Schizophrenia: a disease of the brain?

Scientists in China have unearthed further evidence that a malfunction of the immune system contributes to the development of schizophrenia.

Schizophrenia is a severe mental illness, which affects around 1% of the world’s population. It is traditionally thought to be exclusively caused by problems in the brain. However, there is a growing body of evidence that suggests that the immune system has an important role to play.

Lin He and Chunling Wan from Shanghai Jiao Tong University, and their colleagues, identified over 1300 proteins in the blood and then compared the blood of schizophrenic patients with healthy blood using mass spectrometry. They found that 27 proteins were different in the schizophrenic patients and that all of these proteins were involved in the complement system.

The complement system is a system of proteins in the blood that are part of signalling pathways in which each molecule activates the next, ‘complementing’ – or enhancing – the body’s immune response. There are three main signalling pathways in the system, which are activated in different ways and involve different molecules. One such pathway is the alternative pathway.

The team backed up their study by showing that the alternative pathway is suppressed in schizophrenic patients. And Yang Li, a member of the team, says that ‘further statistical and bioinformatics analysis indicated that a malfunction of the complement system may be involved in schizophrenia’.

David St Clair, an expert in the causes of schizophrenia at the University of Aberdeen, UK, thinks that the study is interesting and scientifically sound, but that ‘the findings need replicating, preferably in cerebrospinal fluid from patients’.

Li is cautious about the work’s impact. ‘We can’t determine whether the alteration of complement pathways is a cause or effect of schizophrenia. The role of complement proteins in the development of the central nervous system also needs further exploration. That’s our future research work,’ he says.