Relationship between negative symptoms and plasma levels of insulin-like growth factor 1 in first-episode schizophrenia and bipolar disorder patients.

Previous studies have suggested that insulin-like growth factor-1 (IGF-1) is altered in schizophrenia. The objective of this study was to investigate whether plasma IGF-1 levels were altered at the onset of psychiatric disorders such as schizophrenia or bipolar disorder. We focused at the first psychotic episode (FPE) and during 1-year follow-up. We also studied if IGF-1 levels were related to clinical symptoms. 50 patients and 43 healthy controls matched by age, gender and educational level were selected from the Basque Country catchment area in Spain. Plasma IGF-1 levels were measured at FPE and 1 month, 6 months and one year later. Patient symptoms were assessed at the same disease stages using the Positive and Negative Symptoms Scale (PANSS), the Global Assessment of Functioning (GAF), the Hamilton Depression Rating Scale (HDRS21) and the Young Mania Rating Scale (YMRS). A statistically significant increase in the plasma levels of IGF-1 was found in the whole cohort of patients one month after FPE compared to matched controls (219.84 ng/ml vs 164.15 ng/ml; p=0.014), as well as in schizophrenia patients alone at that stage (237.60 ng/ml vs 171.60 ng/ml; p=0.039). In turn, negative symptoms in both groups of patients were positively correlated with IGF-1 levels both at FPE (β=0.521; p<0.001) and after 1 year (β=0.659; p=0.001), being patients diagnosed with schizophrenia the main contributors to this relationship. These results indicate that there is a significant change in the plasma levels of IGF-1 at the initial stages of schizophrenia but not in bipolar disorder, and suggest that IGF-1 could have role in the pathophysiology of negative symptoms.