Gene and pathway associations in neurodevelopmental disorders

Neurodevelopmental disorders are complex and heterogenous disorders affecting brain development. In this thesis, we study intellectual disability (ID) and schizophrenia, and we applied genomic, transcriptomic, and proteomic techniques to identify and further investigate candidate variants and important genes and pathways involved in pathology of these two disorders. In paper I, genotyping and exome analyses were performed in a large multi-generational family with non-syndromic ID from a North Swedish isolate, with the aim to identify linkage regions and disease-associated variants. The linkage analysis identified four suggestive linkage regions. The exome sequencing revealed a known pathogenic mutation in the SLC17A5 gene, and potential pathogenic CNVs overlapping the genes KDM3B and MAP3K4/AGPAT4. The overall results indicated that ID is genetically heterogeneous in this family. In paper II, transcriptome sequencing was performed on fibroblast cells from schizophrenia patients and control individuals from a large family in a genetically isolated region in northern Sweden. We detected 48 significant differentially expressed genes, of which eight genes were previously associated with schizophrenia. These results provide further support for the use of fibroblasts, and highlight benefit of using isolated populations in studies of neurodevelopmental disorders. In paper III, transcriptome sequencing was performed on a large cohort of post-mortem brain tissue samples from schizophrenia patients and controls. In total, 71 significant differentially expressed genes were detected, and gene ontology analysis showed enrichment of genes from the immune system and more specifically the complement system. Our results implicate significant upregulation of complement genes in a subset of the patients. In paper IV, we performed further proteomic analysis on the same sample set as paper III. The primary results from proximity extension assays show significant differential expression of schizophrenia-associated proteins in a subgroup of patients. In total, 21 differentially expressed proteins were identified by the immune panel, 12 proteins by the inflammation panel, and two by the custom panel. The protein IL6 was included in all three panels and consistently showed significant expression changes. Our transcriptome and proteome results highlight the important role of immune system in schizophrenia pathology