Individuals who were bullied by their siblings during childhood could be up to three times more likely to develop psychotic disorders such as schizophrenia in early adulthood, says new research.The study found that the more often children are involved in sibling bullying -- as victim or perpetrator -- the more likely they are to develop a psychotic disorder."Bullying by siblings has been until recently widely ignored as a trauma that may lead to serious mental health problems such as psychotic disorder," said Dieter Wolke, Professor at the University of Warwick in Coventry, the UK."Children spend substantial time with their siblings in the confinement of their family home and if bullied and excluded, this can lead to social defeat and self-blame and serious mental health disorder -- as shown here for the first time," Wolke added.Further, children who are victimised both at home and by school peers are even worse off, being four times more likely to develop psychotic disorders than those not involved in bullying at all.For the study, published in the journal Psychological Medicine, 3,600 children completed a detailed questionnaire on sibling bullying at 12 years of age, and then subsequently filled out a standardised clinical examination assessing psychotic symptoms when they were 18 years old."Although we controlled for many pre-existing mental health and social factors, it cannot be excluded that the social relationship problems may be early signs of developing serious mental health problems rather than their cause," said Slava Dantchev, researcher at the varsity.