OBJECTIVES: Since there are clear indications that schizophrenia is a systemic disorder, we sought for a common molecular basis for schizophrenia abnormalities in brain and body. Our hypothesis was that an impaired insulin/ insulin-like growth factor signalling in cells might underlie both structural and functional brain changes and peripheral abnormalities in schizophrenia. No associations between polymorphisms in the genes for insulin-like growth factor 1 or its receptor and schizophrenia have been reported. However, the insulin receptor substrates 1-4 linking both the insulin and insulin-like growth factor 1 receptors with intracellular pathways have not been extensively studied in schizophrenia. In this study, we therefore chose to study the insulin receptor substrate-4 (IRS-4) gene as a candidate gene in schizophrenia.
METHODS: The IRS-4 gene of 93 patients and 59 control subjects was screened for DNA sequence variations, followed by case-control analyses of 10 detected single nucleotide polymorphisms.
RESULTS: No significant genotype, allele or haplotype associations were found with the schizophrenia illness. However, one female patient with paranoid schizophrenia had an IRS-4 gene mutation at position 107863596, resulting in a change in amino acid coding from histidine to tyrosine at position 879.
CONCLUSIONS: Although this study supports the view that the IRS-4 gene is not of major importance for the aetiology of the vast majority of schizophrenia cases, our finding of this single patient with schizophrenia and a mutation in the IRS-4 gene may point to that the insulin/ insulin-like growth factor signalling system in cells is still of interest in the future search for schizophrenia genes.