Recurrent necrotizing cellulitis, multi-organ autoimmune disease and humoral immunodeficiency due to a novel NFKB1 frameshift mutation.

BACKGROUND: Mutations in NFKB1(nuclear factor of kappa light polypeptide gene enhancer in B-cells 1) are associated with a variety of clinical symptoms, including lymphadenopathy, splenomegaly, hepatomegaly, autoimmune haemolytic anaemia, arthralgia, recurrent respiratory tract infections and post-operative necrotizing cellulitis. CASE PRESENTATION: We describe a case of a 47-year-old man, who presented with deep necrotizing cellulitis after incision of a submucous abscess by a dentist. Surgical intervention led to a massive progress. Pyoderma gangraenosum (PG) was diagnosed clinically and confirmed histopathologically. High dose corticosteroids and intravenous immunoglobulins (IVIG) improved wound healing dramatically. Until now, immune mediated inflammation events not only affected the skin, but also multiple inner organs, i.e. the heart, lungs and gut. Sequencing of all coding exons of NFKB1 revealed a heterozygous 1bp deletion in exon 23 predicting a frameshift starting at codon Ala891 and resulting in a subsequent stop codon at position 6 in the new reading frame: NM_003998.4: c.2671del; p.(Ala891Glnfs*6) Acute episodes were always successfully treated with corticosteroids, IVIG and concomitant antibiotics. To prevent further exacerbations, the patient receives IVIG once a month, low-dose corticosteroids and methotrexate. CONCLUSION: This is the first case of a patient with recurrent necrotizing cellulitis and immune mediated multi-organ involvement (heart, lungs, intestine) carrying the novel frameshift mutation c.2671del (p.Ala891Glnfs*6) in NFKB1 effectively treated with IVIG, low-dose corticosteroids and methotrexate.

Genetic CD21 deficiency is associated with hypogammaglobulinemia.

BACKGROUND: Complement receptor 2 (CR2/CD21) is part of the B-cell coreceptor and expressed by mature B cells and follicular dendritic cells. CD21 is a receptor for C3d-opsonized immune complexes and enhances antigen-specific B-cell responses. OBJECTIVE: Genetic inactivation of the murine CR2 locus results in impaired humoral immune responses. Here we report the first case of a genetic CD21 deficiency in human subjects. METHODS: CD21 protein expression was analyzed by means of flow cytometry and Western blotting. CD21 transcripts were quantified by using real-time PCR. The CD21 gene was sequenced. Wild-type and mutant CD21 cDNA expression was studied after transfection of 293T cells. Binding of EBV-gp350 or C3d-containing immune complexes and induction of calcium flux in CD21-deficient B cells were analyzed by means of flow cytometry. Antibody responses to protein and polysaccharide vaccines were measured. RESULTS: A 28-year-old man presented with recurrent infections, reduced class-switched memory B cells, and hypogammaglobulinemia. CD21 receptor expression was undetectable. Binding of C3d-containing immune complexes and EBV-gp350 to B cells was severely reduced. Sequence analysis revealed a compound heterozygous deleterious mutation in the CD21 gene. Functional studies with anti-immunoglobulin- and C3d-containing immune complexes showed a complete loss of costimulatory activity of C3d in enhancing suboptimal B-cell receptor stimulation. Vaccination responses to protein antigens were normal, but the response to pneumococcal polysaccharide vaccination was moderately impaired. CONCLUSIONS: Genetic CD21 deficiency adds to the molecular defects observed in human subjects with hypogammaglobulinemia.

Novel mutations in TACI (TNFRSF13B) causing common variable immunodeficiency.

INTRODUCTION: Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by impaired immunoglobulin production. The disorder is also characterized by co-occurrence of autoimmune, lymphoproliferative, and granulomatous diseases. Mutations in the gene encoding TACI (Transmembrane Activator and CAML Interactor, TNFRSF13B) were previously found to be associated with CVID. MATERIALS AND METHODS: We therefore sequenced TNFRSF13B gene in a cohort of 48 Iranian CVID patients. Expression of TACI and binding of A proliferation-inducing ligand (APRIL) were tested by FACS. RESULTS: We identified one patient with a homozygous G to T substitution in the TNFRSF13B gene at the splice site of intron 1 (c.61+1G>T), which abolished expression of the TACI molecule and binding capacity of APRIL. This represents the second CVID patient in the world with a complete absence of TACI expression. B cell lines from family members carrying the same mutation in a heterozygous form showed a reduced level of TACI expression and APRIL-binding capacity, suggesting a gene dosage effect. In addition, we found the previously recognized C104R and C172Y mutations in a heterozygous form in two patients with CVID and one, novel, heterozygous P42T mutation. CONCLUSION: TACI mutations were observed in Iran CVID patients in a similar frequency as in other Caucasian populations. The novel mutations identified in this study support the notion of a crucial role for TACI in B cell differentiation.

Relevance of biallelic versus monoallelic TNFRSF13B mutations in distinguishing disease-causing from risk-increasing TNFRSF13B variants in antibody deficiency syndromes.

TNFRSF13B encodes transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), a B cell- specific tumor necrosis factor (TNF) receptor superfamily member. Both biallelic and monoallelic TNFRSF13B mutations were identified in patients with common variable immunodeficiency disorders. The genetic complexity and variable clinical presentation of TACI deficiency prompted us to evaluate the genetic, immunologic, and clinical condition in 50 individuals with TNFRSF13B alterations, following screening of 564 unrelated patients with hypogammaglobulinemia. We identified 13 new sequence variants. The most frequent TNFRSF13B variants (C104R and A181E; n=39; 6.9%) were also present in a heterozygous state in 2% of 675 controls. All patients with biallelic mutations had hypogammaglobulinemia and nearly all showed impaired binding to a proliferation-inducing ligand (APRIL). However, the majority (n=41; 82%) of the pa-tients carried monoallelic changes in TNFRSF13B. Presence of a heterozygous mutation was associated with antibody deficiency (P< .001, relative risk 3.6). Heterozygosity for the most common mutation, C104R, was associated with disease (P< .001, relative risk 4.2). Furthermore, heterozygosity for C104R was associated with low numbers of IgD(-)CD27(+) B cells (P= .019), benign lymphoproliferation (P< .001), and autoimmune complications (P= .001). These associations indicate that C104R heterozygosity increases the risk for common variable immunodeficiency disorders and influences clinical presentation.

Common variable immunodeficiency: a multifaceted and puzzling disorder.

Common variable immunodeficiencies (CVIDs) encompass a heterogeneous group of disorders characterized by hypogammaglobulinemia, recurrent infections and a variety of sequelae. Recently, genetic defects in ICOS, TACI, CD19, Msh5 and BAFF-R have been attributed as monogenic disease-causing or risk-increasing factors in the pathogenesis of CVIDs, but may explain only a minority of cases. By contrast, numerous immunological studies have revealed more- or less-common phenotypic and functional abnormalities of T cells, B cells and antigen-presenting cells in patients with CVID. Impaired terminal differentiation of peripheral B cells is found in approximately 80% of CVID patients and provides a framework for classification models. Several recent multicenter clinical studies delineate clinical phenotypes, predictive clinical and immunological markers, and report on the long-term outcomes in large cohorts of CVID patients. Identification of distinct immunological and clinical subtypes in CVID, and the interrelations between genetic defects, immunological abnormalities and clinical phenotypes, will improve our understanding of these diseases and their pathogeneses.

Genetic and physical interaction between the NPHP5 and NPHP6 gene products.

Nephronophthisis (NPHP) is an autosomal recessive cystic kidney disease, caused by mutations of at least nine different genes. Several extrarenal manifestations characterize this disorder, including cerebellar defects, situs inversus and retinitis pigmentosa. While the clinical manifestations vary significantly in NPHP, mutations of NPHP5 and NPHP6 are always associated with progressive blindness. This clinical finding suggests that the gene products, nephrocystin-5 and nephrocystin-6, participate in overlapping signaling pathways to maintain photoreceptor homeostasis. To analyze the genetic interaction between these two proteins in more detail, we studied zebrafish embryos after depletion of NPHP5 and NPHP6. Knockdown of zebrafish zNPHP5 and zNPHP6 produced similar phenotypes, and synergistic effects were observed after the combined knockdown of zNPHP5 and zNPHP6. The N-terminal domain of nephrocystin-6-bound nephrocystin-5, and mapping studies delineated the interacting site from amino acid 696 to 896 of NPHP6. In Xenopus laevis, knockdown of NPHP5 caused substantial neural tube closure defects. This phenotype was copied by expression of the nephrocystin-5-binding fragment of nephrocystin-6, and rescued by co-expression of nephrocystin-5, supporting a physical interaction between both gene products in vivo. Since the N- and C-terminal fragments of nephrocystin-6 engage in the formation of homo- and heteromeric protein complexes, conformational changes seem to regulate the interaction of nephrocystin-6 with its binding partners.