Schizophrenia and microbiota: has the link been confirmed?

Many studies now confirm the existence of a correlation between gut dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) and schizophrenia based on known factors: the risk of developing the disease is 10 to 20 times higher when there was a prenatal infection; frequent gastrointestinal disorders associated with a dysbiosis in schizophrenic patients; as well as disruptions in the neurological, immune and hormonal systems, whose maturation is closely linked to the gut flora. Chinese researchers have thus compared the microbiota of healthy individuals to that of schizophrenic patients, before transferring imbalanced “schizophrenic” flora into microbiota-free mice.

The microbiota is related to the disease and its severity

The microbiota of schizophrenic patients is not only less abundant and less diverse, but there is also a predominance of 23 species (out of the 77 that have been identified); and the remaining 54 are underrepresented. This dysbiosis is specific to schizophrenia according to the authors, who have also identified a bacterial signature made up by 5 families. This signature is able to discriminate between healthy individuals and schizophrenic patients and it is different from the signature found in other psychiatric disorders (such as depression). Moreover, two large bacterial groups could be specifically correlated to the severity of schizophrenic symptoms.

Microbiota transplant and disease onset

Schizophrenia seems to be transferable to healthy microbiota-free mice through a gut microbiota transplant: the bacterial signature of human donors is found in recipient rodents who started to present behavior proper to schizophrenia: hyperactivity, decreased anxiety and depression. Abnormal variations in some neurotransmitter levels (chemical substances that allow neurons to send messages) were also observed, thus indicating that the gut-brain communication is altered. Researchers concluded that gut dysbiosis could play a role in the development of schizophrenia through this pathway. This discovery opens the way to new potential diagnostic and therapeutic strategies.