Depression and psychiatric co morbidities were found to be important in some studies, although others found that the co-existence of mental illness failed to fully explain the QoL differentials in those with and without hepatitis C. While several studies found little association between QoL and ALT or liver fibrosis in clinic populations, advanced liver disease did appear to be closely correlated with reduced QoL in hepatitis C. Here, GPT is linked to major depressive disorder.