Cutaneous histopathological findings of Aicardi-Goutières syndrome, overlap with chilblain lupus

Nucleotide metabolism, leukodystrophies, and CNS pathology

The balance between a protective and a destructive immune response can be precarious, as exemplified by inborn errors in nucleotide metabolism. This class of inherited disorders, which mimics infection, can result in systemic injury and severe neurologic outcomes. The most common of these disorders is Aicardi Goutières syndrome (AGS). AGS results in a phenotype similar to "TORCH" infections (Toxoplasma gondii, Other [Zika virus (ZIKV), human immunodeficiency virus (HIV)], Rubella virus, human Cytomegalovirus [HCMV], and Herpesviruses), but with sustained inflammation and ongoing potential for complications. AGS was first described in the early 1980s as familial clusters of "TORCH" infections, with severe neurology impairment, microcephaly, and basal ganglia calcifications (Aicardi & Goutières, Ann Neurol, 1984;15:49-54) and was associated with chronic cerebrospinal fluid (CSF) lymphocytosis and elevated type I interferon levels (Goutières et al., Ann Neurol, 1998;44:900-907). Since its first description, the clinical spectrum of AGS has dramatically expanded from the initial cohorts of children with severe impairment to including individuals with average intelligence and mild spastic paraparesis. This broad spectrum of potential clinical manifestations can result in a delayed diagnosis, which families cite as a major stressor. Additionally, a timely diagnosis is increasingly critical with emerging therapies targeting the interferon signaling pathway. Despite the many gains in understanding about AGS, there are still many gaps in our understanding of the cell-type drivers of pathology and characterization of modifying variables that influence clinical outcomes and achievement of timely diagnosis.

Childhood-inherited white matter disorders with calcification

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

General approach to treatment of genetic leukoencephalopathies in children and adults

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

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

BACKGROUND

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

DATA SOURCES

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

RESULTS

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

CONCLUSIONS

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

The 2021 European Alliance of Associations for Rheumatology/American College of Rheumatology Points to Consider for Diagnosis and Management of Autoinflammatory Type I Interferonopathies: CANDLE/PRAAS, SAVI, and AGS

OBJECTIVE

Autoinflammatory type I interferonopathies, chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature/proteasome-associated autoinflammatory syndrome (CANDLE/PRAAS), stimulator of interferon genes (STING)-associated vasculopathy with onset in infancy (SAVI), and Aicardi-Goutières syndrome (AGS) are rare and clinically complex immunodysregulatory diseases. With emerging knowledge of genetic causes and targeted treatments, a Task Force was charged with the development of "points to consider" to improve diagnosis, treatment, and long-term monitoring of patients with these rare diseases.

METHODS

Members of a Task Force consisting of rheumatologists, neurologists, an immunologist, geneticists, patient advocates, and an allied health care professional formulated research questions for a systematic literature review. Then, based on literature, Delphi questionnaires, and consensus methodology, "points to consider" to guide patient management were developed.

RESULTS

The Task Force devised consensus and evidence-based guidance of 4 overarching principles and 17 points to consider regarding the diagnosis, treatment, and long-term monitoring of patients with the autoinflammatory interferonopathies, CANDLE/PRAAS, SAVI, and AGS.

CONCLUSION

These points to consider represent state-of-the-art knowledge to guide diagnostic evaluation, treatment, and management of patients with CANDLE/PRAAS, SAVI, and AGS and aim to standardize and improve care, quality of life, and disease outcomes.

The 2021 EULAR and ACR points to consider for diagnosis and management of autoinflammatory type I interferonopathies: CANDLE/PRAAS, SAVI and AGS

OBJECTIVE

Autoinflammatory type I interferonopathies, chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature/proteasome-associated autoinflammatory syndrome (CANDLE/PRAAS), stimulator of interferon genes (STING)-associated vasculopathy with onset in infancy (SAVI) and Aicardi-Goutières syndrome (AGS) are rare and clinically complex immunodysregulatory diseases. With emerging knowledge of genetic causes and targeted treatments, a Task Force was charged with the development of 'points to consider' to improve diagnosis, treatment and long-term monitoring of patients with these rare diseases.

METHODS

Members of a Task Force consisting of rheumatologists, neurologists, an immunologist, geneticists, patient advocates and an allied healthcare professional formulated research questions for a systematic literature review. Then, based on literature, Delphi questionnaires and consensus methodology, 'points to consider' to guide patient management were developed.

RESULTS

The Task Force devised consensus and evidence-based guidance of 4 overarching principles and 17 points to consider regarding the diagnosis, treatment and long-term monitoring of patients with the autoinflammatory interferonopathies, CANDLE/PRAAS, SAVI and AGS.

CONCLUSION

These points to consider represent state-of-the-art knowledge to guide diagnostic evaluation, treatment and management of patients with CANDLE/PRAAS, SAVI and AGS and aim to standardise and improve care, quality of life and disease outcomes.

COVID-19 skin lesions are rarely positive at RT-PCR test: the macrophage activation with vascular impact and SARS-CoV-2-induced cytokine storm

BACKGROUND

Several skin manifestations have been reported since the start of the COVID-19 pandemic: chilblains-like, livedoid lesions, urticaria-like, pseudo-Kawasaki disease, and others. Histopathologic images of these lesions most often show aspects of endothelitis, images similar to autoimmune vasculitis. Cutaneous lesions are often negative at RT-PCR for SARS-CoV-2 virus.

METHOD AND RESULTS

We reviewed recent articles on the mechanisms of COVID-19 and we synthesized main pathways of inflammatory cascade. After the penetration into the cells of the respiratory epithelium, SARS-CoV-2 virus initiates a "cytokine storm" well described in previous publications: the expression of interferon type I (IFN-I) is one of the key elements of the antiviral response in COVID-19 patients, IFN-I expression seems to play an important role in the induction of interleukin 6 (IL-6), chemotactic factors such as Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) and the consequent activation of monocyte-macrophage system followed by the expression of TNF-alpha, and finally by the induction of coagulation factors by both extrinsic and intrinsic pathways.

CONCLUSIONS

The simplified synthesis of the main pathophysiological mechanisms of COVID-19 could help us to understand at least partially the importance of macrophage activation and its vascular involvement in many skin lesions that remain often negative at in␣situ tests for SARS-CoV-2.

Histologic Patterns and Clues to Autoinflammatory Diseases in Children: What a Cutaneous Biopsy Can Tell Us

Autoinflammation is defined by aberrant, antigen-independent activation of the innate immune signaling pathways. This leads to increased, pro-inflammatory cytokine expression and subsequent inflammation. In contrast, autoimmune and allergic diseases are antigen-directed immune responses from activation of the adaptive immune system. The innate and adaptive immune signaling pathways are closely interconnected. The group of 'complex multigenic diseases' are a result of mutual dysregulation of both the autoinflammatory and autoimmune physiologic components. In contrast, monogenic autoinflammatory syndromes (MAIS) result from single mutations and are exclusively autoinflammatory in their pathogenesis. Studying the clinical and histopathological findings for the various MAIS explains the phenotypical correlates of their specific mutations. This review aims to group the histopathologic clues for autoinflammation into three recognizable patterns. The presence of these histologic patterns in a pediatric patient with recurrent fevers and systemic inflammation should raise suspicion of an autoinflammatory component in MAIS, or, more frequently, in a complex multigenic disease. The three major histopathological patterns seen in autoinflammation are as follows: (i) the 'neutrophilic' pattern, seen in urticarial neutrophilic dermatosis, pustular psoriasis, aseptic neutrophilic folliculitis, and Sweet's syndrome; (ii) the 'vasculitic' pattern seen in small vessel-vasculitis (including hypersensitivity/leukocytoclastic vasculitis, thrombosing microangiopathy and lymphocytic vasculitis), and intermediate-sized vessel vasculitis, mimicking polyarteritis nodosa; and (iii) the 'granulomatous' pattern. Beyond these three patterns, there are additional histopathologic clues, which are detailed below. It is important for a dermatopathologist to recognize the patterns of autoinflammation, so that a diagnosis of MAIS or complex multigenic diseases may be obtained. Finally, careful histopathologic analyses could contribute to a better understanding of the various clinical manifestations of autoinflammation.

Cutaneous Manifestations in Patients With COVID-19: Clinical Characteristics and Possible Pathophysiologic Mechanisms

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections soon led to a pandemic with serious health, economic, political, and cultural repercussions across the globe. The disease caused by SARS-CoV-2, coronavirus disease 2019 (COVID-19), is a multisystemic disease that requires a multidisciplinary approach involving specialists from all fields and levels of care. In this article, we review the literature on the diverse cutaneous manifestations associated with COVID-19. We also describe the pathophysiologic mechanisms proposed to date and their possible association with these manifestations. Finally, we propose a system for classifying the cutaneous manifestations of COVID-19 according to their underlying pathophysiologic mechanisms and prognosis.

Monogenic autoinflammatory disorders: Conceptual overview, phenotype, and clinical approach

Autoinflammatory diseases are conditions in which pathogenic inflammation arises primarily through antigen-independent hyperactivation of immune pathways. First recognized just over 2 decades ago, the autoinflammatory disease spectrum has expanded rapidly to include more than 40 distinct monogenic conditions. Related mechanisms contribute to common conditions such as gout and cardiovascular disease. Here, we review the basic concepts underlying the "autoinflammatory revolution" in the understanding of immune-mediated disease and introduce major categories of monogenic autoinflammatory disorders recognized to date, including inflammasomopathies and other IL-1-related conditions, interferonopathies, and disorders of nuclear factor kappa B and/or aberrant TNF activity. We highlight phenotypic presentation as a reflection of pathogenesis and outline a practical approach to the evaluation of patients with suspected autoinflammation.

Cutaneous Manifestations in Patients With COVID-19: Clinical Characteristics and Possible Pathophysiologic Mechanisms

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections soon led to a pandemic with serious health, economic, political, and cultural repercussions across the globe. The disease caused by SARS-CoV-2, coronavirus disease 2019 (COVID-19), is a multisystemic disease that requires a multidisciplinary approach involving specialists from all fields and levels of care. In this article, we review the literature on the diverse cutaneous manifestations associated with COVID-19. We also describe the pathophysiologic mechanisms proposed to date and their possible association with these manifestations. Finally, we propose a system for classifying the cutaneous manifestations of COVID-19 according to their underlying pathophysiologic mechanisms and prognosis.

Cutaneous clues to diagnose autoinflammatory diseases

Systemic autoinflammatory diseases (AIDs) are a group of disorders characterized by recurrent episodes of systemic inflammation. Suspecting the diagnosis can be difficult and many of the clinical manifestations are common to different diseases. Although most of the cutaneous manifestations are non-specific, it is important to know them because sometimes they can lead to the diagnosis. The purpose of this review was to synthesize the main cutaneous lesions of autoinflammatory diseases to aid in their diagnosis.

Interstitial Lung Disease and Psoriasis in a Child With Aicardi-Goutières Syndrome

Aicardi-Goutières syndrome (AGS) is characterized by progressive neurologic decline, cerebral calcification, and variable manifestations of autoimmunity. Seven subtypes of AGS have been defined and aberrant activation of the type I interferon system is a common theme among these conditions. We describe a 13-year-old boy who presented with an unusual constellation of psoriasis, interstitial lung disease (ILD), and pulmonary hypertension in addition to cerebral calcifications and glomerulonephritis. He was found to have late-onset AGS due to a gain-of-function mutation in IFIH1 and over-activation of the type I interferon pathway was confirmed by RNA sequencing. The majority of his clinical manifestations, including ILD, psoriasis and renal disease improved markedly after treatment with the combination of corticosteroids, cyclophosphamide, and the Janus-kinase inhibitor tofacitinib. This case extends the clinical spectrum of AGS and suggests the need for lung disease screening in patients with AGS.

Chilblains in children in the setting of COVID-19 pandemic

BACKGROUND

Different skin manifestations of COVID-19 are being reported. Acral lesions on the hands and feet, closely resembling chilblains, have been recognized during the peak incidence of the COVID-19 pandemic.

MATERIAL AND METHODS

A retrospective review of 22 children and adolescents with chilblain-like lesions seen over a short period of time in the Emergency Department of a children's hospital during the peak incidence of COVID-19 in Madrid, Spain.

RESULTS

All patients had lesions clinically consistent with chilblains of the toes or feet, with three also having lesions of the fingers. Pruritus and mild pain were the only skin symptoms elicited, and only 10 had mild respiratory and/or GI symptoms. None had fever. Coagulation tests, hemogram, serum chemistry, and lupus anticoagulant were normal in all patients tested. One out of 16 tested cases had elevated D-dimer results, but without systemic symptoms or other laboratory anomalies. SARS-CoV-2 PCR tested in 19 cases was positive in just one case. Skin biopsies obtained in six patients were consistent with chilblains. On follow-up, all cases showed spontaneous marked improvement or complete healing.

CONCLUSION

Acute chilblains were observed during COVID-19 pandemic in children and teenagers. It is a mildly symptomatic condition with an excellent prognosis, usually requiring no therapy. Etiopathogenesis remains unknown.

Vasculitis in Juvenile-Onset Systemic Lupus Erythematosus

Juvenile-onset systemic lupus erythematosus (JSLE) is a rare, heterogeneous multisystem autoimmune disease that can affect any organ, and present with diverse clinical and serological manifestations. Vasculitis can be a feature of JSLE. It more commonly presents as cutaneous vasculitis than visceral vasculitis, which can affect the central nervous system, peripheral nervous system, lungs, gut, kidneys, heart, and large vessels. The incidence and prevalence of vasculitis in JSLE has not been well described to date. Symptoms of vasculitis can be non-specific and overlap with other features of JSLE, requiring careful consideration for the diagnosis to be achieved and promptly treated. Biopsies are often required to make a definitive diagnosis and differentiate JSLE related vasculitis from other manifestations of JSLE, vasculopathies, and JSLE related antiphospholipid syndrome. Visceral vasculitis can be life threatening, and its presence at the time of JSLE diagnosis is associated with permanent organ damage, which further highlights the importance of prompt recognition and treatment. This review will focus on the presentation, diagnosis, management and outcomes of vasculitis in JSLE, highlighting gaps in the current evidence base.

Aicardi goutières syndrome is associated with pulmonary hypertension

While pulmonary hypertension (PH) is a potentially life threatening complication of many inflammatory conditions, an association between Aicardi Goutières syndrome (AGS), a rare genetic cause of interferon (IFN) overproduction, and the development of PH has not been characterized to date. We analyzed the cardiac function of individuals with AGS enrolled in the Myelin Disorders Bioregistry Project using retrospective chart review (n = 61). Additional prospective echocardiograms were obtained when possible (n = 22). An IFN signature score, a marker of systemic inflammation, was calculated through the measurement of mRNA transcripts of type I IFN-inducible genes (interferon signaling genes or ISG). Pathologic analysis was performed as available from autopsy samples. Within our cohort, four individuals were identified to be affected by PH: three with pathogenic gain-of-function mutations in the IFIH1 gene and one with heterozygous TREX1 mutations. All studied individuals with AGS were noted to have elevated IFN signature scores (Mann-Whitney p < .001), with the highest levels in individuals with IFIH1 mutations (Mann-Whitney p < .0001). We present clinical and histologic evidence of PH in a series of four individuals with AGS, a rare interferonopathy. Importantly, IFIH1 and TREX1 may represent a novel cause of PH. Furthermore, these findings underscore the importance of screening all individuals with AGS for PH.

Leukodystrophies

PURPOSE OF REVIEW

The leukodystrophies, typically considered incurable neurodegenerative disorders, are often diagnosed after irreversible central and peripheral nervous system injury has occurred. Early recognition of these disorders is imperative to enable potential therapeutic interventions. This article provides a summary of the symptoms of and diagnostic evaluation for leukodystrophies, along with the currently available therapies and recent advances in management.

RECENT FINDINGS

The leukodystrophies are a rapidly expanding field because of advances in neuroimaging and genetics; however, recognition of the clinical and biochemical features of a leukodystrophy is essential to accurately interpret an abnormal MRI or genetic result. Moreover, the initial symptoms of leukodystrophies may mimic other common pediatric disorders, leading to a delay in the recognition of a degenerative disorder.

SUMMARY

This article will aid the clinician in recognizing the clinical features of leukodystrophies and providing accurate diagnosis and management.

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.

Revised consensus statement on the preventive and symptomatic care of patients with leukodystrophies

Leukodystrophies are a broad class of genetic disorders that result in disruption or destruction of central myelination. Although the mechanisms underlying these disorders are heterogeneous, there are many common symptoms that affect patients irrespective of the genetic diagnosis. The comfort and quality of life of these children is a primary goal that can complement efforts directed at curative therapies. Contained within this report is a systems-based approach to management of complications that result from leukodystrophies. We discuss the initial evaluation, identification of common medical issues, and management options to establish a comprehensive, standardized care approach. We will also address clinical topics relevant to select leukodystrophies, such as gallbladder pathology and adrenal insufficiency. The recommendations within this review rely on existing studies and consensus opinions and underscore the need for future research on evidence-based outcomes to better treat the manifestations of this unique set of genetic disorders.

Type I interferon causes thrombotic microangiopathy by a dose-dependent toxic effect on the microvasculature

Many drugs have been reported to cause thrombotic microangiopathy (TMA), yet evidence supporting a direct association is often weak. In particular, TMA has been reported in association with recombinant type I interferon (IFN) therapies, with recent concern regarding the use of IFN in multiple sclerosis patients. However, a causal association has yet to be demonstrated. Here, we adopt a combined clinical and experimental approach to provide evidence of such an association between type I IFN and TMA. We show that the clinical phenotype of cases referred to a national center is uniformly consistent with a direct dose-dependent drug-induced TMA. We then show that dose-dependent microvascular disease is seen in a transgenic mouse model of IFN toxicity. This includes specific microvascular pathological changes seen in patient biopsies and is dependent on transcriptional activation of the IFN response through the type I interferon α/β receptor (IFNAR). Together our clinical and experimental findings provide evidence of a causal link between type I IFN and TMA. As such, recombinant type I IFN therapies should be stopped at the earliest stage in patients who develop this complication, with implications for risk mitigation.

Unusual cutaneous features associated with a heterozygous gain-of-function mutation in IFIH1: overlap between Aicardi-Goutières and Singleton-Merten syndromes

Cutaneous lesions described as chilblain lupus occur in the context of familial chilblain lupus or Aicardi-Goutières syndrome. To date, seven genes related to Aicardi-Goutières syndrome have been described. The most recently described encodes the cytosolic double-stranded RNA receptor IFIH1 (also known as MDA5), a key component of the antiviral type I interferon-mediated innate immune response. Enhanced type I interferon signalling secondary to gain-of-function mutations in IFIH1 can result in a range of neuroinflammatory phenotypes including classical Aicardi-Goutières syndrome. It is of note that none of the patients with a neurological phenotype so far described with mutations in this gene was reported to demonstrate cutaneous involvement. We present a family segregating a heterozygous pathogenic mutation in IFIH1 showing dermatological involvement as a prominent feature, variably associated with neurological disturbance and premature tooth loss. All three affected individuals exhibited increased expression of interferon-stimulated genes in whole blood, and the mutant protein resulted in enhanced interferon signalling in vitro, both in the basal state and following ligand stimulation. Our results further extend the phenotypic spectrum associated with mutations in IFIH1, indicating that the disease can be confined predominantly to the skin, while also highlighting phenotypic overlap with both Aicardi-Goutières syndrome and Singleton-Merten syndrome.

[Type I interferonopathies]

Type I interferonopathies are a group of Mendelian disorders characterized by a common physiopathology: the up-regulation of type I interferons. To date, interferonopathies include Aicardi-Goutières syndrome, familial chilblain lupus, spondyenchondromatosis, PRoteasome-associated auto-inflammatory syndrome (PRAAS) and Singleton-Merten syndrome. These diseases present phenotypic overlap including cutaneous features like chilblain lupus, that can be inaugural or present within the first months of life. This novel set of inborn errors of immunity is evolving rapidly, with recognition of new diseases and genes. Recent and improved understanding of the physiopathology of overexpression of type I interferons has allowed the development of targeted therapies, currently being evaluated, like Janus-kinases or reverse transcriptase inhibitors.

The eukaryotic elongation factor eEF1A1 interacts with SAMHD1

Mutations in SAMHD1 cause Aicardi-Goutières syndrome (AGS), a Mendelian inflammatory disease which displays remarkable clinical and biochemical overlap with congenital viral infection. SAMHD1 (SAM domain and HD domain-containing protein 1) has also been defined as an HIV-1 restriction-factor that, through a novel triphosphohydrolase activity, inhibits early stage HIV-1 replication in myeloid-derived dendritic cells (MDDCs), macrophages and resting CD4+ T-cells. The potent activity of SAMHD1 is likely to be the subject of a variety of regulatory mechanisms. Knowledge of proteins that interact with SAMHD1 may not only enhance our understanding of the pathogenesis of AGS, but may also provide further details on the link between the regulation of cellular dNTPs and HIV-1 restriction. In the present study, we used a yeast two-hybrid screen and pull-down analysis followed by MS to identify the eukaryotic elongation factor 1A1 (eEF1A1) as a potential interaction partner of SAMHD1. This interaction was confirmed by unbiased co-immunoprecipitation and demonstrated in situ by a proximity ligation assay (PLA). We show that this interaction is enhanced in mutant SAMHD1 cell lines and suggest that eEF1A1 may mediate SAMHD1 turnover by targeting it to the proteosome for degradation through association with Cullin4A and Rbx1.

Advances in the diagnosis of leukoencephalopathies

Introduction : Leukoencephalopathies (LEs) are a diverse group of diseases involving cerebral white matter. Some of the disorders may be infectious or immunologically mediated and, therefore, tend to be more amenable to treatment. Most of these disorders have a genetic basis, for which genetic counseling becomes important as currently very few of them have effective therapies. Areas covered : This review calls attention to the diagnostic dilemmas, highlights the diagnostic tests of choice for separating conditions with similar clinical, laboratory or neuroimaging findings, and describes several LEs that have been newly discovered within the last 20 years. Imaging of LEs has progressed rapidly since the introduction of magnetic resonance imaging (MRI) and spectroscopy (MRS), allowing recognition of new diseases, with and without identifiable corresponding biochemical or genetic defects. The distinguishing MRI and MRS features of LEs are described, as well as the resources available for biochemical, CSF and blood sample testing for diagnosis and differentiation from previously known LEs. Expert opinion : Although there is no treatment at present for many of the LEs, their detection as a cause of intellectual and motor disabilities, and as inherited disorders, makes it necessary to accurately categorize them. This knowledge will then allow further elucidation of the etiology, understanding the biological underpinnings, and eventually progress toward rational therapies.

The TREX1 exonuclease R114H mutation in Aicardi-Goutières syndrome and lupus reveals dimeric structure requirements for DNA degradation activity

Mutations in the TREX1 gene cause Aicardi-Goutières syndrome (AGS) and are linked to the autoimmune disease systemic lupus erythematosus. The TREX1 protein is a dimeric 3' DNA exonuclease that degrades DNA to prevent inappropriate immune activation. One of the most common TREX1 mutations, R114H, causes AGS as a homozygous and compound heterozygous mutation and is found as a heterozygous mutation in systemic lupus erythematosus. The TREX1 proteins containing R114H and the insertion mutations aspartate at position 201 (D201ins) and alanine at position 124 (A124ins), found in compound heterozygous AGS with R114H, were prepared and the DNA degradation activities were tested. The homodimer TREX1(R114H/R114H) exhibits a 23-fold reduced single-stranded DNA (ssDNA) exonuclease activity relative to TREX1(WT). The TREX1(D201ins/D201ins) and TREX1(A124ins/A124ins) exhibit more than 10,000-fold reduced ssDNA degradation activities. However, the TREX1(R114H/D201ins) and TREX1(R114H/A124ins) compound heterodimers exhibit activities 10-fold greater than the TREX1(R114H/R114H) homodimer during ssDNA and double-stranded DNA (dsDNA) degradation. These higher levels of activities measured in the TREX1(R114H/D201ins) and TREX1(R114H/A124ins) compound heterodimers are attributed to Arg-114 residues of TREX1(D201ins) and TREX1(A124ins) positioned at the dimer interface contributing to the active sites of the opposing TREX1(R114H) protomer. This interpretation is further supported by exonuclease activities measured for TREX1 enzymes containing R114A and R114K mutations. These biochemical data provide direct evidence for TREX1 residues in one protomer contributing to DNA degradation catalyzed in the opposing protomer and help to explain the dimeric TREX1 structure required for full catalytic competency.

Intracerebral large artery disease in Aicardi-Goutières syndrome implicates SAMHD1 in vascular homeostasis

AIM

To describe a spectrum of intracerebral large artery disease in Aicardi-Goutières syndrome (AGS) associated with mutations in the AGS5 gene SAMHD1.

METHOD

We used clinical and radiological description and molecular analysis.

RESULTS

Five individuals (three males, two females) were identified as having biallelic mutations in SAMHD1 and a cerebral arteriopathy in association with peripheral vessel involvement resulting in chilblains and ischaemic ulceration. The cerebral vasculopathy was primarily occlusive in three patients (with terminal carotid occlusion and basal collaterals reminiscent of moyamoya syndrome) and aneurysmal in two. Three of the five patients experienced intracerebral haemorrhage, which was fatal in two individuals. Post-mortem examination of one patient suggested that the arteriopathy was inflammatory in origin.

INTERPRETATION

Mutations in SAMHD1 are associated with a cerebral vasculopathy which is likely to have an inflammatory aetiology. A similar disease has not been observed in patients with mutations in AGS1 to AGS4, suggesting a particular role for SAMHD1 in vascular homeostasis. Our report raises important questions about the management of patients with mutations in SAMHD1.

Aicardi-Goutieres syndrome

INTRODUCTION

Aicardi-Goutières syndrome (AGS) is an autosomal recessive encephalopathy characterized by acquired microcephaly, cerebral calcifications, leukodystrophy, cerebral atrophy and cerebrospinal fluid findings of chronic lymphocytosis and raised interferon-alpha (INF-alpha). The main extraneurological symptoms are chilblain-like skin lesions, usually on the fingers, toes and ears.

SOURCES OF DATA

This review is based on a search of the published literature on AGS from 1984 onwards (particularly the most recent papers) and on knowledge and experience gained through the authors' work with the International Aicardi-Goutières Syndrome Association (IAGSA).

AREAS OF AGREEMENT

It is accepted that AGS can be mistaken for a congenital infection and that the diagnostic significance of its cardinal signs (raised INF-alpha levels, basal ganglia calcifications) is different in different stages of the disease. Currently, we know of four genes that, if mutated, can give rise to AGS, but at least one other gene is believed to exist. These genes are involved in the DNA damage response, a defect of which could provoke an inappropriate innate immune response, triggering increased secretion of INF-alpha, ultimately responsible for the main features of the disease.

AREAS OF CONTROVERSY

The natural history of AGS has not yet been definitively described given the lack of extensive, long-term neuroradiological follow-up studies. Furthermore, it is not yet clearly understood how the innate immune system is activated, what triggers the onset of the disease or why it tends to 'burn out' after several months. Immunosuppressive therapy in the active stage of the disease does not seem to produce any real change in the clinical course, but more data are needed.

GROWING POINTS AND AREAS TIMELY FOR DEVELOPING RESEARCH

Current studies aim to clarify the molecular mechanisms underlying the pathogenesis of AGS and to establish the exact pathway by which retained nucleic acids activate the immune system. This knowledge could allow the development of therapeutic strategies.

The TREX1 double-stranded DNA degradation activity is defective in dominant mutations associated with autoimmune disease

Mutations in TREX1 have been linked to a spectrum of human autoimmune diseases including Aicardi-Goutières syndrome (AGS), familial chilblain lupus (FCL), systemic lupus erythematosus, and retinal vasculopathy and cerebral leukodystrophy. A common feature in these conditions is the frequent detection of antibodies to double-stranded DNA (dsDNA). TREX1 participates in a cell death process implicating this major 3' --> 5' exonuclease in genomic DNA degradation to minimize potential immune activation by persistent self DNA. The TREX1 D200N and D18N dominant heterozygous mutations were identified in AGS and FCL, respectively. TREX1 enzymes containing the D200N and D18N mutations were compared using nicked dsDNA and single-stranded DNA (ssDNA) degradation assays. The TREX1WT/D200N and TREX1WT/D18N heterodimers are completely deficient at degrading dsDNA and degrade ssDNA at an expected approximately 2-fold lower rate than TREX1WT enzyme. Further, the D200N- and D18N-containing TREX1 homo- and heterodimers inhibit the dsDNA degradation activity of TREX1WT enzyme, providing a likely explanation for the dominant phenotype of these TREX1 mutant alleles in AGS and FCL. By comparison, the TREX1 R114H homozygous mutation causes AGS and is found as a heterozygous mutation in systemic lupus erythematosus. The TREX1R114H/R114H homodimer has dysfunctional dsDNA and ssDNA degradation activities and does not detectibly inhibit the TREX1WT enzyme, whereas the TREX1WT/R114H heterodimer has a functional dsDNA degradation activity, supporting the recessive genetics of TREX1 R114H in AGS. The dysfunctional dsDNA degradation activities of these disease-related TREX1 mutants could account for persistent dsDNA from dying cells leading to an aberrant immune response in these clinically related disorders.