A team from Ireland, Finland and Sweden found, in a study of all those born in Helsinki in a 30-year period (1960 to 1990) who had lost a father or sibling between their conception and 5 years of age, that the sudden loss of a father or sibling led to a significantly greater risk of developing bipolar disorder or schizophrenia in adulthood, compared to those who lost a father or sibling to a protracted illness. The team concludes that stress during early development can increase the risk of psychotic illness.
Clarke, M., Tanskanen, A., Huttunen, M., Cannon, M.; Sudden Death of Father or Sibling in Early Childhood Increases Risk for Psychotic Disorder. Schizophrenia Research. Online December 23, 2012