2024-08-18 04:00:08
How to assess the risk of psychosis in an individual? In psychiatry, the identification of predictive markers is a major research issue.
By working on a cohort of patients carrying the microdeletion of the 22q11.2DS gene – an anomaly promoting psychotic disorders – a team from the University of Geneva (UNIGE), within the framework of the Synapsy Center for Research in Neuroscience for the mental healthshows that these people present a “coupling” between the structure and theactivity of their own brain areas.
Some regions of their brain would have lost their optimum coherence during development. They would thus be too much or not enough “coupled”. This specificity opens the way to the identification of reliable risk markers. These results are published in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.
The 22q11.2DS gene microdeletion is the most common genetic deletion. It affects one in 2,000 people and results in the absence of a small sequence of DNA on chromosome 22. It can lead to heart defects and immune dysfunction. It also causes psychotic disorders in adolescence or adulthood in 35% of carriers.
At UNIGE, the team of Stéphan Eliez, professor in the Department of Psychiatry and at the Synapsy Center for Research in Neuroscience for Mental Health at the Faculty of Medicine, has been following a cohort of 300 individuals aged 5 to 34 affected by this microdeletion for twenty years, nearly 40% of whom have developed psychosis. By its size and its longevitythis Geneva cohort constitutes a unique case study in the world. It has enabled the publication of many works.
Atypical brain development from childhood
In a new study, the UNIGE team looked at the development of the “coupling” of brain regions in members of this cohort, from childhood to adulthood. “Our cognitive processes are the result of interactions – of ‘couplings’ – between our different brain regions,” explains Silas Forrer, PhD student in Stephan Eliez’s team and first author of the study. “We wanted to know if, in individuals carrying the microdeletion of the 22q11.2DS gene, less efficient coupling was synonymous with an increased risk of developing psychosis.”
Purple: Coupling too weak in 22q11.2DS patients with psychotic symptoms. Yellow: Coupling too strong in 22q11.2DS patients with psychotic symptoms.
©UNIGE / Eliez
This brain “synchronization”, and in particular its optimization, develops during adolescence and into adulthood. Using magnetic resonance imaging techniques, neuroscientists observed its maturation over a period of twelve years, within the cohort and within a control group. “We found that patients with the microdeletion had a persistent developmental lag since childhood, with regions of hyper- and hypo-coupling in theensemble of the brain,” reveals Silas Forrer. This shift is particularly marked in adolescence in three regions of the brain in 22q11.2DS individuals who have developed schizophrenia: in the frontal cortex, responsible for voluntary motor coordination and language; the cingulate cortex, at the interface of the two hemispheres of the brain, in charge of making certain decisions; and the temporal cortex, the seat of somatosensory functions. We observe hypo-coupling in the first two and hyper-coupling in the third.
Towards the identification of reliable markers
The strong correlation between the developmental shift in the coupling and the 22q11.2DS microdeletion is a significant step towards identifying predictive markers of the disease. “The next step will be to ask how these couplings can constitute an individual ‘fingerprint’ of the brain that can clearly identify whether a individual is more at risk than another of going towards psychosis, or on the contrary, is protected from it,” explains Stephan Eliez, who led this study.
This study, supported by the Swiss National Science Foundation (SNSF), also presents a methodological novelty in combining observations on both the structure (morphology) and function (its efficiency) of the brain, in order to assess the development trajectory of a population in the context of psychiatric illnesses.
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