Gray matter deficits in bipolar disorder are associated with genetic variability at interleukin-1 beta gene (2q13).

Twin, family and recent molecular studies support the hypothesis of genetic overlapping between schizophrenia and bipolar disorder. Brain structural features shared by both psychiatric disorders might be the phenotypic expression of a common genetic risk background. Interleukin-1 (IL-1) cluster (chromosome 2q13) genetic variability, previously associated with an increased risk both for schizophrenia and for bipolar disorder, has been also associated with gray matter (GM) deficits, ventricular enlargement and hypoactivity of prefrontal cortex in schizophrenia. The aim of the present study was to analyze the influence of IL-1 cluster on brain morphology in bipolar disorder. Genetic variability at IL-1B and IL-1RN genes was analyzed in 20 DSM-IV (Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition) bipolar patients. Magnetic resonance imaging (MRI) measurements were obtained for whole-brain GM and white matter, dorsolateral prefrontal cortex (DLPFC), superior temporal gyrus, hippocampus and lateral ventricles. MRI data were corrected for age and cranial size using regression parameters from a group of 45 healthy subjects. A -511C/T polymorphism (rs16944) of IL-1B gene was associated with whole-brain GM deficits (P = 0.031) and left DLPFCGM deficits (P = 0.047) in bipolar disorder patients. These findings support the hypothesis of IL-1 cluster variability as a shared genetic risk factor contributing to GM deficits both in bipolar disorder and in schizophrenia. Independent replication in larger samples would be of interest to confirm these results.