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

Objectives: Mutations in the TREX1 gene cause Aicardi-Goutières syndrome (AGS) 1, associated with a spectrum of autoimmune and neurodegenerative manifestations. AGS 1, the most severe neonatal type of AGS, is characterized by abnormal neurologic findings, visual inattention, hepatosplenomegaly, thrombocytopenia, skin rash, restlessness, and fever. Materials & Methods: The present study described two affected siblings from an Iranian family whose phenotypes overlap with intrauterine infections. They had almost similar presentations, including developmental delay, microcephaly, no fix and follow epileptic seizures and the same pattern of brain CT scan involvements. Following clinical and paraclinical assessments, whole-exome sequencing was employed to determine the disease-causing variant, and subsequently, PCR-Sanger sequencing was performed to indicate the segregation pattern of the candidate variant in family members. Results: Genetic analysis revealed a novel homozygous missense variant (c.461A>C; p.D154A) in the TREX1 gene in affected family members. Sanger sequencing of other family members showed the expected zygosities. Conclusion: This study identifies a novel mutation in the TREX1 gene in this family and highlights the efficiency of next-generation sequencing-based techniques for obtaining a definite diagnosis in patients with early-onset encephalopathy.

T-Rex escaped from the cytosolic park: Re-thinking the impact of TREX1 exonuclease deficiencies on genomic stability.

The Three Prime Repair Exonuclease 1 (TREX1) has been implicated in several pathologies characterized by chronic and inborn inflammation. Aberrant innate immunity caused by DNA sensing through the cGAS-STING pathway has been proposed to play a major role in the etiology of these interferonopathies. However, the molecular source of this DNA sensing and the possible involvement of TREX1 in genome (in)stability remains poorly understood. Recent findings reignite the debate about the cellular functions performed by TREX1 nuclease, notably in chromosome biology and stability. Here I put into perspective recent findings that suggest that TREX1 is at the crossroads of DNA damage response and inflammation in different pathological contexts.

The brain microvasculature is a primary mediator of interferon-α neurotoxicity in human cerebral interferonopathies.

Aicardi-Goutières syndrome (AGS) is an autoinflammatory disease characterized by aberrant interferon (IFN)-α production. The major cause of morbidity in AGS is brain disease, yet the primary source and target of neurotoxic IFN-α remain unclear. Here, we demonstrated that the brain was the primary source of neurotoxic IFN-α in AGS and confirmed the neurotoxicity of intracerebral IFN-α using astrocyte-driven Ifna1 misexpression in mice. Using single-cell RNA sequencing, we demonstrated that intracerebral IFN-α-activated receptor (IFNAR) signaling within cerebral endothelial cells caused a distinctive cerebral small vessel disease similar to that observed in individuals with AGS. Magnetic resonance imaging (MRI) and single-molecule ELISA revealed that central and not peripheral IFN-α was the primary determinant of microvascular disease in humans. Ablation of endothelial Ifnar1 in mice rescued microvascular disease, stopped the development of diffuse brain disease, and prolonged lifespan. These results identify the cerebral microvasculature as a primary mediator of IFN-α neurotoxicity in AGS, representing an accessible target for therapeutic intervention.

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

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

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

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

Intracranial calcifications simulating Aicardi-Goutières syndrome in PARS2-related mitochondrial disease.

PARS2 encodes an aminoacyl-tRNA synthetase that catalyzes the ligation of proline to mitochondrial prolyl-tRNA molecules. Diseases associated with PARS2 primarily affect the central nervous system, causing early infantile developmental epileptic encephalopathies (EIDEE; DEE75; MIM #618437) with infantile-onset neurodegeneration. Dilated cardiomyopathy has also been reported in the affected individuals. About 10 individuals to date have been described with pathogenic biallelic variants in PARS2. While many of the reported individuals succumbed to the disease in the first two decades of life, autopsy findings have not yet been reported. Here, we describe neuropathological findings in a deceased male with evidence of intracranial calcifications in the basal ganglia, thalamus, cerebellum, and white matter, similar to Aicardi-Goutières syndrome. This report describes detailed autopsy findings in a child with PARS2-related mitochondrial disease and provides plausible evidence that intracranial calcifications may be a previously unrecognized feature of this disorder.

Corrigendum: Newborn screening for X-linked adrenoleukodystrophy in Italy: diagnostic algorithm and disease monitoring.

[This corrects the article DOI: 10.3389/fneur.2022.1072256.].

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

OBJECTIVE: Aicardi Goutières Syndrome (AGS) is a genetic interferonopathy associated with multisystemic heterogeneous disease and neurologic dysfunction. AGS includes a broad phenotypic spectrum which is only partially explained by genotype. To better characterize this variability, we will perform a systematic analysis of phenotypic variability in familial cases of AGS. METHODS: Among thirteen families, twenty-six siblings diagnosed with AGS were identified from the Myelin Disorders and Biorepository Project (MDBP) at the Children's Hospital of Philadelphia. Data were collected on the age of onset, genotype, neurologic impairment, and systemic complications. Neurologic impairment was assessed by a disease-specific scale (AGS Severity Scale) at the last available clinical encounter (range: 0-11 representing severe - attenuated phenotypes). The concordance of clinical severity within sibling pairs was categorized based on the difference in AGS Scale (discordant defined as >2-unit difference). The severity classifications were compared between sibling sets and by genotype. RESULTS: Five genotypes were represented: TREX1 (n = 4 subjects), RNASEH2B (n = 8), SAMHD1 (n = 8) ADAR1 (n = 4), and IFIH1 (n = 2). The older sibling was diagnosed later relative to the younger affected sibling (median age 7.32 years [IQR = 14.1] compared to 1.54 years [IQR = 10.3]). Common presenting neurologic symptoms were tone abnormalities (n = 10/26) and gross motor dysfunction (n = 9/26). Common early systemic complications included dysphagia and chilblains. The overall cohort median AGS severity score at the last encounter was 8, while subjects presenting with symptoms before one year had a median score of 5. The TREX1 cohort presented at the youngest age and with the most severe phenotype on average. AGS scores were discordant for 5 of 13 sibling pairs, most commonly in the SAMHD1 pairs. Microcephaly, feeding tube placement, seizures and earlier onset sibling were associated with lower AGS scores (respectively, Wilcoxon rank sum: p = 0.0001, p < 0.0001, p = 0.0426, and Wilcoxon signed rank: p = 0.0239). CONCLUSIONS: In this systematic analysis of phenotypic variability in familial cases, we found discordance between siblings affected by AGS. Our results underscore the heterogeneity of AGS and suggest factors beyond AGS genotype may affect phenotype. Understanding the critical variables associated with disease onset and severity can guide future therapeutic interventions and clinical monitoring. This report reinforces the need for further studies to uncover potential factors to better understand this phenotypic variability, and consequently identify potential targets for interventions in attempt to change the natural history of the disease.

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.

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

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

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

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

LINE-1: an emerging initiator of cGAS-STING signalling and inflammation that is dysregulated in disease.

The cGAS-STING (cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING)) axis integrates DNA damage and cellular stress with type I interferon (IFN) signalling to facilitate transcriptional changes underlying inflammatory stress responses. The cGAS-STING pathway responds to cytosolic DNA in the form of double-stranded DNA, micronuclei, and long interspersed nuclear element 1 (L1) retroelements. L1 retroelements are a class of self-propagating non-long terminal repeat transposons that have remained highly active in mammalian genomes. L1 retroelements are emerging as important inducers of cGAS-STING and IFN signalling, which are often dysregulated in several diseases, including cancer. A key repressor of cGAS-STING and L1 activity is the exonuclease three prime repair exonuclease 1 (TREX1), and loss of TREX1 promotes the accumulation of L1. In addition, L1 dysregulation is a common theme among diseases with chronic induction of type I IFN signalling through cGAS-STING, such as Aicardi-Goutières syndrome, Fanconi anemia, and dermatomyositis. Although TREX1 is highly conserved in tetrapod species, other suppressor proteins exist that inhibit L1 retrotransposition. These suppressor genes when mutated are often associated with diseases characterized by unchecked inflammation that is associated with high cGAS-STING activity and elevated levels of L1 expression. In this review, we discuss these interconnected pathways of L1 suppression and their role in the regulation of cGAS-STING and inflammation in disease.

STING signaling in the brain: Molecular threats, signaling activities, and therapeutic challenges.

Stimulator of interferon genes (STING) is an innate immune signaling protein critical to infections, autoimmunity, and cancer. STING signaling is also emerging as an exciting and integral part of many neurological diseases. Here, we discuss recent advances in STING signaling in the brain. We summarize how molecular threats activate STING signaling in the diseased brain and how STING signaling activities in glial and neuronal cells cause neuropathology. We also review human studies of STING neurobiology and consider therapeutic challenges in targeting STING to treat neurological diseases.

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

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

Dyschromatosis symmetrica hereditaria: A clue to early diagnosis of Aicardi-Goutières syndrome.

A 6-year-old female with a history of Aicardi-Goutières syndrome (AGS) presented to dermatology clinic with hypopigmented and hyperpigmented macules and patches consistent with dyschromatosis symmetrica hereditaria (DSH). Previous genetic workup demonstrated a de novo, heterozygous mutation in the adenosine deaminase acting on RNA 1 (ADAR) gene. While the co-occurrence of AGS and DSH has previously been described in mutations of the ADAR gene, our case highlights the potential association between these disorders that may aid in earlier future diagnosis of AGS.

TREX-1 related Aicardi-Goutières syndrome improved by Janus kinase inhibitor.

Aicardi-Goutières syndrome (AGS) is a genetic interferonopathy classically characterized by early onset of severe neurologic injury with basal ganglia calcifications, white matter abnormalities, and progressive cerebral atrophy, along with lymphocytosis and raised interferon alpha (INFα) in the cerebrospinal fluid (CSF). Here, we report a 31/2 year-old patient born with prenatal onset AGS, first manifesting as intra-uterine growth retardation. Cranial ultrasonography and cerebral MRI revealed ventriculomegaly and periventricular and basal ganglia calcifications, along with cerebral atrophy. Perinatal infections and known metabolic disorders were excluded. Both CSF lymphocytosis and raised INFα were present. Molecular analysis disclosed two already described compound heterozygous pathogenic variants in TREX1 (c. 309dup, p.(Thr104Hisfs*53) and c. 506G > A, p.(Arg169His)). The evolution was marked by severe global developmental delay with progressive microcephaly. Promptly, the patient developed irritability, quadri-paretic dyskinetic movements, and subsequently tonic seizures. Sensorineural hearing loss was detected as well as glaucoma. Initially, he was symptomatically treated with trihexyphenidyl followed by levetiracetam and topiramate. At age 22 months, baricitinib (0.4 mg/kg/day) was introduced, leading to normal serum INFα levels. Clinically, dyskinetic movements significantly decreased as well as irritability and sleep disturbance. We confirmed that baricitinib was a useful treatment with no major side effect.

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

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

Tocilizumab reduces the unmanageable inflammatory reaction of a patient with Aicardi-Goutières syndrome type 7 during treatment with ruxolitinib.

BACKGROUND: Aicardi-Goutières syndrome (AGS) is a rare hereditary early-onset encephalopathy characterized by upregulation of the type I interferon pathway, poorly responsive to conventional immunosuppression. CASE PRESENTATION: We describe a 7-year-old Chinese boy who developed symptoms at the age of 6 months. He presented with a chilblain-like rash, leukopenia, neutropenia, elevated liver enzymesgrowth retardation, microcephaly, elevated acute phase reactants, intracranial calcification and leukodystrophy. At the age of 3 years old, whole-exome sequencing confirmed a de novo heterozygous gain-of-function mutation, c.1016 C > A (p.Ala339Asp), in the IFIH1 gene, and he was diagnosed with AGS7. He was treated with ruxolitinib accompanied by steroids and thalidomide for about four years. The rash, hematological manifestations, and the liver function were all improved, but the erythrocyte sedimentation rate remained consistently elevated until the addition of tocilizumab, a monoclonal antibody against interleukin 6. CONCLUSIONS: Ruxolitinib was not successful in suppressing the inflammatory process, and tocilizumab produced highly encouraging results in reducing the inflammatory reaction of AGS. The study makes a significant contribution to the literature because we may found a potential alternative therapeutic option for AGS.

Type I Interferonopathies: A Clinical Review.

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

Subacute Partially Reversible Leukoencephalopathy Expands the Aicardi-Goutières Syndrome Phenotype.

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