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

Diagnosis of Aicardi-Goutières Syndrome in Adults: A Case Series

Introduction

Aicardi-Goutières syndrome (AGS) is a genetic disease presenting with early-onset encephalopathy, generalized dystonia, spasticity, and cognitive disability. Diagnosis may be difficult in adults, as the clinical course seems static from infancy.

Methods

AGS patients from an adult movement disorders outpatient clinic were retrospectively analyzed.

Results

A total of 5 patients and 1 asymptomatic carrier from 3 different families were identified. All had a homozygous c.529G>A,p.A177T mutation in exon 7 of the RNASEH2B gene. Two patients had neonatal-onset AGS, 2 had later onset forms, and 1 was slightly symptomatic. All were diagnosed in adulthood after chilblains, and basal ganglia calcifications were identified on computed tomography scans.

Discussion

AGS patients have marked phenotypic variability regarding psychomotor development and morbidity. The present series included 1 asymptomatic carrier and 1 slightly symptomatic patient, both with homozygous RNASEH2B mutations. Chilblains and basal ganglia calcifications identified on computed tomography scan (but not on magnetic resonance imaging) are important clues for late diagnosis.

Molecular and physiological consequences of faulty eukaryotic ribonucleotide excision repair

The duplication of the eukaryotic genome is an intricate process that has to be tightly safe-guarded. One of the most frequently occurring errors during DNA synthesis is the mis-insertion of a ribonucleotide instead of a deoxyribonucleotide. Ribonucleotide excision repair (RER) is initiated by RNase H2 and results in error-free removal of such mis-incorporated ribonucleotides. If left unrepaired, DNA-embedded ribonucleotides result in a variety of alterations within chromosomal DNA, which ultimately lead to genome instability. Here, we review how genomic ribonucleotides lead to chromosomal aberrations and discuss how the tight regulation of RER timing may be important for preventing unwanted DNA damage. We describe the structural impact of unrepaired ribonucleotides on DNA and chromatin and comment on the potential consequences for cellular fitness. In the context of the molecular mechanisms associated with faulty RER, we have placed an emphasis on how and why increased levels of genomic ribonucleotides are associated with severe autoimmune syndromes, neuropathology, and cancer. In addition, we discuss therapeutic directions that could be followed for pathologies associated with defective removal of ribonucleotides from double-stranded DNA.

Toward a better understanding of type I interferonopathies: a brief summary, update and beyond

BACKGROUNDS

Type I interferonopathy is a group of autoinflammatory disorders associated with prominent enhanced type I interferon signaling. The mechanisms are complex, and the clinical phenotypes are diverse. This review briefly summarized the recent progresses of type I interferonopathy focusing on the clinical and molecular features, pathogeneses, diagnoses and potential therapies.

DATA SOURCES

Original research articles and literature reviews published in PubMed-indexed journals.

RESULTS

Type I interferonopathies include Aicardi-Goutières syndrome, spondyloenchondro-dysplasia with immune dysregulation, stimulator of interferon genes-associated vasculopathy with onset in infancy, X-linked reticulate pigmentary disorder, ubiquitin-specific peptidase 18 deficiency, chronic atypical neutrophilic dermatitis with lipodystrophy, and Singleton-Merten syndrome originally. Other disorders including interferon-stimulated gene 15 deficiency and DNAse II deficiency are believed to be interferonopathies as well. Intracranial calcification, skin vasculopathy, interstitial lung disease, failure to thrive, skeletal development problems and autoimmune features are common. Abnormal responses to nucleic acid stimuli and defective regulation of protein degradation are main mechanisms in disease pathogenesis. First generation Janus kinase inhibitors including baricitinib, tofacitinib and ruxolitinib are useful for disease control. Reverse transcriptase inhibitors seem to be another option for Aicardi-Goutières syndrome.

CONCLUSIONS

Tremendous progress has been made for the discovery of type I interferonopathies and responsible genes. Janus kinase inhibitors and other agents have potential therapeutic roles. Future basic, translational and clinical studies towards disease monitoring and powerful therapies are warranted.

Toward a better understanding of type I interferonopathies: a brief summary, update and beyond

BACKGROUNDS

Type I interferonopathy is a group of autoinflammatory disorders associated with prominent enhanced type I interferon signaling. The mechanisms are complex, and the clinical phenotypes are diverse. This review briefly summarized the recent progresses of type I interferonopathy focusing on the clinical and molecular features, pathogeneses, diagnoses and potential therapies.

DATA SOURCES

Original research articles and literature reviews published in PubMed-indexed journals.

RESULTS

Type I interferonopathies include Aicardi-Goutières syndrome, spondyloenchondro-dysplasia with immune dysregulation, stimulator of interferon genes-associated vasculopathy with onset in infancy, X-linked reticulate pigmentary disorder, ubiquitin-specific peptidase 18 deficiency, chronic atypical neutrophilic dermatitis with lipodystrophy, and Singleton-Merten syndrome originally. Other disorders including interferon-stimulated gene 15 deficiency and DNAse II deficiency are believed to be interferonopathies as well. Intracranial calcification, skin vasculopathy, interstitial lung disease, failure to thrive, skeletal development problems and autoimmune features are common. Abnormal responses to nucleic acid stimuli and defective regulation of protein degradation are main mechanisms in disease pathogenesis. First generation Janus kinase inhibitors including baricitinib, tofacitinib and ruxolitinib are useful for disease control. Reverse transcriptase inhibitors seem to be another option for Aicardi-Goutières syndrome.

CONCLUSIONS

Tremendous progress has been made for the discovery of type I interferonopathies and responsible genes. Janus kinase inhibitors and other agents have potential therapeutic roles. Future basic, translational and clinical studies towards disease monitoring and powerful therapies are warranted.

Contribution of rare and predicted pathogenic gene variants to childhood-onset lupus: a large, genetic panel analysis of British and French cohorts

BACKGROUND

Systemic lupus erythematosus (SLE) is a rare immunological disorder and genetic factors are considered important in its causation. Monogenic lupus has been associated with around 30 genotypes in humans and 60 in mice, while genome-wide association studies have identified more than 90 risk loci. We aimed to analyse the contribution of rare and predicted pathogenic gene variants in a population of unselected cases of childhood-onset SLE.

METHODS

For this genetic panel analysis we designed a next-generation sequencing panel comprising 147 genes, including all known lupus-causing genes in humans, and potentially lupus-causing genes identified through GWAS and animal models. We screened 117 probands fulfilling American College of Rheumatology (ACR) criteria for SLE, ascertained through British and French cohorts of childhood-onset SLE, and compared these data with those of 791 ethnically matched controls from the 1000 Genomes Project and 574 controls from the FREX Consortium.

FINDINGS

After filtering, mendelian genotypes were confirmed in eight probands, involving variants in C1QA, C1QC, C2, DNASE1L3, and IKZF1. Seven additional patients carried heterozygous variants in complement or type I interferon-associated autosomal recessive genes, with decreased concentrations of the encoded proteins C3 and C9 recorded in two patients. Rare variants that were predicted to be damaging were significantly enriched in the childhood-onset SLE cohort compared with controls; 25% of SLE probands versus 5% of controls were identified to harbour at least one rare, predicted damaging variant (p=2·98 × 10-11). Inborn errors of immunity were estimated to account for 7% of cases of childhood-onset SLE, with defects in innate immunity representing the main monogenic contribution.

INTERPRETATION

An accumulation of rare variants that are predicted to be damaging in SLE-associated genes might contribute to disease expression and clinical heterogeneity.

FUNDING

European Research Council.

Clinical approach to the diagnosis of autoimmune encephalitis in the pediatric patient

Objective

Autoimmune encephalitis (AE) is an important and treatable cause of acute encephalitis. Diagnosis of AE in a developing child is challenging because of overlap in clinical presentations with other diseases and complexity of normal behavior changes. Existing diagnostic criteria for adult AE require modification to be applied to children, who differ from adults in their clinical presentations, paraclinical findings, autoantibody profiles, treatment response, and long-term outcomes.

Methods

A subcommittee of the Autoimmune Encephalitis International Working Group collaborated through conference calls and email correspondence to consider the pediatric-specific approach to AE. The subcommittee reviewed the literature of relevant AE studies and sought additional input from other expert clinicians and researchers.

Results

Existing consensus criteria for adult AE were refined for use in children. Provisional pediatric AE classification criteria and an algorithm to facilitate early diagnosis are proposed. There is also discussion about how to distinguish pediatric AE from conditions within the differential diagnosis.

Conclusions

Diagnosing AE is based on the combination of a clinical history consistent with pediatric AE and supportive diagnostic testing, which includes but is not dependent on antibody testing. The proposed criteria and algorithm require validation in prospective pediatric cohorts.

Relapsing-remitting clinical course expands the phenotype of Aicardi-Goutières syndrome

Aicardi-Goutières syndrome (AGS) is a rare and likely underdiagnosed genetic leukoencephalopathy, typically presenting in infancy with encephalopathy and characteristic neuroimaging features, with residual static neurological deficits. We describe a patient who, following an initial presentation at the age of 12 months in keeping with AGS, exhibited a highly atypical relapsing course of neurological symptoms in adulthood with essentially normal neuroimaging. Whole-exome sequencing confirmed a pathogenic RNASEH2B gene variant consistent with AGS. This case highlights the expanding phenotypes associated with AGS and the potential role of whole-exome sequencing in facilitating an increase in the rate of diagnosis.

ADAR1 mediated regulation of neural crest derived melanocytes and Schwann cell development

The neural crest gives rise to numerous cell types, dysfunction of which contributes to many disorders. Here, we report that adenosine deaminase acting on RNA (ADAR1), responsible for adenosine-to-inosine editing of RNA, is required for regulating the development of two neural crest derivatives: melanocytes and Schwann cells. Neural crest specific conditional deletion of Adar1 in mice leads to global depigmentation and absence of myelin from peripheral nerves, resulting from alterations in melanocyte survival and differentiation of Schwann cells, respectively. Upregulation of interferon stimulated genes precedes these defects, which are associated with the triggering of a signature resembling response to injury in peripheral nerves. Simultaneous extinction of MDA5, a key sensor of unedited RNA, rescues both melanocytes and myelin defects in vitro, suggesting that ADAR1 safeguards neural crest derivatives from aberrant MDA5-mediated interferon production. We thus extend the landscape of ADAR1 function to the fields of neural crest development and disease.

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.

Genetic Basis of Myocarditis: Myth or Reality?

The genetic basis of myocarditis remains an intriguing concept, at least as long as the definition of myocarditis constitutes the definitive presence of myocardial inflammation sufficient to cause the observed ventricular dysfunction in the setting of cardiotropic infections. Autoimmune or immune-mediated myocardial inflammation constitutes a complex area of clinical interest, wherein numerous and not yet fully understood role of hereditary auto-inflammatory diseases can result in inflammation of the pericardium and myocardium. Finally, myocardial involvement in hereditary immunodeficiency diseases, cellular and humoral, is a possible trigger for infections which may complicate the diseases themselves. Whether the role of constitutional genetics can make the patient susceptible to myocardial inflammation remains yet to be explored.

Developmental Outcomes of Aicardi Goutières Syndrome

Aicardi Goutières syndrome is a monogenic interferonopathy caused by abnormalities in the intracellular nucleic acid sensing machinery (TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR1, or IFIH1). Most individuals affected by Aicardi Goutières syndrome exhibit some degree of neurologic impairment, from spastic paraparesis with relatively preserved cognition to tetraparesis and severe intellectual disability. Because of this heterogeneity, it is important to fully characterize the developmental trajectory in Aicardi Goutières syndrome. To characterize the clinical presentation in Aicardi Goutières syndrome, early features were collected from an international cohort of children (n = 100) with genetically confirmed Aicardi Goutières syndrome. There was a heterogeneous age of onset, with overlapping clusters of presenting symptoms: altered mental status, systemic inflammatory symptoms, and acute neurologic disability. Next, we created genotype-specific developmental milestone acquisition curves. Individuals with microcephaly or TREX1-related Aicardi Goutières syndrome secondary were the most severely affected and less likely to reach milestones, including head control, sitting, and nonspecific mama/dada. Individuals affected by SAMHD1, IFIH1, and ADAR attained the most advanced milestones, with 44% achieving verbal communication and 31% independently ambulating. Retrospective function scales (Gross Motor Function Classification System, Manual Ability Classification System, and Communication Function Classification System) demonstrated that two-thirds of the Aicardi Goutières syndrome population are severely affected. Our results suggest multifactorial influences on developmental trajectory, including a strong contribution from genotype. Further studies are needed to identify the additional factors that influence overall outcomes to better counsel families and to design clinical trials with appropriate clinical endpoints.

Treatments in Aicardi-Goutières syndrome

Comprehensive reviews of the clinical characteristics and pathogenesis of Aicardi-Goutières syndrome (AGS), particularly its contextualization within a putative type I interferonopathy framework, already exist. However, recent reports of attempts at treatment suggest that an assessment of the field from a therapeutic perspective is warranted at this time. Here, we briefly summarize the neurological phenotypes associated with mutations in the seven genes so far associated with AGS, rehearse current knowledge of the pathology as it relates to possible treatment approaches, critically appraise the potential utility of therapies, and discuss the challenges in assessing clinical efficacy. WHAT THIS PAPER ADDS: Progress in understanding AGS disease pathogenesis has led to the first attempts at targeted treatment. Further rational therapies are expected to become available in the short- to medium-term.

Characterization of six recombinant human RNase H2 bearing Aicardi-Goutiéres syndrome causing mutations

Mammalian RNase H2 is a heterotrimeric enzyme consisting of one catalytic subunit (A) and two accessory subunits (B and C). RNase H2 is involved in the removal of a single ribonucleotide embedded in genomic DNA and removal of RNA of RNA/DNA hybrids. In humans, mutation of the RNase H2 gene causes a severe neuroinflammatory disorder Aicardi-Goutières syndrome (AGS). Here, we examined the activity and stability of six recombinant human RNase H2 variants bearing one AGS-causing mutation, A-G37S (Gly37 in the A subunit is replaced with Ser), A-N212I, A-R291H, B-A177T, B-V185G, or C-R69W. The activity of A-G37S was 0.3-1% of that of the wild-type RNase H2 (WT), while those of other five variants were 51-120%. In circular dichroism measurement, the melting temperatures of variants were 50-53°C, lower than that of WT (56°C). These results suggested that A-G37S had decreased activity and stability than WT, while other five variants had decreased stability but retained activity. In gel filtration chromatography of the purified enzyme preparation, WT migrated as a heterotrimer, while A-R291H eluted in two separate peaks containing either the heterotrimer or only the A subunit, suggesting that some AGS-causing mutations affect the heterotrimer-forming stability of RNase H2.

Current State of Precision Medicine in Primary Systemic Vasculitides

Precision medicine (PM) is an emerging data-driven health care approach that integrates phenotypic, genomic, epigenetic, and environmental factors unique to an individual. The goal of PM is to facilitate diagnosis, predict effective therapy, and avoid adverse reactions specific for each patient. The forefront of PM is in oncology; nonetheless, it is developing in other fields of medicine, including rheumatology. Recent studies on elucidating the genetic architecture of polygenic and monogenic rheumatological diseases have made PM possible by enabling physicians to customize medical treatment through the incorporation of clinical features and genetic data. For complex inflammatory disorders, the prevailing paradigm is that disease susceptibility is due to additive effects of common reduced-penetrance gene variants and environmental factors. Efforts have been made to calculate cumulative genetic risk score (GRS) and to relate specific susceptibility alleles for use of target therapies. The discovery of rare patients with single-gene high-penetrance mutations informed our understanding of pathways driving systemic inflammation. Here, we review the advances in practicing PM in patients with primary systemic vasculitides (PSVs). We summarize recent genetic studies and discuss current knowledge on the contribution of epigenetic factors and extracellular vesicles (EVs) in disease progression and treatment response. Implementation of PM in PSVs is a developing field that will require analysis of a large cohort of patients to validate data from genomics, transcriptomics, metabolomics, proteomics, and epigenomics studies for accurate disease profiling. This multi-omics approach to study disease pathogeneses should ultimately provide a powerful tool for stratification of patients to receive tailored optimal therapies and for monitoring their disease activity.

An update on clinical, pathological, diagnostic, and therapeutic perspectives of childhood leukodystrophies

Introduction: Leukodystrophies constitute heterogenous group of rare heritable disorders primarily affecting the white matter of central nervous system. These conditions are often under-appreciated among physicians. The first clinical manifestations of leukodystrophies are often nonspecific and can occur in different ages from neonatal to late adulthood periods. The diagnosis is, therefore, challenging in most cases.Area covered: Herein, the authors discuss different aspects of leukodystrophies. The authors used MEDLINE, EMBASE, and GOOGLE SCHOLAR to provide an extensive update about epidemiology, classifications, pathology, clinical findings, diagnostic tools, and treatments of leukodystrophies. Comprehensive evaluation of clinical findings, brain magnetic resonance imaging, and genetic studies play the key roles in the early diagnosis of individuals with leukodystrophies. No cure is available for most heritable white matter disorders but symptomatic treatments can significantly decrease the burden of events. New genetic methods and stem cell transplantation are also under investigation to further increase the quality and duration of life in affected population.Expert opinion: The improvements in molecular diagnostic tools allow us to identify the meticulous underlying etiology of leukodystrophies and result in higher diagnostic rates, new classifications of leukodystrophies based on genetic information, and replacement of symptomatic managements with more specific targeted therapies.Abbreviations: 4H: Hypomyelination, hypogonadotropic hypogonadism and hypodontia; AAV: Adeno-associated virus; AD: autosomal dominant; AGS: Aicardi-Goutieres syndrome; ALSP: Axonal spheroids and pigmented glia; APGBD: Adult polyglucosan body disease; AR: autosomal recessive; ASO: Antisense oligonucleotide therapy; AxD: Alexander disease; BAEP: Brainstem auditory evoked potentials; CAA: Cerebral amyloid angiopathy; CADASIL: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy; CARASAL: Cathepsin A-related arteriopathy with strokes and leukoencephalopathy; CARASIL: Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy; CGH: Comparative genomic hybridization; ClC2: Chloride Ion Channel 2; CMTX: Charcot-Marie-Tooth disease, X-linked; CMV: Cytomegalovirus; CNS: central nervous system; CRISP/Cas9: Clustered regularly interspaced short palindromic repeat/CRISPR-associated 9; gRNA: Guide RNA; CTX: Cerebrotendinous xanthomatosis; DNA: Deoxyribonucleic acid; DSB: Double strand breaks; DTI: Diffusion tensor imaging; FLAIR: Fluid attenuated inversion recovery; GAN: Giant axonal neuropathy; H-ABC: Hypomyelination with atrophy of basal ganglia and cerebellum; HBSL: Hypomyelination with brainstem and spinal cord involvement and leg spasticity; HCC: Hypomyelination with congenital cataracts; HEMS: Hypomyelination of early myelinated structures; HMG CoA: Hydroxy methylglutaryl CoA; HSCT: Hematopoietic stem cell transplant; iPSC: Induced pluripotent stem cells; KSS: Kearns-Sayre syndrome; L-2-HGA: L-2-hydroxy glutaric aciduria; LBSL: Leukoencephalopathy with brainstem and spinal cord involvement and elevated lactate; LCC: Leukoencephalopathy with calcifications and cysts; LTBL: Leukoencephalopathy with thalamus and brainstem involvement and high lactate; MELAS: Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke; MERRF: Myoclonic epilepsy with ragged red fibers; MLC: Megalencephalic leukoencephalopathy with subcortical cysts; MLD: metachromatic leukodystrophy; MRI: magnetic resonance imaging; NCL: Neuronal ceroid lipofuscinosis; NGS: Next generation sequencing; ODDD: Oculodentodigital dysplasia; PCWH: Peripheral demyelinating neuropathy-central-dysmyelinating leukodystrophy-Waardenburg syndrome-Hirschprung disease; PMD: Pelizaeus-Merzbacher disease; PMDL: Pelizaeus-Merzbacher-like disease; RNA: Ribonucleic acid; TW: T-weighted; VWM: Vanishing white matter; WES: whole exome sequencing; WGS: whole genome sequencing; X-ALD: X-linked adrenoleukodystrophy; XLD: X-linked dominant; XLR: X-linked recessive.

Two RNase H2 Mutants with Differential rNMP Processing Activity Reveal a Threshold of Ribonucleotide Tolerance for Embryonic Development

RNase H2 has two distinct functions: initiation of the ribonucleotide excision repair (RER) pathway by cleaving ribonucleotides (rNMPs) incorporated during DNA replication and processing the RNA portion of an R-loop formed during transcription. An RNase H2 mutant lacking RER activity but supporting R-loop removal revealed that rNMPs in DNA initiate p53-dependent DNA damage response and early embryonic arrest in mouse. However, an RNase H2 AGS-related mutant with residual RER activity develops to birth. Estimations of the number of rNMPs in DNA in these two mutants define a ribonucleotide threshold above which p53 induces apoptosis. Below the threshold, rNMPs in DNA trigger an innate immune response. Compound heterozygous cells, containing both defective enzymes, retain rNMPs above the threshold, indicative of competition for RER substrates between active and inactive enzymes, suggesting that patients with compound heterozygous mutations in RNASEH2 genes may not reflect the properties of recombinantly expressed proteins.

Uehara et al. use RNase H2 mice with differing activity levels for removal of rNMPs embedded in DNA. Moderate levels of rNMPs lead to perinatal lethality activating the cGAS-Sting DNA sensing innate immune response. Exceeding a threshold, high abundance of rNMPs activates p53-dependent DNA damage, causing early embryonic lethality.

The pathogenesis of systemic lupus erythematosus: Harnessing big data to understand the molecular basis of lupus

Systemic lupus erythematosus (SLE) is a chronic, systemic autoimmune disease that causes damage to multiple organ systems. Despite decades of research and available murine models that capture some aspects of the human disease, new treatments for SLE lag behind other autoimmune diseases such as Rheumatoid Arthritis and Crohn's disease. Big data genomic assays have transformed our understanding of SLE by providing important insights into the molecular heterogeneity of this multigenic disease. Gene wide association studies have demonstrated more than 100 risk loci, supporting a model of multiple genetic hits increasing SLE risk in a non-linear fashion, and providing evidence of ancestral diversity in susceptibility loci. Epigenetic studies to determine the role of methylation, acetylation and non-coding RNAs have provided new understanding of the modulation of gene expression in SLE patients and identified new drug targets and biomarkers for SLE. Gene expression profiling has led to a greater understanding of the role of myeloid cells in the pathogenesis of SLE, confirmed roles for T and B cells in SLE, promoted clinical trials based on the prominent interferon signature found in SLE patients, and identified candidate biomarkers and cellular signatures to further drug development and drug repurposing. Gene expression studies are advancing our understanding of the underlying molecular heterogeneity in SLE and providing hope that patient stratification will expedite new therapies based on personal molecular signatures. Although big data analyses present unique interpretation challenges, both computationally and biologically, advances in machine learning applications may facilitate the ability to predict changes in SLE disease activity and optimize therapeutic strategies.

Cardiac valve involvement in ADAR-related type I interferonopathy

Background

Adenosine deaminases acting on RNA (ADAR) mutations cause a spectrum of neurological phenotypes ranging from severe encephalopathy (Aicardi-Goutières syndrome) to isolated spastic paraplegia and are associated with enhanced type I interferon signalling. In children, non-neurological involvement in the type I interferonopathies includes autoimmune and rheumatological phenomena, with calcifying cardiac valve disease only previously reported in the context of MDA5 gain-of-function.

Results

We describe three patients with biallelic ADAR mutations who developed calcifying cardiac valvular disease in late childhood (9.5–14 years). Echocardiography revealed progressive calcification of the valvular leaflets resulting in valvular stenosis and incompetence. Two patients became symptomatic with biventricular failure after 5–6.5 years. In one case, disease progressed to severe cardiac failure despite maximal medical management, with death occurring at 17 years. Another child received mechanical mitral and aortic valve replacement at 16 years with good postoperative outcome. Histological examination of the affected valves showed fibrosis and calcification.

Conclusions

Type I interferonopathies of differing genetic aetiology demonstrate an overlapping phenotypic spectrum which includes calcifying cardiac valvular disease. Individuals with ADAR-related type I interferonopathy may develop childhood-onset multivalvular stenosis and incompetence which can progress insidiously to symptomatic, and ultimately fatal, cardiac failure. Regular surveillance echocardiograms are recommended to detect valvular disease early.

How common are single gene mutations as a cause for lacunar stroke? A targeted gene panel study

OBJECTIVES

To determine the frequency of rare and pertinent disease-causing variants in small vessel disease (SVD)-associated genes (such as NOTCH3, HTRA1, COL4A1, COL4A2, FOXC1, TREX1, and GLA) in cerebral SVD, we performed targeted gene sequencing in 950 patients with younger-onset apparently sporadic SVD stroke using a targeted sequencing panel.

METHODS

We designed a high-throughput sequencing panel to identify variants in 15 genes (7 known SVD genes, 8 SVD-related disorder genes). The panel was used to screen a population of 950 patients with younger-onset (≤70 years) MRI-confirmed SVD stroke, recruited from stroke centers across the United Kingdom. Variants were filtered according to their frequency in control databases, predicted effect, presence in curated variant lists, and combined annotation dependent depletion scores. Whole genome sequencing and genotyping were performed on a subset of patients to provide a direct comparison of techniques. The frequency of known disease-causing and pertinent variants of uncertain significance was calculated.

RESULTS

We identified previously reported variants in 14 patients (8 cysteine-changing NOTCH3 variants in 11 patients, 2 HTRA1 variants in 2 patients, and 1 missense COL4A1 variant in 1 patient). In addition, we identified 29 variants of uncertain significance in 32 patients.

CONCLUSION

Rare monogenic variants account for about 1.5% of younger onset lacunar stroke. Most are cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy variants, but the second most common gene affected is HTRA1. A high-throughput sequencing technology platform is an efficient, reliable method to screen for such mutations.

Constitutively Active MDA5 Proteins Are Inhibited by Paramyxovirus V Proteins

Excessive interferon (IFN) production and signaling can lead to immunological and developmental defects giving rise to autoimmune diseases referred to collectively as "type I interferonopathies." A subset of these diseases is caused by monogenic mutations affecting proteins involved in nucleic acid sensing, homeostasis, and metabolism. Interferonopathic mutations in the cytosolic antiviral sensor MDA5 render it constitutively hyperactive, resulting in chronic IFN production and IFN-stimulated gene expression. Few therapeutic options are available for patients with interferonopathic diseases, but a large number of IFN evasion and antagonism strategies have evolved in viral pathogens that can counteract IFN production and signaling to enhance virus replication. To test the hypothesis that these natural IFN suppressors could be used to subdue the activity of interferonopathic signaling proteins, hyperactive MDA5 variants were assessed for susceptibility to a family of viral MDA5 inhibitors. In this study, Paramyxovirus V proteins were tested for their ability to counteract constitutively active MDA5 proteins. Results indicate that the V proteins are able to bind to and disrupt the signaling activity of these MDA5 proteins, irrespective of their specific mutations, reducing IFN production and IFN-stimulated gene expression to effectively suppress the hyperactive antiviral response.

Microglia responses to interleukin-6 and type I interferons in neuroinflammatory disease

Microglia are the resident macrophages of the central nervous system (CNS). They are a heterogenous, exquisitely responsive, and highly plastic cell population, which enables them to perform diverse roles. They sense and respond to the local production of many different signals, including an assorted range of cytokines. Microglia respond strongly to interleukin-6 (IL-6) and members of the type I interferon (IFN-I) family, IFN-alpha (IFN-α), and IFN-beta (IFN-β). Although these cytokines are essential in maintaining homeostasis and for activating and regulating immune responses, their chronic production has been linked to the development of distinct human neurological diseases, termed "cerebral cytokinopathies." IL-6 and IFN-α have been identified as key mediators in the pathogenesis of neuroinflammatory disorders including neuromyelitis optica and Aicardi-Goutières syndrome, respectively, whereas IFN-β has an emerging role as a causal factor in age-associated cognitive decline. One of the key features that unites these diseases is the presence of highly reactive microglia. The current understanding is that microglia contribute to the development of cerebral cytokinopathies and represent an important therapeutic target. However, it remains to be resolved whether microglia have beneficial or detrimental effects. Here we review and discuss what is currently known about the microglial response to IL-6 and IFN-I, based on both animal models and clinical studies. Foundational knowledge regarding the microglial response to IL-6 and IFN-I is now being used to devise therapeutic strategies to ameliorate neuroinflammation and promote repair: either through targeting microglia, or by targeting the reduction of CNS levels or downstream biological pathways of IL-6 or IFN-I.

Mosaic Tetrasomy 9p Associated With Inflammatory Bowel Disease

The genetic basis of inflammatory bowel disease remains to be elucidated completely. Here we report on a patient with inflammatory bowel disease who has mosaic tetrasomy of the short arm of chromosome 9, a genomic region that harbours the type I interferon gene cluster. We show that increased interferon activation is present in peripheral blood and intestinal tissue from this patient, similar to previous reports of autoinflammatory organ damage driven by interferon activation in other patients with this chromosomal abnormality. To our knowledge, this is the first case of tetrasomy 9p-associated interferonopathy driving intestinal inflammation and highlights the role that type-I interferon pathways can play in the pathogenesis of intestinal inflammation.

Trypanosoma brucei ribonuclease H2A is an essential R-loop processing enzyme whose loss causes DNA damage during transcription initiation and antigenic variation

Ribonucleotides represent a threat to DNA genome stability and transmission. Two types of Ribonuclease H (RNase H) excise ribonucleotides when they form part of the DNA strand, or hydrolyse RNA when it base-pairs with DNA in structures termed R-loops. Loss of either RNase H is lethal in mammals, whereas yeast survives the absence of both enzymes. RNase H1 loss is tolerated by the parasite Trypanosoma brucei but no work has examined the function of RNase H2. Here we show that loss of T. brucei RNase H2 (TbRH2A) leads to growth and cell cycle arrest that is concomitant with accumulation of nuclear damage at sites of RNA polymerase (Pol) II transcription initiation, revealing a novel and critical role for RNase H2. Differential gene expression analysis reveals limited overall changes in RNA levels for RNA Pol II genes after TbRH2A loss, but increased perturbation of nucleotide metabolic genes. Finally, we show that TbRH2A loss causes R-loop and DNA damage accumulation in telomeric RNA Pol I transcription sites, also leading to altered gene expression. Thus, we demonstrate separation of function between two nuclear T. brucei RNase H enzymes during RNA Pol II transcription, but overlap in function during RNA Pol I-mediated gene expression during host immune evasion.

Dawn of Epitranscriptomic Medicine

Medicine is at the crossroads of expanding disciplines. Prompt adaptation of medicine to each rapidly advancing research field, bridging bench to bedside, is a key step toward health improvement. Cardiovascular disease still ranks first among the mortality causes in the Western world, indicating a poor adaptation rate of cardiovascular medicine, albeit the gigantic scientific breakthroughs of this century. This urges the cardiovascular research field to explore novel concepts with promising prognostic and therapeutic potential. This review attempts to introduce the newly emerging field of epitranscriptome (or else known as RNA epigenetics) to cardiovascular researchers and clinicians summarizing its applications on health and disease. The traditionally perceived, intermediate carrier of genetic information or as contemporary revised as, occasionally, even the final product of gene expression, RNA, is dynamically subjected to >140 different kinds of chemical modifications determining its fate, which may profoundly impact the cellular responses and thus both health and disease course. Which are the most prevalent types of these RNA modifications, how are they catalyzed, how are they regulated, which role may they play in health and disease, and which are the implications for the cardiovascular medicine are few important questions that are discussed in the present review.

The missing link: allostery and catalysis in the anti-viral protein SAMHD1

Vertebrate protein SAMHD1 (sterile-α-motif and HD domain containing protein 1) regulates the cellular dNTP (2'-deoxynucleoside-5'-triphosphate) pool by catalysing the hydrolysis of dNTP into 2'-deoxynucleoside and triphosphate products. As an important regulator of cell proliferation and a key player in dNTP homeostasis, mutations to SAMHD1 are implicated in hypermutated cancers, and germline mutations are associated with Chronic Lymphocytic Leukaemia and the inflammatory disorder Aicardi-Goutières Syndrome. By limiting the supply of dNTPs for viral DNA synthesis, SAMHD1 also restricts the replication of several retroviruses, such as HIV-1, and some DNA viruses in dendritic and myeloid lineage cells and resting T-cells. SAMHD1 activity is regulated throughout the cell cycle, both at the level of protein expression and post-translationally, through phosphorylation. In addition, allosteric regulation further fine-tunes the catalytic activity of SAMHD1, with a nucleotide-activated homotetramer as the catalytically active form of the protein. In cells, GTP and dATP are the likely physiological activators of two adjacent allosteric sites, AL1 (GTP) and AL2 (dATP), that bridge monomer-monomer interfaces to stabilise the protein homotetramer. This review summarises the extensive X-ray crystallographic, biophysical and molecular dynamics experiments that have elucidated important features of allosteric regulation in SAMHD1. We present a comprehensive mechanism detailing the structural and protein dynamics components of the allosteric coupling between nucleotide-induced tetramerization and the catalysis of dNTP hydrolysis by SAMHD1.

Hereditary spastic paraplegia associated with a rare IFIH1 mutation: a case report and literature review

Here, the pathogenesis of an IFIH1 gene mutation is discussed through the analysis of a sporadic case of hereditary spastic paraplegia. Next-generation sequencing was performed for the patient and his family members to detect mutations at the IFIH1 locus. The patient and his father were found to carry the same heterozygous missense mutation (c.1093A > G; p.Gly495Arg), while the patient’s mother does not carry this mutation. This is the first report of this heterozygous IFIH1 mutation and it is predicted to be disease-causing.

Whole exome sequencing in childhood-onset lupus frequently detects single gene etiologies

BACKGROUND

Systemic lupus erythematosus (SLE) comprise a diverse range of clinical manifestations. To date, more than 30 single gene causes of lupus/lupus like syndromes in humans have been identified. In the clinical setting, identifying the underlying molecular diagnosis is challenging due to phenotypic and genetic heterogeneity.

METHODS

We employed whole exome sequencing (WES) in patients presenting with childhood-onset lupus with severe and/or atypical presentations to identify cases that are explained by a single-gene (monogenic) cause.

RESULTS

From January 2015 to June 2018 15 new cases of childhood-onset SLE were diagnosed in Edmond and Lily Safra Children's Hospital. By WES we identified causative mutations in four subjects in five different genes: C1QC, SLC7A7, MAN2B1, PTEN and STAT1. No molecular diagnoses were established on clinical grounds prior to genetic testing.

CONCLUSIONS

We identified a significant fraction of monogenic SLE etiologies using WES and confirm the genetic locus heterogeneity in childhood-onset lupus. These results highlight the importance of establishing a genetic diagnosis for children with severe or atypical lupus by providing accurate and early etiology-based diagnoses and improving subsequent clinical management.

ADAR1: "Editor-in-Chief" of Cytoplasmic Innate Immunity

Specialized receptors that recognize molecular patterns such as double stranded RNA duplexes-indicative of viral replication-are potent triggers of the innate immune system. Although their activation is beneficial during viral infection, RNA transcribed from endogenous mobile genetic elements may also act as ligands potentially causing autoimmunity. Recent advances indicate that the adenosine deaminase ADAR1 through RNA editing is involved in dampening the canonical antiviral RIG-I-like receptor-, PKR-, and OAS-RNAse L pathways to prevent autoimmunity. However, this inhibitory effect must be overcome during viral infections. In this review we discuss ADAR1's critical role in balancing immune activation and self-tolerance.

TREX1 variants in Sjogren's syndrome related lymphomagenesis

Genetic variants of the three-prime repair exonuclease 1 (TREX1) -an exonuclease involved in DNA repair and degradation- have been previously found to increase susceptibility to Aicardi Goutieres syndrome, familial chilblain lupus and systemic lupus erythematosus. We aimed to explore whether TREX1 common variants could influence the risk of primary Sjogren's syndrome (SS) and SS-related lymphoma. Three single nucleotide polymorphisms (SNPs) of the TREX1 gene (rs11797, rs3135941 and rs3135945) were evaluated in 229 SS, 89 SS-lymphoma (70 SS-MALT and 19 SS non-MALT) and 240 healthy controls by PCR-based assays. In available 52 peripheral blood and 26 minor salivary gland tissues from our SS cohort, mRNA expression of type I interferon (IFN) related genes and TREX1 was determined by real-time PCR. Significantly decreased prevalence of rs11797 A minor allele was detected in SS patients complicated by non-MALT lymphoma compared to controls (ΟR [95% CI]: 0.4 [0.2-0.9], p-value: 0.02). SS patients carrying the rs11797 AA genotype had increased type I IFN related gene mRNA expression in minor salivary gland tissues. These data support genetically related dampened type I IFN production as an additional mechanism for SS-related lymphomagenesis.

Genome-wide mutagenesis resulting from topoisomerase 1-processing of unrepaired ribonucleotides in DNA

Ribonucleotides are the most common non-canonical nucleotides incorporated into DNA during replication, and their processing leads to mutations and genome instability. Yeast mutation reporter systems demonstrate that 2-5 base pair deletions (Δ2-5bp) in repetitive DNA are a signature of unrepaired ribonucleotides, and that these events are initiated by topoisomerase 1 (Top1) cleavage. However, a detailed understanding of the frequency and locations of ribonucleotide-dependent mutational events across the genome has been lacking. Here we present the results of genome-wide mutational analysis of yeast strains deficient in Ribonucleotide Excision Repair (RER). We identified mutations that accumulated over thousands of generations in strains expressing either wild-type or variant replicase alleles (M644G Pol ε, L612M Pol δ, L868M Pol α) that confer increased ribonucleotide incorporation into DNA. Using a custom-designed mutation-calling pipeline called muver (for mutationes verificatae), we observe a number of surprising mutagenic features. This includes a 24-fold preferential elevation of AG and AC relative to AT dinucleotide deletions in the absence of RER, suggesting specificity for Top1-initiated deletion mutagenesis. Moreover, deletion rates in di- and trinucleotide repeat tracts increase exponentially with tract length. Consistent with biochemical and reporter gene mutational analysis, these deletions are no longer observed upon deletion of TOP1. Taken together, results from these analyses demonstrate the global impact of genomic ribonucleotide processing by Top1 on genome integrity.

The TREX1 Dinosaur Bites the Brain through the LINE

In this issue of Cell Stem Cell, Thomas et al. (2017) define the nature of accumulated ssDNA present in the neuron and astrocyte cytoplasm of TREX1 mutated stem cell-derived organoids. Accumulated ssDNAs are derived from LINE-1 endogenous retroelements, providing new clues as to the development of Aicardi-Goutières syndrome in the neural system.

Management strategies and future directions for systemic lupus erythematosus in adults

Systemic lupus erythematosus (SLE) is an autoimmune disease characterised by the loss of self-tolerance and formation of nuclear autoantigens and immune complexes resulting in inflammation of multiple organs. The clinical presentation of SLE is heterogeneous, can involve one or more organs, including the skin, kidneys, joints, and nervous system, and take a chronic or relapsing and remitting disease course. SLE is most common in women and in those of non-white ethnicity. Because of the multitude of presentations, manifestations, and serological abnormalities in patients with SLE, diagnosis can be challenging. Therapeutic approaches predominantly involve immunomodulation and immunosuppression and are targeted to the specific organ manifestation, with the aim of achieving low disease activity. Despite many treatment advances and improved diagnostics, SLE continues to cause substantial morbidity and premature mortality. Current management strategies, although helpful, are limited by high failure rates and toxicity. An overreliance on corticosteroid therapy contributes to much of the long-term organ damage. In this Seminar, we outline the classification criteria for SLE, current treatment strategies and medications, the evidence supporting their use, and explore potential future therapies.

Brain organoids and insights on human evolution

Human brain organoids, generated from pluripotent stem cells, have emerged as a promising technique for modeling early stages of human neurodevelopment in controlled laboratory conditions. Although the applications for disease modeling in a dish have become routine, the use of these brain organoids as evolutionary tools is only now getting momentum. Here, we will review the current state of the art on the use of brain organoids from different species and the molecular and cellular insights generated from these studies. Besides, we will discuss how this model might be beneficial for human health and the limitations and future perspectives of this technology.

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.

Ribonucleotides in mitochondrial DNA

The incorporation of ribonucleotides (rNMPs) into DNA during genome replication has gained substantial attention in recent years and has been shown to be a significant source of genomic instability. Studies in yeast and mammals have shown that the two genomes, the nuclear DNA (nDNA) and the mitochondrial DNA (mtDNA), differ with regard to their rNMP content. This is largely due to differences in rNMP repair - whereas rNMPs are efficiently removed from the nuclear genome, mitochondria lack robust mechanisms for removal of single rNMPs incorporated during DNA replication. In this minireview, we describe the processes that determine the frequency of rNMPs in the mitochondrial genome and summarise recent findings regarding the effect of incorporated rNMPs on mtDNA stability and function.

Non-self mutation: double-stranded RNA elicits antiviral pathogenic response in a Drosophila model of expanded CAG repeat neurodegenerative diseases

Inflammation is activated prior to symptoms in neurodegenerative diseases, providing a plausible pathogenic mechanism. Indeed, genetic and pharmacological ablation studies in animal models of several neurodegenerative diseases demonstrate that inflammation is required for pathology. However, while there is growing evidence that inflammation-mediated pathology may be the common mechanism underlying neurodegenerative diseases, including those due to dominantly inherited expanded repeats, the proximal causal agent is unknown. Expanded CAG.CUG repeat double-stranded RNA causes inflammation-mediated pathology when expressed in Drosophila. Repeat dsRNA is recognized by Dicer-2 as a foreign or ‘non-self’ molecule triggering both antiviral RNA and RNAi pathways. Neither of the RNAi pathway cofactors R2D2 nor loquacious are necessary, indicating antiviral RNA activation. RNA modification enables avoidance of recognition as ‘non-self’ by the innate inflammatory surveillance system. Human ADAR1 edits RNA conferring ‘self’ status and when co-expressed with expanded CAG.CUG dsRNA in Drosophila the pathology is lost. Cricket Paralysis Virus protein CrPV-1A is a known antagonist of Argonaute-2 in Drosophila antiviral defense. CrPV-1A co-expression also rescues pathogenesis, confirming anti-viral-RNA response. Repeat expansion mutation therefore confers ‘non-self’ recognition of endogenous RNA, thereby providing a proximal, autoinflammatory trigger for expanded repeat neurodegenerative diseases.

Sources of Pathogenic Nucleic Acids in Systemic Lupus Erythematosus

A hallmark of systemic lupus erythematosus (SLE), and several related autoimmune diseases, is the presence of autoantibodies against nucleic acids and nucleic acid-binding proteins, as well as elevated type I interferons (IFNs), which appear to be instrumental in disease pathogenesis. Here we discuss the sources and proposed mechanisms by which a range of cellular RNA and DNA species can become pathogenic and trigger the nucleic acid sensors that drive type I interferon production. Potentially SLE-promoting DNA may originate from pieces of chromatin, from mitochondria, or from reverse-transcribed cellular RNA, while pathogenic RNA may arise from mis-localized, mis-processed, ancient retroviral, or transposable element-derived transcripts. These nucleic acids may leak out from dying cells to be internalized and reacted to by immune cells or they may be generated and remain to be sensed intracellularly in immune or non-immune cells. The presence of aberrant DNA or RNA is normally counteracted by effective counter-mechanisms, the loss of which result in a serious type I IFN-driven disease called Aicardi-Goutières Syndrome. However, in SLE it remains unclear which mechanisms are most critical in precipitating disease: aberrant RNA or DNA, overly sensitive sensor mechanisms, or faulty counter-acting defenses. We propose that the clinical heterogeneity of SLE may be reflected, in part, by heterogeneity in which pathogenic nucleic acid molecules are present and which sensors and pathways they trigger in individual patients. Elucidation of these events may result in the recognition of distinct "endotypes" of SLE, each with its distinct therapeutic choices.

Pathogenesis and treatment of autoimmune rheumatic diseases

PURPOSE OF REVIEW

Autoimmune diseases are of unknown origin, and they represent significant causes of morbidity and mortality. Here, we review new developments in the understanding of their pathogenesis that have led to development of well tolerated and effective treatments.

RECENT FINDINGS

In addition to the long-recognized genetic impact of the HLA locus, interferon regulatory factors, PTPN22, STAT4, and NOX have been implicated in pathogenesis of systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Smoking, ultraviolet light, diet, and microbiota exert strong environmental influence on development of RA and SLE. Metabolism has been recognized as a critical integrator of genetic and environmental factors, and it controls immune cell differentiation both under physiological and pathological conditions.

SUMMARY

With the advent of high-throughput genetic, proteomic, and metabolomic technologies, the field of medicine has been shifting towards systems-based and personalized approaches to diagnose and treat common conditions, including rheumatic diseases. Regulatory checkpoints of metabolism and signal transduction, such as glucose utilization, mitochondrial electron transport, JAK, mTOR, and AMPK pathway activation, and production of pro-inflammatory cytokines IL-1, IL-6, and IL-17 have presented new targets for therapeutic intervention. This review amalgamates recent discoveries in genetics and metabolomics with immunological pathways of pathogenesis in rheumatic diseases.

Aicardi-Goutières syndrome gene Rnaseh2c is a metastasis susceptibility gene in breast cancer

Breast cancer is the second leading cause of cancer-related deaths in the United States, with the majority of these deaths due to metastatic lesions rather than the primary tumor. Thus, a better understanding of the etiology of metastatic disease is crucial for improving survival. Using a haplotype mapping strategy in mouse and shRNA-mediated gene knockdown, we identified Rnaseh2c, a scaffolding protein of the heterotrimeric RNase H2 endoribonuclease complex, as a novel metastasis susceptibility factor. We found that the role of Rnaseh2c in metastatic disease is independent of RNase H2 enzymatic activity, and immunophenotyping and RNA-sequencing analysis revealed engagement of the T cell-mediated adaptive immune response. Furthermore, the cGAS-Sting pathway was not activated in the metastatic cancer cells used in this study, suggesting that the mechanism of immune response in breast cancer is different from the mechanism proposed for Aicardi-Goutières Syndrome, a rare interferonopathy caused by RNase H2 mutation. These results suggest an important novel, non-enzymatic role for RNASEH2C during breast cancer progression and add Rnaseh2c to a panel of genes we have identified that together could determine patients with high risk for metastasis. These results also highlight a potential new target for combination with immunotherapies and may contribute to a better understanding of the etiology of Aicardi-Goutières Syndrome autoimmunity.

An extremely severe case of Aicardi-Goutières syndrome 7 with a novel variant in IFIH1

We describe herein an extremely severe case of Aicardi-Goutières syndrome 7 (AGS7). The female patient was the daughter of nonconsanguineous parents and developed cardiomegaly, pericardial effusion, splenomegaly, and intracranial calcification during the fetal period. Because her cardiotocogram showed a non-reassuring fetal status, she was delivered at 29 weeks and 4 days of gestation by an emergency cesarean section. After birth, she suffered from respiratory distress, pulmonary hypertension, refractory fever, recurrent thrombocytopenia, and abdominal distention caused by hepatomegaly and ascites. She showed a lenticulostriate vasculopathy, which was compatible with the fetal intracranial calcification. Despite various intensive care procedures, she died of gradually progressive pulmonary hypertension at 3 months of age. After her death, whole exome sequencing on the patient and the parents was performed and revealed a novel, de novo, heterozygous mutation in the IFIH1 gene (IFIH1:NM_022168:exon12:c.2439A > T:p.Glu813Asp). On the basis of the mutation and the clinical features, the diagnosis was AGS7. Although AGS7 has been regarded as a relatively mild subtype of Aicardi-Goutières syndrome, this case indicates that the c.2439A > T variant of AGS7 can be fatal in early infancy.

Genome instability consequences of RNase H2 Aicardi-Goutières syndrome alleles

The RNase H2 complex is a conserved heterotrimeric enzyme that degrades RNA:DNA hybrids and promotes excision of rNMPs misincorporated during DNA replication. Failure to remove ribonucleotides from DNA leads to genomic instability in yeast and humans. The monogenic Aicardi-Goutières syndrome (AGS) results from mutation in one of several genes, among which are those encoding the RNase H2 subunits. The complete cellular and genomic consequences of RNASEH2 mutations and the precise connection to disease remain unclear. To learn more about the effect of RNASEH2 mutations on the cell, we used yeast as a model of AGS disease. We have generated yeast strains bearing AGS-associated mutations in RNASEH2 genes. There is a range of disease presentation in patients bearing these RNASEH2 variants. Here we report on in vivo phenotypes of genomic instability, including mutation and recombination rates, and synthetic gene interactions. These phenotypes provide insight into molecular consequences of RNASEH2 mutations, and lay the groundwork for further study of genomic instability as a contributing factor to AGS disease.

Spontaneous MRI improvement and absence of cerebral calcification in Aicardi-Goutières syndrome: Diagnostic and disease-monitoring implications

BACKGROUND

Aicardi-Goutières syndrome (AGS) is a rare genetic leukoencephalopathy related to inappropriate activation of type I interferon. Neuroradiological findings are typically characterized by white matter abnormalities, cerebral atrophy and cerebral calcification. The disease usually manifests itself during the first year of life in the form of an initial "encephalitic-like" phase followed by a chronic phase of stabilization of the neurological signs. Recently new therapeutic strategies have been proposed aimed at blocking the abnormal activation of the interferon cascade.

MATERIALS AND METHODS

We reviewed clinical and MRI findings in three young RNASEH2B-mutated patients studied with serial CT and MRI studies.

RESULTS

All three patients presented clinical and MRI features consistent with AGS but, very unexpectedly, an improving neuroradiological course. In patient 1, the MRI improvement was noted some months after treatment with high-dose steroid and IVIg treatment; in patients 2 and 3 it occurred spontaneously. Patient 2 did not show cerebral calcification on CT images.

CONCLUSIONS

Our series highlights the possibility of spontaneous neuroradiological improvement in AGS2 patients, as well as the possibility of absence of cerebral calcification in AGS. The study underlines the need for extreme caution when using MRI as an outcome measure in therapeutic trials specific for this disease. MRI follow-up studies in larger series are necessary to describe the natural course of AGS.

Current therapies and therapeutic decision making for childhood-onset movement disorders

Movement disorders differ in children to adults. First, neurodevelopmental movement disorders such as tics and stereotypies are more prevalent than parkinsonism, and second, there is a genomic revolution which is now explaining many early-onset dystonic syndromes. We outline an approach to children with movement disorders starting with defining the movement phenomenology, determining the level of functional impairment due to abnormal movements, and screening for comorbid psychiatric conditions and cognitive impairments which often contribute more to disability than the movements themselves. The rapid improvement in our understanding of the etiology of movement disorders has resulted in an increasing focus on precision medicine, targeting treatable conditions and defining modifiable disease processes. We profile some of the key disease-modifying therapies in metabolic, neurotransmitter, inflammatory, and autoimmune conditions and the increasing focus on gene or cellular therapies. When no disease-modifying therapies are possible, symptomatic therapies are often all that is available. These classically target dopaminergic, cholinergic, alpha-adrenergic, or GABAergic neurochemistry. Increasing interest in neuromodulation has highlighted that some clinical syndromes respond better to DBS, and further highlights the importance of "disease-specific" therapies with a future focus on individualized therapies according to the genomic findings or disease pathways that are disrupted. We summarize some pragmatic applications of symptomatic therapies, neuromodulation techniques, and some rehabilitative interventions and provide a contemporary overview of treatment in childhood-onset movement disorders. © 2019 International Parkinson and Movement Disorder Society.

Brain organoids as a model system for human neurodevelopment and disease

The ability to reproduce early stages of human neurodevelopment in the laboratory is one of the most exciting fields in modern neuroscience. The inaccessibility of the healthy human brain developing in utero has delayed our understanding of the initial steps in the formation of one of the most complex tissues in the body. Animal models, postmortem human tissues and cellular systems have been instrumental in contributing to our understanding of the human brain. However, all model systems have intrinsic limitations. The emerging field of brain organoids, which are three-dimensional self-assembled multicellular structures derived from human pluripotent stem cells, offers a promising complementary cellular model for the study of the human brain. Here, we will discuss the initial experiments that were the foundation for this emerging field, highlight recent uses of the technology and offer our perspective on future directions that might guide further exploratory experimentation to improve the human brain organoid model system.