Characterization of human disease phenotypes associated with mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR, and IFIH1

Crucial Roles of RSAD2/viperin in Immunomodulation, Mitochondrial Metabolism and Autoimmune Diseases

Autoimmune diseases are typically characterized by aberrant activation of immune system that leads to excessive inflammatory reactions and tissue damage. Nevertheless, precise targeted and efficient therapies are limited. Thus, studies into novel therapeutic targets for the management of autoimmune diseases are urgently needed. Radical S-adenosyl methionine domain-containing 2 (RSAD2) is an interferon-stimulated gene (ISG) renowned for the antiviral properties of the protein it encodes, named viperin. An increasing number of studies have underscored the new roles of RSAD2/viperin in immunomodulation and mitochondrial metabolism. Previous studies have shown that there is a complex interplay between RSAD2/vipeirn and mitochondria and that binding of the iron-sulfur (Fe-S) cluster is necessary for the involvement of viperin in mitochondrial metabolism. Viperin influences the proliferation and development of immune cells as well as inflammation via different signaling pathways. However, the function of RSAD2/viperin varies in different studies and a comprehensive overview of this emerging theme is lacking. This review will describe the characteristics of RSAD2/viperin, decipher its function in immunometabolic processes, and clarify the crosstalk between RSAD2/viperin and mitochondria. Furthermore, we emphasize the crucial roles of RSAD2 in autoimmune diseases and its potential application value.

Aicardi-Goutières Syndrome Type 1: A Novel Missense Variant and Review of the Mutational Spectrum

Objectives

Mutations in the TREX1 gene cause Aicardi-Goutières syndrome (AGS) 1, associated with a spectrum of autoimmune and neurodegenerative manifestations. AGS 1, the most severe neonatal type of AGS, is characterized by abnormal neurologic findings, visual inattention, hepatosplenomegaly, thrombocytopenia, skin rash, restlessness, and fever.

Materials & Methods

The present study described two affected siblings from an Iranian family whose phenotypes overlap with intrauterine infections. They had almost similar presentations, including developmental delay, microcephaly, no fix and follow epileptic seizures and the same pattern of brain CT scan involvements. Following clinical and paraclinical assessments, whole-exome sequencing was employed to determine the disease-causing variant, and subsequently, PCR-Sanger sequencing was performed to indicate the segregation pattern of the candidate variant in family members.

Results

Genetic analysis revealed a novel homozygous missense variant (c.461A>C; p.D154A) in the TREX1 gene in affected family members. Sanger sequencing of other family members showed the expected zygosities.

Conclusion

This study identifies a novel mutation in the TREX1 gene in this family and highlights the efficiency of next-generation sequencing-based techniques for obtaining a definite diagnosis in patients with early-onset encephalopathy.

Distinct features of ribonucleotides within genomic DNA in Aicardi-Goutières syndrome ortholog mutants of Saccharomyces cerevisiae

Ribonucleoside monophosphates (rNMPs) are abundantly found within genomic DNA of cells. The embedded rNMPs alter DNA properties and impact genome stability. Mutations in ribonuclease (RNase) H2, a key enzyme for rNMP removal, are associated with the Aicardi-Goutières syndrome (AGS), a severe neurological disorder. Here, we engineered orthologs of the human RNASEH2A-G37S and RNASEH2C-R69W AGS mutations in yeast Saccharomyces cerevisiae: rnh201-G42S and rnh203-K46W. Using the ribose-seq technique and the Ribose-Map bioinformatics toolkit, we unveiled rNMP abundance, composition, hotspots, and sequence context in these AGS-ortholog mutants. We found a high rNMP presence in the nuclear genome of rnh201-G42S-mutant cells, and an elevated rCMP content in both mutants, reflecting preferential cleavage of RNase H2 at rGMP. We discovered unique rNMP patterns in each mutant, showing differential activity of the AGS mutants on the leading or lagging replication strands. This study guides future research on rNMP characteristics in human genomes with AGS mutations.

IFN-signaling gene expression as a diagnostic biomarker for monogenic interferonopathies

IFN-signaling gene (ISG) expression scores are potential markers of inflammation with significance from cancer to genetic syndromes. In Aicardi Goutières Syndrome (AGS), a disorder of abnormal DNA and RNA metabolism, this score has potential as a diagnostic biomarker, although the approach to ISG calculation has not been standardized or validated. To optimize ISG calculation and validate ISG as a diagnostic biomarker, mRNA levels of 36 type I IFN response genes were quantified from 997 samples (including 334 AGS), and samples were randomized into training and test data sets. An independent validation cohort (n = 122) was also collected. ISGs were calculated using all potential combinations up to 6 genes. A 4-gene approach (IFI44L, IFI27, USP18, IFI6) was the best-performing model (AUC of 0.8872 [training data set], 0.9245 [test data set]). The majority of top-performing gene combinations included IFI44L. Performance of IFI44L alone was 0.8762 (training data set) and 0.9580 (test data set) by AUC. The top approaches were able to discriminate individuals with genetic interferonopathy from control samples. This study validates the context of use for the ISG score as a diagnostic biomarker and underscores the importance of IFI44L in diagnosis of genetic interferonopathies.

ACK1 and BRK non-receptor tyrosine kinase deficiencies are associated with familial systemic lupus and involved in efferocytosis

Systemic Lupus Erythematosus (SLE) is an autoimmune disease, the pathophysiology and genetic basis of which are incompletely understood. Using a forward genetic screen in multiplex families with systemic lupus erythematosus (SLE) we identified an association between SLE and compound heterozygous deleterious variants in the non-receptor tyrosine kinases (NRTKs) ACK1 and BRK. Experimental blockade of ACK1 or BRK increased circulating autoantibodies in vivo in mice and exacerbated glomerular IgG deposits in an SLE mouse model. Mechanistically, non-receptor tyrosine kinases (NRTKs) regulate activation, migration, and proliferation of immune cells. We found that the patients' ACK1 and BRK variants impair efferocytosis, the MERTK-mediated anti-inflammatory response to apoptotic cells, in human induced Pluripotent Stem Cell (hiPSC)-derived macrophages, which may contribute to SLE pathogenesis. Overall, our data suggest that ACK1 and BRK deficiencies are associated with human SLE and impair efferocytosis in macrophages.

The Exonuclease TREX1 Constitutes an Innate Immune Checkpoint Limiting cGAS/STING-Mediated Antitumor Immunity

The DNA exonuclease three-prime repair exonuclease 1 (TREX1) is critical for preventing autoimmunity in mice and humans by degrading endogenous cytosolic DNA, which otherwise triggers activation of the innate cGAS/STING pathway leading to the production of type I IFNs. As tumor cells are prone to aberrant cytosolic DNA accumulation, we hypothesized that they are critically dependent on TREX1 activity to limit their immunogenicity. Here, we show that in tumor cells, TREX1 restricts spontaneous activation of the cGAS/STING pathway, and the subsequent induction of a type I IFN response. As a result, TREX1 deficiency compromised in vivo tumor growth in mice. This delay in tumor growth depended on a functional immune system, systemic type I IFN signaling, and tumor-intrinsic cGAS expression. Mechanistically, we show that tumor TREX1 loss drove activation of CD8+ T cells and NK cells, prevented CD8+ T-cell exhaustion, and remodeled an immunosuppressive myeloid compartment. Consequently, TREX1 deficiency combined with T-cell-directed immune checkpoint blockade. Collectively, we conclude that TREX1 is essential to limit tumor immunogenicity, and that targeting this innate immune checkpoint remodels the tumor microenvironment and enhances antitumor immunity by itself and in combination with T-cell-targeted therapies. See related article by Toufektchan et al., p. 673.

Multi-dimensional Insight into the Coexistence of Pathogenic Genes for ADAR1 and TSC2: Careful Consideration is Essential for Interpretation of ADAR1 Variants

Aicardi-Goutières syndrome 6 (AGS6) is a serious auto-immunization-associated acute neurologic decompensation. AGS6 manifests as acute onset of severe generalized dystonia of limbs and developmental regression secondary to febrile illness mostly. Dyschromatosis symmetrica hereditaria (DSH), as pigmentary genodermatosis, is a characterized mixture of hyperpigmented and hypopigmented macules. Both AGS6 and DSH are associated with ADAR1 pathogenic variants. To explore the etiology of a proband with developmental regression with mixture of hyperpigmentation and hypopigmentation macules, we used the trio-WES. Later, to clarify the association between variants and diseases, we used guidelines of ACMG for variants interpretation and quantitative Real-time PCR for verifying elevated expression levels of interferon-stimulated genes, separately. By WES, we detected 2 variants in ADAR1 and a variant in TSC2, respectively, were NM_001111.5:c.1096_1097del, NM_001111.5:c.518A>G, and NM_000548.5:c.1864C>T. Variants interpretation suggested that these 3 variants were both pathogenic. Expression levels of interferon-stimulated genes also elevated as expected. We verified the co-occurrence of pathogenic variants of ADAR1 and TSC2 in AGS6 patients with DSH. Our works contributed to the elucidation of ADAR1 pathogenic mechanism, given the specific pathogenic mechanism of ADAR1, and it is necessary to consider with caution when variants were found in ADAR1.

The landscape of rare genetic variants in familial Waldenström macroglobulinemia

Waldenström macroglobulinemia (WM) is a rare hematological malignancy. Risk for WM is elevated 20-fold among first-degree relatives of patients with WM. However, the list of variants and genes that cause WM remains incomplete. In this study we analyzed exomes from 64 WM pedigrees for evidence of genetic susceptibility for this malignancy. We determined the frequency of pathogenic (P) or likely pathogenic (LP) variants among patients with WM; performed variant- and gene-level association analyses with the set of 166 WM cases and 681 unaffected controls; and examined the segregation pattern of deleterious variants among affected members in each pedigree. We identified P/LP variants in TREX1 and SAMHD1 (genes that function at the interface between innate immune response, genotoxic surveillance, and DNA repair) segregating in patients with WM from 2 pedigrees. There were additional P/LP variants in cancer-predisposing genes (eg, POT1, RECQL4, PTPN11, PMS2). In variant- and gene-level analyses, no associations were statistically significant after multiple testing correction. On a pathway level, we observed involvement of genes that play a role in telomere maintenance (q-value = 0.02), regulation of innate immune response (q-value = 0.05), and DNA repair (q-value = 0.08). Affected members of each pedigree shared multiple deleterious variants (median, n = 18), but the overlap between the families was modest. In summary, P/LP variants in highly penetrant genes constitute a modest proportion of the deleterious variants; each pedigree is largely unique in its genetic architecture, and multiple genes are likely involved in the etiology of WM.

The Sixth Sense: Self-nucleic acid sensing in the brain

Our innate immune system uses pattern recognition receptors (PRRs) as a first line of defense to detect microbial ligands and initiate an immune response. Viral nucleic acids are key ligands for the activation of many PRRs and the induction of downstream inflammatory and antiviral effects. Initially it was thought that endogenous (self) nucleic acids rarely activated these PRRs, however emerging evidence indicates that endogenous nucleic acids are able to activate host PRRs in homeostasis and disease. In fact, many regulatory mechanisms are in place to finely control and regulate sensing of self-nucleic acids by PRRs. Sensing of self-nucleic acids is particularly important in the brain, as perturbations to nucleic acid sensing commonly leads to neuropathology. This review will highlight the role of nucleic acid sensors in the brain, both in disease and homeostasis. We also indicate the source of endogenous stimulatory nucleic acids where known and summarize future directions for the study of this growing field.

Systematic analysis of genotype-phenotype variability in siblings with Aicardi Goutières Syndrome (AGS)

OBJECTIVE

Aicardi Goutières Syndrome (AGS) is a genetic interferonopathy associated with multisystemic heterogeneous disease and neurologic dysfunction. AGS includes a broad phenotypic spectrum which is only partially explained by genotype. To better characterize this variability, we will perform a systematic analysis of phenotypic variability in familial cases of AGS.

METHODS

Among thirteen families, twenty-six siblings diagnosed with AGS were identified from the Myelin Disorders and Biorepository Project (MDBP) at the Children's Hospital of Philadelphia. Data were collected on the age of onset, genotype, neurologic impairment, and systemic complications. Neurologic impairment was assessed by a disease-specific scale (AGS Severity Scale) at the last available clinical encounter (range: 0-11 representing severe - attenuated phenotypes). The concordance of clinical severity within sibling pairs was categorized based on the difference in AGS Scale (discordant defined as >2-unit difference). The severity classifications were compared between sibling sets and by genotype.

RESULTS

Five genotypes were represented: TREX1 (n = 4 subjects), RNASEH2B (n = 8), SAMHD1 (n = 8) ADAR1 (n = 4), and IFIH1 (n = 2). The older sibling was diagnosed later relative to the younger affected sibling (median age 7.32 years [IQR = 14.1] compared to 1.54 years [IQR = 10.3]). Common presenting neurologic symptoms were tone abnormalities (n = 10/26) and gross motor dysfunction (n = 9/26). Common early systemic complications included dysphagia and chilblains. The overall cohort median AGS severity score at the last encounter was 8, while subjects presenting with symptoms before one year had a median score of 5. The TREX1 cohort presented at the youngest age and with the most severe phenotype on average. AGS scores were discordant for 5 of 13 sibling pairs, most commonly in the SAMHD1 pairs. Microcephaly, feeding tube placement, seizures and earlier onset sibling were associated with lower AGS scores (respectively, Wilcoxon rank sum: p = 0.0001, p < 0.0001, p = 0.0426, and Wilcoxon signed rank: p = 0.0239).

CONCLUSIONS

In this systematic analysis of phenotypic variability in familial cases, we found discordance between siblings affected by AGS. Our results underscore the heterogeneity of AGS and suggest factors beyond AGS genotype may affect phenotype. Understanding the critical variables associated with disease onset and severity can guide future therapeutic interventions and clinical monitoring. This report reinforces the need for further studies to uncover potential factors to better understand this phenotypic variability, and consequently identify potential targets for interventions in attempt to change the natural history of the disease.

High throughput functional profiling of genes at intraocular pressure loci reveals distinct networks for glaucoma

INTRODUCTION

Primary open angle glaucoma (POAG) is a leading cause of blindness globally. Characterized by progressive retinal ganglion cell degeneration, the precise pathogenesis remains unknown. Genome-wide association studies (GWAS) have uncovered many genetic variants associated with elevated intraocular pressure (IOP), one of the key risk factors for POAG. We aimed to identify genetic and morphological variation that can be attributed to trabecular meshwork cell (TMC) dysfunction and raised IOP in POAG.

METHODS

62 genes across 55 loci were knocked-out in a primary human TMC line. Each knockout group, including five non-targeting control groups, underwent single-cell RNA-sequencing (scRNA-seq) for differentially-expressed gene (DEG) analysis. Multiplexed fluorescence coupled with CellProfiler image analysis allowed for single-cell morphological profiling.

RESULTS

Many gene knockouts invoked DEGs relating to matrix metalloproteinases and interferon-induced proteins. We have prioritized genes at four loci of interest to identify gene knockouts that may contribute to the pathogenesis of POAG, including ANGPTL2, LMX1B, CAV1, and KREMEN1. Three genetic networks of gene knockouts with similar transcriptomic profiles were identified, suggesting a synergistic function in trabecular meshwork cell physiology. TEK knockout caused significant upregulation of nuclear granularity on morphological analysis, while knockout of TRIOBP, TMCO1 and PLEKHA7 increased granularity and intensity of actin and the cell-membrane.

CONCLUSION

High-throughput analysis of cellular structure and function through multiplex fluorescent single-cell analysis and scRNA-seq assays enabled the direct study of genetic perturbations at the single-cell resolution. This work provides a framework for investigating the role of genes in the pathogenesis of glaucoma and heterogenous diseases with a strong genetic basis.

Multifaceted roles of RNA editing enzyme ADAR1 in innate immunity

Innate immunity must be tightly regulated to enable sensitive pathogen detection while averting autoimmunity triggered by pathogen-like host molecules. A hallmark of viral infection, double-stranded RNAs (dsRNAs) are also abundantly encoded in mammalian genomes, necessitating surveillance mechanisms to distinguish "self" from "nonself." ADAR1, an RNA editing enzyme, has emerged as an essential safeguard against dsRNA-induced autoimmunity. By converting adenosines to inosines (A-to-I) in long dsRNAs, ADAR1 covalently marks endogenous dsRNAs, thereby blocking the activation of the cytoplasmic dsRNA sensor MDA5. Moreover, beyond its editing function, ADAR1 binding to dsRNA impedes the activation of innate immune sensors PKR and ZBP1. Recent landmark studies underscore the utility of silencing ADAR1 for cancer immunotherapy, by exploiting the ADAR1-dependence developed by certain tumors to unleash an antitumor immune response. In this perspective, we summarize the genetic and mechanistic evidence for ADAR1's multipronged role in suppressing dsRNA-mediated autoimmunity and explore the evolving roles of ADAR1 as an immuno-oncology target.

Interferons and interferon-related pathways in heart disease

Interferons (IFNs) and IFN-related pathways play key roles in the defence against microbial infection. However, these processes may also be activated during the pathogenesis of non-infectious diseases, where they may contribute to organ injury, or function in a compensatory manner. In this review, we explore the roles of IFNs and IFN-related pathways in heart disease. We consider the cardiac effects of type I IFNs and IFN-stimulated genes (ISGs); the emerging role of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway; the seemingly paradoxical effects of the type II IFN, IFN-γ; and the varied actions of the interferon regulatory factor (IRF) family of transcription factors. Recombinant IFNs and small molecule inhibitors of mediators of IFN receptor signaling are already employed in the clinic for the treatment of some autoimmune diseases, infections, and cancers. There has also been renewed interest in IFNs and IFN-related pathways because of their involvement in SARS-CoV-2 infection, and because of the relatively recent emergence of cGAS-STING as a pattern recognition receptor-activated pathway. Whether these advances will ultimately result in improvements in the care of those experiencing heart disease remains to be determined.

SAMHD1 dysfunction induces IL-34 expression via NF-κB p65 in neuronal SH-SY5Y cells

Dysfunctional mutations in SAMHD1 cause Aicardi-Goutières Syndrome, an autoinflammatory encephalopathy with elevated interferon-α levels in the cerebrospinal fluid. Whether loss of function mutations in SAMHD1 trigger the expression of other cytokines apart from type I interferons in Aicardi-Goutières Syndrome is largely unclear. This study aimed to explore whether SAMHD1 dysfunction regulated the expression of IL-34, a key cytokine controlling the development and maintenance of microglia, in SH-SY5Y neural cells. We found that downregulation of SAMHD1 in SH-SY5Y cells resulted in the upregulation of IL-34 expression. The protein and mRNA levels of NF-κB p65, the transactivating subunit of a transcription factor NF-κB, were also upregulated in SAMHD1-knockdown SH-SY5Y cells. It was further found SAMHD1 knockdown in SH-SY5Y cells induced an upregulation of IL-34 expression through the canonical NF-κB-dependent pathway in which NF-κB p65, IKKα/β and the NF-κB inhibitor IκBα were phosphorylated. Moreover, knockdown of SAMHD1 in SH-SY5Y cells led to the translocation of NF-κB p65 into the nucleus and promoted NF-κB transcriptional activity. In conclusion, we found SAMHD1 dysfunction induced IL-34 expression via NF-κB p65 in neuronal SH-SY5Y cells. This finding could lay the foundation for exploring the role of IL-34-targeting microglia in the pathogenesis of Aicardi-Goutières Syndrome.

SAMHD1 compound heterozygous rare variants associated with moyamoya and mitral valve disease in the absence of other features of Aicardi-Goutières syndrome

Aicardi-Goutières syndrome (AGS) is an autosomal recessive inflammatory syndrome that manifests as an early-onset encephalopathy with both neurologic and extraneurologic clinical findings. AGS has been associated with pathogenic variants in nine genes: TREX1, RNASEH2B, RNASEH2C, RNASEH2A, SAMHD1, ADAR, IFIH1, LSM11, and RNU7-1. Diagnosis is established by clinical findings (encephalopathy and acquired microcephaly, intellectual and physical impairments, dystonia, hepatosplenomegaly, sterile pyrexia, and/or chilblains), characteristic abnormalities on cranial CT (calcification of the basal ganglia and white matter) and MRI (leukodystrophic changes), or the identification of pathogenic/likely pathogenic variants in the known genes. One of the genes associated with AGS, SAMHD1, has also been associated with a spectrum of cerebrovascular diseases, including moyamoya disease (MMD). In this report, we describe a 31-year-old male referred to genetics for MMD since childhood who lacked the hallmark features of AGS patients but was found to have compound heterozygous SAMHD1 variants. He later developed mitral valve insufficiency due to recurrent chordal rupture and ultimately underwent a heart transplant at 37 years of age. Thus, these data suggest that SAMHD1 pathogenic variants can cause MMD without typical AGS symptoms and support that SAMHD1 should be assessed in MMD patients even in the absence of AGS features.

Genetic interrogation for sequence and copy number variants in systemic lupus erythematosus

Early-onset systemic lupus erythematosus presents with a more severe disease and is associated with a greater genetic burden, especially in patients from Black, Asian or Hispanic ancestries. Next-generation sequencing techniques, notably whole exome sequencing, have been extensively used in genomic interrogation studies to identify causal disease variants that are increasingly implicated in the development of autoimmunity. This Review discusses the known casual variants of polygenic and monogenic systemic lupus erythematosus and its implications under certain genetic disparities while suggesting an age-based sequencing strategy to aid in clinical diagnostics and patient management for improved patient care.

TREX1 is required for microglial cholesterol homeostasis and oligodendrocyte terminal differentiation in human neural assembloids

Three Prime Repair Exonuclease 1 (TREX1) gene mutations have been associated with Aicardi-Goutières Syndrome (AGS) - a rare, severe pediatric autoimmune disorder that primarily affects the brain and has a poorly understood etiology. Microglia are brain-resident macrophages indispensable for brain development and implicated in multiple neuroinflammatory diseases. However, the role of TREX1 - a DNase that cleaves cytosolic nucleic acids, preventing viral- and autoimmune-related inflammatory responses - in microglia biology remains to be elucidated. Here, we leverage a model of human embryonic stem cell (hESC)-derived engineered microglia-like cells, bulk, and single-cell transcriptomics, optical and transmission electron microscopy, and three-month-old assembloids composed of microglia and oligodendrocyte-containing organoids to interrogate TREX1 functions in human microglia. Our analyses suggest that TREX1 influences cholesterol metabolism, leading to an active microglial morphology with increased phagocytosis in the absence of TREX1. Notably, regulating cholesterol metabolism with an HMG-CoA reductase inhibitor, FDA-approved atorvastatin, rescues these microglial phenotypes. Functionally, TREX1 in microglia is necessary for the transition from gliogenic intermediate progenitors known as pre-oligodendrocyte precursor cells (pre-OPCs) to precursors of the oligodendrocyte lineage known as OPCs, impairing oligodendrogenesis in favor of astrogliogenesis in human assembloids. Together, these results suggest routes for therapeutic intervention in pathologies such as AGS based on microglia-specific molecular and cellular mechanisms.

Impact of Disease-Associated Mutations on the Deaminase Activity of ADAR1

The innate immune system relies on molecular sensors to detect distinctive molecular patterns, including viral double-stranded RNA (dsRNA), which triggers responses resulting in apoptosis and immune infiltration. Adenosine Deaminases Acting on RNA (ADARs) catalyze the deamination of adenosine (A) to inosine (I), serving as a mechanism to distinguish self from non-self RNA and prevent aberrant immune activation. Loss-of-function mutations in the ADAR1 gene are one cause of Aicardi Goutières Syndrome (AGS), a severe autoimmune disorder in children. Although seven out of the eight AGS-associated mutations in ADAR1 occur within the catalytic domain of the ADAR1 protein, their specific effects on the catalysis of adenosine deamination remain poorly understood. In this study, we carried out a biochemical investigation of four AGS-causing mutations (G1007R, R892H, K999N, and Y1112F) in ADAR1 p110 and truncated variants. These studies included adenosine deamination rate measurements with two different RNA substrates derived from human transcripts known to be edited by ADAR1 p110 (glioma-associated oncogene homologue 1 (hGli1), 5-hydroxytryptamine receptor 2C (5-HT2cR)). Our results indicate that AGS-associated mutations at two amino acid positions directly involved in stabilizing the base-flipped conformation of the ADAR-RNA complex (G1007R and R892H) had the most detrimental impact on catalysis. The K999N mutation, positioned near the RNA binding interface, altered catalysis contextually. Finally, the Y1112F mutation had small effects in each of the assays described here. These findings shed light on the differential effects of disease-associated mutations on adenosine deamination by ADAR1, thereby advancing our structural and functional understanding of ADAR1-mediated RNA editing.

Generation of three induced pluripotent stem cell lines from individuals with Aicardi-Goutières syndrome caused by a c.3019G>A (p.G1007R) autosomal dominant pathogenic variant in ADAR1

Mutations in Adenosine deaminase acting on RNA 1 (ADAR1) gene encoding RNA editing enzyme ADAR1 results in the neuroinflammatory leukodystrophy Aicardi Goutières Syndrome (AGS). AGS is an early onset leukoencephalopathy with an exacerbated interferon response leading to neurological regression with intellectual disability, spasticity, and motor deficits. We have generated three induced pluripotent stem cell (iPSC) lines from peripheral blood mononuclear cells (PBMCs) of individuals with ADAR1G1007R mutation. The generated iPSCs were investigated to confirm a normal karyotype, pluripotency, and trilineage differentiation potential. The reprogrammed iPSCs will allow us to model AGS, dissect the cellular mechanisms and testing different treatment targets.

Leukodystrophy Imaging: Insights for Diagnostic Dilemmas

Leukodystrophies, a group of rare demyelinating disorders, mainly affect the CNS. Clinical presentation of different types of leukodystrophies can be nonspecific, and thus, imaging techniques like MRI can be used for a more definitive diagnosis. These diseases are characterized as cerebral lesions with characteristic demyelinating patterns which can be used as differentiating tools. In this review, we talk about these MRI study findings for each leukodystrophy, associated genetics, blood work that can help in differentiation, emerging diagnostics, and a follow-up imaging strategy. The leukodystrophies discussed in this paper include X-linked adrenoleukodystrophy, metachromatic leukodystrophy, Krabbe's disease, Pelizaeus-Merzbacher disease, Alexander's disease, Canavan disease, and Aicardi-Goutières Syndrome.

Interferon-α receptor antisense oligonucleotides reduce neuroinflammation and neuropathology in a mouse model of cerebral interferonopathy

Chronic and elevated levels of the antiviral cytokine IFN-α in the brain are neurotoxic. This is best observed in patients with genetic cerebral interferonopathies such as Aicardi-Goutières syndrome. Cerebral interferonopathies typically manifest in early childhood and lead to debilitating disease and premature death. There is no cure for these diseases with existing treatments largely aimed at managing symptoms. Thus, an effective therapeutic strategy is urgently needed. Here, we investigated the effect of antisense oligonucleotides targeting the murine IFN-α receptor (Ifnar1 ASOs) in a transgenic mouse model of cerebral interferonopathy. Intracerebroventricular injection of Ifnar1 ASOs into transgenic mice with brain-targeted chronic IFN-α production resulted in a blunted cerebral interferon signature, reduced neuroinflammation, restoration of blood-brain barrier integrity, absence of tissue destruction, and lessened neuronal damage. Remarkably, Ifnar1 ASO treatment was also effective when given after the onset of neuropathological changes, as it reversed such disease-related features. We conclude that ASOs targeting the IFN-α receptor halt and reverse progression of IFN-α-mediated neuroinflammation and neurotoxicity, opening what we believe to be a new and promising approach for the treatment of patients with cerebral interferonopathies.

Mutations in the non-catalytic polyproline motif destabilize TREX1 and amplify cGAS-STING signaling

The cGAS-STING pathway detects cytosolic DNA and activates a signaling cascade that results in a type I interferon (IFN) response. The endoplasmic reticulum (ER)-associated exonuclease TREX1 suppresses cGAS-STING by eliminating DNA from the cytosol. Mutations that compromise TREX1 function are linked to autoinflammatory disorders, including systemic lupus erythematosus (SLE) and Aicardi-Goutières syndrome (AGS). Despite key roles in regulating cGAS-STING and suppressing excessive inflammation, the impact of many disease-associated TREX1 mutations - particularly those outside of the core catalytic domains - remains poorly understood. Here, we characterize a recessive AGS-linked TREX1 P61Q mutation occurring within the poorly characterized polyproline helix (PPII) motif. In keeping with its position outside of the catalytic core or ER targeting motifs, neither the P61Q mutation, nor aggregate proline-to-alanine PPII mutation, disrupt TREX1 exonuclease activity, subcellular localization, or cGAS-STING regulation in overexpression systems. Introducing targeted mutations into the endogenous TREX1 locus revealed that PPII mutations destabilize the protein, resulting in impaired exonuclease activity and unrestrained cGAS-STING activation. Overall, these results demonstrate that TREX1 PPII mutations, including P61Q, impair proper immune regulation and lead to autoimmune disease through TREX1 destabilization.

Childhood-inherited white matter disorders with calcification

Intracranial calcification (ICC) occurs in many neurologic disorders both acquired and genetic. In some inherited white matter disorders, it is a common or even invariable feature where the presence and pattern of calcification provides an important pointer to the specific diagnosis. This is particularly the case for the Aicardi-Goutières syndrome (AGS) and for Coats plus (CP) and leukoencephalopathy with calcifications and cysts (LCC), which are discussed in detail in this chapter. AGS is a genetic disorder of type 1 interferon regulation, caused by mutations in any of the nine genes identified to date. In its classic form, AGS has very characteristic clinical and neuroimaging features which will be discussed here. LCC is a purely neurologic disorder caused by mutations in the SNORD118 gene, whereas CP is a multisystem disorder of telomere function that may result from mutations in the CTC1, POT1, or STN genes. In spite of the different pathogenetic basis for LCC and CP, they share remarkably similar neuroimaging and neuropathologic features. Cockayne syndrome, in which ICC is usually present, is discussed elsewhere in this volume. ICC may occur as an occasional feature of many other white matter diseases, including Alexander disease, Krabbe disease, X-ALD, and occulodentodigital dysplasia.

Rare forms of hypomyelination and delayed myelination

Hypomyelination is defined by the evidence of an unchanged pattern of deficient myelination on two MRIs performed at least 6 months apart in a child older than 1 year. When the temporal criteria are not fulfilled, and the follow-up MRI shows a progression of the myelination even if still not adequate for age, hypomyelination is excluded and the pattern is instead consistent with delayed myelination. This can be mild and nonspecific in some cases, while in other cases there is a severe delay that in the first disease stages could be difficult to differentiate from hypomyelination. In hypomyelinating leukodystrophies, hypomyelination is due to a primary impairment of myelin deposition, such as in Pelizaeus Merzabcher disease. Conversely, myelin lack is secondary, often to primary neuronal disorders, in delayed myelination and some condition with hypomyelination. Overall, the group of inherited white matter disorders with abnormal myelination has expanded significantly during the past 20 years. Many of these disorders have only recently been described, for many of them only a few patients have been reported and this contributes to make challenging the diagnostic process and the interpretation of Next Generation Sequencing results. In this chapter, we review the clinical and radiologic features of rare and lesser known forms of hypomyelination and delayed myelination not mentioned in other chapters of this handbook.

General approach to treatment of genetic leukoencephalopathies in children and adults

Despite the enormous advancements seen in recent years, curative therapies for patients with genetic leukoencephalopathies are available for only a relatively small number of disorders. Therefore, symptomatic treatment and preventive management of the multiple clinical manifestations of patients with genetic leukoencephalopathies are critical in their care. The goals of the symptomatic treatment are to improve patients' quality of life, increase their survival, and reduce the impact on medical resources and related expenses. The coordinated work of a multidisciplinary team, including all specialists involved in the care of these patients, is the gold standard approach to manage and treat their complex and evolving clinical picture. Along with a multidisciplinary team, the relationship and close collaboration with the patient and their caregivers are essential. Their insight into the disease manifestations and management of the different issues should be integrated with the assessments of the multidisciplinary team to prevent clinical complications and preserve the quality of life of patients and their caregivers. Genetic leukoencephalopathies are very heterogeneous in terms of age of onset, clinical features, and disease course. However, many clinical features and problems are shared by most forms. Consequently, common therapeutic strategies apply to the majority of these diseases. This chapter presents the symptomatic approach for shared core clinical features presented by patients with genetic leukoencephalopathies divided by systems and, for each system, the specificities of some genetic leukoencephalopathies.

Necroptosis and Its Involvement in Various Diseases

Necroptosis is a regulated form of cell death involved in the development of various pathological conditions. In contrast to apoptosis, plasma membrane rupture (PMR) occurs in cells in the relatively early stage of necroptosis; therefore, necroptosis induces a strong inflammatory response. Stimuli, including tumor necrosis factor (TNF), interferon (IFN)α/β, lipopolysaccharide, polyI:C, and viral infection, induce the formation of necrosomes that lead to membrane rupture and the release of intracellular contents, termed danger-associated molecular patterns (DAMPs). DAMPs are the collective term for molecules that normally reside in the cytoplasm or nucleus in living cells without inducing inflammation but induce strong inflammatory responses when released outside cells. Recent studies have provided a better understanding of the mechanisms underlying PMR and the release of DAMPs. Moreover, necroptosis is involved in various pathological conditions, and mutations in necroptosis-related genes can cause hereditary autoinflammatory syndromes. Thus, manipulating necroptosis signaling pathways may be useful for treating diseases involving necroptosis.

Early arteriopathy in Aicardi-Goutières syndrome 5. Case report and review of literature

Aicardi-Goutières syndrome (AGS) is an autosomal recessive disease that mimics congenital viral infection and mainly affects the brain, immune system, and skin. The dominant clinical symptom is the subacute onset of severe encephalopathy, which manifests as irritability, loss of ability, slowing of head growth, and poor nutrition. Arteriopathy in AGS is an uncommon manifestation usually associated with mutations in the SAMHD1 gene. We present a rare case of a 3-year-old male due to failure to thrive, global developmental delay, microcephaly, poor vision, upper and lower limbs spasticity, and gastroesophageal reflux disease (GERD), who harbored early stenotic lesions of the large and medium intracranial arteries with ischemic sequelae in the early postnatal life. Performed genetic testing confirmed homozygous gene mutation, SAMHD1 associated with AGS type 5. By reviewing the available literature, we were able to find only one patient whose arterial lesions were diagnosed after 6 months.

How to Build a Fire: The Genetics of Autoinflammatory Diseases

Systemic autoinflammatory diseases (SAIDs) are a heterogeneous group of disorders caused by excess activation of the innate immune system in an antigen-independent manner. Starting with the discovery of the causal gene for familial Mediterranean fever, more than 50 monogenic SAIDs have been described. These discoveries, paired with advances in immunology and genomics, have allowed our understanding of these diseases to improve drastically in the last decade. The genetic causes of SAIDs are complex and include both germline and somatic pathogenic variants that affect various inflammatory signaling pathways. We provide an overview of the acquired SAIDs from a genetic perspective and summarize the clinical phenotypes and mechanism(s) of inflammation, aiming to provide a comprehensive understanding of the pathogenesis of autoinflammatory diseases.

Aicardi-Goutières Syndrome with Congenital Glaucoma Caused by Novel TREX1 Mutation

BACKGROUND

Aicardi-Goutières syndrome (AGS) is a rare genetic disorder characterized by microcephaly, white matter lesions, numerous intracranial calcifications, chilblain skin lesions and high levels of interferon-α (IFN-α) in the cerebrospinal fluid (CSF). However, ocular involvement is reported significantly less frequently.

CASE PRESENTATION

We present a case of a neonate with hypotrophy, microcephaly, frostbite-like skin lesions, thrombocytopenia, elevated liver enzymes and hepatosplenomegaly. Magnetic resonance imaging (MRI) of the brain showed multiple foci of calcification, white matter changes, cerebral atrophy, and atrophic dilatation of the ventricular system. The inflammatory parameters were not elevated, and the infectious etiology was excluded. Instead, elevated levels of IFN-α in the serum were detected. Based on the related clinical symptoms, imaging and test findings, the diagnosis of AGS was suspected. Genetic testing revealed two pathogenic mutations, c.490C>T and c.222del (novel mutation), in the three prime repair exonuclease 1 (TREX1) gene, confirming AGS type 1 (AGS1). An ophthalmologic examination of the child at 10 months of age revealed an impaired pupillary response to light, a corneal haze with Haab lines in the right eye (RE), pale optic nerve discs and neuropathy in both eyes (OU). The intraocular pressure (IOP) was 51 mmHg in the RE and 49 in the left eye (LE). The flash visual evoked potential (FVEP) showed prolonged P2 latencies of up to 125% in the LE and reduced amplitudes of up to approximately 10% OU. This girl was diagnosed with congenital glaucoma, and it was managed with a trabeculectomy with a basal iridectomy of OU, resulting in a reduction and stabilization in the IOP to 12 mmHg in the RE and 10 mmHg in the LE without any hypotensive eyedrops.

CONCLUSIONS

We present the clinical characteristics, electrophysiological and imaging findings, as well as the genetic test results of a patient with AGS1. Our case contributes to the extended ophthalmic involvement of the pathogenic c.490C>T and c.222del mutations in TREX1.

'From R-lupus to cancer': Reviewing the role of R-loops in innate immune responses

Cells possess an inherent and evolutionarily conserved ability to detect and respond to the presence of foreign and pathological 'self' nucleic acids. The result is the stimulation of innate immune responses, signalling to the host immune system that defence mechanisms are necessary to protect the organism. To date, there is a vast body of literature describing innate immune responses to various nucleic acid species, including dsDNA, ssDNA and ssRNA etc., however, there is limited information available on responses to R-loops. R-loops are 3-stranded nucleic acid structures that form during transcription, upon DNA damage and in various other settings. Emerging evidence suggests that innate immune responses may also exist for the detection of R-loop related nucleic acid structures, implicating R-loops as drivers of inflammatory states. In this review, we aim to summarise the evidence indicating that R-loops are immunogenic species that can trigger innate immune responses in physiological and pathological settings and discuss the implications of this in the study of various diseases and therapeutic development.

Helicases in R-loop Formation and Resolution

With the development and wide usage of CRISPR technology, the presence of R-loop structures, which consist of an RNA-DNA hybrid and a displaced single-strand (ss) DNA, has become well accepted. R-loop structures have been implicated in a variety of circumstances and play critical roles in the metabolism of nucleic acid and relevant biological processes, including transcription, DNA repair, and telomere maintenance. Helicases are enzymes that use an ATP-driven motor force to unwind double-strand (ds) DNA, dsRNA, or RNA-DNA hybrids. Additionally, certain helicases have strand-annealing activity. Thus, helicases possess unique positions for R-loop biogenesis: they utilize their strand-annealing activity to promote the hybridization of RNA to DNA, leading to the formation of R-loops; conversely, they utilize their unwinding activity to separate RNA-DNA hybrids and resolve R-loops. Indeed, numerous helicases such as senataxin (SETX), Aquarius (AQR), WRN, BLM, RTEL1, PIF1, FANCM, ATRX (alpha-thalassemia/mental retardation, X-linked), CasDinG, and several DEAD/H-box proteins are reported to resolve R-loops; while other helicases, such as Cas3 and UPF1, are reported to stimulate R-loop formation. Moreover, helicases like DDX1, DDX17, and DHX9 have been identified in both R-loop formation and resolution. In this review, we will summarize the latest understandings regarding the roles of helicases in R-loop metabolism. Additionally, we will highlight challenges associated with drug discovery in the context of targeting these R-loop helicases.

Type I Interferonopathies: A Clinical Review

This review will discuss when clinicians should consider evaluating for Type I interferonopathies, review clinical phenotypes and molecular defects of Type I interferonopathies, and discuss current treatments.

Type 1 Interferon-Stimulated Gene Expression and Disease Activity in Pediatric Rheumatic Diseases: No Composite Scores Needed?

OBJECTIVE

Rheumatic diseases are characterized by different patterns of immune overactivation. This study investigated the correlation of whole blood type 1 interferon (IFN) stimulated gene (ISG), IL18, and CXCL9 expression with clinical disease activity in pediatric rheumatic diseases and assessed the required number of ISGs to be included in a composite type 1 IFN score.

METHODS

Whole blood-derived RNA and clinical data were collected from 171 mostly pediatric patients with connective tissue diseases (CTDs), systemic autoinflammatory diseases (SAIDs), monogenic interferonopathies (IFNPs) and other inflammatory diseases, and from 38 controls. The expression of six previously established ISGs, IL18, and CXCL9 was assessed by real-time polymerase chain reaction (471 samples). Individual and composite gene expression was assessed, and correlation and threshold analyses were performed.

RESULTS

Correlation between ISG expression and clinical disease activity was strongest in CTD, especially in juvenile dermatomyositis (JDM) and IFNP, and modest in patients with SAID. Threshold ISG expression levels for the detection of at least mild clinical disease activity were substantially higher in patients with systemic lupus erythematosus compared with JDM. The correlation of expression levels of limited sets of ISGs and even individual ISGs with clinical disease activity were not inferior to a composite score of six ISGs.

CONCLUSION

In a real-world cohort, individual ISG expression levels robustly reflected clinical disease activity in CTD and IFNP, especially in JDM, which would simplify such analyses in clinical routine and be more cost-effective. Threshold levels varied across diseases, potentially reflecting different mechanisms of type 1 IFN overactivation.

A case report of two Moroccan patients with hereditary neurological disorders and molecular modeling study on the S72L de novo PMP22 variant

Hereditary neurological disorders represent a wild group of hereditary illnesses affecting mainly the nervous system, the majority of which have a Mendelian inheritance pattern. Here we present the case of two Moroccan patients each affected by a different hereditary neurological disorder. In the first patient WES analysis revealed the presence of the p.Ser72Leu de novo mutation in the PMP22 gene reported for the first time in Africa, specifically in Morocco. This variant is predicted to be in a mutation "hot-spot" region causing Dejerine-Sottas syndrome called also Charcot-Marie-Tooth type 3. The molecular modeling study suggests an important alteration of hydrogen and hydrophobic interactions between the residue in position 72 of the PMP22 protein and its surrounding amino acids. On the other hand, the p.Ala177Thr mutation on the RNASEH2B gene, responsible of Aicardi-Goutières syndrome 2, was carried in a homozygous state by the second patient descending from a consanguineous family. This mutation is common among the Moroccan population as well as in other North African countries. The present results contributed to a better follow-up of both cases allowing better symptom management with convenient treatments.

Childhood rheumatic diseases: bites not only the joint, but also the heart

Cardiovascular involvement in juvenile rheumatic diseases is the primary manifestation in paediatric vasculitis and a major organ manifestation in paediatric connective tissue diseases. Though coronary vasculitis is the prototypical manifestation of Kawasaki disease, it can also be seen in patients with polyarteritis nodosa. Pericarditis is the most common manifestation seen in juvenile rheumatic diseases like systemic onset JIA, and lupus. Cardiac tamponade, valvular insufficiency, aortic root dilatation and arrhythmias are seen rarely. Cardiac involvement is often recognized late in children. The development of cardiac disease in juvenile systemic sclerosis is associated with a poor outcome. In long term, childhood onset of rheumatic diseases predisposes to diastolic dysfunction and premature atherosclerosis during adulthood. Key Points • Pericarditis is the most common cardiac manifestation in SLE and can lead to tamponade. • Conduction defects are common in juvenile mixed connective tissue disease and systemic sclerosis. • Pulmonary hypertension is a significant contributor to mortality in juvenile systemic sclerosis. • In Kawasaki disease, early treatment can reduce risk of coronary artery aneurysms.

Aicardi-Goutières syndrome: A monogenic type I interferonopathy

Aicardi-Goutières syndrome (AGS) is a rare monogenic autoimmune disease that primarily affects the brains of children patients. Its main clinical features include encephalatrophy, basal ganglia calcification, leukoencephalopathy, lymphocytosis and increased interferon-α (IFN-α) levels in the patient's cerebrospinal fluid (CSF) and serum. AGS may be caused by mutations in any one of nine genes (TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR1, IFIH1, LSM11 and RNU7-1) that result in accumulation of self-nucleic acids in the cytoplasm or aberrant sensing of self-nucleic acids. This triggers overproduction of type I interferons (IFNs) and subsequently causes AGS, the prototype of type I interferonopathies. This review describes the discovery history of AGS with various genotypes and provides the latest knowledge of clinical manifestations and causative genes of AGS. The relationship between AGS and type I interferonopathy and potential therapeutic methods for AGS are also discussed in this review.

cGAS‐STING signaling in cancer: Regulation and therapeutic targeting

Immunotherapy has revolutionized antitumor therapy. Since the discovery of stimulators of interferon genes (STING), efforts have been made to elucidate their mechanisms and physiological functions and explore the potential of STING as a therapeutic target in immune‐related diseases and malignant tumors. In recent years, STING agonists have become a popular research topic. Activation of the cyclic GMP–AMP synthase (cGAS)‐STING pathway produces large amounts of type I interferons, which play key roles in activating innate and acquired immune responses. The cGAS‐STING pathway influences almost all aspects of tumorigenesis and has great antitumor potential. In addition, the activation of the cGAS‐STING pathway is associated with tumor regression, prolonged survival of patients with cancer, and enhanced immunotherapy. Given the positive role of STING in antitumor immunity, the development of STING‐targeted drugs is important. In this review, we summarize the activation and potential mechanisms of the cGAS‐STING pathway, discuss the association of the cGAS‐STING pathway with tumors and autoimmune diseases, and highlight research progress, clinical applications, and combination drug strategies for STING agonists.

Genetics of SLE: mechanistic insights from monogenic disease and disease-associated variants

The past few years have provided important insights into the genetic architecture of systemic autoimmunity through aggregation of findings from genome-wide association studies (GWAS) and whole-exome or whole-genome sequencing studies. In the prototypic systemic autoimmune disease systemic lupus erythematosus (SLE), monogenic disease accounts for a small fraction of cases but has been instrumental in the elucidation of disease mechanisms. Defects in the clearance or digestion of extracellular or intracellular DNA or RNA lead to increased sensing of nucleic acids, which can break B cell tolerance and induce the production of type I interferons leading to tissue damage. Current data suggest that multiple GWAS SLE risk alleles act in concert with rare functional variants to promote SLE development. Moreover, introduction of orthologous variant alleles into mice has revealed that pathogenic X-linked dominant and recessive SLE can be caused by novel variants in TLR7 and SAT1, respectively. Such bespoke models of disease help to unravel pathogenic pathways and can be used to test targeted therapies. Cell type-specific expression data revealed that most GWAS SLE risk genes are highly expressed in age-associated B cells (ABCs), which supports the view that ABCs produce lupus autoantibodies and contribute to end-organ damage by persisting in inflamed tissues, including the kidneys. ABCs have thus emerged as key targets of promising precision therapeutics.

Interferonopathies masquerading as non-Mendelian autoimmune diseases: pattern recognition for early diagnosis

Type I interferonopathies are a broad category of conditions associated with increased type I interferon gene expression and include monogenic autoinflammatory diseases and non-Mendelian autoimmune diseases such as dermatomyositis and systemic lupus erythematosus. While a wide range of clinical presentations among type I interferonopathies exists, these conditions often share several clinical manifestations and implications for treatment. Presenting symptoms may mimic non-Mendelian autoimmune diseases, including vasculitis and systemic lupus erythematosus, leading to delayed or missed diagnosis. This review aims to raise awareness about the varied presentations of monogenic interferonopathies to provide early recognition and appropriate treatment to prevent irreversible damage and improve quality of life and outcomes in this unique patient population.

Neuropsychiatric involvement in juvenile-onset systemic lupus erythematosus (jSLE)

Systemic lupus erythematosus (SLE) is a rare autoimmune/inflammatory disease with significant morbidity and mortality. Approximately 15-20% of SLE patients develop the disease during childhood or adolescence (juvenile-onset SLE/jSLE). Patients with jSLE exhibit more variable and severe disease when compared to patients with disease-onset during adulthood. Neuropsychiatric (NP) involvement is a clinically heterogenous and potentially severe complication. Published reports on the incidence and prevalence of NP-jSLE are scarce, and the exact pathophysiology is poorly understood.This manuscript provides a review of the existing literature, suggesting NP involvement in 13.5-51% of jSLE patients. Among patients with NP-jSLE affecting the CNS, we propose two main subgroups: (i) a chronic progressive, predominantly type 1 interferon-driven form that poorly responds to currently used treatments, and (ii) an acutely aggressive form that usually presents early during the disease that may be primarily mediated by auto-reactive effector lymphocytes. While this hypothesis requires to be tested in large collaborative international cohort studies, it may offer future patient stratification and individualised care.

Godoy LF, Pessoa A, A. Costa L, C. Monti F, Souza-Cabral K, Listik C, Castro D, Della-Ripa B, Freua F, C. Pires L, T. Krüger L, D. Gherpelli JL, B. Piazzon F, P. Monteiro F, T. Lucato L, Kok F. Subacute Partially Reversible Leukoencephalopathy Expands the Aicardi-Goutières Syndrome Phenotype

OBJECTIVE

To report a series of atypical presentations of Aicardi-Goutières syndrome.

METHODS

Clinical, neuroimaging, and genetic data.

RESULTS

We report a series of six unrelated patients (five males) with a subacute loss of developmental milestones, pyramidal signs, and regression of communication abilities, with onset at ages ranging from 7 to 20 months, reaching a nadir after 4 to 24 weeks. A remarkable improvement of lost abilities occurred in the follow-up, and they remained with residual spasticity and dysarthria but preserved cognitive function. Immunization or febrile illness occurred before disease onset in all patients. CSF was normal in two patients, and in four, borderline or mild lymphocytosis was present. A brain CT scan disclosed a subtle basal ganglia calcification in one of six patients. Brain MRI showed asymmetric signal abnormalities of white matter with centrum semi-ovale involvement in five patients and a diffuse white matter abnormality with contrast enhancement in one. Four patients were diagnosed and treated for acute demyelinating encephalomyelitis (ADEM). Brain imaging was markedly improved with one year or more of follow-up (average of 7 years), but patients remained with residual spasticity and dysarthria without cognitive impairment. Demyelination relapse occurred in a single patient four years after the first event. Whole-exome sequencing (WES) was performed in all patients: four of them disclosed biallelic pathogenic variants in RNASEH2B (three homozygous p.Ala177Thr and one compound heterozygous p.Ala177Thr/p.Gln58*) and in two of them the same homozygous deleterious variants in RNASEH2A (p.Ala249Val).

CONCLUSIONS

This report expands the phenotype of AGS to include subacute developmental regression with partial clinical and neuroimaging improvement. Those clinical features might be misdiagnosed as ADEM.

JAK Inhibition in Aicardi-Goutières Syndrome: a Monocentric Multidisciplinary Real-World Approach Study

The paradigm type I interferonopathy Aicardi-Goutières syndrome (AGS) is most typically characterized by severe neurological involvement. AGS is considered an immune-mediated disease, poorly responsive to conventional immunosuppression. Premised on a chronic enhancement of type I interferon signaling, JAK1/2 inhibition has been trialed in AGS, with clear improvements in cutaneous and systemic disease manifestations. Contrastingly, treatment efficacy at the level of the neurological system has been less conclusive. Here, we report our real-word approach study of JAK1/2 inhibition in 11 patients with AGS, providing extensive assessments of clinical and radiological status; interferon signaling, including in cerebrospinal fluid (CSF); and drug concentrations in blood and CSF. Over a median follow-up of 17 months, we observed a clear benefit of JAK1/2 inhibition on certain systemic features of AGS, and reproduced results reported using the AGS neurologic severity scale. In contrast, there was no change in other scales assessing neurological status; using the caregiver scale, only patient comfort, but no other domain of everyday-life care, was improved. Serious bacterial infections occurred in 4 out of the 11 patients. Overall, our data lead us to conclude that other approaches to treatment are urgently required for the neurologic features of AGS. We suggest that earlier diagnosis and adequate central nervous system penetration likely remain the major factors determining the efficacy of therapy in preventing irreversible brain damage, implying the importance of early and rapid genetic testing and the consideration of intrathecal drug delivery.

Exploration of Gross Motor Function in Aicardi-Goutières Syndrome

Background: Aicardi-Goutières syndrome (AGS) is a rare genetic disorder characterized by a spectrum of motor abilities. While the Aicardi-Goutières syndrome severity score favors severely impacted individuals, there is an unmet need to define tools measuring function across the Aicardi-Goutières syndrome spectrum as potential outcome assessments for future clinical trials. Methods: Gross Motor Function Measure-88 (GMFM-88) and AGS Severity Scale were administered in individuals affected by Aicardi-Goutières syndrome (n = 71). We characterized the performance variability by genotype. Derived versions of the GMFM-88, including the GMFM-66, GMFM-66 item set (GMFM-66IS), and GMFM-66 Basal&Ceiling (GMFM-66BC) were calculated. The Aicardi-Goutières syndrome cohort was divided into severe (AGS Severity Scale score <4) or attenuated (≥4). Performance on the AGS Severity Scale highly correlated with total GMFM-88 scores (Spearman Correlation: R = 0.91). To assess variability of the GMFM-88 within genotypic subcohorts, interquartile ranges (IQRs) were compared. Results: GMFM-88 performance in the TREX1 cohort had least variability while the SAMHD1 cohort had the largest IQR (4.23 vs 81.8). Floor effect was prominent, with most evaluations scoring below 20% (n = 46, 64.79%), particularly in TREX1- and RNASEH2-cohorts. Performance by the GMFM-66, GMFM-66IS, and GMFM-66BC highly correlated with the full GMFM-88. The Aicardi-Goutières syndrome population represents a broad range of gross motor skills. Conclusions: This work identified the GMFM-88 as a potential clinical outcome assessment in subsets of the Aicardi-Goutières syndrome population but underscores the need for additional validation of outcome measures reflective of the diverse gross motor function observed in this population, including low motor function. When time is limited by resources or patient endurance, shorter versions of the GMFM-88 may be a reasonable alternative.

Pathogenesis of systemic lupus erythematosus: risks, mechanisms and therapeutic targets

Research elucidating the pathogenesis of systemic lupus erythematosus (SLE) has defined two critical families of mediators, type I interferon (IFN-I) and autoantibodies targeting nucleic acids and nucleic acid-binding proteins, as fundamental contributors to the disease. On the fertile background of significant genetic risk, a triggering stimulus, perhaps microbial, induces IFN-I, autoantibody production or most likely both. When innate and adaptive immune system cells are engaged and collaborate in the autoimmune response, clinical SLE can develop. This review describes recent data from genetic analyses of patients with SLE, along with current studies of innate and adaptive immune function that contribute to sustained IFN-I pathway activation, immune activation and autoantibody production, generation of inflammatory mediators and tissue damage. The goal of these studies is to understand disease mechanisms, identify therapeutic targets and stimulate development of therapeutics that can achieve improved outcomes for patients.

ADAR1 Zα domain P195A mutation activates the MDA5-dependent RNA-sensing signaling pathway in brain without decreasing overall RNA editing

Variants of the RNA-editing enzyme ADAR1 cause Aicardi-Goutières syndrome (AGS), in which severe inflammation occurs in the brain due to innate immune activation. Here, we analyze the RNA-editing status and innate immune activation in an AGS mouse model that carries the Adar P195A mutation in the N terminus of the ADAR1 p150 isoform, the equivalent of the P193A human Zα variant causal for disease. This mutation alone can cause interferon-stimulated gene (ISG) expression in the brain, especially in the periventricular areas, reflecting the pathologic feature of AGS. However, in these mice, ISG expression does not correlate with an overall decrease in RNA editing. Rather, the enhanced ISG expression in the brain due to the P195A mutant is dose dependent. Our findings indicate that ADAR1 can regulate innate immune responses through Z-RNA binding without changing overall RNA editing.

Activation of the cGAS-STING innate immune response in cells with deficient mitochondrial topoisomerase TOP1MT

The recognition that cytosolic mitochondrial DNA (mtDNA) activates cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) innate immune signaling has unlocked novel disease mechanisms. Here, an uncharacterized variant predicted to affect TOP1MT function, P193L, was discovered in a family with multiple early onset autoimmune diseases, including Systemic Lupus Erythematosus (SLE). Although there was no previous genetic association between TOP1MT and autoimmune disease, the role of TOP1MT as a regulator of mtDNA led us to investigate whether TOP1MT could mediate the release of mtDNA to the cytosol, where it could then activate the cGAS-STING innate immune pathway known to be activated in SLE and other autoimmune diseases. Through analysis of cells with reduced TOP1MT expression, we show that loss of TOP1MT results in release of mtDNA to the cytosol, which activates the cGAS-STING pathway. We also characterized the P193L variant for its ability to rescue several TOP1MT functions when expressed in TOP1MT knockout cells. We show that the P193L variant is not fully functional, as its re-expression at high levels was unable to rescue mitochondrial respiration deficits, and only showed partial rescue for other functions, including repletion of mtDNA replication following depletion, nucleoid size, steady state mtDNA transcripts levels and mitochondrial morphology. Additionally, expression of P193L at endogenous levels was unable to rescue mtDNA release-mediated cGAS-STING signaling. Overall, we report a link between TOP1MT and mtDNA release leading to cGAS-STING activation. Moreover, we show that the P193L variant has partial loss of function that may contribute to autoimmune disease susceptibility via cGAS-STING mediated activation of the innate immune system.

Clinical spectrum and currently available treatment of type I interferonopathy Aicardi-Goutières syndrome

BACKGROUND

Aicardi-Goutières syndrome (AGS) is a genetically determined disorder with a variable phenotype. Since the original description of AGS, advances in gene sequencing techniques have resulted in a significant broadening of the phenotypic spectrum associated with AGS genes, and new clinical pictures have emerged beyond the classic presentation. The aim of this review is to provide a comprehensive analysis of the clinical spectrum of AGS and report currently available treatments and new immunosuppressive strategies.

DATA SOURCES

Literature reviews and original research articles were collected from databases, including PubMed and ClinicalTrials.gov. Relevant articles about AGS were included.

RESULTS

The involvement of the nervous system certainly represents the major cause of mortality and morbidity in AGS patients. However, other clinical manifestations, such as chilblains, hepatosplenomegaly, and hematological disturbances, may lead to the diagnosis and considerably impact the prognosis and overall quality of life of these patients. Therapeutic approaches of AGS are limited to interventions aimed at specific symptoms and the management of multiple comorbidities. However, advances in understanding the pathogenesis of AGS could open new and more effective therapies.

CONCLUSIONS

The over-activation of innate immunity due to upregulated interferon production plays a critical role in AGS, leading to multi-organ damage with the main involvement of the central nervous system. To date, there is no specific and effective treatment for AGS. New drugs specifically targeting the interferon pathway may bring new hope to AGS patients.

Multiple pals gene modules control a balance between immunity and development in Caenorhabditis elegans

The immune system continually battles against pathogen-induced pressures, which often leads to the evolutionary expansion of immune gene families in a species-specific manner. For example, the pals gene family expanded to 39 members in the Caenorhabditis elegans genome, in comparison to a single mammalian pals ortholog. Our previous studies have revealed that two members of this family, pals-22 and pals-25, act as antagonistic paralogs to control the Intracellular Pathogen Response (IPR). The IPR is a protective transcriptional response, which is activated upon infection by two molecularly distinct natural intracellular pathogens of C. elegans-the Orsay virus and the fungus Nematocida parisii from the microsporidia phylum. In this study, we identify a previously uncharacterized member of the pals family, pals-17, as a newly described negative regulator of the IPR. pals-17 mutants show constitutive upregulation of IPR gene expression, increased immunity against intracellular pathogens, as well as impaired development and reproduction. We also find that two other previously uncharacterized pals genes, pals-20 and pals-16, are positive regulators of the IPR, acting downstream of pals-17. These positive regulators reverse the effects caused by the loss of pals-17 on IPR gene expression, immunity, and development. We show that the negative IPR regulator protein PALS-17 and the positive IPR regulator protein PALS-20 colocalize inside and at the apical side of intestinal epithelial cells, which are the sites of infection for IPR-inducing pathogens. In summary, our study demonstrates that several pals genes from the expanded pals gene family act as ON/OFF switch modules to regulate a balance between organismal development and immunity against natural intracellular pathogens in C. elegans.

SAMHD1 impairs type I interferon induction through the MAVS, IKKε, and IRF7 signaling axis during viral infection

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) restricts human immunodeficiency virus type 1 (HIV-1) infection by reducing the intracellular dNTP pool. We have shown that SAMHD1 suppresses nuclear factor kappa-B activation and type I interferon (IFN-I) induction by viral infection and inflammatory stimuli. However, the mechanism by which SAMHD1 inhibits IFN-I remains unclear. Here, we show that SAMHD1 inhibits IFN-I activation induced by the mitochondrial antiviral-signaling protein (MAVS). SAMHD1 interacted with MAVS and suppressed MAVS aggregation in response to Sendai virus infection in human monocytic THP-1 cells. This resulted in increased phosphorylation of TANK binding kinase 1 (TBK1), inhibitor of nuclear factor kappa-B kinase epsilon (IKKε), and IFN regulatory factor 3 (IRF3). SAMHD1 suppressed IFN-I activation induced by IKKε and prevented IRF7 binding to the kinase domain of IKKε. We found that SAMHD1 interaction with the inhibitory domain (ID) of IRF7 (IRF7-ID) was necessary and sufficient for SAMHD1 suppression of IRF7-mediated IFN-I activation in HEK293T cells. Computational docking and molecular dynamics simulations revealed possible binding sites between IRF7-ID and full-length SAMHD1. Individual substitution of F411, E416, or V460 in IRF7-ID significantly reduced IRF7 transactivation activity and SAMHD1 binding. Furthermore, we investigated the role of SAMHD1 inhibition of IRF7-mediated IFN-I induction during HIV-1 infection. We found that THP-1 cells lacking IRF7 expression had reduced HIV-1 infection and viral transcription compared to control cells, indicating a positive role of IRF7 in HIV-1 infection. Our findings suggest that SAMHD1 suppresses IFN-I induction through the MAVS, IKKε, and IRF7 signaling axis.

Preimplantation genetic testing for Aicardi-Goutières syndrome induced by novel compound heterozygous mutations of TREX1: an unaffected live birth

BACKGROUND

Aicardi-Goutières syndrome (AGS) is a rare, autosomal recessive, hereditary neurodegenerative disorder. It is characterized mainly by early onset progressive encephalopathy, concomitant with an increase in interferon-α levels in the cerebrospinal fluid. Preimplantation genetic testing (PGT) is a procedure that could be used to choose unaffected embryos for transfer after analysis of biopsied cells, which prevents at-risk couples from facing the risk of pregnancy termination.

METHODS

Trio-based whole exome sequencing, karyotyping and chromosomal microarray analysis were used to determine the pathogenic mutations for the family. To block the inheritance of the disease, multiple annealing and looping-based amplification cycles was used for whole genome amplification of the biopsied trophectoderm cells. Sanger sequencing and next-generation sequencing (NGS)-based single nucleotide polymorphism (SNP) haplotyping were used to detect the state of the gene mutations. Copy number variation (CNV) analysis was also carried out to prevent embryonic chromosomal abnormalities. Prenatal diagnosis was preformed to verify the PGT outcomes.

RESULTS

A novel compound heterozygous mutation in TREX1 gene was found in the proband causing AGS. A total of 3 blastocysts formed after intracytoplasmic sperm injection were biopsied. After genetic analyses, an embryo harbored a heterozygous mutation in TREX1 and without CNV was transferred. A healthy baby was born at 38th weeks and prenatal diagnosis results confirmed the accuracy of PGT.

CONCLUSIONS

In this study, we identified two novel pathogenic mutations in TREX1, which has not been previously reported. Our study extends the mutation spectrum of TREX1 gene and contributes to the molecular diagnosis as well as genetic counseling for AGS. Our results demonstrated that combining NGS-based SNP haplotyping for PGT-M with invasive prenatal diagnosis is an effective approach to block the transmission of AGS and could be applied to prevent other monogenic diseases.