Lipopolysaccharide-responsive Beige-like Anchor Protein Research Articles

Genome‐wide association meta‐analysis identifies a novel LRBA locus for brain age acceleration in two independent Korean Cohorts

AbstractBackgroundAging is a key risk factor for Alzheimer’s disease (AD) and has a significant structural impact on the brain. Machine learning approaches have been developed to estimate the biological age of the brain from MRI scans. Here, we performed genome‐wide association (GWA) analysis of accelerated brain aging in two independent Korean AD cohorts.MethodParticipants included 1,738 Korean older adults from two independent cohorts that consisted of preclinical and clinical stages of AD (n = 1,209 from the K‐ROAD cohort (Korea‐Registries to Overcome and Accelerate Dementia Research Project) and n = 529 from the KBASE cohort (Korean Brain Aging Study for the Early Diagnosis and Prediction of Alzheimer’s Disease)). Brain age was estimated from structural MRI scans using brainageR. Brain age acceleration (predicted brain age ‐ chronological age) was calculated for each participant. Genetic variants associated with brain age acceleration were assessed after accounting for age, sex, APOE e4 carrier status, and diagnosis. Meta‐analysis was performed using METAL, followed by transcriptomic analysis. Polygenic risk scores for brain age acceleration were calculated with PRS‐CS using GWAS meta‐analysis summary statistics, followed by molecular imaging analysis.ResultGWA meta‐analysis identified six intronic SNPs in the LRBA (Lipopolysaccharide responsive Beige‐like Anchor) locus on chromosome 4 as significantly associated with brain age acceleration with the most significant signal at rs7699001 (Fig. 1; p<5´10−8). LRBA is highly expressed in the brain, especially in microglia. The LRBA gene is differentially expressed in AD compared to cognitively normal older adults. rs7699001 was associated with expression levels of the LRBA gene in tissue from several organs including brain. rs7690001 has been reported to be associated with inferior parietal cortical thickness in non‐Hispanic whites (p = 5´10−3). Polygenic risk scores of brain age acceleration in the K‐ROAD cohort were significantly associated with amyloid‐β deposition measured from amyloid PET scans (Fig. 2; p = 2.7´10−4).Conclusion LRBA is a novel genetic risk factor for brain aging in the Korean population with relevance for AD. The microglial LRBA protein may be involved in phagocytosis, which has been implicated in aging processes and AD progression. Replication in other populations and mechanistic follow‐up studies are warranted.This work was supported by U01AG072177.

LRBA signalosomes activate vasopressin-induced AQP2 trafficking at recycling endosomes.

Aquaporin-2 (AQP2) water channels are proteins that are recycled between intracellular vesicles and the apical plasma membrane in renal collecting ducts. Lipopolysaccharide-responsive beige-like anchor protein (LRBA) is a protein kinase A (PKA) anchoring protein that creates compartmentalized PKA signalling responsible for AQP2 phosphorylation. In response to increased plasma osmolality, vasopressin/cyclic adenosine monophosphate (cAMP)/PKA signalling phosphorylates AQP2, promoting AQP2 trafficking into the apical plasma membrane and increasing water reabsorption from urine. However, the molecular mechanisms by which LRBA mediates vasopressin-induced AQP2 phosphorylation remain unknown. To investigate AQP2 intracellular localization and phosphorylation status in vivo, a density gradient ultracentrifugation technique was combined with an in situ proximity ligation assay, super-resolution structured illumination microscopy and immunoelectron microscopy. Most of the AQP2 was localized on the recycling endosome in the presence of tolvaptan, a vasopressin type 2 receptor (V2R) antagonist. Desmopressin, a V2R agonist, phosphorylated AQP2, translocating it from the recycling endosome to the apical plasma membrane. In contrast, LRBA was constitutively localized at the recycling endosome. Therefore, LRBA and AQP2 were well colocalized in the absence of vasopressin stimulation. The loss of LRBA/PKA signalling by Lrba knockout impaired vasopressin-induced AQP2 phosphorylation, resulting in AQP2 retention at the recycling endosome. Defective AQP2 trafficking caused low urinary concentrating ability in Lrba-/- mice. The LRBA-PKA complex created compartmentalized PKA signalling at the recycling endosome, which facilitated AQP2 phosphorylation in response to vasopressin. KEY POINTS: Membrane proteins are continuously internalized into the endosomal system via endocytosis, after which they are either recycled back to the plasma membrane or degraded at the lysosome. In T cells, lipopolysaccharide-responsive beige-like anchor protein (LRBA) binds directly to the cytotoxic T lymphocyte antigen 4 (CTLA-4), a checkpoint immune molecule, to prevent CTLA-4 lysosomal degradation and promote its vesicle recycling. LRBA has different physiological functions in renal collecting ducts. LRBA and aquaporin-2 (AQP2) water channels were colocalized on the recycling endosome in vivo in the absence of the anti-diuretic hormone vasopressin. LRBA promoted vasopressin-induced AQP2 trafficking, increasing water reabsorption from urine via AQP2. LRBA determined renal responsiveness to vasopressin at recycling endosomes. LRBA is a ubiquitously expressed anchor protein. LRBA signalosomes might regulate membrane trafficking of several constitutively recycled proteins at recycling endosomes.

A circular RNA produced by LRBA promotes cirrhotic mouse liver regeneration through facilitating the ubiquitination degradation of p27.

Accumulating circular RNAs (circRNAs) play important roles in tissue repair and organ regeneration. However, the biological effects of circRNAs on liver regeneration remain largely unknown. This study aims to systematically elucidate the functions and mechanisms of circRNAs derived from lipopolysaccharide-responsive beige-like anchor protein (LRBA) in regulating liver regeneration. CircRNAs derived from mouse LRBA gene were identified using CircBase. In vivo and in vitro experiments were conducted to confirm the effects of circLRBA on liver regeneration. RNA pull-down and RNA immunoprecipitation assays were used to investigate the underlying mechanisms. Clinical samples and cirrhotic mouse models were used to evaluate the clinical significance and transitional value of circLRBA. Eight circRNAs derived from LRBA were registered in CircBase. The circRNA mmu_circ_0018031 (circLRBA) was significantly upregulated in the liver tissues after 2/3 partial hepatectomy (PHx). Adeno-associated virus serotype 8 (AAV8)-mediated knockdown of circLRBA markedly inhibited mouse liver regeneration after 2/3 PHx. In vitro experiments confirmed that circLRBA exerted its growth-promoting function mainly through liver parenchymal cells. Mechanistically, circLRBA acted as a scaffold for the interaction between E3 ubiquitin-protein ligase ring finger protein 123 and p27, facilitating the ubiquitination degradation of p27. Clinically, circLRBA was lowly expressed in cirrhotic liver tissues and negatively correlated with perioperative levels of total bilirubin. Furthermore, overexpression of circLRBA enhanced cirrhotic mouse liver regeneration after 2/3 PHx. We conclude that circLRBA is a novel growth promoter in liver regeneration and a potential therapeutic target related to deficiency of cirrhotic liver regeneration.

Interstitial cystitis caused by immune dysregulation in LRBA deficiency: one among the rare urological manifestations in inborn errors of immunity

Inborn errors of immunity (IEI) rarely present with associated urological manifestations. Chronic cystitis and urethritis caused by ureaplasma and mycoplasma infection in hypogammaglobulinemia may result in bladder fibrosis. Papovaviridae such as BK or JC, can cause hemorrhagic cystitis in patients with T cell defects. Bladder granulomtata and urethral strictures can occur in chronic granulomatous disease. This is the first reported case of severe lymphocytic interstitial cystitis in a patient with lipopolysaccharide-responsive beige-like anchor protein (LRBA) deficiency. LRBA deficiency is known to impair CTLA-4 recycling, leading to decreased Treg cell function. A 13 year old male refugee presented with chronic recurrent debilitating suprapubic pain and dysuria, which progressed to extreme urinary frequency. He had a prior history of recurrent aseptic urinary tract infections, and one episode of gross hematuria. Extensive infectious investigations of urine (bacterial, mycobacterial cultures; viral PCRs), blood, and stool (Schistosoma) failed to isolate a pathogen. Bladder biopsy was positive for EBV by PCR but blood remained EBV-negative. Urinalysis showed microscopic hematuria while urodynamic studies were normal, and cystoscopy showed bladder and urethral irritation. Pathology confirmed lymphocytic interstitial cystitis, with primarily T cell infiltration. Immunological investigations revealed low IgG, IgA and IgM levels, B lymphopenia (1%), with low class-switched memory B cell development (3%) and absent response to protein and polysaccharide vaccine antigens. There were no signs of autoimmunity. Parents are consanguineous, and a sibling was likewise diagnosed with LRBA deficiency. Sanger sequencing of DNA confirmed the same homozygous family mutation in the LRBA gene, a likely pathogenic splice donor variant, c.2258+2T>G. The patient was started on immunoglobulin replacement. Trials of analgesics including NSAIDs, gabapentin, and morphine, and immunosuppression with corticosteroids and sirolimus, were unsuccessful in reducing urinary symptoms. Physiotherapy and antispasmodics were introduced when pelvic-floor dyssynergia with rectal pain developed. Subsequently-presenting enteropathy was managed with Abatacept (CTLA-4 IgG1 fusion protein), ultimately improving bladder symptoms after several months of therapy. Patient has since undergone HSCT and is now free of urinary tract symptoms. LRBA deficiency presents with hypogammaglobulinemia, infections, and immune dysregulation presenting with lymphocytic infiltration of non-lymphoid organs. This report highlights the phenotypic diversity of this disease.

An Unreported homozygous variant within Lipopolysaccharide responsive beige-like anchor (LRBA) gene in a child exhibiting with infantile type 1 diabetes mellitus

We report a patient who was born at term as the first son of consanguineous Saudi parents. He developed IDDM at the age of 7 months; the initial symptoms included fever and vomiting. The laboratory findings indicated pronounced ketoacidosis, initial fluid replacement with normal saline, followed by continuous IV insulin infusion. After a while, the baby was out of DKA. Our endocrinologist advised us to start administering S/C insulin NPH 1 unit BID. Fortunately, we suspected a primary immune deficiency acer a few days from the first presentation. The WES revealed A homozygous likely pathogenic variant was identified in the LRBA gene. The result is consistent with a genetic diagnosis of autosomal recessive CVID type 8 with autoimmunity. The LRBA protein regulates the expression of CTLA-4, which is a potent immune checkpoint receptor expressed by activated and regulatory by the T-cells. CTLA-4 blocks the stimulation/proliferation of T-cells and modulates immune responses.

Comparison of Clinical Manifestations, Immunological Analyses Between LRBA and CVID Patients: A Longitudinal Study

Background: Common variable immunodeficiency (CVID), is generally recognized as the most frequent type of Symptomatic primary immunodeficiencies (PID). Mutations in lipopolysaccharideresponsive beige-like anchor protein (LRBA) gene, are the most common genetic alterations amongst CVID patients. To date, there are no published studies to compare clinical and immunologic features of LRBA-deficient patients with those who do not harbor any known genetic mutations. Therefore, this study aims to compare the clinical manifestations and laboratory findings of Iranian patients with LRBA-deficiency and CVID with no known genetic alterations.
 Methods: We performed a longitudinal study on patients who had been diagnosed with CVID. Demographic and clinical features were obtained via the databank of the Iranian Registry of Primary Immunodeficiencies, and the direct interviews with patients. To assess the presence of LRBA or other genetic mutations, whole-exome sequencing (WES) was used. Immunologic characteristics of patients were evaluated using flow cytometry, nephelometry, and conventional blood counts. The current study is conducted at Tehran’s Children Medical Center and is approved by the ethics committee of Tehran University of Medical Sciences.
 Results: Between March 2013 and October 2019, we enrolled 30 patients with LRBA-deficiency and 13 patients with CVID, who had no identified genetic mutations. Regarding clinical features, there were no significant differences for the prevalence of infections at different sites (lung, sinuses, and middle ear) among the two groups (all P-values > 0.05). However, the incidences of autoimmune disorders and enteropathy were significantly higher among LRBA-deficient cases (P < 0.001). In serum levels of immunoglobulins, there were significant differences for IgG and IgM between the two groups (P-values of 0.014 and 0.004, respectively); however, this was not seen for IgA and IgE levels. Likewise, we did not see any significant differences for the cluster of differentiation (CD) markers between the two groups (all P-values > 0.05).
 Conclusion: Compared to the CVID patients with no identified genetic mutations, LRBA-deficient patients have a significantly greater chance of parental consanguinity and developing autoimmune disorders and enteropathy, and have significantly higher values of serum IgG and IgM. The rate of infectious complications and other basic laboratory features, do not show significant differences between the two groups.

Different Apples, Same Tree: Visualizing Current Biological and Clinical Insights into CTLA-4 Insufficiency and LRBA and DEF6 Deficiencies.

Cytotoxic T lymphocyte antigen-4 (CTLA-4) is a crucial immune checkpoint that is constitutively expressed in regulatory T (Treg) cells. Following T-cell activation, CTLA-4 is rapidly mobilized from its intracellular vesicle pool to the cell surface to control the availability of co-stimulatory B7 molecules, thereby maintaining immune homeostasis. Heterozygous mutations in CTLA-4 lead to defects in (i) CTLA-4 ligand binding, (ii) homo-dimerization, (iii) B7-transendocytosis, and (iv) CTLA-4 vesicle trafficking, resulting in an inborn error of immunity with predominant autoimmunity. CTLA-4 vesicle trafficking impairment is also observed in patients with lipopolysaccharide-responsive beige-like anchor protein (LRBA) deficiency or the differentially expressed in FDCP6 homolog (DEF6) deficiency, caused by biallelic mutations in LRBA and DEF6, respectively. Therefore, patients with CTLA-4 insufficiency, LRBA deficiency, and—most recently reported—DEF6 deficiency present an overlapping clinical phenotype mainly attributed to a defective suppressive activity of Tregs, as all three diseases reduce overall surface expression of CTLA-4. In this paper, we describe the clinical phenotypes of these immune checkpoint defects, their patho-mechanisms, and visually compare them to other immune regulatory disorders (IPEX syndrome, CD27, and CD70 deficiencies) by using the immune deficiency and dysregulation (IDDA version 2.1) “kaleidoscope” score. This illustrates the variability of the degrees and manifestations of immune deficiency and dysregulation. Patients characteristically present with an increased risk of infections, autoimmune cytopenias, multi-organ autoimmunity, and inflammation, which are often severe and life-threatening. Furthermore, these patients suffer an increased risk of developing malignancies, especially Non-Hodgkin's lymphoma. Successful treatment options include regular administration of soluble CTLA-4-Ig fusion protein, Treg cell-sparing immune suppressants like sirolimus or mycophenolate mofetil, and hematopoietic stem cell transplantation. This mini-review highlights the most relevant biological and clinical features as well as treatment options for CTLA-4 insufficiency and LRBA and DEF6 deficiencies.

Screening for Genetic Mutations for the Early Diagnosis of Common Variable Immunodeficiency in Children With Refractory Immune Thrombocytopenia: A Retrospective Data Analysis From a Tertiary Children's Center.

Aim: This study aimed to identify common variable immunodeficiency (CVID) by high-throughput next-generation sequencing (NGS) in children with refractory immune thrombocytopenia (RITP) to facilitate early diagnosis.Methods: CVID-related genetic mutations were explored in patients with RITP during 2016–2019. They were tested consecutively through NGS by the ITP team of the tertiary children hospital in China. An evaluation system was devised based on the phenotype, genetic rule, and serum immunoglobulins (Igs) of all patients with RITP. The patients were divided into highly suspicious, suspicious, and negative groups using the evaluation system.Results: Among 176 patients with RITP, 16 (9.1%) harbored CVID-related genetic mutations: 8 (4.5%) were highly suspicious of CVIDs. Five had mutations in tumor necrosis factor receptor superfamily 13B (TNFRSF13B), one in lipopolysaccharide responsive beige-like anchor protein (LRBA), one in nuclear factor kappa-B2 (NF-κB2), and one in caspase recruitment domain11 (CARD11). Others were classified into the suspicious group because the clinical phenotype and pedigree were suggestive, yet insufficient, for diagnosis. Repeated infection existed in all patients. Two had an allergic disease. Positive autoimmune serologies were noted in 62.5%. Five had a definite positive family history. The median serum immunoglobulin (Ig)A, IgG, and IgM levels were 0.3875, 6.14, and 0.522 g/L, respectively. Nearly 85.7% of patients had insufficient serum IgA levels, while 37.5% had low IgG and IgM levels.Conclusions: High-throughput NGS and a thorough review of the medical history are beneficial for the early diagnosis of patients without any significant clinical characteristics, distinguishing them from those with primary pediatric ITP. The cases suspicious of CVID need further investigation and follow-up to avoid deterioration.

Unusual Late-onset Enteropathy in a Patient With Lipopolysaccharide-responsive Beige-like Anchor Protein Deficiency

In recent years, monogenic causes of immune dysregulation syndromes, with variable phenotypes, have been documented. Mutations in the lipopolysaccharide-responsive beige-like anchor (LRBA) protein are associated with common variable immunodeficiency, autoimmunity, chronic enteropathy, and immune dysregulation disorders. The LRBA protein prevents degradation of cytotoxic T-lymphocyte antigen 4 (CTLA4) protein, thus inhibiting immune responses. Both LRBA and CTLA4 deficiencies usually present with immune dysregulation, mostly characterized by autoimmunity and lymphoproliferation. In this report, we describe a patient with an atypical clinical onset of LRBA deficiency and the patient's response to abatacept, a fusion protein-drug that mimics the action of CTLA4.

Disorders of CTLA-4 expression, how they lead to CVID and dysregulated immune responses.

The landscape of common variable immunodeficiency disorder (CVID) is rapidly evolving as the availability of next-generation sequencing leads to the discovery of new monogenic causes with the clinical phenotype of CVID. Herein, the biology of cytotoxic T lymphocyte-associated protein four (CTLA-4), differentially expressed in FDCP6 homolog (DEF6), and lipopolysaccharide responsive beige-like anchor protein (LRBA), and their impact on the development of a dysregulated, rather than an isolated, infectious phenotype of CVID are explored. The broad clinical phenotype associated with these monogenic forms of CVID is described, and common approaches to treatment are reviewed. Knowledge of the biology, clinical manifestations, and treatment options trialed thus far in patients with CTLA-4 insufficiency, DEF6 deficiency, and LRBA deficiency are essential in the consideration and effective management of patients with CVID stemming from these monogenic causes.

Rapid Flow Cytometry-Based Test for the Diagnosis of Lipopolysaccharide Responsive Beige-Like Anchor (LRBA) Deficiency.

The diagnosis of lipopolysaccharide-responsive beige-like-anchor-protein (LRBA) deficiency currently relies on gene sequencing approaches that do not support a timely diagnosis and clinical management. We developed a rapid and sensitive test for clinical implementation based on the detection of LRBA protein by flow cytometry in peripheral blood cells after stimulation. LRBA protein was assessed in a prospective cohort of 54 healthy donors and 57 patients suspected of LRBA deficiency. Receiver operating characteristics analysis suggested an LRBA:MFI ratio cutoff point of 2.6 to identify LRBA-deficient patients by FACS with 94% sensitivity and 80% specificity and to discriminate them from patients with a similar clinical picture but other disease-causing mutations. This easy flow cytometry-based assay allows a fast screening of patients with suspicion of LRBA deficiency reducing therefore the number of patients requiring LRBA sequencing and accelerating the treatment implementation. Detection of biallelic mutations in LRBA is however required for a definitive diagnosis.

Identification of Variants in RET and IHH Pathway Members in a Large Family With History of Hirschsprung Disease

Hirschsprung disease (HSCR) is an inherited congenital disorder characterized by absence of enteric ganglia in the distal part of the gut. Variants in ret proto-oncogene (RET) have been associated with up to 50% of familial and 35% of sporadic cases. We searched for variants that affect disease risk in a large, multigenerational family with history of HSCR in a linkage region previously associated with the disease (4q31.3-q32.3) and exome wide. We performed exome sequencing analyses of a family in the Netherlands with 5 members diagnosed with HSCR and 2 members diagnosed with functional constipation. We initially focused on variants in genes located in 4q31.3-q32.3; however, we also performed an exome-wide analysis in which known HSCR or HSCR-associated gene variants predicted to be deleterious were prioritized for further analysis. Candidate genes were expressed in HEK293, COS-7, and Neuro-2a cells and analyzed by luciferase and immunoblot assays. Morpholinos were designed to target exons of candidate genes and injected into 1-cell stage zebrafish embryos. Embryos were allowed to develop and stained for enteric neurons. Within the linkage region, we identified 1 putative splice variant in the lipopolysaccharide responsive beige-like anchor protein gene (LRBA). Functional assays could not confirm its predicted effect on messenger RNA splicing or on expression of the mab-21 like 2 gene (MAB21L2), which is embedded in LRBA. Zebrafish that developed following injection of the lrba morpholino had a shortened body axis and subtle gut morphological defects, but no significant reduction in number of enteric neurons compared with controls. Outside the linkage region, members of 1 branch of the family carried a previously unidentified RET variant or an in-frame deletion in the glial cell line derived neurotrophic factor gene (GDNF), which encodes a ligand of RET. This deletion was located 6 base pairs before the last codon. We also found variants in the Indian hedgehog gene (IHH) and its mediator, the transcription factor GLI family zinc finger 3 (GLI3). When expressed in cells, the RET-P399L variant disrupted protein glycosylation and had altered phosphorylation following activation by GDNF. The deletion in GDNF prevented secretion of its gene product, reducing RET activation, and the IHH-Q51K variant reduced expression of the transcription factor GLI1. Injection of morpholinos that target ihhreduced the number of enteric neurons to 13% ± 1.4% of control zebrafish. In a study of a large family with history of HSCR, we identified variants in LRBA, RET, the gene encoding the RET ligand (GDNF), IHH, and a gene encoding a mediator of IHH signaling (GLI3). These variants altered functions of the gene products when expressed in cells and knockout of ihh reduced the number of enteric neurons in the zebrafish gut.

LRBA Eksikliği Tanısında Akan Hücre Ölçerde Protein İfadesi

Objective: Lipopolysaccharide-responsive beige-like anchor (LRBA) plays a role in cell surface expression of inhibitory cytotoxic T lymphocyte-associated protein-4 (CTLA-4) protein. Recently identified LRBA deficiency leads to immune deficiency and autoimmunity and is diagnosed by mutation analyses and protein expression. Herein, we quantified stimulated and unstimulated intracellular LRBA protein expression by flow cytometry in LRBA deficiency patients.Materials and Methods: Five LRBA deficient patients and seven healthy controls were evaluated. The LRBA expressions were assessed in peripheral-blood-mononuclear-cells in the presence or absence of phorbol-miristat-acetate and ionomycin stimulation. The difference in mean-fluorescence-intensity (ΔMFI) was calculated.Results: The differences in mean-fluorescence-intensity values of LRBA by flow cytometry were 24±9 for the healthy controls and 4.8±2.8 for the patients. ΔMFIs were 20.8 for P3, 19 for P4 and 49.6 for healthy controls with stimulants and 4.8, 4.6 and 20.1 respectively without stimulants.Conclusion: As a rapid and widely available assay, flow cytometric assessment of intracellular LRBA expression has been found to be an effective and reliable method in the identification of LRBA deficiency.

Consanguineous Siblings with a Novel Mutation in Lipopolysaccharide-Responsive Beige-like Anchor protein (LRBA)

Consanguineous Siblings with a Novel Mutation in Lipopolysaccharide-Responsive Beige-like Anchor protein (LRBA)

The plethora, clinical manifestations and treatment options of autoimmunity in patients with primary immunodeficiency.

Although the association between primary immunodeficiency and autoimmunity is already well-known, it has once again become a topic of debate with the discovery of newly-defined immunodeficiencies. Thus, investigation of the mechanisms of development of autoimmunity in primary immunodefficiency and new target-specific therapeutic options has come to the fore. In this study, we aimed to examine the clinical findings of autoimmunity, autoimmunity varieties, and treatment responses in patients who were genetically diagnosed as having primary immunodeficiency. The files of patients with primary immunodeficiency who had clinical findings of autoimmunity, who were diagnosed genetically, and followed up in our clinic were investigated. The demographic and clinical features of the patients and their medical treatments were evaluated. Findings of autoimmunity were found in 30 patients whose genetic mutations were identified. The mean age at the time of the first symptoms was 8.96±14.64 months, and the mean age of receiving a genetic diagnosis was 82.55±84.71 months. The most common diseases showing findings of autoimmunity included immune dysregulation, polyendocrinopathy, enteropathy X-linked syndrome (16.7%); autoimmune lymphoproliferative syndrome (10%); lipopolysaccharide-responsive beige-like anchor protein deficiency (10%); and DiGeorge syndrome (10%). Twelve (40%) patients showed findings of autoimmunity at the time of first presentation. The most common findings of autoimmunity included inflammatory bowel disease, inflammatory bowel disease-like findings (n=14, 46.7%), immune thrombocytopenic purpura (n=11, 36.7%), and autoimmune hemolytic anemia (n=9, 30.0%). A response to immunosupressive agents was observed in 15 (50%) patients. Ten patients underwent hematopoietic stem cell transplantation. Six patients were lost to follow-up due to a variety of complications. Autoimmunity is frequently observed in patients with primary immunodeficiency. The possibility of primary immunodeficiency should be considered in patients with early-onset manifestations of autoimmunity, and these patients should be carefully monitored in terms of immunodeficiency development. Early diagnosis of primary immunodeficiency may provide favorable outcomes in terms of survival.

Infancy-Onset T1DM, Short Stature, and Severe Immunodysregulation in Two Siblings With a Homozygous LRBA Mutation.

Type 1 diabetes mellitus (T1DM) is caused by autoimmunity against pancreatic β-cells. Although a significant number of T1DM patients have or will develop further autoimmune disorders during their lifetime, coexisting severe immunodysregulation is rare. Presuming autosomal-recessive inheritance in a complex immunodysregulation disorder including T1DM and short stature in two siblings, we performed whole-exome sequencing. Two Libyan siblings born to consanguineous parents were presented to our diabetology department at ages 12 and 5 years, respectively. Apart from T1DM diagnosed at age 2 years, patient 1 suffered from chronic restrictive lung disease, mild enteropathy, hypogammaglobulinemia, and GH deficiency. Fluorescence-activated cell sorting analysis revealed B-cell deficiency. In addition, CD4(+)/CD25(+) and CD25(high)/FoxP3(+) cells were diminished, whereas an unusual CD25(-)/FoxP3(+) population was detectable. The younger brother, patient 2, also developed T1DM during infancy. Although his enteropathy was more severe and electrolyte derangements repeatedly led to hospitalization, he did not have significant pulmonary problems. IgG levels and B-lymphocytes were within normal ranges. By whole-exome sequencing we identified a homozygous truncating mutation (c.2445_2447del(C)3ins(C)2, p.P816Lfs*4) in the lipopolysaccharide-responsive beige-like anchor (LRBA) gene in both siblings. The diagnosis of LRBA deficiency was confirmed by a fluorescence-activated cell sorting-based immunoassay showing the absence of LRBA protein in phytohemagglutinin-stimulated peripheral blood mononuclear cells. We identified a novel truncating LRBA mutation in two siblings with T1DM, short stature, and severe immunodysregulation. LRBA mutations have previously been reported to cause multiorgan autoimmunity and immunodysfunction. In light of the variable phenotypes reported so far in LRBA-mutant individuals, LRBA deficiency should be considered in all patients presenting with T1DM and signs of severe immunodysregulation.

The extended phenotype of LRBA deficiency

Event Abstract Back to Event The extended phenotype of LRBA deficiency Laura Gámez-Díaz1*, Dietrich August1, Polina Stepensky2, Shoshana Revel-Vilk2, Markus G. Seidel3, Mitsuiki Noriko4, Tomohiro Morio4, Austen Worth5, Jacob Bleesing6, Frank Van De Veerdonk7, Tobias Feuchtinger8, Maria G. Kanariou9, Annette Schmitt-Gräff1, Suranjith Seneviratne10, Siobhan Burns10, Bernd Belohradsky11, Nima Rezaei12, Shahrzad Bakhtiar13, Carsten Speckmann1, Michael Jordan7 and Bodo Grimbacher1, 10 1 University Medical Center Freiburg, Center for Chronic Immunodeficiency, Germany 2 Hadassah Hebrew University Hospital, Pediatric Hematology-Oncology and Bone Marrow Transplantation, Israel 3 Medical University Graz, Deparment of Pediatrics and Adolescent Medicine, Divisioni of Pediatric Hematology-Oncology, Austria 4 Medical and Dental University, Tokyo, Japan, Department of Pediatrics and Developmental Biology Graduate School of Medical and Dental Sciences, Japan 5 Great Ormond Street Hospital for Children, Department of Immunology, United Kingdom 6 Cincinnati Childrens Hospital Medical Center, University of Cincinnati Medical School, United States 7 Radboud University of Cincinnati Medical School, Cincinnati Childrens Hospital Medical Center, Netherlands 8 University Hospital Tübingen, laboratory of Immunotherapy, Germany 9 Aghia Sophia Childrens Hospital, Department of Immunology, Greece 10 Royal Free Hospital Foundation Trust, UCL Center for Immunodeficiency, United Kingdom 11 University Childrens Hospital Munich, Division of Immunology and Infectious Disease, Germany 12 Tehran University of Medical Sciences, Research Center for Immunodeficiencies, Iran 13 Goethe University Frankfurt am Main, Division for Stem Cell Transplantation and Immunology, Germany Background: LRBA (lipopolysaccharide-responsive-beige-like-anchor-protein) deficiency is a primary immunodeficiency caused by biallelic mutations in LRBA that abolish LRBA protein expression. Objective: We sought to report the extended phenotype of LRBA deficiency in a cohort of 22 LRBA-deficient patients. Methods: Clinical criteria, protein detection, and genetic sequencing were applied to diagnose LRBA deficiency. Results: Ninety-three patients met the inclusion criteria, and were considered “possible” LRBA deficiency. Twenty-four patients failed to express LRBA protein and were labeled “probable” LRBA deficiency whereas 22 were genetically confirmed as “definitive” LRBA deficiency, having biallelic mutations in LRBA. Seventeen of these were novel and included homozygous or compound heterozygous mutations. Immune dysregulation (95%), organomegaly (86%), recurrent infections (71%), and hypogammaglobulinemia (57%) were the main clinical complications observed in LRBA-deficient patients. Although 81% of LRBA-deficient patients had normal T cell counts, 73% had reduced regulatory T cell numbers. Most LRBA-deficient patients had low counts in the B cell subsets mainly in switched memory B cells (80%) and plasmablasts (92%) with a defective specific antibody response in 67%. Out of the 22 patients, three were deceased, two had successfully been treated by HSCT, seven patients are under immunoglobulin replacement, and 15 are on immunosuppressive treatment with systemic corticosteroids, alone or in combination with steroids sparing agents. Conclusion: This report describes the largest cohort of patients with LRBA deficiency and offers guidelines for physicians to identify LRBA deficiency, supporting an appropriate clinical management. Acknowledgements This study was supported by the Bundesministerium für Bildung und Forschung (BMBF) grant numbers: IFB/CCI: 01E01303, E-med SysINFLAME: 012X1306F, DZIF: 8000805-3, and BMBF PID-NET:01GM1111B.

Deleterious Mutations in LRBA Are Associated with a Syndrome of Immune Deficiency and Autoimmunity

Most autosomal genetic causes of childhood-onset hypogammaglobulinemia are currently not well understood. Most affected individuals are simplex cases, but both autosomal-dominant and autosomal-recessive inheritance have been described. We performed genetic linkage analysis in consanguineous families affected by hypogammaglobulinemia. Four consanguineous families with childhood-onset humoral immune deficiency and features of autoimmunity shared genotype evidence for a linkage interval on chromosome 4q. Sequencing of positional candidate genes revealed that in each family, affected individuals had a distinct homozygous mutation in LRBA (lipopolysaccharide responsive beige-like anchor protein). All LRBA mutations segregated with the disease because homozygous individuals showed hypogammaglobulinemia and autoimmunity, whereas heterozygous individuals were healthy. These mutations were absent in healthy controls. Individuals with homozygous LRBA mutations had no LRBA, had disturbed B cell development, defective in vitro B cell activation, plasmablast formation, and immunoglobulin secretion, and had low proliferative responses. We conclude that mutations in LRBA cause an immune deficiency characterized by defects in B cell activation and autophagy and by susceptibility to apoptosis, all of which are associated with a clinical phenotype of hypogammaglobulinemia and autoimmunity.