A more recent study by Kheir et al (2018) in patients with total hip/knee arthroplasty and schizophrenia/bipolar disorders proved that these patients have higher rate of periprosthetic joint infection, due to defective immune status caused by chronic psychiatric disorders leading to increased level of inflammatory cytokines such as interleukin-6, tumour necrosis factor alpha, and interferon gamma. This evidence concerns the gene IL6 and schizophrenia.