A Study of the Behavioral Variant of Frontotemporal Dementia and Bipolar Disorder: a Neuroimaging and Epigenetics Integrated Approach

Following the inclusion and exclusion criteria, the participants will be recruited and subdivided into three groups:

• bvFTD patients, followed prospectively for at least 2 years. These include bvFTD carriers of G4C2 expansion in the C9orf72 gene (best model of the two diseases because such expansion is widely associated with the development of psychosis)
• BD patients who are part of a cohort of multi affected families (MAF) followed since January 2017 at the Psychiatry Operating Unit of the Policlinico di Milano and who have positive family history of neurodegenerative diseases.
• Healthy subjects who underwent neurocognitive tests at baseline that excluded the presence of dementia and psychiatric diseases.

The investigators will be collecting participants blood samples, which will be processed and analyzed. More specifically, total exosomes will be isolated from 500 microliters of plasma by ExoQuick precipitation solution (SBI). Isolation and purification of NDEs will be performed by ExoFlow purification kit using biotinylated anti-human CD171 (L1CAM) antibody (clone 5G3, Ebiosciences). Total RNA contained in NDEs will be extracted by Total Exosome RNA and Protein Isolation Kit and miRNA expression analysis by TaqMan OpenArray Human Advanced MicroRNA Panel (Thermo Fisher Scientific). Expression analysis of lncRNAs will be conducted by LincFinder Array and inflammatory and autoimmunity arrays (Qiagen).

The participants will also undergo a neuroimaging session, where structural MRI and 1H-MRS sessions will be performed using a 3T MRI scanner available at the Neuroradiology Unit. The 1H-MRS will provide sensitive and reliable assessment of neurochemical changes in specific brain areas. The acquisition voxels will be palced in the dorso- and ventrolateral prefrontal cortex (DLPFC/VLPFC), amygdala, and hippocampus. Finally, an FDG-PET scan will be performed with a Biograph Truepoint 64 PET/TC scanner. T1-weighted and FDG-PET images will be used to explore brain morphological/metabolic differences between the groups. Gray matter and white matter volumes will be estimated locally and compared between groups using voxel-based morphometry. A parallel region of interest comparison (ROIs) will be performed to estimate regional volumes using the Automated Anatomical Labelling (AAL) atlas as a reference, again focusing on the DLPFC/VLPFC, amygdala and hippocampus. Finally, an additional regional analysis based on Freesurfer software will allow the investigators to estimate the cortical thickness, cortical surface area, and cortical gyrification of the Desikan-Killiany atlas regions. All MRI and PET analyses will be performed in the context of a general linear model using a specific software implementation in MATLAB called Statistical Parametric Mapping (SPM).

Lastly, neuroimaging data and ncRNA expression profiles will be used as predictors in the ML analysis. Given the small sample size, initially linear models (e.g., Support Vector Machine) will be used. Later, to improve the predictive power of our models, the investigators will apply the ML method called random forest, a more versatile and powerful classification algorithm, and the XGBoost (eXtreme Gradient Boosting) algorithm. To avoid overfitting of the learning process, a "grid" search of model hyperparameters will be performed. A 5-fold cross-validation will be used to validate the results, with a split between training-tests of 80%-20%.

Inclusion criteria

• byFTD group: patients of either sex; 18 years of age or older; diagnosis of behavioral variant Frontotemporal Dementia according to current diagnostic criteria; presence of a signed informed consent.
• BD group: patients of either sex; 18 years of age or older; diagnosis of bipolar disorder according to DSM-V criteria; presence of a signed informed consent.
• HC group: patients of either sex; 18 years of age or older; subjects who have gone through the same diagnostic process as patients under suspicion of a central nervous system and/or psychiatric disorder, resulting in the absence of cognitive deficits and mood disorders; presence of a signed informed consent.

Exclusion criteria

• Diagnosis of Alzheimer's disease
• Comorbidities interfering with the studied condition (e.g. other neurological diseases or history of substance or alcohol abuse)
• Diseases with an inflammatory component (e.g. autoimmune diseases, tumors)
• Pregnancy