Systemic lupus erythematosus (SLE) presents a complex clinical landscape with diverse manifestations, suggesting a multifactorial etiology. However, the identification of rare monogenic forms of the disease has shed light on specific genetic defects underlying SLE pathogenesis, offering valuable insights into its underlying mechanisms and clinical heterogeneity. By categorizing these monogenic forms based on the implicated signaling pathways, such as apoptotic body clearance, type I interferon signaling, JAK-STAT pathway dysregulation, innate immune receptor dysfunction and lymphocytic abnormalities, a more nuanced understanding of SLE\'s molecular basis emerges. Particularly in pediatric populations, where monogenic forms are more prevalent, routine genetic testing becomes increasingly important, with a diagnostic yield of approximately 10% depending on the demographic and methodological factors involved. This approach not only enhances diagnostic accuracy but also informs personalized treatment strategies tailored to the specific molecular defects driving the disease phenotype.
UNASSIGNED: Maladies auto-immunes rares : place de la génétique, exemple du lupus systémique.
UNASSIGNED: Le lupus érythémateux systémique (LES) est une maladie auto-immune chronique caractérisée par une grande hétérogénéité clinique. Certaines formes rares de LES sont causées par des mutations génétiques spécifiques, contrairement à la nature multifactorielle généralement associée à la maladie. Ces formes monogéniques ont été décrites particulièrement dans les cas de LES à début pédiatrique. Leur découverte a permis une meilleure compréhension de la physiopathologie du LES, mettant en lumière la grande complexité des présentations cliniques. Nous proposons ici une classification basée sur les voies de signalisation sous-jacentes, impliquant la clairance des corps apoptotiques et des complexes immuns, les interférons de type I, les voies JAK-STAT, les récepteurs de l’immunité innée et les fonctions lymphocytaires. Dans les formes pédiatriques, un test génétique devrait être proposé systématiquement avec un rendement diagnostique autour de 10 % selon la population et les approches utilisées.

A case of a 28-year-old woman with known C1-inhibitor deficiency (functional, Type II) with persistent bilateral non-pruritic, mildly photosensitive facial rash for 10 months following delivery of her second child is presented. Histology of the skin was suggestive of tumid lupus erythematosus (LE), but no other features of systemic LE (ANA, dsDNA negative) were evident. She had stopped danazol which was controlling the underlying disease, and once this was restarted and treatment for tumid lupus was started, she improved. More rigorous control preventing all C1-inhibitor deficiency-related attacks proved successful. The hypothesis that uncontrolled classical pathway complement activation that led to the lupus-like skin lesions is being presented as a clinical case, highlighting the complex interrelationships between immunodeficiency and autoimmunity in inborn errors in immunity.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that is characterized by its large heterogeneity in terms of clinical presentation and severity. The pathophysiology of SLE involves an aberrant autoimmune response against various tissues, an excess of apoptotic bodies, and an overproduction of type-I interferon. The genetic contribution to the disease is supported by studies of monozygotic twins, familial clustering, and genome-wide association studies (GWAS) that have identified numerous risk loci. In the early 70s, complement deficiencies led to the description of familial forms of SLE caused by a single gene defect. High-throughput sequencing has recently identified an increasing number of monogenic defects associated with lupus, shaping the concept of monogenic lupus and enhancing our insights into immune tolerance mechanisms. Monogenic lupus (moSLE) should be suspected in patients with either early-onset lupus or syndromic lupus, in male, or in familial cases of lupus. This review discusses the genetic basis of monogenic SLE and proposes its classification based on disrupted pathways. These pathways include defects in the clearance of apoptotic cells or immune complexes, interferonopathies, JAK-STATopathies, TLRopathies, and T and B cell dysregulations.

METHODS: A 68-year-old woman was referred for immunological investigation following an episode of meningococcal epiglottitis with associated septicaemia. Several years previously, she had been diagnosed with undifferentiated connective tissue disease. On investigation, alternative pathway complement function was normal; however, classical pathway complement activation was reduced. C1q, C3 and C4 levels were all measured and found to be within their respective normal ranges, but C2 levels were low. Sequencing of the C2 gene was subsequently performed, confirming a diagnosis of type 1 C2 deficiency (C2D).
CONCLUSIONS: C2D is usually hereditary and inherited in an autosomal recessive manner. C2D is often asymptomatic, however, some patients suffer from infections with encapsulated bacteria and/or autoimmune diseases, particularly systemic lupus erythematosus. Recognition of complement pathway deficiency is important due to the predisposition to severe and/or recurrent infections by encapsulated bacteria. Immunisations have the potential to reduce both mortality and morbidity not only for the patient but also for any affected relatives.

Hereditary complement deficiencies are relatively rare worldwide, they account for about 1-10% of primary immunodeficiencies. Acquired complement deficiencies are more prevalent and with the more frequent use of complement inhibitor therapy, the incidence of patients with iatrogenic complement deficiency is increasing. Alike in the inherited forms, patients have a high risk of severe and life-threatening infections caused by encapsulated bacteria (sepsis, meningitis). The most frequent pathogens are Neisseria meningitidis, Streptococcus pneumoniae and Haemophilus influenzae. C5 and C3 complement inhibitor therapies are available in Hungary, which are mostly indicated in the treatment of paroxysmal nocturnal hemoglobinuria, myasthenia gravis, neuromyelitis optica and atypical haemolytic uremic syndrome. It is of utmost importance to prevent severe, potentially life-threatening bacterial infections in this group of patients. Nevertheless, there is no Hungarian guidance to decrease the risk of infections, preventive measures are incomplete and not standardized posing potential risk of infections for these patients, so far. In this review, we aim to summarize the international clinical practices and guidance on the infection prevention in complement deficient patients. This recommendation might be a source of an evidence-based Hungarian guideline regarding vaccination and antibiotic prophylaxis in this specifically vulnerable group of patients. Orv Hetil. 2023; 164(25): 971-980.
A veleszületett komplementdefektusok világszerte ritkán fordulnak elő, a primer immunhiányok 1–10%-át teszik ki. A szerzett komplementdefektusok gyakoribbak, és a komplementgátló kezelések egyre elterjedtebb alkalmazásával a szerzett komplementhiányos betegek incidenciája nő. A terápia okozta komplementdeficientia a genetikailag meghatározott formákhoz hasonlóan döntően tokos baktériumok által okozott, visszatérően jelentkező, életveszélyes fertőzésekre hajlamosít (sepsis, meningitis). A leggyakoribb kórokozók a Neisseria meningitidis, a Streptococcus pneumoniae és a Haemophilus influenzae. Hazánkban C5- és C3-komplement-gátló gyógyszerek érhetők el a klinikai gyakorlatban, melyek elsődlegesen paroxysmalis nocturnalis haemoglobinuria, myasthenia gravis, neuromyelitis optica és atípusos haemolyticus uraemiás szindrómás betegek kezelésére indikáltak. A fenti kezelésben részesülő betegek körében kiemelt jelentőségű és a kezelésnek elengedhetetlen feltétele a súlyos, potenciálisan életet veszélyeztető, gyors progressziójú bakteriális fertőzések megelőzése. Ennek ellenére az infekciós kockázatot csökkentő hazai ajánlás nem létezik, a megelőzési stratégia nem standardizált, gyakran hiányos, ami az érintett betegeket súlyosan veszélyezteti. Közleményünk célja a nemzetközi gyakorlat és klinikai útmutatók áttekintésével a komplementhiányos betegeknél alkalmazható szakmai javaslat megfogalmazása a bakteriális fertőzések prevenciójára vonatkozóan, mely egy későbbi hazai irányelv alapjául szolgálhat. Orv Hetil. 2023; 164(25): 971–980.

Primary complement system (C) deficiencies are rare but notably associated with an increased risk of infections, autoimmunity, or immune disorders. Patients with terminal pathway C-deficiency have a 1,000- to 10,000-fold-higher risk of Neisseria meningitidis infections and should be therefore promptly identified to minimize the likelihood of further infections and to favor vaccination. In this paper, we performed a systematic review about clinical and genetic patterns of C7 deficiency starting from the case of a ten-year old boy infected by Neisseria meningitidis B and with clinical presentation suggestive of reduced C activity. Functional assay via Wieslab ELISA Kit confirmed a reduction in total C activity of the classical (0.6% activity), lectin (0.2% activity) and alternative (0.1% activity) pathways. Western blot analysis revealed the absence of C7 in patient serum. Sanger sequencing of genomic DNA extracted from peripheral blood of the patient allowed the identification of two pathogenetic variants in the C7 gene: the already well-characterized missense mutation G379R and a novel heterozygous deletion of three nucleotides located at the 3\'UTR (c.*99_*101delTCT). This mutation resulted in an instability of the mRNA; thus, only the allele containing the missense mutation was expressed, making the proband a functional hemizygote for the expression of the mutated C7 allele.

C3 is a crucial protein of the complement system. Congenital C3 deficiency is extremely rare and manifests through recurrent, severe infections and should always be considered as a differential diagnosis of recurrent pyogenic infections. We report a case of a patient with a novel C3 gene mutation, responsible for complete C3 deficiency with impaired complement system activation and recurrent infections.

OBJECTIVE: Complement component 6 (C6) deficiency is a very rare genetic defect that leads to significantly diminished synthesis, secretion, or function of C6. In the current report, we demonstrate a previously undescribed, homozygous missense mutation in exon 17 of the C6 gene (c.2545A>G p.Arg849Gly) in a 35-year-old Japanese woman with moyamoya disease and extremely low levels of CH50 (<7.0 U/mL).
METHODS: The complement gene analysis using hybridization capture-based next generation sequencing was performed. CH50 was determined in patient\'s plasma mixed with plasma from a healthy donor or purified human C6 protein. Western blot was performed on patient\'s plasma using polyclonal antibodies against C6, with healthy donor\'s plasma and purified human C6 protein as positive controls while C6-depleted human serum as a negative control. The carriage of ring finger protein 213 variant (c.14576G>A p.Arg4859Lys), a susceptibility gene for moyamoya disease, was examined by direct sequencing.
RESULTS: CH50 mixing test clearly showed a deficiency pattern, being rescued by addition of only 1% healthy donor\'s plasma or 1 μg/mL purified human C6 protein (1/50-1/100 of physiological concentration). Western blot revealed the absence of C6 protein in the patient\'s plasma, confirming a quantitative deficiency of C6. The ring finger protein 213 variant was not detected.
CONCLUSIONS: Our data implies that unrecognized complement deficiencies would be harbored in cerebrovascular diseases with unknown etiologies.

Complement deficiencies have been considered to be rare for many decades, but this assumption is changing year by year. Recognition of these conditions significantly increases thanks to the availability of different testing approaches and due to clinical awareness. Furthermore, sequencing technologies (including Sanger sequencing, targeted gene panels, and whole exome/genome sequencing) may facilitate the identification of the underlying disease-causing genetic background. On the other hand, functional characterization of the identified possibly pathogenic variations and performing family studies, as illustrated by some of our cases, remain similarly important to establish a precise clinical diagnosis facilitating the most appropriate management. Here, we present 4 illustrative cases with complement deficiencies of diverse etiologies and also provide an educative, step-by-step description on how to identify the underlying cause of complement deficiency based on the results of complement laboratory testing.

During the last years, studies investigating the intriguing association between immunodeficiency and autoimmunity led to the discovery of new monogenic disorders, the improvement in the knowledge of the pathogenesis of autoimmunity, and the introduction of targeted treatments. Autoimmunity is observed with particular frequency in patients with primary antibody deficiencies, such as common variable immunodeficiency (CVID) and selective IgA deficiency, but combined immunodeficiency disorders (CIDs) and disorders of innate immunity have also been associated with autoimmunity. Among CIDs, the highest incidence of autoimmunity is described in patients with autoimmune polyendocrine syndrome 1, LRBA, and CTLA-4 deficiency, and in patients with STAT-related disorders. The pathogenesis of autoimmunity in patients with immunodeficiency is far to be fully elucidated. However, altered germ center reactions, impaired central and peripheral lymphocyte negative selection, uncontrolled lymphocyte proliferation, ineffective cytoskeletal function, innate immune defects, and defective clearance of the infectious agents play an important role. In this paper, we review the main immunodeficiencies associated with autoimmunity, focusing on the pathogenic mechanisms responsible for autoimmunity in each condition and on the therapeutic strategies. Moreover, we provide a diagnostic algorithm for the diagnosis of PIDs in patients with autoimmunity.