A rare polymorphism affects a mitogen-activated protein kinase site in synapsin III: Possible relationship to schizophrenia

Background: Synapsin III plays a role in neuronal plasticity and maps to chromosome 22q12-13, a region suggested to be linked to schizophrenia. To determine if synapsin III plays a role in this disease, we searched, for polymorphisms in this gene in patients with schizophrenia and controls, Methods: The synapsin III gene was initially sequenced from 10 individuals with schizophrenia to identify polymorphisms. Association analysis was then performed using 118 individuals with schizophrenia and 330 population controls. Synapsin III expression was studied by immunoblot analyses, and phosphorylation sites were mapped by sequencing trypsin-digested synapsin X fragments phosphorylated with phosphorus-32. Results: A rare, missense polymorphism, S470N, was identified in the synapsin III gene and appeared more frequently in individuals with schizophrenia than in controls (p = .0048). The site affected by the polymorphism, Ser470, was determined to be a substrate for mitogen-activated protein kinase, a downstream effector of neurotropbin action. Phosphorylation at Ser470 was increased during neonatal development and in response to neurotropbin-3 in cultured hippocampal neurons. Conclusions. Our observations suggest an association of a rare polymorphism in synapsin III with schizophrenia, but further studies will be required to clarify its role in this disease.