medwireNews: Researchers have applied a frailty model to schizophrenia and identified patterns of susceptibility for the disorder as well as ages at diagnosis for which certain early risk factors are of importance.
"One advantage of frailty modeling is that it estimates the liable subpopulations; our estimations suggest that about 5% of the population without familial schizophrenia are susceptible to the disease, while the corresponding figure for those with familial schizophrenia is more than 3-fold higher (18%)," say Elisabeth Svensson (Norwegian Institute of Public Health, Oslo) and colleagues.
"This suggests that the 'frail' part of the population will acquire the disease with advancing age, while the remainder of the population will stay at low risk of the disease."
A total of 15,340 individuals aged 18 to 45 years and diagnosed with schizophrenia between 1974 and 2008 participated in the study. Of these, 856 had familial schizophrenia, defined as having a sibling with the disorder. Chosen for being well-documented environmental risk factors for schizophrenia, covariates included in the frailty model were gender, birth cohort, paternal age, and place of birth.
As reported in Schizophrenia Research, Svensson and team found that for individuals without familial schizophrenia, a significant protective effect was seen for being female compared with male; born to a father younger than 40 years compared with older; born in rural rather than urban areas; and being born in later birth cohorts compared with between 1955 and 1964.
Only seasonality of birth was found to have no effect on schizophrenia susceptibility.
For participants with familial schizophrenia, the significantly protective factors were being female compared with male for individuals aged between 18 and 30 years, being born in rural areas compared with urban for most ages, and for being born in later rather than earlier birth cohorts.
A lower incidence of schizophrenia was also seen for individuals born to fathers younger than 40 years, but only for those diagnosed between the ages of 18 and 25 years.
"We have shown that it is possible to model the development of schizophrenia in the Swedish population using a frailty model, based on large heterogeneity in risk between individuals, implying that the population may be divided into high- and low-susceptible groups," the researchers comment.
medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013