worsening and this may even delay or prevent illness onset," Reichenberg added. For the study, the researchers included 4,322 individuals and followed them from 18 months to 20 years of age.