Aicardi–Goutieres syndrome, a rare neurological disease in children: A new autoimmune disorder?

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.

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.

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.

Distinct features of ribonucleotides within genomic DNA in Aicardi-Goutières syndrome (AGS)-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 two AGS-ortholog mutations in 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 yeast AGS-ortholog mutants. We found higher rNMP incorporation in the nuclear genome of rnh201-G42S than in wild-type and rnh203-K46W-mutant cells, and an elevated rCMP content in both mutants. Moreover, we uncovered unique rNMP patterns in each mutant, highlighting a differential activity of the AGS mutants towards rNMPs embedded on the leading or on the lagging strand of DNA replication. This study guides future research on rNMP characteristics in human genomic samples carrying AGS mutations.

In Silico Characterization of RNASEH2A Pathogenic Variants and Identification of Novel Splice Site Donor Variant c.549+1G>T in Indian Population

Background Aicardi-Goutieres syndrome (AGS) is a genetic disorder that has variable manifestations including neurological, immunological, and sometimes other system involvement in various combinations. Considering the high genetic and clinical diversity of AGS and the importance of RNASEH2 complex in the biological system, it is important to take a systematic approach to delineate the genetic diagnosis and impact of missense mutations. Methods Clinical targeted gene sequencing followed by Sanger validation was performed in an individual with the clinical features of AGS. Protein modeling studies of all the reported RNASEH2A missense variants till date were performed using freely available web servers BioGrid, ShinyGO. Protein structures were visualized using Pymol. Results and discussion We identified a novel homozygous splice site donor variant c.549+1G>T in RNASEH2A. Furthermore protein-interactome studies identifiedpotential genetic interactors that include RNASEH2A, RNASEH2B, TYMS, RNASEH2C, RPA1, ORC3, ORC2, CDC6, PCNA, LIG1, PRIM1, RFC2, DUT, GINS1, MCM7, FEN1, MCM4, GINS2, CDK4, and MCM5. Identified genes were mapped to specific pathways using SHINY GO. DNA replication and cell cycle, centrosome cycle, post-replication repair, nucleic acid and metabolic process, cellular response to stress, DNA metabolic process, nucleic acid phosphodiester bond hydrolysis, RNA phosphodiester bond hydrolysis, and DNA biosynthetic process were identified as the linked pathways with the prioritized genes. Conclusion In conclusion, a sophisticated genotype and phenotype correlation followed by linking the genes to the key biological pathways opens new avenues to understand disease pathology and plan for therapeutic interventions.

A case of Aicardi-Goutières syndrome caused by TREX1 gene mutation

Aicardi-Goutières syndrome (AGS) is a rare genetic disorder involving the central nervous system and autoimmune abnormalities, leading to severe intellectual and physical disability with poor prognosis. AGS has a phenotype similar to intrauterine viral infection, which often leads to delays in genetic counseling. In this study, we report a case with a prenatal diagnosis of AGS. The first fetal ultrasound detected bilateral lateral ventricle cystic structures, and fetal MRI was performed to identify other signs. The right parietal lobe signal showed cerebral white matter abnormalities, and fetal brain development level was lower than that of normal fetuses of the same gestational age. Whole-exome sequencing revealed that the fetus carried the TREX1:NM_033629.6:exon2:c.294dup:p. C99Mfs*3 variant, suggesting that the c.294dup mutation of the TREX1 gene was the pathogenic mutation site, and the final comprehensive diagnosis was AGS1. In this article, we also reviewed the previous literature for possible phenotypes in the fetus and found that microcephaly and intrauterine growth retardation may be the first and most important markers of the intrauterine phenotype of AGS.

Comparison between D-loop methylation and mtDNA copy number in patients with Aicardi-Goutières Syndrome

INTRODUCTION

Aicardi-Goutières Syndrome (AGS) is a rare encephalopathy with early onset that can be transmitted in both dominant and recessive forms. Its phenotypic covers a wide range of neurological and extraneurological symptoms. Nine genes that are all involved in nucleic acids (NAs) metabolism or signaling have so far been linked to the AGS phenotype. Recently, a link between autoimmune or neurodegenerative conditions and mitochondrial dysfunctions has been found. As part of the intricate system of epigenetic control, the mtDNA goes through various alterations. The displacement (D-loop) region represents one of the most methylated sites in the mtDNA. The term "mitoepigenetics" has been introduced as a result of increasing data suggesting that epigenetic processes may play a critical role in the control of mtDNA transcription and replication. Since we showed that RNASEH2B and RNASEH2A-mutated Lymphoblastoid Cell Lines (LCLs) derived from AGS patients had mitochondrial alterations, highlighting changes in the mtDNA content, the main objective of this study was to examine any potential methylation changes in the D-loop regulatory region of mitochondria and their relationship to the mtDNA copy number in peripheral blood cells of AGS patients with mutations in various AGS genes and healthy controls.

MATERIALS AND METHODS

We collected blood samples from 25 AGS patients and we performed RT-qPCR to assess the mtDNA copy number and pyrosequencing to measure DNA methylation levels in the D-loop region.

RESULTS

Comparing AGS patients to healthy controls, D-loop methylation levels and mtDNA copy number increased significantly. We also observed that in AGS patients, the mtDNA copy number increased with age at sampling, but not the D-loop methylation levels, and there was no relationship between sex and mtDNA copy number. In addition, the D-loop methylation levels and mtDNA copy number in the AGS group showed a non-statistically significant positive relation.

CONCLUSION

These findings, which contradict the evidence for an inverse relationship between D-loop methylation levels and mtDNA copy number, show that AGS patients have higher D-loop methylation levels than healthy control subjects. Additional research is needed to identify the function of these features in the etiology and course of AGS.

A Case Report and Literature Review of Pseudo-TORCH Syndrome Type 2 (PTORCH2)

A pseudo-TORCH syndrome is a rare autosomal recessive disease characterized by intracranial calcification and microcephaly, leading to spasticity and seizures, but the serology of TORCH infection is negative. We present a 4-day-old female patient with jaundice, abnormal movement, and convulsions who was found to be homozygous for the missense USP18 gene mutation that causes pseudo-TORCH syndrome 2 (PTORCH2). The patient was managed with conservative measures.

Defects of the Innate Immune System and Related Immune Deficiencies

The innate immune system is the host's first line of defense against pathogens. Toll-like receptors (TLRs) are pattern recognition receptors that mediate recognition of pathogen-associated molecular patterns. TLRs also activate signaling transduction pathways involved in host defense, inflammation, development, and the production of inflammatory cytokines. Innate immunodeficiencies associated with defective TLR signaling include mutations in NEMO, IKBA, MyD88, and IRAK4. Other innate immune defects have been associated with susceptibility to herpes simplex encephalitis, viral infections, and mycobacterial disease, as well as chronic mucocutaneous candidiasis and epidermodysplasia verruciformis. Phagocytes and natural killer cells are essential members of the innate immune system and defects in number and/or function of these cells can lead to recurrent infections. Complement is another important part of the innate immune system. Complement deficiencies can lead to increased susceptibility to infections, autoimmunity, or impaired immune complex clearance. The innate immune system must work to quickly recognize and eliminate pathogens as well as coordinate an immune response and engage the adaptive immune system. Defects of the innate immune system can lead to failure to quickly identify pathogens and activate the immune response, resulting in susceptibility to severe or recurrent infections.

Intracellular virus sensor MDA5 mutation develops autoimmune myocarditis and nephritis

Mutations in IFIH1 gene encoding viral RNA sensor MDA5 have been reported responsible for many interferonopathies, including Aicardi-Goutières syndrome (AGS) and monogenic lupus, however, the pathological link between IFIH1 mutations and various autoimmune symptoms remains unclear. Here, we generated transgenic mice expressing human MDA5 R779H mutant (R779H Tg), reported in AGS and monogenic lupus patient. Mice spontaneously developed myocarditis and nephritis with upregulation of type I IFNs in the major organs. R779H Tg Mavs-/- and R779H Tg Ifnar-/- showed no phenotypes, indicating direct MDA5-signaling pathway involvement. Rag-2 deficiency and bone marrow cells transfer from wild type to adult mice did not prevent myocarditis development, while mice with cardiomyocyte-specific expression of hMDA5 R779H showed cardiomegaly and high expression of inflammatory cytokines. Taken together, our study clarifies that type I IFNs production and chemokines from cardiomyocytes starts in neonatal period and is critical for the development of myocarditis. Activated lymphocytes and auto-antibodies exacerbate the pathogenesis but are dispensable for the onset.

Novel Mutations in ACP5 and SAMHD1 in a Patient With Pediatric Systemic Lupus Erythematosus

BACKGROUND

The study of genetic predisposition to pediatric systemic lupus erythematosus (pSLE) has brought new insights into the pathophysiology of SLE, as it is hypothesized that genetic predisposition is greater in children. Furthermore, identifying genetic variants and linking disrupted genes to abnormal immune pathways and clinical manifestations can be beneficial for both diagnosis and treatment. Here, we identified genetic alterations in a patient with childhood-onset SLE and analyzed the immunological mechanisms behind them to support future diagnosis, prognosis, and treatment.

METHODS

Whole exome sequencing (WES) was adopted for genetic analysis of a patient with childhood-onset SLE. Gene mutations were confirmed by Sanger sequencing. Clinical data of this patient were collected and summarized. Ingenuity Pathway Analysis was used to provide interacting genes of the perturbed genes. Online Enrichr tool and Cytoscape software were used to analysis the related pathways of these genes.

RESULTS

We present a case of a 2-year-old girl who was diagnosed with idiopathic thrombocytopenic purpura (ITP) and SLE. The patient was characterized by cutaneous bleeding spots on both lower extremities, thrombocytopenia, decreased serum complements levels, increased urinary red blood cells, and positive ANA and dsDNA. The patient was treated with methylprednisolone and mycophenolate, but clinical remission could not be achieved. The genomic analysis identified three novel mutations in this pSLE patient, a double-stranded missense mutation in ACP5 (c.1152G>T and c.420G>A) and a single-stranded mutation in SAMHD1 (c.1423G>A). Bioinformatic analysis showed that these two genes and their interacting genes are enriched in the regulation of multiple immune pathways associated with SLE, including cytokine signaling and immune cell activation or function. Analysis of the synergistic regulation of these two genes suggests that abnormalities in the type I interferon pathway caused by genetic variants may contribute to the pathogenesis of SLE.

CONCLUSION

The combined complexity of polymorphisms in the coding regions of ACP5 and SAMHD1 influences the susceptibility to SLE. Alterations in these genes may lead to abnormalities in the type I interferon pathway. Our study extends the spectrum of mutations in the ACP5 and SAMHD1 genes. The identification of these mutations could aid in the diagnosis of SLE with genetic counseling and suggest potential precise treatments for specific pathways.

IFN Regulatory Factor 3 in Health and Disease

Immunity to viruses requires an array of critical cellular proteins that include IFN regulatory factor 3 (IRF3). Consequently, most viruses that infect vertebrates encode proteins that interfere with IRF3 activation. This review describes the cellular pathways linked to IRF3 activation and where those pathways are targeted by human viral pathogens. Moreover, key regulatory pathways that control IRF3 are discussed. Besides viral infections, IRF3 is also involved in resistance to some bacterial infections, in anticancer immunity, and in anticancer therapies involving DNA damage agents. A recent finding shows that IRF3 is needed for T cell effector functions that are involved in anticancer immunity and also in T cell autoimmune diseases. In contrast, unregulated IRF3 activity is clearly not beneficial, considering it is implicated in certain interferonopathies, in which heightened IRF3 activity leads to IFN-β-induced disease. Therefore, IRF3 is involved largely in maintaining health but sometimes contributing to disease.

Nucleic Acid Sensors as Therapeutic Targets for Human Disease

Innate immune sensors that detect nucleic acids are attractive targets for therapeutic intervention because of their diverse roles in many disease processes. In detecting RNA and DNA from either self or non-self, nucleic acid sensors mediate the pathogenesis of many autoimmune and inflammatory conditions. Despite promising pre-clinical data and investigational use in the clinic, relatively few drugs targeting nucleic acid sensors are approved for therapeutic use. Nevertheless, there is growing appreciation for the untapped potential of nucleic acid sensors as therapeutic targets, driven by the need for better therapies for cancer, infectious diseases, and autoimmune disorders. This review highlights the diverse mechanisms by which nucleic acid sensors are activated and exert their biological effects in the context of various disease settings. We discuss current therapeutic strategies utilizing agonists and antagonists targeting nucleic acid sensors to treat infectious disease, cancer, and autoimmune and inflammatory disorders.

Case Report: The JAK-Inhibitor Ruxolitinib Use in Aicardi-Goutieres Syndrome Due to ADAR1 Mutation

Type I Interferonopathies comprise inherited inflammatory diseases associated with perturbation of the type I IFN response. Use of Janus kinase (JAK) inhibitors has been recently reported as possible tools for treating some of those rare diseases. We describe herein the clinical picture and treatment response to the JAK-inhibitor ruxolitinib in a 5-year-old girl affected by Aicardi-Goutières Syndrome type 6 (AGS6) due to ADAR1 mutation. The girl's interferon score (IS) was compared with that of her older brother, suffering from the same disorder, who was not treated. We observed a limited, but distinct neurological improvement (Gross Motor Function and Griffiths Mental Development Scales). Analysis of IS values of the two siblings during the treatment showed several changes, especially related to infections; the IS values of the child treated with ruxolitinib were consistently lower than those measured in her brother. Based on these observations we suggest that the use of ruxolitinib in children with the same condition might be effective in inhibiting type I interferon response and that starting this therapy at early age in children with AGS could mitigate the detrimental effects of type I interferon hyperproduction.

Case Report: Aicardi-Goutières Syndrome Caused by Novel TREX1 Variants

TREX1 (three prime repair exonuclease 1) gene encodes DNA 3' end repair exonuclease that plays an important role in DNA repair. Mutations in TREX1 gene have been identified as the cause of a rare autoimmune neurological disease, Aicardi-Goutières syndrome (AGS). Here, we report an AGS case of a 6-month-old Chinese girl with novel TREX1 variants. The patient had mild rashes on the face and legs, increased muscle tensions in the limbs, and positive cervical correction reflex. Cranial magnetic resonance imaging showed that there were patches of slightly longer T1 and T2 signals in the bilateral cerebral hemisphere and brainstem white matter, mainly in the frontotemporal lobe, together with decreased white matter volume, enlarged ventricles, and widened sulcus fissure. Total exon sequencing showed that the TREX1 gene of the child had mutations of c.137_138insC and c.292_293insA, which had not been reported before. In addition, elevated type I interferons were detected by using enzyme-linked immunosorbent assay in the patient's serum. Together, our study demonstrated that novel TREX1 variants (c.137_138insC and c.292_293insA) cause AGS for the first time.

The translational value of animal models in orphan medicines designations for rare paediatric neurological diseases

Rare diseases are characterized by a substantial unmet need mostly because the majority have limited, or no treatment options and a large number also affect children. Appropriate animal models, based on the knowledge of the molecular pathology of the human disease, are a significant element to support the medical plausibility of an orphan designation during the development of orphan medicines for rare neurological diseases. This observational, retrospective study aims to investigate the clinical or nonclinical nature of data submitted to support medical plausibility of orphan designations in the EU (2001-2019), for a group of rare and paediatric neurological diseases. From our sample of 30 diseases, 70% are rare with paediatric onset and 37% have approved orphan designations. The use of nonclinical data was significantly higher than clinical data (65% vs. 35%, p = 0.013) to support medical plausibility. Examples of diseases, with orphan designations based only in nonclinical data, are also discussed: Aicardi-Goutières syndrome and Centronuclear myopathy animal disease models, potentially used to support medical plausibility of medicines. Nonclinical appropriate models, assessing disease relevant endpoints, may contribute to increase the translational value of animal models, in paediatric and rare neurological area, to accelerate research and the effective development of treatment options.

Glial cells in the driver seat of leukodystrophy pathogenesis

Glia cells are often viewed as support cells in the central nervous system, but recent discoveries highlight their importance in physiological functions and in neurological diseases. Central to this are leukodystrophies, a group of progressive, neurogenetic disease affecting white matter pathology. In this review, we take a closer look at multiple leukodystrophies, classified based on the primary glial cell type that is affected. While white matter diseases involve oligodendrocyte and myelin loss, we discuss how astrocytes and microglia are affected and impinge on oligodendrocyte, myelin and axonal pathology. We provide an overview of the leukodystrophies covering their hallmark features, clinical phenotypes, diverse molecular pathways, and potential therapeutics for clinical trials. Glial cells are gaining momentum as cellular therapeutic targets for treatment of demyelinating diseases such as leukodystrophies, currently with no treatment options. Here, we bring the much needed attention to role of glia in leukodystrophies, an integral step towards furthering disease comprehension, understanding mechanisms and developing future therapeutics.

A Novel Mutation in Aicardi–Goutières' Syndrome: A Case Report

Aicardi–Goutières' syndrome (AGS) is a rare heterogeneous genetic disorder characterized by encephalopathy and may bear resemblance to congenital infections. The prevalence of AGS is estimated at more than 4,000 worldwide. Mutations in TREX1 gene are present in ∼22% of patients. We present the case of a 2-year-old boy who came to the Biogene laboratory (Tehran, Iran) with a constellation of congenital disorders but no clear diagnosis. His clinical phenotype consisted of neonatal jaundice, relative microcephaly with diffuse cerebral atrophy in both hemispheres, developmental delay, hypotonia, and nystagmus. There was history of parental consanguineous marriage and prematurity. In our study, a homozygous potentially pathogenic mutation in TREX1 gene associated with AGS1 was detected. This mutation has not been reported in the other patients with AGS. A novel frameshift homozygous potentially pathogenic mutation in TREX1 is postulated to be the cause of disease in our patient.

A homozygote frameshift mutation in OCLN gene result in Pseudo-TORCH syndrome type I: A case report extending the phenotype with central diabetes insipidus and renal dysfunction

Intrauterine infections with the pathogens, including toxoplasmosis, other (syphilis, varicella, mumps, parvovirus, and HIV), rubella, cytomegalovirus, and herpes simplex (TORCH) in susceptible individuals during pregnancy, result in microcephaly, white matter disease, cerebral atrophy, and calcifications in the fetus. Pseudo-TORCH syndrome is an umbrella term, consisting of several syndromes, resultant from different genetic alterations and pathogenetic mechanisms. Band-like calcification with simplified gyration and polymicrogyria (BLC-PMG) is one of these conditions, resultant from biallelic mutations in the OCLN gene, located in the chromosome 5q13.2. OCLN gene encodes occludin, a tight junction protein, which is expressed in the endothelia. The absence of occludin in the developing brain subsequently results in abnormal blood-brain barrier, thus immune-cell mediated tissue damage and cortical malformation. Herein, we present a pediatric patient who had progressive microcephaly, spasticity, multi-drug resistant epilepsy, PMG and intracranial band-type calcifications, accompanied by central diabetes insipidus and renal dysfunction. Whole exome sequencing revealed a homozygote W58Ffs*10 (c.173_194del) frameshift mutation in the OCLN gene. Of 34 BLC-PMG cases with demonstrable OCLN mutations, only three had renal manifestations, which is responsible for the majority of the demises. This is the first case diagnosed as having central diabetes insipidus and responded to desmopressin treatment to the best of our knowledge, however, this clinical improvement could not prevent the patient from renal dysfunction. The patient deceased at four years of age from sepsis, therefore early diagnosis, optimal follow-up for renal involvement and infection prevention measures are necessary for the patients with BLC-PMG.

Novel and emerging treatments for Aicardi-Goutières syndrome

Introduction: Aicardi-Goutières syndrome (AGS) is the prototype of the type I interferonopathies, a new heterogeneous group of autoinflammatory disorders in which type I interferon plays a pivotal role. The disease usually manifests itself during infancy, primarily affecting the brain and the skin, and is characterized by cerebrospinal fluid chronic lymphocytosis and raised levels of interferon-alpha and by cardinal neuroradiological features: cerebral calcification, leukoencephalopathy and cerebral atrophy. Recently many aspects of the pathogenesis of AGS have been clarified, making it possible to hypothesize new therapeutic strategies.Areas covered: We here review recent data concerning pathogenesis and novel therapeutic strategies in AGS, including the use of Janus kinase inhibitors, reverse transcriptase inhibitors, anti-IFN-α antibodies, anti-interleukin antibodies, antimalarial drugs and other cGAS inhibitors.Expert opinion: Thanks to the identification of the molecular basis of AGS, many aspects of its pathogenesis have been clarified, making it possible to propose new therapeutic strategies for AGS and type I interferonopathies. A number of therapeutic options are now becoming possible, even though their efficacy is still to be proven. However, in spite of research advances coming from clinical trials and case series, there are still a number of open questions, which urgently need to be addressed.

Invention and Early History of Gapmers

Gapmers are antisense oligonucleotides composed of a central DNA segment flanked by nucleotides of modified chemistry. Hybridizing with transcripts by sequence complementarity, gapmers recruit ribonuclease H and induce target RNA degradation. Since its concept first emerged in the 1980s, much work has gone into developing gapmers for use in basic research and therapy. These include improvements in gapmer chemistry, delivery, and therapeutic safety. Gapmers have also successfully entered clinical trials for various genetic disorders, with two already approved by the U.S. Food and Drug Administration for the treatment of familial hypercholesterolemia and transthyretin amyloidosis-associated polyneuropathy. Here, we review the events surrounding the early development of gapmers, from conception to their maturity, and briefly conclude with perspectives on their use in therapy.

Generation of three iPSC lines from fibroblasts of a patient with Aicardi Goutières Syndrome mutated in TREX1

Fibroblasts from a patient with Aicardi Goutières Syndrome (AGS) carrying a compound heterozygous mutation in TREX1, were reprogrammed into induced pluripotent stem cells (iPSCs) to establish isogenic clonal stem cell lines: UNIBSi006-A, UNIBSi006-B, and UNIBSi006-C. Cells were transduced using the episomal Sendai viral vectors, containing human OCT4, SOX2, c-MYC and KLF4 transcription factors. The transgene-free iPSC lines showed normal karyotype, expressed pluripotent markers and displayed in vitro differentiation potential toward cells of the three embryonic germ layers.

Multiple Autoimmune Disorders in Aicardi-Goutières Syndrome

BACKGROUND

Aicardi-Goutières syndrome is an early-onset encephalopathy with presumed immune pathogenesis caused by inherited defects in nucleic acid metabolism. It is a model disease to study systemic autoimmunity, and there are many clinical, genetic, and basic science considerations that underline a possible overlap between Aicardi-Goutières syndrome and systemic lupus erythematosus.

RESULTS

We describe a 15-year-old girl with Aicardi-Goutières syndrome due to compound heterozygous pathogenic variants in SAMHD1 (sterile alpha motif domain and HD domain-containing protein 1). Over time, she developed multiple autoimmune diseases (vitiligo, alopecia areata, immune thrombocytopenia, positive antithyroglobulin antibodies) without positive antinuclear antibody or features of systemic lupus erythematosus. Her thrombocytopenia was refractory to treatment with corticosteroids and intravenous immunoglobulin but responded to a standard course of rituximab.

CONCLUSION

This is the first report of a multiple autoimmune syndrome in a patient with molecularly proven Aicardi-Goutières syndrome. This study illustrates an emerging pattern of the natural history of Aicardi-Goutières syndrome characterized by early encephalopathic presentation followed by symptoms of systemic autoimmunity.

Molecular Genetics and Interferon Signature in the Italian Aicardi Goutières Syndrome Cohort: Report of 12 New Cases and Literature Review

Aicardi-Goutières syndrome (AGS) is a genetically determined early onset encephalopathy characterized by cerebral calcification, leukodystrophy, and increased expression of interferon-stimulated genes (ISGs). Up to now, seven genes (TREX1, RNASEH2B, RNASEH2C, RNASEH2A, ADAR1, SAMHD1, IFIH1) have been associated with an AGS phenotype. Next Generation Sequencing (NGS) analysis was performed on 51 AGS patients and interferon signature (IS) was investigated in 18 AGS patients and 31 healthy controls. NGS identified mutations in 48 of 51 subjects, with three patients demonstrating a typical AGS phenotype but not carrying mutations in known AGS-related genes. Five mutations, in RNASEH2B, SAMHD1 and IFIH1 gene, were not previously reported. Eleven patients were positive and seven negatives for the upregulation of interferon signaling (IS > 2.216). This work presents, for the first time, the genetic data of an Italian cohort of AGS patients, with a higher percentage of mutations in RNASEH2B and a lower frequency of mutations in TREX1 than those seen in international series. RNASEH2B mutated patients showed a prevalence of negative IS consistent with data reported in the literature. We also identified five novel pathogenic mutations that warrant further functional investigation. Exome/genome sequencing will be performed in future studies in patients without a mutation in AGS-related genes.

A STING to inflammation and autoimmunity

Various intracellular pattern recognition receptors (PRRs) recognize cytosolic pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Cyclic GMP-AMP synthase (cGAS), a cytosolic PRR, recognizes cytosolic nucleic acids including dsDNAs. The recognition of dsDNA by cGAS generates cyclic GMP-AMP (GAMP). The cGAMP is then recognized by STING generating type 1 IFNs and NF-κB-mediated generation of pro-inflammatory cytokines and molecules. Thus, cGAS-STING signaling mediated recognition of cytosolic dsDNA causing the induction of type 1 IFNs plays a crucial role in innate immunity against cytosolic pathogens, PAMPs, and DAMPs. The overactivation of this system may lead to the development of autoinflammation and autoimmune diseases. The article opens with the introduction of different PRRs involved in the intracellular recognition of dsDNA and gives a brief introduction of cGAS-STING signaling. The second section briefly describes cGAS as intracellular PRR required to recognize intracellular nucleic acids (dsDNA and CDNs) and the formation of cGAMP. The cGAMP acts as a second messenger to activate STING- and TANK-binding kinase 1-mediated generation of type 1 IFNs and the activation of NF-κB. The third section of the article describes the role of cGAS-STING signaling in the induction of autoinflammation and various autoimmune diseases. The subsequent fourth section describes both chemical compounds developed and the endogenous negative regulators of cGAS-STING signaling required for its regulation. Therapeutic targeting of cGAS-STING signaling could offer new ways to treat inflammatory and autoimmune diseases.

Brain microglia activation induced by intracranial administration of oligonucleotides and its pharmacological modulation

Oligonucleotide overloading results in type I interferonopathies such as the Aicardi-Goutiéres Syndrome, a progressive encephalopathy determined by an immune response against endogenous DNA/RNA molecules. No therapy targeting pathogenic mechanisms is available for affected patients. Accordingly, we set up an in vitro/in vivo experimental model aimed at reproducing the pathogenic mechanisms of type I interferonopathies, in order to develop an effective pharmacological modulation and toxicological alterations caused by intracranial delivery of encapsulated CpG. The in vitro model used Aicardi-Goutiéres Syndrome immortalized lymphocytes activated by interferon I and co-cultured with human astrocytes; lymphocyte neurotoxicity was attenuated by the calcineurin-inhibitor Tacrolimus and by the anti-interferon monoclonal antibody Sifalimumab. The in vivo model was set up in mice by subcutaneous injection of encapsulated CpG oligonucleotides; the immune-stimulating activity was demonstrated by cytometric analysis in the spleen. To mime pathogenesis of type I interferonopathies in the central nervous system, CpG oligonucleotides were administered intracranially in mice. In the brain, CpG overload induced a rapid activation of macrophage-like microglial cells and focal accumulation mononuclear cells. The subcutaneous administration of Tacrolimus and, more potently, Sifalimumab attenuated CpG-induced brain alterations. These findings shed light on molecular mechanisms triggered by oligonucleotides to induce brain damage. Monoclonal antibodies inhibiting interferon seem a promising therapeutic strategy to protect brain in type I interferonopathies.

Sine causa tetraparesis: A pilot study on its possible relationship with interferon signature analysis and Aicardi Goutières syndrome related genes analysis

Tetraparesis is usually due to cerebral palsy (CP), inborn errors of metabolism, neurogenetic disorders and spinal cord lesions. However, literature data reported that about 10% of children with tetraparesis show a negative/non-specific neuroradiological findings without a specific etiological cause. Aicardi Goutières Syndrome (AGS) is a genetic encephalopathy that may cause tetraparesis. Interferon signature is a reliable biomarker for AGS and could be performed in sine-causa tetraparesis. The aim of the study was to examine the type I interferon signature and AGS related-genes in children with sine causa tetraparesis, to look for misdiagnosed AGS. A secondary aim was to determine which aspects of the patient history, clinical picture and brain imaging best characterize tetraparesis due to an interferonopathy.Seven out of 78 patients affected by tetraparesis, characterized by unremarkable pre-peri-postnatal history and normal/non-specific brain magnetic resonance imaging (MRI) were selected and underwent anamnestic data collection, clinical examination, brain imaging review, peripheral blood interferon signature and AGS-related genes analysis.At our evaluation time (mean age of 11.9 years), all the 7 patients showed spastic-dystonic tetraparesis. At clinical onset brain MRI was normal in 4 and with non-specific abnormalities in 3; at follow-up 3 patients presented with new white-matter lesions, associated with brain calcification in 1 case. Interferon signature was elevated in one subject who presented also a mutation of the IFIH1 gene.AGS should be considered in sine-causa tetraparesis. Core features of interferonopathy-related tetraparesis are: onset during first year of life, psychomotor regression with tetraparesis evolution, brain white-matter lesions with late calcifications. A positive interferon signature may be a helpful marker to select patients with spastic tetraparesis who should undergo genetic analysis for AGS.

Aicardi-Goutières Syndrome: Brief Case Report

The case of a term newborn diagnosed with Aicardi-Goutières syndrome, a rare encephalopathy in our environment, with Mendelian inheritance pattern, characterized by a set of nonspecific neurological symptoms associated with typical findings of intracerebral calcifications. The case is presented with diagnostic imaging, in addition to elevated levels of interferon alpha and cerebrospinal fluid lymphocytosis.

Phenotypic and Molecular Spectrum of Aicardi-Goutières Syndrome: A Study of 24 Patients

BACKGROUND

Aicardi-Goutières syndrome is a rare genetic neurological disorder with variable clinical manifestations. Molecular detection of specific mutations is required to confirm the diagnosis. The aim of this study was to review the clinical and molecular diagnostic findings in 24 individuals with Aicardi-Goutières syndrome who presented during childhood in an Arab population.

MATERIALS AND METHODS

We reviewed the records of 24 patients from six tertiary hospitals in different Arab countries. All included patients had a molecular diagnosis of Aicardi-Goutières syndrome.

RESULTS

Six individuals with Aicardi-Goutières syndrome (25%) had a neonatal presentation, whereas the remaining patients presented during the first year of life. Patients presented with developmental delay (24 cases, 100%); spasticity (24 cases, 100%); speech delay (23 cases, 95.8%); profound intellectual disability (21 cases, 87.5%); truncal hypotonia (21 cases, 87.5%); seizures (eighteen cases, 75%); and epileptic encephalopathy (15 cases, 62.5%). Neuroimaging showed white matter abnormalities (22 cases, 91.7%), cerebral atrophy (75%), and small, multifocal calcifications in the lentiform nuclei and deep cerebral white matter (54.2%). Homozygous mutations were identified in RNASEH2B (54.2%), RNASEH2A (20.8%), RNASEH2C (8.3%), SAMHD1 (8.3%), TREX1 (4.2%), and heterozygous mutations in IFIH1 (4.2%), with c.356A>G (p.Asp119Gly) in RNASEH2B being the most frequent mutation. Three novel mutations c.987delT and c.625 + 1G>A in SAMHD1 gene and c.961G>T in the IFIHI1 gene were identified.

CONCLUSIONS

This is the largest molecularly confirmed Aicardi-Goutières syndrome cohort from Arabia. By presenting these clinical and molecular findings, we hope to raise awareness of Aicardi-Goutières syndrome and to demonstrate the importance of specialist referral and molecular diagnosis.

Neurometabolic and neurodegenerative diseases in children

Neurometabolic and neurodegenerative diseases in children (NDDC) differ from those in adults in that most of the former are autosomal-recessively inherited - few have X-linked inheritance - while the latter are often sporadic or autosomal-dominantly inherited. NDDC may be catabolic and/or anabolic conditions, some of which combine maldevelopmental and degenerative features, for instance, peroxisomal biogenesis disorders or congenital disorders of glycosylation. NDDC are often multiorgan disorders, such as lysosomal, peroxisomal, and polyglucosan disorders. This multiorgan involvement may be marked by extracerebral formation of disease-specific neuropathologic findings, especially in lysosomal diseases allowing diagnostic biopsies in easily accessible tissues, e.g., blood lymphocytes, skin, skeletal muscle, and rectum to be investigated by electron microscopy. NDDC comprise nonvacuolar and vacuolar lysosomal, peroxisomal, polyglucosan, amino and organic acid, white-matter disorders, and congenital disorders of glycosylation.

Nucleic acid-sensing TLRs and autoimmunity: novel insights from structural and cell biology

Invasion of pathogenic microorganisms or tissue damage activates innate immune signaling receptors that sample subcellular locations for foreign molecular structures, altered host molecules, or signs of compartment breaches. Upon engagement of innate immune receptors an acute but transient inflammatory response is initiated, aimed at the clearance of pathogens and cellular debris. Among the molecules that are sensed are nucleic acids, which activate several members of the transmembrane Toll-like receptor (TLR) family. Inappropriate recognition of nucleic acids by TLRs can cause inflammatory pathologies and autoimmunity. Here, we review the mechanisms involved in triggering nucleic acid-sensing TLRs and indicate checkpoints that restrict their activation to endolysosomal compartments. These mechanisms are crucial to sample the content of endosomes for nucleic acids in the context of infection or tissue damage, yet prevent accidental activation by host nucleic acids under physiological conditions. Decoding the molecular mechanisms that regulate nucleic acid recognition by TLRs is central to understand pathologies linked to unrestricted nucleic acid sensing and to develop novel therapeutic strategies.

Exploring Autoimmunity in a Cohort of Children with Genetically Confirmed Aicardi-Goutières Syndrome

PURPOSE

The purpose of this study was to explore the presence of autoimmune manifestations and characterize the autoantibody production in a cohort of patients with Aicardi-Goutières syndrome (AGS).

METHODS

Seventeen patients with a genetically-confirmed diagnosis of AGS were recruited. At the time of enrollment, past medical and family history was reviewed, looking for possible signs or symptoms of autoimmune disorders. Blood samples were taken, for the detection of a panel of autoantibodies: anti-nuclear, anti-double-stranded-DNA, anti-nucleosome, anti-extractable nuclear antigens, anti-cardiolipin IgG/IgM, anti-β2glycoprotein I IgG/IgM, and anti-neutrophil cytoplasmic. We also measured complement levels determined as C3 and C4 quantification and total complement activity, measured as CH50.

RESULTS

Nine of seventeen patients presented with at least one first- or second-degree relative with a history of autoimmune diseases (the childrens' mother or grand-mother in the majority of cases). A specific autoimmune disease was present in only one AGS patient, namely an autoimmune thyroiditis. Autoantibodies were present in 9/17 patients, with different patterns of positivity. Complement levels were normal in all the patients. There was no correlation between auto-antibody production and personal or family history of autoimmune diseases.

CONCLUSIONS

Definite autoimmune diseases are not common in patients with AGS. Autoantibodies are mainly directed towards nucleic acids-containing elements but seem not to be pathogenic and, rather, may represent an epiphenomenon of the enhanced interferon production.

The diagnosis and clinical management of the neuropsychiatric manifestations of lupus

Neuropsychiatric (NP) involvement in Systemic Lupus Erythematosus (SLE), can be a severe and troubling manifestation of the disease that heavily impacts patient's health, quality of life and disease outcome. It is one of the most complex expressions of SLE which can affect central, peripheral and autonomous nervous system. Complex interrelated pathogenetic mechanisms, including genetic factors, vasculopathy, vascular occlusion, neuroendocrine-immune imbalance, tissue and neuronal damage mediated by autoantibodies, inflammatory mediators, blood brain barrier dysfunction and direct neuronal cell death can be all involved. About NPSLE a number of issues are still matter of debate: from classification and burden of NPSLE to attribution and diagnosis. The role of neuroimaging and new methods of investigation still remain pivotal and rapidly evolving as well as is the increasing knowledge in the pathogenesis. Overall, two main pathogenetic pathways have been recognized yielding different clinical phenotypes: a predominant ischemic-vascular one involving large and small blood vessels, mediated by aPL, immune complexes and leuko-agglutination which it is manifested with more frequent focal NP clinical pictures and a predominantly inflammatory-neurotoxic one mediated by complement activation, increased permeability of the BBB, intrathecal migration of autoantibodies, local production of immune complexes and pro-inflammatory cytokines and other inflammatory mediators usually appearing as diffuse NP manifestations. In the attempt to depict a journey throughout NPSLE from diagnosis to a reasoned therapeutic approach, classification, epidemiology, attribution, risk factors, diagnostic challenges, neuroimaging techniques and pathogenesis will be considered in this narrative review based on the most relevant and recent published data.

Practice parameter for the diagnosis and management of primary immunodeficiency

The American Academy of Allergy, Asthma & Immunology (AAAAI) and the American College of Allergy, Asthma & Immunology (ACAAI) have jointly accepted responsibility for establishing the "Practice parameter for the diagnosis and management of primary immunodeficiency." This is a complete and comprehensive document at the current time. The medical environment is a changing environment, and not all recommendations will be appropriate for all patients. Because this document incorporated the efforts of many participants, no single individual, including those who served on the Joint Task Force, is authorized to provide an official AAAAI or ACAAI interpretation of these practice parameters. Any request for information about or an interpretation of these practice parameters by the AAAAI or ACAAI should be directed to the Executive Offices of the AAAAI, the ACAAI, and the Joint Council of Allergy, Asthma & Immunology. These parameters are not designed for use by pharmaceutical companies in drug promotion.

Unique topics and issues in rheumatology and clinical immunology

Clinicians are facing unexpected issues in everyday practice, and these may become counterintuitive or challenging. Illustrative examples are provided by the hypersensitivity to universally used immunosuppressants such as corticosteroids or antibiotics such as beta-lactam. Secondly, additional issues are represented by the discovery of new pathogenetic mechanisms involved in rheumatoid and psoriatic arthritis or other chronic inflammatory diseases, genomic susceptibility to enigmatic diseases such as giant cell arteritis, or the shared role of specific mediators such as semaphorins. Third, the therapeutic armamentarium has dramatically changed over the past decade following the introduction of biotechnological drugs, and new mechanisms are being proposed to reduce adverse events or increase the drug effectiveness, particularly on cardiovascular comorbidities. Finally, rare diseases continue to represent difficult cases, as for Cogan's syndrome, with limited literature available for clinical recommendations. For these reason, the present issue of Clinical Reviews in Allergy and Immunology is timely and dedicated to these and other unique topics in clinical immunology and allergy. The aim of this issue is thus to help clinicians involved in internal medicine as well as allergists and clinical immunologists while discussing new pathways that will prove important in the near future.

SAMHD1 Inhibits LINE-1 Retrotransposition by Promoting Stress Granule Formation

The SAM domain and HD domain containing protein 1 (SAMHD1) inhibits retroviruses, DNA viruses and long interspersed element 1 (LINE-1). Given that in dividing cells, SAMHD1 loses its antiviral function yet still potently restricts LINE-1, we propose that, instead of blocking viral DNA synthesis by virtue of its dNTP triphosphohydrolase activity, SAMHD1 may exploit a different mechanism to control LINE-1. Here, we report a new activity of SAMHD1 in promoting cellular stress granule assembly, which correlates with increased phosphorylation of eIF2α and diminished eIF4A/eIF4G interaction. This function of SAMHD1 enhances sequestration of LINE-1 RNP in stress granules and consequent blockade to LINE-1 retrotransposition. In support of this new mechanism of action, depletion of stress granule marker proteins G3BP1 or TIA1 abrogates stress granule formation and overcomes SAMHD1 inhibition of LINE-1. Together, these data reveal a new mechanism for SAMHD1 to control LINE-1 by activating cellular stress granule pathway.

Long interspersed element 1 (LINE-1 or L1) comprises 17% of human genome, and has played a major role in shaping the evolution of human genome. Approximately 100 copies of LINE-1 are still active in an average individual genome. Movement of these LINE-1 sequences to new loci in the genome has the potential of causing sporadic cases of disease. Among the multi-layered mechanisms by which the host controls LINE-1 activity is a group of host restriction factors including APOBEC3 proteins. SAMHD1 was known for the association of its mutations with the Aicardi-Goutieres syndrome (AGS), a congenital autoimmune disease. SAMHD1 was recently reported as a host restriction factor that inhibits a number of retroviruses and DNA viruses including human immunodeficiency virus type 1 (HIV-1) and herpes simplex virus 1 (HSV-1). Here, we demonstrate that SAMHD1 inhibits LINE-1 retrotransposition through promoting the sequestration of LINE-1 RNP within the cytoplasmic stress granules. SAMHD1 promotes the formation of large stress granules by inducing phosphorylation of eIF2α and disrupting eIF4A/eIF4G interaction. This is the first report describing the role of SAMHD1 in modulating the formation of stress granules. We envision that this function of SAMHD1 not only contributes to the inhibition of LINE-1, but also the restriction of various viruses.

Posterior reversible encephalopathy syndrome--Insight into pathogenesis, clinical variants and treatment approaches

Posterior reversible encephalopathy syndrome is a rare clinicoradiological entity characterized by typical MRI findings located in the occipital and parietal lobes, caused by subcortical vasogenic edema. It was first described as a distinctive syndrome by Hinchey in 1996. Etiopathogenesis is not clear, although it is known that it is an endotheliopathy of the posterior cerebral vasculature leading to failed cerebral autoregulation, posterior edema and encephalopathy. A possible pathological activation of the immune system has been recently hypothesized in its pathogenesis. At clinical onset, the most common manifestations are seizures, headache and visual changes. Besides, tinnitus and acute vertigo have been frequently reported. Symptoms can be reversible but cerebral hemorrhage or ischemia may occur. Diagnosis is based on magnetic resonance imaging, in the presence of acute development of clinical neurologic symptoms and signs and arterial hypertension and/or toxic associated conditions with possible endotheliotoxic effects. Mainstay on the treatment is removal of the underlying cause. Further investigation and developments in endothelial cell function and in neuroimaging of cerebral blood flow are needed and will help to increase our understanding of pathophysiology, possibly suggesting novel therapies.

Dysregulation of the immune system in Aicardi-Goutières syndrome: another example in a TREX1-mutated patient

Aicardi-Goutières syndrome (AGS) is a rare genetic encephalopathy characterized by neurological and extraneurological involvement. A clinical overlap between AGS and systemic lupus erythematosus (SLE) has been reported. We describe an AGS patient who developed autoimmune manifestations: thyroiditis, cANCA positivity, antiphospholipid antibodies and cerebral ischemia. This first description of antiphospholipid syndrome in a TREX1-mutated patient further expands the clinical spectrum of AGS. Although the clinical overlap with SLE may indicate common pathogenic mechanisms, the autoimmune manifestations in AGS are so extensive that we suggest they should be considered a clinical feature of the disease, rather than a sign of coexistent SLE.

Nucleotide embargo by SAMHD1: a strategy to block retroviral infection

SAMHD1 (sterile alpha motif and histidine/aspartic acid (HD) domain-containing protein 1) has been identified as a novel HIV-1 restriction factor in myeloid cells and resting CD4+ T lymphocytes. SAMHD1 restriction is antagonized by the lentiviral protein Vpx. Here, we comment on the latest knowledge of SAMHD1 biology, focusing on how it regulates the pool of intracellular nucleotides to control HIV replication. We discuss how HIV restriction by SAMHD1 and viral counter-restriction mechanisms may suggest new strategies for therapeutic intervention.