Genetic and phenotypic spectrum associated with IFIH1 gain-of-function

IFIH1 gain-of-function has been reported as a cause of a type I interferonopathy encompassing a spectrum of autoinflammatory phenotypes including Aicardi–Goutières syndrome and Singleton Merten syndrome. Ascertaining patients through a European and North American collaboration, we set out to describe the molecular, clinical and interferon status of a cohort of individuals with pathogenic heterozygous mutations in IFIH1. We identified 74 individuals from 51 families segregating a total of 27 likely pathogenic mutations in IFIH1. Ten adult individuals, 13.5% of all mutation carriers, were clinically asymptomatic (with seven of these aged over 50 years). All mutations were associated with enhanced type I interferon signaling, including six variants (22%) which were predicted as benign according to multiple in silico pathogenicity programs. The identified mutations cluster close to the ATP binding region of the protein. These data confirm variable expression and nonpenetrance as important characteristics of the IFIH1 genotype, a consistent association with enhanced type I interferon signaling, and a common mutational mechanism involving increased RNA binding affinity or decreased efficiency of ATP hydrolysis and filament disassembly rate

Identification of disease-causing genetic variants in patients with severe early-onset immunological disorders: a whole-exome sequencing approach

This work focuses on the identification of disease-causing genetic variants in paediatric patients with primary immunodeficiency (PID) and/or autoimmune/autoinflammatory disease. Although paediatric immune pathology is rare, these disorders are associated with a high morbidity and mortality and decreased quality of life. Treatment is often accompanied with serious side-effects and can hold risks on its own. Understanding the genetic cause of paediatric immune pathologies is critical for the diagnosis and correct treatment of these patients, and for the development of new therapeutics. While common disorders are thought to have a complex multifactorial causation, severe early-onset diseases are more likely to be monogenic making them good candidates for genetic studies. Although monogenic diseases make up only a small fraction of immunological disorders, they provide insight into mechanistic pathways that are likely to contribute to common forms of disease when less deleterious variants are inherited. Additionally, genetics studies on patients with severe early-onset immune pathologies can increase our understanding of the physiology and functioning of the healthy immune system. To clarify the contribution of novel genes in severe immunological disorders, the following methodology is used: 1) identification of candidate genetic variants through the use of whole-exome sequencing, 2) detailed assessment of the peripheral immune system in order to gain insight in disease mechanisms and pathways and 3) verification of the role of an identified candidate genetic variant in disease pathogenesis by developing functional tests on a case-by-case basis. This approach was successfully used to identify disease-causing variants in three different genes responsible for severe early-onset immune pathology in four unrelated families with very different clinical presentations. We identified a de novo gain-of-function mutation in IFIH1 in a 16-year-old girl with severe early-onset and refractory systemic lupus erythematosus (SLE), IgA-deficiency and mild lower limb spasticity without neuroradiological manifestations. The same missense mutation was recently found in patients with Aicardi-Goutières syndrome (AGS), a rare neuroimmunological disorder associated with elevated levels of type I interferon (IFN) and a severely debilitating encephalopathy, as well as in two asymptomatic family members. IFIH1 detects viral RNA and induces production of type I IFN. These findings indicate that the clinical phenotype associated with IFIH1 gain-of-function mutations can range from asymptomatic to a severe inflammatory encephalopathy to a prototypic systemic autoimmune disease. We also identified recessive loss-of-function mutations in CECR1, encoding adenosine deaminase 2 (ADA2), in a 9-year-old boy with Castleman’s-like disease and in two siblings (< 5 years old) with combined immunodeficiency (CID), lymphoproliferation, autoimmunity and vasculopathy. Recently, recessive loss-of-function mutations in CECR1 have been found in patient with systemic inflammation, systemic vasculopathy in the form of early-onset recurrent stroke, livedoid rash or vasculitis, hepatosplenomegaly, hypogammaglobulinemia and lymphopenia. Absence of ADA2 plasma activity was demonstrated and an important IL-6 signature was found in all three patients. In the patient with Castleman’s disease treatment with anti-IL-6 Receptor Antibody (tocilizumab) resulted in a rapid, complete, and persistent suppression of clinical features and laboratory abnormalities. This result indicates that ADA2 deficiency could be a cause of IL-6–mediated lymphoproliferation and systemic inflammation and should be investigated as a cause of Castleman's disease. Allogeneic hematopoietic stem cell transplantation (HSCT) of the oldest sibling with CID was successful both in rescuing the immunologic phenotype and in preventing further vascular disease, possibly through the observed restauration of ADA2 plasma activity. These findings suggest that the diagnosis of ADA2-deficiency should also be considered in patients with systemic inflammation without vasculopathy, or in patients with an undiagnosed PID characterized by lymphoproliferation and autoimmunity, even in the absence of overt vasculopathy or inflammation. Finally, we identified compound heterozygous STAT2 mutations in two siblings suffering from severe viral illness. Absent STAT2 expression, failure to signal through the type I IFN pathway and increased susceptibility of STAT2-deficient fibroblasts to in vitro viral infections was demonstrated. STAT2 deficiency was previously described as the cause of unusually severe viral illness in infancy in two families, and identification of STAT2 deficiency in this third unrelated family strengthens this data. Increased susceptibility to vaccine-strain measles with complicated measles infection following routine immunization was documented in both families, and may be a warning sign for STAT2 deficiency. Although in the first described family the majority of childhood viral illnesses were reported to be remarkably mild, the siblings described in this work appeared to present with a more severe phenotype. In both families a decrease in frequency and severity of viral infections with increasing age was observed, probably due to maturation of the adaptive immune system. However, the older sibling suddenly died at age 7 years from overwhelming viral illness associated with immune dysregulation and diffuse intravascular coagulopathy. This demonstrates that STAT2-deficient patients may still be at risk for overwhelming viral illness at a later age. In the younger sibling a good response to high-dose intravenous immunoglobulins (IVIG) treatment was observed during severe (viral) infectious episodes with signs of emerging coagulopathy and immune dysregulation.status: publishe

Mutant ADA2 in Vasculopathies

To the Editor: Zhou et al.(1) and Navon Elkan et al.(2) (both in the March 6 issue) speculate that hematopoietic stem-cell transplantation (HSCT) or enzyme-replacement therapy may be beneficial in patients with adenosine deaminase 2 (ADA2) deficiency. We report the clinical course of two brothers with recently diagnosed ADA2 deficiency resulting from a homozygous mutation in CECR1 (p.R169Q). One sibling underwent HSCT in 2003. (CECR1 encodes the protein ADA2.) One brother presented in 1999, at 6 months of age, with livedo reticularis, hepatosplenomegaly, hypercoagulability, granulocytopenia, and complete red-cell aplasia. He underwent HSCT in 2003 for a presumed diagnosis of . . .status: publishe

Machine learning identifies the immunological signature of Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is the most common childhood rheumatic disease, with a strongly debated pathophysiological origin. Both adaptive and innate immune processes have been proposed as primary drivers, which may account for the observed clinical heterogeneity, but few high-depth studies have been performed. Here we profiled the adaptive immune system of 85 JIA patients and 43 age-matched controls, identifying immunological changes unique to JIA and others common across a broad spectrum of childhood inflammatory diseases. The JIA immune signature was shared between clinically distinct subsets, but was accentuated in the systemic JIA patients and those patients with active disease. Despite the extensive overlap in the immunological spectrum exhibited by healthy children and JIA patients, machine learning analysis of the dataset proved capable of diagnosis of JIA patients with ~90% accuracy. These results pave the way for large-scale longitudinal studies of JIA, where machine learning could be used to predict immune signatures that correspond to treatment response group.status: publishe

IFIH1 mutation causes systemic lupus erythematosus with selective IgA-deficiency

To identify the underlying genetic defect in a 16-year-old girl with severe early-onset and refractory systemic lupus erythematosus (SLE), IgA-deficiency and mild lower limb spasticity without neuroradiological manifestations.status: publishe

Machine learning identifies an immunological pattern associated with multiple juvenile idiopathic arthritis subtypes

OBJECTIVES: Juvenile idiopathic arthritis (JIA) is the most common class of childhood rheumatic diseases, with distinct disease subsets that may have diverging pathophysiological origins. Both adaptive and innate immune processes have been proposed as primary drivers, which may account for the observed clinical heterogeneity, but few high-depth studies have been performed. METHODS: Here we profiled the adaptive immune system of 85 patients with JIA and 43 age-matched controls with indepth flow cytometry and machine learning approaches. RESULTS: Immune profiling identified immunological changes in patients with JIA. This immune signature was shared across a broad spectrum of childhood inflammatory diseases. The immune signature was identified in clinically distinct subsets of JIA, but was accentuated in patients with systemic JIA and those patients with active disease. Despite the extensive overlap in the immunological spectrum exhibited by healthy children and patients with JIA, machine learning analysis of the data set proved capable of discriminating patients with JIA from healthy controls with ~90% accuracy. CONCLUSIONS: These results pave the way for large-scale immune phenotyping longitudinal studies of JIA. The ability to discriminate between patients with JIA and healthy individuals provides proof of principle for the use of machine learning to identify immune signatures that are predictive to treatment response group.status: publishe

Disease-associated mutations identify a novel region in human STING necessary for the control of type I interferon signaling

International audienc

TBK1 / IKKE blockade inhibits mutant STING mediated inflammatory response in patient cells

International audienceMethods: Gain-of-function mutations in TMEM173, encoding the stimulator of interferon (IFN) genes (STING) protein, underlie a novel type I interferonopathy that is minimally responsive to conventional immunosuppressive therapies and associated with high frequency of childhood morbidity and mortality. STING gain-of-function causes constitutive oversecretion of IFN. This study was undertaken to determine the effects of a TANK-binding kinase 1 (TBK-1)/IKKɛ inhibitor (BX795) on secretion and signaling of IFN in primary peripheral blood mononuclear cells (PBMCs) from patients with mutations in STING.Objective: PBMCs from 4 patients with STING-associated disease were treated with BX795. The effect of BX795 on IFN pathways was assessed by Western blotting and an IFNβ reporter assay, as well as by quantification of IFNα in cell lysates, staining for STAT-1 phosphorylation, and measurement of IFN-stimulated gene (ISG) messenger RNA (mRNA) expression.Results: Treatment of PBMCs with BX795 inhibited the phosphorylation of IFN regulatory factor 3 and IFNβ promoter activity induced in HEK 293T cells by cyclic GMP-AMP or by genetic activation of STING. In vitro exposure to BX795 inhibited IFNα production in PBMCs of patients with STING-associated disease without affecting cell survival. In addition, BX795 decreased STAT-1 phosphorylation and ISG mRNA expression independent of IFNα blockade.Conclusion: These findings demonstrate the effect of BX795 on reducing type I IFN production and IFN signaling in cells from patients with gain-of-function mutations in STING. A combined inhibition of TBK-1 and IKKɛ therefore holds potential for the treatment of patients carrying STING mutations, and may also be relevant in other type I interferonopathies

Hematopoietic stem cell transplantation rescues the immunologic phenotype and prevents vasculopathy in patients with adenosine deaminase 2 deficiency

status: publishe