L'haploinsuffisance de A20 : que doit connaître le clinicien?

A20 Haploinsufficiency (HA20) is a monogenic autoinflammatory disease associated with an autosomal dominant mutation in the TNFAIP3 gene. It induces a defect in the inactivation of the pro-inflammatory NF-κB pathway. Less than 200 cases have been described worldwide. The clinical picture of the disease is essentially based on the association of recurrent fever and/or biologic inflammatory syndrome, aphtosis, often bipolar, and cutaneous folliculitis. However, the clinical spectrum of HA20 is very broad, including gastrointestinal (mainly colonic ulceration), articular, cutaneous, pericardial and lymph node involvement, as well as frequent association with organ-specific or non-specific autoimmune manifestations and/or autoantibodies, including antinuclear antibodies and anti-dsDNA. As a result, the diagnosis of a number of systemic or organic disorders, most notably Behçet's disease, Crohn's disease, and sometimes even systemic lupus, has been corrected to HA20 by molecular research for a heterozygous mutation with functional deficiency of TNFAIP3. Although the first signs of the disease often appear in the first years of life, the diagnosis is often made in adulthood and requires the involvement of both paediatric and adult physicians. Treatment for HA20 is not codified and relies on conventional or biological immunomodulators and immunosuppressants adapted to the patient's symptomatology. This review highlights the enormous diagnostic challenges in this autoinflammatory disease.

Type I interferon response and vascular alteration in chilblain-like lesions during the COVID-19 outbreak.

BACKGROUND: The outbreak of chilblain-like lesions (CLL) during the COVID-19 pandemic has been reported extensively, potentially related to SARS-CoV-2 infection, yet its underlying pathophysiology is unclear. OBJECTIVES: To study skin and blood endothelial and immune system activation in CLL in comparison with healthy controls and seasonal chilblains (SC), defined as cold-induced sporadic chilblains occurring during 2015 and 2019 with exclusion of chilblain lupus. METHODS: This observational study was conducted during 9-16 April 2020 at Saint-Louis Hospital, Paris, France. All patients referred with CLL seen during this period of the COVID-19 pandemic were included in this study. We excluded patients with a history of chilblains or chilblain lupus. Fifty patients were included. RESULTS: Histological patterns were similar and transcriptomic signatures overlapped in both the CLL and SC groups, with type I interferon polarization and a cytotoxic-natural killer gene signature. CLL were characterized by higher IgA tissue deposition and more significant transcriptomic activation of complement and angiogenesis factors compared with SC. We observed in CLL a systemic immune response associated with IgA antineutrophil cytoplasmic antibodies in 73% of patients, and elevated type I interferon blood signature in comparison with healthy controls. Finally, using blood biomarkers related to endothelial dysfunction and activation, and to angiogenesis or endothelial progenitor cell mobilization, we confirmed endothelial dysfunction in CLL. CONCLUSIONS: Our findings support an activation loop in the skin in CLL associated with endothelial alteration and immune infiltration of cytotoxic and type I IFN-polarized cells leading to clinical manifestations.

Clinical Heterogeneity of Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-Linked Syndrome: A French Multicenter Retrospective Study.

OBJECTIVE: Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is an autoimmune disease caused by mutations in the forkhead box protein 3 gene (FOXP3), which encodes a key regulator of immune tolerance. The aim of this study was to describe the clinical heterogeneity of the disease in a national French cohort. METHODS: Multicenter retrospective study of patients diagnosed with IPEX syndrome caused by mutations in FOXP3. RESULTS: Thirty children from 26 families were included. Age at disease onset (median [first to third quartile]) was 1.5 mo [0-84] and at death 3.5 years [0-10.5] (n = 15) indicating a high heterogeneity. Initial presentation was diarrhoea (68%), type 1 diabetes (T1D; 25%), skin lesions (7%) and nephropathy (3%). During the course of the disease the following main symptoms were observed: diarrhoea (100%), skin lesions (85%), T1DM (50%), severe food allergies (39%), haematological disorders (28%), nephropathies (25%), hepatitis (14%) as well as the presence of a variety of autoantibodies. Immunosuppressive mono- or combination therapy led to improvement in eight children. Three boys displayed a stable disease course without any immunosuppressive medication. Overall 10-year survival rate was 43% (42% in transplanted patients and 52% in patients on immunosuppressive therapy). Five out of 22 identified FOXP3 mutations have not been described yet: c.-23 + 1G > A, c.-23 + 5G > A, c.264delC, c.1015C > T and c.1091A > G. The first two produced atypical, attenuated phenotypes. Missense and frameshift mutations affecting the forkhead domain were associated with poor survival (Gehan-Wilcoxon p = 0.002). CONCLUSION: The broad phenotypic heterogeneity of IPEX raises questions about modifying factors and justifies early FOXP3 sequencing in suspected cases.

Investigation of common variable immunodeficiency patients and healthy individuals using autoimmune lymphoproliferative syndrome biomarkers.

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of dysregulated lymphocyte homeostasis. Biomarkers including elevated CD3+TCRαß+CD4-CD8- double negative T cells (TCRαß+ DNT), IL-10, sCD95L and vitamin B12 can be used to differentiate between ALPS and common variable immunodeficiency (CVID) patients with an overlapping clinical phenotype. We investigated the utility of ALPS biomarkers in 13 CVID patients with lymphoproliferation and/or autoimmune cytopaenia with comparison to 33 healthy controls. Vitamin B12 (P < 0.01) and IL-10 (P < 0.0001), but not sCD95L or TCRαß+ DNT, were increased in CVID compared to controls. The 95th percentile for TCRαß+ DNT in healthy controls was used to define a normal range up to 2.3% of total lymphocytes or 3.4% of T cells. These frequencies lie markedly beyond the cut offs used in current ALPS diagnostic criteria (≥ 1.5% of total lymphocytes or 2.5% of CD3+ lymphocytes), suggesting these limits may have poor specificity for ALPS.

[Childhood-onset systemic lupus erythematosus: polygenic or monogenic disorder?]. / Le lupus systémique à début pédiatrique : une pathologie polygénique ou monogénique ?

Systemic lupus erythematosus (SLE) results from the complex interaction between genetic and environmental factors. It is usually thought that SLE results from the combined effect of variants in a large number of genes, and several genome whole association studies (GWAS) have identified a great number of single-nucleotide polymorphisms (SNP) associated with SLE. However, the loci identified so far can account for only about 15% of the heritability of SLE. Recently, some Mendelian variants of lupus have been identified, especially in childhood-onset SLE. Children present with more severe illness, a lower sex-ratio female:male and a higher genetic contribution compared to adults with SLE. pSLE phenotype heterogeneity could be related to genetic heterogeneity, and pSLE in part might consist in a collection of rare, genetically distinct monogenic disorders.

Autoimmune lymphoproliferative syndrome (ALPS). Case report and family history.

Autoimmune lymphoproliferative syndrome (ALPS) is a rare disease caused by defective lymphocyte apoptosis and is characterized by non-malignant lymphoproliferation, hepatosplenomegaly, autoimmune manifestations and increased risk of both Hodgkin's and non-Hodgkin's lymphoma. Most forms of the disease are due to germ line mutations of the FAS gene and manifest during the first years of life with fluctuating lymphadenopathies, hemolysis, immune thrombocytopenia. During the second decade of life disease manifestations improve spontaneously but autoimmune problems still occur and there is an increased risk of lymphoproliferative malignancy. We describe a typical case of ALPS in a now 44 year old man, followed since the age of 2 for disease manifestations that were unclear at the beginning.

Cutaneous manifestations of immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome.

BACKGROUND: Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare disorder characterized by neonatal autoimmune enteropathy, diabetes and thyroiditis, food allergies and skin rash. IPEX syndrome is caused by mutations in FOXP3, a master control gene of regulatory T cells (Tregs), resulting in absent or dysfunctional Tregs. Data in the literature are scarce and the cutaneous manifestations are rarely depicted. OBJECTIVES: To evaluate the frequency and characteristics of cutaneous manifestations found in IPEX. METHODS: Retrospective single-centre study of a case series of IPEX. Patients' data were retrieved from medical files and numerous parameters concerning general and cutaneous characteristics of the disease were recorded. RESULTS: Ten children with IPEX were studied. Cutaneous involvement was present in seven of 10 children; age at onset was 0-4 months, median 1.5. All patients presented with atopic dermatitis (AD). Three presented more psoriasiform lesions. Eczema was severe; most affected areas were lower limbs, trunk and face. Pruritus was present in four of seven, and painful fissurary cheilitis in four of seven. Hyper-IgE was found in seven of 10 and hypereosinophilia in five of 10. Skin biopsies showed eczematiform or psoriasiform features. Affected patients were improved by dermocorticoids; no clear improvement was obtained with immunosuppressive regimens. Other features were urticaria secondary to food allergies and staphylococcal sepsis, mostly Staphylococcus aureus and catheter related. CONCLUSIONS: AD seems to be a frequent finding in IPEX syndrome, which is characterized by Treg anomalies. This hints to a possible role of Tregs in AD, which is then discussed in this study.

Overexpression of the antiapoptotic gene Bfl-1 in B cells from patients with familial systemic lupus erythematosus.

Genetic determinants taking part in the development of systemic lupus erythematosus (SLE) are complex and not fully characterized. Dysregulated expression of genes involved in the control of apoptosis has been previously suggested. We report here a consanguineous family with SLE manifestations in three siblings associated in one of them with severe lymphoproliferative features. Laboratory studies showed no defect in CD95-mediated cell death. Screening expression of Bcl-2 family genes that regulate mitochondrial apoptosis pathway showed an overexpression of the antiapoptotic Bfl-1 gene. Real time RT-PCR analysis indicated that overexpression of Bfl-1 was restricted to B-cells, with normal expression in T-cells. Those results suggest that overexpression of Bfl-1 could result in impaired B-lymphocyte homeostasis and inappropriate immune response leading to autoimmune manifestations.

Induction of T lymphocyte apoptosis by sulphasalazine in patients with Crohn's disease.

BACKGROUND: Lamina propria T lymphocytes (LPL) of the intestinal mucosa are chronically activated in Crohn's disease (CD). Defective apoptosis of activated LPL was proposed as a key pathogenic mechanism. In fact, increased expression of antiapoptotic molecules was observed in CD LPL. In the present work, we aimed to analyse the effects and underlying molecular mechanisms of 5-amino salicylic acid (5-ASA) and derivatives on apoptosis of LPL and peripheral blood lymphocytes (PBL) in patients with CD compared with ulcerative colitis (UC) and in non-inflammatory controls. METHODS: PBL and LPL were isolated by Ficoll-Hypopaque gradient centrifugation and the EGTA-collagenase method, respectively. PBL/LPL were stimulated with FasL, 5-ASA, sulphapyridine, and sulphasalazine for 24/48 hours and apoptosis was quantified by flow cytometry (annexin V- propidium iodide method) and immunofluorescence. The molecular mechanisms of drug induced apoptosis were analysed in wild-type and FADD-/- Jurkat T cells using western blots and caspase assays. RESULTS: While PBL displayed a normal apoptosis pattern after Fas stimulation in patients with active CD, LPL from inflammatory areas were highly resistant. Comparable resistance to apoptosis was observed in LPL of UC patients. In contrast with 5-ASA, which did not induce apoptosis in lymphocytes, sulphasalazine proved to be a potent proapoptotic agent. Sulphasalazine induced T lymphocyte apoptosis was independent of the Fas pathway but associated with marked downregulation of antiapoptotic bcl-xl and bcl2, activation of the mitochondrial apoptosis signalling pathway, and subsequent activation of caspase-9 and caspase-3. CONCLUSION: The beneficial effect of sulphasalazine in treating inflammatory bowel disease is at least in part attributable to its proapoptotic effects on LPL which allows potent downregulation of lymphocyte activation.

Childhood linear IgA disease in association with autoimmune lymphoproliferative syndrome.

A child is described who had the signs of autoimmune lymphoproliferative syndrome from an early age and later developed a blistering dermatosis that was shown to be childhood linear IgA disease.

Autoimmune lymphoproliferative syndromes: genetic defects of apoptosis pathways.

Human and mouse natural mutants presenting with lymphoproliferative syndrome and autoimmunity (ALPS) have enlightened the role of the Fas and FasL in lymphocyte cell death and peripheral tolerance. Further study of the genetic basis of the human pathology led to the identification of apoptosis signaling defect, and pointed out to the crucial role of caspase-10 in the process of apoptosis induction. In contrast, the absence of lymproliferation in engineered mutants of 'death pathways' suggests that additional events are necessary to recapitulate the overt phenotype of ALPS patients or MRL/lpr mice. Moreover, these models highlight the roles of Fas and associated molecules, such as FADD and caspase-8, in lymphocyte development or activation. This review will discuss the main findings provided by the study of mouse models and human conditions.

Inactivation of the Fas gene by Alu insertion: retrotransposition in an intron causing splicing variation and autoimmune lymphoproliferative syndrome.

Mutations in the Fas (apo-1, CD95) gene result in autoimmune lymphoproliferative syndrome (ALPS). These mutations are dominated by small deletions and point mutations that result in splicing errors or missense changes. We report here a novel mutation caused by retrotransposon insertion, which results in loss of exon 8 and ALPS. A father and son suffering from recurrent lymphadenopathy were examined for resistance to Fas-mediated apoptosis. A functional defect was detected and RT-PCR analysis revealed two different copies of Fas mRNA, one normal and a second shorter version lacking exon 8. DNA analysis of the genomic region between exons seven and nine in the longer copy revealed two PCR products, one being 331 base pairs (bp) longer than expected. Sequencing revealed that intron 7 had undergone an insertion event with an Alu element (99.31% homology with Alu-Sb1) of 331 bp. This element included a 34-bp Poly A tract that was flanked on each side by a perfect 17 bp direct duplication of the target site. Both patients were heterozygous for the mutated allele that produced Fas mRNA lacking exon 8, although not due to loss of a splice junction. The structure of the insertion suggests that the Alu element may have integrated by retrotransposition, and represents the first report of a retrotransposon causing ALPS.

Diffuse large B-cell non-Hodgkin's lymphoma in a patient with autoimmune lymphoproliferative syndrome.

Mutations of Fas or Fas ligand genes result in the autoimmune lymphoproliferative syndrome (ALPS) in humans. We report here a diffuse large B-cell non-Hodgkin's lymphoma occurring in a man with ALPS. Fas-mediated lymphocyte apoptosis was defective in vitro, owing to a mutation within the death domain of the Fas molecule. High-dose methotrexate and doxorubicin-based chemotherapy led to complete remission of lymphoma.

Cytomegalovirus infection in infants with autoimmune lymphoproliferative syndrome (ALPS).

Fas-mediated apoptosis may be one of the effector pathways leading to the elimination of virus-infected cells. Cytomegalovirus (CMV) infection in two brothers with Fas deficiency associated with autoimmunity and benign lymphoproliferation (ALPS) provided a unique opportunity to study the clinical course of CMV infection in children with defective apoptosis. The clinical courses of two brothers with autosomal dominant ALPS who were infected with CMV in the neonatal period are described. CMV was detected from throat and urine culture from the brothers. ALPS was confirmed by in vitro anti-CD95 MoAb-induced T lymphocyte apoptosis assay and subsequent sequencing and identification of mutations in the Fas gene. A de novo mutation in the Fas gene, leading to a truncated cytoplasmic Fas product, was associated with autosomal dominant ALPS in a mother and her two sons. Both boys had evidence of CMV infection acquired early in infancy which cleared by the age of 2-3 years. There were no neurodevelopmental sequelae. The natural history of CMV infection in two infants with ALPS was similar to that described in normal children.

Dyserythropoiesis associated with a fas-deficient condition in childhood.

Defective lymphocyte apoptosis caused by mutations of the Fas gene can result in an autoimmune lymphoproliferative syndrome (ALPS) in humans. We report two cases of dyserythropoiesis associated with a Fas-deficient condition in childhood. In both cases, dyserythropoiesis predominated on the more mature erythroblasts, and was associated with a lymphoproliferative syndrome as well as with haemolytic anaemia, hypergammaglobulinaemia and the expansion of an unusual population of CD4- CD8- T cells that express the alpha/beta T-cell receptor. The regression of dyserythropoiesis under steroid therapy suggested that it resulted from an autoimmune mechanism, itself secondary to the lymphocyte Fas apoptosis deficiency. Fas-defective apoptosis may be a new aetiology for childhood dyserythropoiesis.

Autoimmune lymphoproliferative syndromes (ALPS): models for the study of peripheral tolerance.

Lymphocyte cell death is a key event in the homeostasis of the immune system. Lymphocytes can be induced to die because of exposure to toxic agents, because of cytokine withdrawal or because specific cell surface receptors are engaged by their ligands. A number of such receptors belonging to the TNF receptor have been described in the recent past. Among these, the role of the Fas ligand/receptor interaction in the induction of lymphocyte cell death has been enlightened by the study of natural mutants, first described in mouse strains, then in humans. This review discusses the main findings provided by murine studies and clinical observations.

Lymphoproliferative syndrome with autoimmunity: A possible genetic basis for dominant expression of the clinical manifestations.

Fas (CD95/Apo-1) mutations were previously reported as the genetic defect responsible for human lymphoproliferative syndrome associated with autoimmune manifestations (also known as autoimmune lymphoproliferative syndrome or Canale-Smith syndrome). We have identified 14 new heterozygous Fas mutations. Analysis of patients and families allow us to further dissect this syndrome with regards to the relationship between Fas mutations, inheritance pattern, and phenotype as observed on long-term follow-up. In vitro studies show that lymphocytes from all Fas mutant carriers exhibit a Fas-antibody-induced apoptosis defect. However, among the 8 inherited mutations, 4 of 4 Fas missense mutations were associated with high clinical penetrance, whereas 3 of 4 mutations leading to a truncated Fas product were associated with variable clinical penetrance. This suggests that a second defect, in another yet undefined factor involved in apoptosis and/or lymphoproliferation control, is necessary to induce full clinical expression of the disease. These results also indicate that the currently available antibody-mediated in vitro apoptosis assay does not necessarily reflect the in vivo ability of abnormal Fas molecules to trigger lymphocyte death. In addition, we found that lymphoproliferative manifestations resolved with age, whereas immunological disorders [ie, hypergammaglobulinemia and detection of TcR alphabeta(+) CD4(-) CD8(-) lymphocytes] persisted. This observation suggests that Fas-mediated apoptosis plays a more important role in lymphocyte homeostasis in early childhood than later on in life.

Combined immunodeficiency associated with increased apoptosis of lymphocytes and radiosensitivity fibroblasts.

Severe immunodeficiency characterized by lymphopenia was found in two siblings, one of whom was examined in detail. The calcium flux, pattern of tyrosine phosphorylation of proteins, and interleukin 2 (IL-2) production and proliferation in response to mitogens suggested that the peripheral blood T cells activated normally. The peripheral blood T cells were shown to have an activated phenotype with increased expression of CD45RO+ and CD95/Fas. Increased spontaneous apoptosis occurred in unstimulated lymphocyte cultures. The elevated apoptosis was not due to alterations in expression or to mutations in Bcl-2, Bcl-X(L), or Flip, nor could the spontaneous apoptosis be prevented by blocking Fas, suggesting that it was independent of Fas signaling. This is the first inherited combined immunodeficiency associated with impaired lymphocyte survival. Fibroblasts derived from the patient showed appreciable radiosensitivity in clonal assays, but apoptosis was not elevated. Our results show that the fibroblasts represent a new radiosensitive phenotype not associated with cell cycle checkpoint defects, V(D)J recombination defects, or elevated chromosome breakage. We suggest that the affected gene plays a role in an undetermined damage response mechanism that results in elevated spontaneous apoptosis in lymphoid cells and radiosensitivity in fibroblasts.

Highly restricted human T cell repertoire in peripheral blood and tissue-infiltrating lymphocytes in Omenn's syndrome.

Omenn's syndrome is an inherited human combined immunodeficiency condition characterized by the presence of a large population of activated and tissue-infiltrating T cells. Analysis of the TCRB repertoire revealed a highly restricted TCRBV usage in three patients. More strikingly, T cell clones from the three patients expressed TCRB chains with VDJ junction similarities, suggesting a common antigenic specificity. Analysis of the TCRA repertoire in one patient also revealed a restricted TCRAV usage. Finally, analysis of the TCRBV repertoire of tissue-infiltrating T cells in one patient suggested nonrandom tissue migration. These results suggest that the oligoclonal expansion of T cells observed in Omenn's syndrome could be the consequence of autoimmune proliferation generated by a profound defect in lymphocyte development.