In order to be included in the study, patients needed to have been diagnosed with either biallelic mutations in the mutated genes (found in underlying genomic mutations) or a dominant mutation in TREX1 or ADAR. Control samples were from a diverse population of individuals with no preexisting medical conditions and who were not taking medication during specimen collection. Additionally, data was collected from existing samples in which ISG activity was analyzed. 

Sample Population

The 6 interferon stimulated genes (ISGs) were tested with 9 other ISGs and were selected for this experiment because they were highly expressed and easily differentiated from the controls. The median fold change of the ISGs compared to the median fold change of the control samples was used to construct an interferon score. The experiment included running the samples, the six ISGs and two internal controls, through the RT-PCR to measure the fold change of each ISG. The internal controls were housekeeping genes: HPRT1 and 18S. 

Procedure

Interferon (IFN) scores higher than 2 SD of the mean IFN scores of the controls were denoted as positive IFN signatures. Repeated samples were averaged and the mean value was used to determine the interferon signature. ISG values and interferon scores were plotted logarithmically and analyzed with parametric testing (t tests for two groups and ANOVA for more than 2 groups). Spearman rank correlation was used to compare age and CSF and serum interferon activity. 

Statistical Analysis

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.

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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

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.

Results of Interferon Biomarker Assessment in AGS

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.

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