Genetic basis of complex traits in schizophrenia

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Twin and family studies show schizophrenia has a genetic basis. Attempts to find and characterise the underlying genes have not been successful so far. A main reason for this is that insufficient attention has been paid to the complexity of the underlying genetic architecture of the disorder. The pathway from genes to symptoms of schizophrenia is likely to involve elementary processes at neuronal and neural circuitry levels that vary between individuals and this variation is reflected in a graded susceptibility to schizophrenia. During the last three years we have recruited a large number of families with at least one family member diagnosed with schizophrenia. The proband and all participating first-degree relatives have been assessed with a neurocognitive test battery including measures of sustained attention, working memory, speed of information processing, auditory verbal learning and executive function. Analysis of the neurocognitive data on this sample produced strong evidence that several measures are altered in patients with schizophrenia and a proportion of their asymptomatic first-degree relatives compared to unrelated normal controls. In the study we will systematically search the human genome for DNA markers linked to these measures. This will set the stage for the systematic search and characterisation of the underlying genes. This will allow us to better understand the predisposition to develop schizophrenia. In the individual case it is likely that this vulnerability results from a high-risk combination of a number of relatively common alleles which contribute to basic neural processes.