T1IFNs are Mendelian genetic diseases associated with chronically enhanced type I interferon signalling, proposed to be directly relevant to pathogenicity. Through the use of a pipeline for the systematic identification of human mutant genetic states predisposing to upregulated type I interferon signalling, this ERC Advanced Fellowship (running from 11/2018 to 10/2024) has defined multiple new T1IFNs, and further characterised a number of previously described T1IFNs. Notable outputs of the project have included the identification of novel disease-associated Mendelian genotypes due to mutations in the mitochondrial protein ATAD3A, the small GTPase ARF1, the protein tyrosine phosphatase PTP1B, and in components of the replication-dependent histone pre-mRNA processing complex. In this way, the project has highlighted the importance of mitochondrial nucleic acid, intracellular trafficking of the adaptor protein STING, and chromatin modification of genomic DNA in the maintenance of cellular immunological homeostasis. Further, the project has made step-change contributions to the development of rational therapeutic approaches to the treatment of the T1IFNs, most particularly through studies on the JAK1/2 inhibitors ruxolitinib and baricitinib, and the use of reverse transcriptase inhibitors.