Altered gene expression profiles impair the nervous system development in patients with 15q13.3 microdeletion

Background: The 15q13.3 microdeletion has pleiotropic effects ranging from apparently healthy to severely affected individuals with intellectual disability, epilepsy, and neuropsychiatric disorders. Previous studies have investigated several genes within the deletion as potential drivers, but the pathomechanism and the underlying basis of the variable phenotype remain elusive. Methods: We analyzed the effects of the 15q13.3 microdeletion on genome-wide gene expression using native RNA-seq data from blood of 3 probands with the 15q13.3 microdeletion and 4 sex- and age-matched control subjects. We assessed differentially expressed genes (DEGs), gene ontology (GO) enrichment, protein-protein interaction (PPI) functional modules, as well as gene expression in different brain developmental stages. Results: The haploinsufficiency of genes within the deleted region was not transcriptionally compensated, suggesting that a dosage effect may contribute to the pathomechanism. Although GO and PPI showed that regulation of gene expression is perturbed, we could not identify a singular driving transcription factor. We observed network-wide dysregulatory effects suggesting that the phenotype is not caused by a singular critical gene. A significant proportion of DEGs, which are silenced in the adult brain, have maximum expression during the prenatal stage of brain development. Based on DEGs and their PPI partners we identified altered functional modules related to immune and inflammatory processes, as well as nervous system development. Conclusions: We show that the 15q13.3 microdeletion has a ubiquitous impact on transcriptome pattern, especially dysregulation of genes involved in brain development. The effect on immune and inflammatory responses cannot be fully assessed based on the test material, i.e. blood. Possibly, the high phenotypic variability seen in 15q13.3 microdeletion could stem from an increased vulnerability during brain development, instead of a specific pathomechanism. Overall design: RNAseq data of whole blood samples from three 15q13.3 microdeletion patients and four controls