Type I IFN is produced by cells in response to an intracellular viral infection, blocking reinfection of the virus. Multiple forms of IFN exist, evidenced by the 17 genes located on chromosome 9p. A significant factor of the cellular antiviral response induced by type I IFN, is the expression of interferon stimulated genes (ISGs). A multitude of ISGs have been identified and their relation to interferon signatures has been published numerous times. However, there is little information about the genes products of ISGs and their antiviral properties, signaling cascades and specificity. 

ISG Expression & Type I IFN Signaling

Patients with mutations in one of these genes referenced produced a reportable type I IFN signature, suggesting a strong relationship between these genotypes and IFN. 

Mutations in TREX1, RNASEH2, SAMHD1 and ADAR

7 of the 8 patients presenting with negative IS were positive in mutations of RNASEH2B and 98% of patients with mutations in other AGS related genes had positive IS. Additionally, a lower morbidity and mortality rate is associated with RNASEH2B positive patients compared to the other tested genotypes. 

Mutations in RNASEH2B

- Correlation between IFN score and age
- Repeat Testing Yields Similar Results

Age Correlation & Precision of Repeat Testing

The discussion section of the study assessing interferon-related biomarkers in Aicardi-Goutières syndrome (AGS) focuses on interferon-stimulated gene (ISG) expression and type I IFN signaling, the implications of mutations in relevant genes (such as TREX1, RNASEH2, SAMHD1, ADAR, and RNASEH2B), and the correlation between the interferon score and patient age.

Tulane University

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This paper, authored by Yanick J. Crowe, measures the ability of an interferon signature  to serve as a diagnostic tool for type I interferonopathies, including AGS. 
- Methods
- Results
- Discussion
- Significance

Assessment of Interferon Related Biomarkers in AGS

Rice GI, Forte GM, Szynkiewicz M, Chase DS, Aeby A, Abdel-Hamid MS, Ackroyd S, Allcock R, Bailey KM, Balottin U, Barnerias C, Bernard G, Bodemer C, Botella MP, Cereda C, Chandler KE, Dabydeen L, Dale RC, De Laet C, De Goede CG, Del Toro M, Effat L, Enamorado NN, Fazzi E, Gener B, Haldre M, Lin JP, Livingston JH, Lourenco CM, Marques W Jr, Oades P, Peterson P, Rasmussen M, Roubertie A, Schmidt JL, Shalev SA, Simon R, Spiegel R, Swoboda KJ, Temtamy SA, Vassallo G, Vilain CN, Vogt J, Wermenbol V, Whitehouse WP, Soler D, Olivieri I, Orcesi S, Aglan MS, Zaki MS, Abdel-Salam GM, Vanderver A, Kisand K, Rozenberg F, Lebon P, Crow YJ. Assessment of interferon-related biomarkers in Aicardi-Goutières syndrome associated with mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, and ADAR: a case-control study. Lancet Neurol. 2013 Dec;12(12):1159-69. doi: 10.1016/S1474-4422(13)70258-8. Epub 2013 Oct 30. PMID: 24183309; PMCID: PMC4349523.

Assessment of interferon-related biomarkers in Aicardi-Goutières syndrome associated with mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, and ADAR: a case-control study

AGS is a debilitating inflammatory disease characterized by a high morbidity and mortality rate, warranting the immediate development of therapeutics and diagnostic tools to combat the disease. The results of this paper identify interferon scores as an acceptable biomarker that relates the expression of ISGs to interferon activity and AGS. Mendelian type I interferonpathies can be effectively diagnosed utilizing this signature and the mechanisms of the IFN signaling cascade should be investigated. Similar to autoinflammatory disorders and primary immunodeficiencies, type I interferonopathies may be attributed to errors in the immune system, specifically the stimulation of type I interferon pathways. Additionally, mutations in ISGs may produce defective regulatory proteins that lead to the accumulation of potent type I IFN. Other type I interferonopathies may exist and remain unidentified today. Researchers suggest screening patients with clinical phenotypes involving immunological and neurological characteristics for interferon signatures. Furthermore, whole exome sequencing can be used to isolate specific mutations in target genes and locate more ISGs. 

Significance

The methodology for assessing interferon-related biomarkers in Aicardi-Goutières syndrome (AGS) involves defining a specific sample population with relevant mutations, conducting experimental procedures to measure the fold change of interferon-stimulated genes (ISGs) using RT-PCR, and performing statistical analysis to calculate and compare interferon scores against healthy controls.

Methods for Assessing Interferon-Related Biomarkers in AGS

The case-control study assessing interferon-related biomarkers in Aicardi-Goutières syndrome (AGS) yielded several key findings. An interferon signature was calculated, revealing that a positive interferon score (>$$ 2.466 $$) was recorded in $$ 90 $$ percent of patient samples compared to $$ 7 $$ percent of controls. Additionally, while patients with mutations in interferon-stimulated genes (ISGs) had higher median expression values, there was no clear correlation between the extent of upregulation, genotype, or patient age.

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