Autoimmune lymphoproliferative syndrome with defective Fas: genotype influences penetrance

Combined germline and somatic human FADD mutations cause autoimmune lymphoproliferative syndrome

BACKGROUND

The autoimmune lymphoproliferative syndrome (ALPS) is a noninfectious and nonmalignant lymphoproliferative disease frequently associated with autoimmune cytopenia resulting from defective FAS signaling. We previously described germline monoallelic FAS (TNFRSF6) haploinsufficient mutations associated with somatic events, such as loss of heterozygosity on the second allele of FAS, as a cause of ALPS-FAS. These somatic events were identified by sequencing FAS in DNA from double-negative (DN) T cells, the pathognomonic T-cell subset in ALPS, in which the somatic events accumulated.

OBJECTIVE

We sought to identify whether a somatic event affecting the FAS-associated death domain (FADD) gene could be related to the disease onset in 4 unrelated patients with ALPS carrying a germline monoallelic mutation of the FADD protein inherited from a healthy parent.

METHODS

We sequenced FADD and performed array-based comparative genomic hybridization using DNA from sorted CD4+ or DN T cells.

RESULTS

We found homozygous FADD mutations in the DN T cells from all 4 patients, which resulted from uniparental disomy. FADD deficiency caused by germline heterozygous FADD mutations associated with a somatic loss of heterozygosity was a phenocopy of ALPS-FAS without the more complex symptoms reported in patients with germline biallelic FADD mutations.

CONCLUSIONS

The association of germline and somatic events affecting the FADD gene is a new genetic cause of ALPS.

Autoimmune lymphoproliferative syndrome: A disorder of immune dysregulation

Autoimmune Lymphoproliferative Syndrome (ALPS) is an autoimmune disease that has been reported in over 2200 patients. It is a rare, genetic disease where pathogenic variants occur in the extrinsic pathway of apoptosis. Various mutations in different genes, such as FAS, FASL, and CASP10, can result in ALPS. Most commonly, pathogenic variants occur in the FAS receptor. This malfunctioning pathway allows for the abnormal accumulation of lymphocytes, namely CD3 + TCRαβ+CD4 - CD8- (double negative (DN) T) cells, which are a hallmark of the disease. This disease usually presents in childhood with lymphadenopathy and splenomegaly as a result of lymphoproliferation. Over time, these patients may develop cytopenias or lymphomas because of irregularities in the immune system. Current treatments include glucocorticoids, mycophenolate mofetil, sirolimus, immunoglobulin G, and rituximab. These medications serve to manage the symptoms and there are no standardized recommendations for the management of ALPS. The only curative therapy is a bone marrow transplant, but this is rarely done because of the complications. This review serves to broaden the understanding of ALPS by discussing the mechanism of immune dysregulation, how the symptoms manifest, and the mechanisms of treatment. Additionally, we discuss the epidemiology, comorbidities, and medications relating to ALPS patients across the United States using data from Cosmos.

Synthetic receptor platform to identify loss-of-function single nucleotide variants and designed mutants in the death receptor Fas/CD95

Synthetic biology has emerged as a useful technology for studying cytokine signal transduction. Recently, we described fully synthetic cytokine receptors to phenocopy trimeric receptors such as the death receptor Fas/CD95. Using a nanobody as an extracellular-binding domain for mCherry fused to the natural receptor's transmembrane and intracellular domain, trimeric mCherry ligands were able to induce cell death. Among the 17,889 single nucleotide variants in the SNP database for Fas, 337 represent missense mutations that functionally remained largely uncharacterized. Here, we developed a workflow for the Fas synthetic cytokine receptor system to functionally characterize missense SNPs within the transmembrane and intracellular domain of Fas. To validate our system, we selected five functionally assigned loss-of-function (LOF) polymorphisms and included 15 additional unassigned SNPs. Moreover, based on structural data, 15 gain-of-function or LOF candidate mutations were additionally selected. All 35 nucleotide variants were functionally investigated through cellular proliferation, apoptosis and caspases 3 and 7 cleavage assays. Collectively, our results showed that 30 variants resulted in partial or complete LOF, while five lead to a gain-of-function. In conclusion, we demonstrated that synthetic cytokine receptors are a suitable tool for functional SNPs/mutations characterization in a structured workflow.

Genetics of Inborn Errors of Immunity in highly consanguineous Middle Eastern and North African populations

Consanguineous marriages in Middle Eastern and North African (MENA) countries are deeply-rooted tradition and highly prevalent resulting into increased prevalence of autosomal recessive diseases including Inborn Errors of Immunity (IEIs). Molecular genetic testing is an important diagnostic tool for IEIs since it provides a definite diagnosis, genotype-phenotype correlation, and guide therapy. In this review, we will discuss the current state and challenges of genomic and variome studies in MENA region populations, as well as the importance of funding advanced genome projects. In addition, we will review the MENA underlying molecular genetic defects of over 2457 patients published with the common IEIs, where autosomal recessive mode of inheritance accounts for 76% of cases with increased prevalence of combined immunodeficiency diseases (50%). The efforts made in the last three decades in terms of international collaboration and of in situ capacity building in MENA region countries led to the discovery of more than 150 novel genes involved in IEIs. Expanding sequencing studies within the MENA will undoubtedly be a unique asset for the IEI genetics which can advance research, and support precise genomic diagnostics and therapeutics.

Genetics of Immune Dysregulation and Cancer Predisposition: Two Sides of the Same Coin

Approximately 10% of cancers have a hereditary predisposition. However, no genetic diagnosis is available in 60%-80% of familial cancers. In some of these families, immune dysregulation-mediated disease is frequent. The immune system plays a critical role in identifying and eliminating tumors; thus, dysregulation of the immune system can increase the risk of developing cancer. This review focuses on some of the genes involved in immune dysregulation the promote the risk for cancer. Genetic counseling for patients with cancer currently focuses on known genes that raise the risk of cancer. In missing hereditary familial cases, the history family of immune dysregulation should be recorded, and genes related to the immune system should be analyzed in relevant families. On the other hand, patients with immune disorders diagnosed with a pathogenic mutation in an immune regulatory gene may have an increased risk of cancer. Therefore, those patients need to be under surveillance for cancer. Gene panel and exome sequencing are currently standard methods for genetic diagnosis, providing an excellent opportunity to jointly test cancer and immune genes.

Detection and evolutionary dynamics of somatic FAS variants in autoimmune lymphoproliferative syndrome: Diagnostic implications

Autoimmune lymphoproliferative syndrome (ALPS) is a rare primary immune disorder characterized by impaired apoptotic homeostasis. The clinical characteristics include lymphoproliferation, autoimmunity (mainly cytopenia), and an increased risk of lymphoma. A distinctive biological feature is accumulation (>2.5%) of an abnormal cell subset composed of TCRαβ+ CD4-CD8- T cells (DNTs). The most common genetic causes of ALPS are monoallelic pathogenic variants in the FAS gene followed by somatic FAS variants, mainly restricted to DNTs. Identification of somatic FAS variants has been typically addressed by Sanger sequencing in isolated DNTs. However, this approach can be costly and technically challenging, and may not be successful in patients with normal DNT counts receiving immunosuppressive treatment. In this study, we identified a novel somatic mutation in FAS (c.718_719insGTCG) by Sanger sequencing on purified CD3+ cells. We then followed the evolutionary dynamics of the variant along time with an NGS-based approach involving deep amplicon sequencing (DAS) at high coverage (20,000-30,000x). Over five years of clinical follow-up, we obtained six blood samples for molecular study from the pre-treatment (DNTs>7%) and treatment (DNTs<2%) periods. DAS enabled detection of the somatic variant in all samples, even the one obtained after five years of immunosuppressive treatment (DNTs: 0.89%). The variant allele frequency (VAF) range was 4%-5% in pre-treatment samples and <1.5% in treatment samples, and there was a strong positive correlation between DNT counts and VAF (Pearson’s R: 0.98, p=0.0003). We then explored whether the same approach could be used in a discovery setting. In the last follow-up sample (DNT: 0.89%) we performed somatic variant calling on the FAS exon 9 DAS data from whole blood and purified CD3+ cells using VarScan 2. The c.718_719insGTCG variant was identified in both samples and showed the highest VAF (0.67% blood, 1.58% CD3+ cells) among >400 variants called. In summary, our study illustrates the evolutionary dynamics of a somatic FAS mutation before and during immunosuppressive treatment. The results show that pathogenic somatic FAS variants can be identified with the use of DAS in whole blood of ALPS patients regardless of their DNT counts.

Allogeneic Bone Marrow Transplant as a Cure for Refractory T-Cell Large Granular Lymphocytic Leukemia in an Adolescent

T-cell large granular lymphocytic (T-LGL) leukemia is a rare, typically indolent neoplasm with a median age of onset above 60 years. Pathogenesis involves clonal T-cell expansion, and nearly all reported pediatric cases have been associated with concurrent autoimmune disease. Immunosuppressive therapy often mitigates sequelae, but definitive cure is not routinely achieved. Here we present an otherwise healthy 13-year-old with T-LGL leukemia refractory to all standard treatments. Our patient ultimately underwent allogeneic bone marrow transplant (BMT) and is now stable in remission 3 years post-BMT. BMT may offer a viable definitive cure for refractory T-LGL leukemia in very young patients.

The Contribution of Rare Copy Number Variants in FAS Towards Pathogenesis of Autoimmune Lymphoproliferative Syndrome

Rare copy number variants in FAS can cause ALPS by method of haploinsufficiency.

CNV analysis can provide a molecular diagnosis for patients with ALPS when whole exome sequencing or panel-based testing are inconclusive.

Autoimmune lymphoproliferative syndrome (ALPS) is characterized by chronic nonmalignant lymphadenopathy, splenomegaly, cytopenias, and other autoimmune manifestations. ALPS is caused by lymphocyte accumulation from defects in FAS-mediated apoptosis. Heterozygous germline or somatic pathogenic single nucleotide variants in FAS are the most common molecular etiology of ALPS. Through the Centralized Sequencing Program at the National Institute of Allergy and Infectious Diseases, we performed exome sequencing on subjects with a clinical diagnosis of ALPS, with a subset receiving copy number variant (CNV) analysis. In this cohort, we identified 3 subjects from unrelated families with CNVs at the FAS locus. One subject had a de novo ∼0.828 Mb copy number loss encompassing all of FAS. The second subject had a maternally inherited ∼1.004 Mb copy number loss encompassing all of FAS. The third subject had a paternally inherited ∼0.044 Mb copy number loss encompassing exons 7 through 9 of FAS. Subjects with deletions in FAS had clinical presentations and biomarker profiles similar to those with ALPS and with germline and somatic FAS variants. We demonstrate that CNV analysis should be pursued if there is clinical and biomarker evidence of ALPS because it can lead to a molecular diagnosis and appropriate treatment when FAS sequencing is inconclusive.

Impact of human CD95 mutations on cell death and autoimmunity: a model

CD95/Fas/APO-1 can trigger apoptotic as well as nonapoptotic pathways in immune cells. CD95 signaling in humans can be inhibited by several mechanisms, including mutations in the gene encoding CD95. CD95 mutations lead to autoimmune disorders, such as autoimmune lymphoproliferative syndrome (ALPS). Gaining further insight into the reported mutations of CD95 and resulting alterations of its signaling networks may provide further understanding of their presumed role in certain autoimmune diseases. For illustrative purposes and to better understand the potential outcomes of CD95 mutations, here we assign their positions to the recently determined 3D structures of human CD95. Based on this, we make certain predictions and speculate on the putative role of CD95 mutation defects in CD95-mediated signaling for certain autoimmune diseases.

Clinical, immunological, and genetic features in 780 patients with autoimmune lymphoproliferative syndrome (ALPS) and ALPS-like diseases: A systematic review

BACKGROUND

Autoimmune lymphoproliferative syndrome (ALPS) is a group of genetic disorders characterized by early-onset lymphoproliferation, autoimmune cytopenias, and susceptibility to lymphoma. The majority of ALPS patients carry heterozygous germline mutations in the TNFRSF6 gene. In this study, we conducted a systematic review of patients with ALPS and ALPS-like syndrome.

METHODS

The literature search was performed in Web of Science, Scopus, and PubMed databases to find eligible studies. Additionally, the reference list of all included papers was hand-searched for additional studies. Demographic, clinical, immunological, and molecular data were extracted and compared between the ALPS and ALPS-like syndrome.

RESULTS

Totally, 720 patients with ALPS (532 genetically determined and 189 genetically undetermined ALPS) and 59 cases with ALPS-like phenotype due to mutations in genes other than ALPS genes were assessed. In both ALPS and ALPS-like patients, splenomegaly was the most common clinical presentation followed by autoimmune cytopenias and lymphadenopathy. Among other clinical manifestations, respiratory tract infections were significantly higher in ALPS-like patients than ALPS. The immunological analysis showed a lower serum level of IgA, IgG, and lymphocyte count in ALPS-like patients compared to ALPS. Most (85%) of the ALPS and ALPS-like cases with determined genetic defects carry mutations in the FAS gene. About one-third of patients received immunosuppressive therapy with conventional or targeted immunotherapy agents. A small fraction of patients (3.3%) received hematopoietic stem cell transplantation with successful engraftment, and all except two patients survived after transplantation.

CONCLUSION

Our results showed that the FAS gene with 85% frequency is the main etiological cause of genetically diagnosed patients with ALPS phenotype; therefore, the genetic defect of the majority of suspected ALPS patients could be confirmed by mutation analysis of FAS gene.

Primary Immune Regulatory Disorders With an Autoimmune Lymphoproliferative Syndrome-Like Phenotype: Immunologic Evaluation, Early Diagnosis and Management

Primary immune regulatory disorders (PIRD) are associated with autoimmunity, autoinflammation and/or dysregulation of lymphocyte homeostasis. Autoimmune lymphoproliferative syndrome (ALPS) is a PIRD due to an apoptotic defect in Fas-FasL pathway and characterized by benign and chronic lymphoproliferation, autoimmunity and increased risk of lymphoma. Clinical manifestations and typical laboratory biomarkers of ALPS have also been found in patients with a gene defect out of the Fas-FasL pathway (ALPS-like disorders). Following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA), we identified more than 600 patients suffering from 24 distinct genetic defects described in the literature with an autoimmune lymphoproliferative phenotype (ALPS-like syndromes) corresponding to phenocopies of primary immunodeficiency (PID) (NRAS, KRAS), susceptibility to EBV (MAGT1, PRKCD, XIAP, SH2D1A, RASGRP1, TNFRSF9), antibody deficiency (PIK3CD gain of function (GOF), PIK3R1 loss of function (LOF), CARD11 GOF), regulatory T-cells defects (CTLA4, LRBA, STAT3 GOF, IL2RA, IL2RB, DEF6), combined immunodeficiencies (ITK, STK4), defects in intrinsic and innate immunity and predisposition to infection (STAT1 GOF, IL12RB1) and autoimmunity/autoinflammation (ADA2, TNFAIP3,TPP2, TET2). CTLA4 and LRBA patients correspond around to 50% of total ALPS-like cases. However, only 100% of CTLA4, PRKCD, TET2 and NRAS/KRAS reported patients had an ALPS-like presentation, while the autoimmunity and lymphoproliferation combination resulted rare in other genetic defects. Recurrent infections, skin lesions, enteropathy and malignancy are the most common clinical manifestations. Some approaches available for the immunological study and identification of ALPS-like patients through flow cytometry and ALPS biomarkers are provided in this work. Protein expression assays for NKG2D, XIAP, SAP, CTLA4 and LRBA deficiencies and functional studies of AKT, STAT1 and STAT3 phosphorylation, are showed as useful tests. Patients suspected to suffer from one of these disorders require rapid and correct diagnosis allowing initiation of tailored specific therapeutic strategies and monitoring thereby improving the prognosis and their quality of life.

Immunologic evaluation and genetic defects of apoptosis in patients with autoimmune lymphoproliferative syndrome (ALPS)

Apoptosis plays an important role in controlling the adaptive immune response and general homeostasis of the immune cells, and impaired apoptosis in the immune system results in autoimmunity and immune dysregulation. In the last 25 years, inherited human diseases of the Fas-FasL pathway have been recognized. Autoimmune lymphoproliferative syndrome (ALPS) is an inborn error of immunity, characterized clinically by nonmalignant and noninfectious lymphoproliferation, autoimmunity, and increased risk of lymphoma due to a defect in lymphocyte apoptosis. The laboratory hallmarks of ALPS are an elevated percentage of T-cell receptor αβ double negative T cells (DNTs), elevated levels of vitamin B12, soluble FasL, IL-10, IL-18 and IgG, and defective in vitro Fas-mediated apoptosis. In order of frequency, the genetic defects associated with ALPS are germinal and somatic ALPS-FAS, ALPS-FASLG, ALPS-CASP10, ALPS-FADD, and ALPS-CASP8. Partial disease penetrance and severity suggest the combination of germline and somatic FAS mutations as well as other risk factor genes. In this report, we summarize human defects of apoptosis leading to ALPS and defects that are known as ALPS-like syndromes that can be clinically similar to, but are genetically distinct from, ALPS. An efficient genetic and immunological diagnostic approach to patients suspected of having ALPS or ALPS-like syndromes is essential because this enables the establishment of specific therapeutic strategies for improving the prognosis and quality of life of patients.

Key diagnostic markers for autoimmune lymphoproliferative syndrome with molecular genetic diagnosis

Autoimmune lymphoproliferative syndrome (ALPS) is a rare immunodeficiency caused by mutations in genes affecting the extrinsic apoptotic pathway (FAS, FASL, CASP10). This study evaluated the clinical manifestations, laboratory findings, and molecular genetic results of 215 patients referred as possibly having ALPS. Double-negative T-cell (DNT) percentage and in vitro apoptosis functional tests were evaluated by fluorescence-activated cell sorting; interleukin 10 (IL-10) and IL-18 and soluble FAS ligand (sFASL) were measured by enzyme-linked immunosorbent assay. Genetic analysis was performed by next-generation sequencing. Clinical background data were collected from patients’ records. Patients were categorized into definite, suspected, or unlikely ALPS groups, and laboratory parameters were compared among these groups. Of 215 patients, 38 met the criteria for definite ALPS and 17 for suspected ALPS. The definite and suspected ALPS patient populations showed higher DNT percentages than unlikely ALPS and had higher rates of lymphoproliferation. Definite ALPS patients had a significantly more abnormal in vitro apoptosis function, with lower annexin, than patients with suspected ALPS (P = .002) and patients not meeting ALPS criteria (P < .001). The combination of elevated DNTs and an abnormal in vitro apoptosis functional test was the most useful in identifying all types of ALPS patients; the combination of an abnormal in vitro apoptosis functional test and elevated sFASLs was a predictive marker for ALPS-FAS group identification. Lymphoproliferation, apoptosis functional test, and DNTs are the most sensitive markers; elevated IL-10 and IL-18 are additional indicators for ALPS. The combination of elevated sFASLs and abnormal apoptosis function was the most valuable prognosticator for patients with FAS mutations.

Incomplete penetrance in primary immunodeficiency: a skeleton in the closet

Primary immunodeficiencies (PIDs) comprise a diverse group of over 400 genetic disorders that result in clinically apparent immune dysfunction. Although PIDs are classically considered as Mendelian disorders with complete penetrance, we now understand that absent or partial clinical disease is often noted in individuals harboring disease-causing genotypes. Despite the frequency of incomplete penetrance in PID, no conceptual framework exists to categorize and explain these occurrences. Here, by reviewing decades of reports on incomplete penetrance in PID we identify four recurrent themes of incomplete penetrance, namely genotype quality, (epi)genetic modification, environmental influence, and mosaicism. For each of these principles, we review what is known, underscore what remains unknown, and propose future experimental approaches to fill the gaps in our understanding. Although the content herein relates specifically to inborn errors of immunity, the concepts are generalizable across genetic diseases.

Autoimmune Lymphoproliferative Syndrome: An Overview

Autoimmune lymphoproliferative syndrome (ALPS) is an inherited nonmalignant lymphoproliferative disorder characterized by heterozygous mutations within the first apoptosis signal receptor (FAS) signaling pathway. Defects in FAS-mediated apoptosis cause an expansion and accumulation of autoreactive CD4- and CD8- (double-negative) T cells, leading to cytopenias, splenomegaly, lymphadenopathy, autoimmune disorders, and a greatly increased lifetime risk of lymphoma. The differential diagnosis of ALPS includes infection, other inherited immunodeficiency disorders, primary and secondary autoimmune syndromes, and lymphoma. The most consistent pathologic feature is a florid paracortical expansion of double-negative T cells in lymph nodes. A presumptive clinical diagnosis can be made from symptoms and a constellation of laboratory test results. However, a definitive diagnosis requires ancillary testing and enables disease subclassification. Recognition of ALPS is critical, as treatment with immunosuppressive therapies can effectively reduce or ameliorate symptoms for most patients.

An updated review on phenocopies of primary immunodeficiency diseases

Primary immunodeficiency diseases (PIDs) refer to a heterogenous group of disorders characterized clinically by increased susceptibility to infections, autoimmunity and increased risk of malignancies.

These group of disorders present with clinical manifestations similar to PIDs with known genetic defects but have either no genetic defect or have a somatic mutation and thus have been labelled as “Phenocopies of PIDs”. These diseases have been further subdivided into those associated with somatic mutations and those associated with presence of auto-antibodies against various cytokines.

In this review, we provide an update on clinical manifestations, diagnosis and management of these diseases.

Apoptosis of tumor-infiltrating T lymphocytes: a new immune checkpoint mechanism

Immunotherapy based on checkpoint inhibitors is providing substantial clinical benefit, but only to a minority of cancer patients. The current priority is to understand why the majority of patients fail to respond. Besides T-cell dysfunction, T-cell apoptosis was reported in several recent studies as a relevant mechanism of tumoral immune resistance. Several death receptors (Fas, DR3, DR4, DR5, TNFR1) can trigger apoptosis when activated by their respective ligands. In this review, we discuss the immunomodulatory role of the main death receptors and how these are shaping the tumor microenvironment, with a focus on Fas and its ligand. Fas-mediated apoptosis of T cells has long been known as a mechanism allowing the contraction of T-cell responses to prevent immunopathology, a phenomenon known as activation-induced cell death, which is triggered by induction of Fas ligand (FasL) expression on T cells themselves and qualifies as an immune checkpoint mechanism. Recent evidence indicates that other cells in the tumor microenvironment can express FasL and trigger apoptosis of tumor-infiltrating lymphocytes (TIL), including endothelial cells and myeloid-derived suppressor cells. The resulting disappearance of TIL prevents anti-tumor immunity and may in fact contribute to the absence of TIL that is typical of "cold" tumors that fail to respond to immunotherapy. Interfering with the Fas-FasL pathway in the tumor microenvironment has the potential to increase the efficacy of cancer immunotherapy.

T cells genetically engineered to overcome death signaling enhance adoptive cancer immunotherapy

Across clinical trials, T cell expansion and persistence following adoptive cell transfer (ACT) have correlated with superior patient outcomes. Herein, we undertook a pan-cancer analysis to identify actionable ligand-receptor pairs capable of compromising T cell durability following ACT. We discovered that FASLG, the gene encoding the apoptosis-inducing ligand FasL, is overexpressed within the majority of human tumor microenvironments (TMEs). Further, we uncovered that Fas, the receptor for FasL, is highly expressed on patient-derived T cells used for clinical ACT. We hypothesized that a cognate Fas-FasL interaction within the TME might limit both T cell persistence and antitumor efficacy. We discovered that genetic engineering of Fas variants impaired in the ability to bind FADD functioned as dominant negative receptors (DNRs), preventing FasL-induced apoptosis in Fas-competent T cells. T cells coengineered with a Fas DNR and either a T cell receptor or chimeric antigen receptor exhibited enhanced persistence following ACT, resulting in superior antitumor efficacy against established solid and hematologic cancers. Despite increased longevity, Fas DNR-engineered T cells did not undergo aberrant expansion or mediate autoimmunity. Thus, T cell-intrinsic disruption of Fas signaling through genetic engineering represents a potentially universal strategy to enhance ACT efficacy across a broad range of human malignancies.

Diagnosis and management of chronic and refractory immune cytopenias in children, adolescents, and young adults

Children, adolescents, and young adults with chronic refractory autoimmune cytopenias represent a rare but challenging group of patients, who are managed frequently by pediatric hematologists. Novel diagnostic tests and genomic discoveries are refining historical diagnoses of Evans syndrome and common variable immunodeficiency, while also elucidating the cellular and molecular basis for these disorders. Genetic characterization of chronic and refractory autoimmune cytopenias has led to targeted therapies with improved clinical outcomes and fewer off-target toxicities. In this review, we focus on the appropriate diagnostic workup, expanded genetic testing, and novel treatment opportunities that are available for these challenging patients.

Autoimmunity and primary immunodeficiency: two sides of the same coin?

Autoimmunity and immunodeficiency were previously considered to be mutually exclusive conditions; however, increased understanding of the complex immune regulatory and signalling mechanisms involved, coupled with the application of genetic analysis, is revealing the complex relationships between primary immunodeficiency syndromes and autoimmune diseases. Single-gene defects can cause rare diseases that predominantly present with autoimmune symptoms. Such genetic defects also predispose individuals to recurrent infections (a hallmark of immunodeficiency) and can cause primary immunodeficiencies, which can also lead to immune dysregulation and autoimmunity. Moreover, risk factors for polygenic rheumatic diseases often exist in the same genes as the mutations that give rise to primary immunodeficiency syndromes. In this Review, various primary immunodeficiency syndromes are presented, along with their pathogenetic mechanisms and relationship to autoimmune diseases, in an effort to increase awareness of immunodeficiencies that occur concurrently with autoimmune diseases and to highlight the need to initiate appropriate genetic tests. The growing knowledge of various genetically determined pathologic mechanisms in patients with immunodeficiencies who have autoimmune symptoms opens up new avenues for personalized molecular therapies that could potentially treat immunodeficiency and autoimmunity at the same time, and that could be further explored in the context of autoimmune rheumatic diseases.

Novel insights into FAS defects underlying autoimmune lymphoproliferative syndrome revealed by studies in consanguineous patients

Autoimmune lymphoproliferative syndrome (ALPS) is a primary immunodeficiency disease due to impaired Fas-Fas ligand apoptotic pathway. It is characterized by chronic nonmalignant, noninfectious lymphadenopathy and/or splenomegaly associated with autoimmune manifestations primarily directed against blood cells. Herein, we review the heterogeneous ALPS molecular bases and discuss recent findings revealed by the study of consanguineous patients. Indeed, this peculiar genetic background favored the identification of a novel form of AR ALPS-FAS associated with normal or residual protein expression, expanding the spectrum of ALPS types. In addition, rare mutational mechanisms underlying the splicing defects of FAS exon 6 have been identified in AR ALPS-FAS with lack of protein expression. These findings will help decipher critical regions required for the tight regulation of FAS exon 6 splicing. We also discuss the genotype-phenotype correlation and disease severity in AR ALPS-FAS. Altogether, the study of ALPS molecular bases in endogamous populations helps to better classify the disease subgroups and to unravel the Fas pathway functioning.

Mechanism-Based Strategies for the Management of Autoimmunity and Immune Dysregulation in Primary Immunodeficiencies

A broad spectrum of autoimmunity is now well described in patients with primary immunodeficiencies (PIDs). Management of autoimmune disease in the background of PID is particularly challenging given the seemingly discordant goals of immune support and immune suppression. Our growing ability to define the molecular underpinnings of immune dysregulation has facilitated novel targeted therapeutics. This review focuses on mechanism-based treatment strategies for the most common autoimmune and inflammatory complications of PID including autoimmune cytopenias, rheumatologic disease, and gastrointestinal disease. We aim to provide guidance regarding the rational use of these agents in the complex PID patient population.

Lessons from Genetic Studies of Primary Immunodeficiencies in a Highly Consanguineous Population

During the last decades, the study of primary immunodeficiencies (PIDs) has contributed tremendously to unravel novel pathways involved in a variety of immune responses. Many of these PIDs have an autosomal recessive (AR) mode of inheritance. Thus, the investigation of the molecular basis of PIDs is particularly relevant in consanguineous populations from Middle East and North Africa (MENA). Although significant efforts have been made in recent years to develop genetic testing across the MENA region, few comprehensive studies reporting molecular basis of PIDs in these settings are available. Herein, we review genetic characteristics of PIDs identified in 168 patients from an inbred Tunisian population. A spectrum of 25 genes involved was analyzed. We show that AR forms compared to X-linked or autosomal dominant forms are clearly the most frequent. Furthermore, the study of informative consanguineous families did allow the identification of a novel hyper-IgE syndrome linked to phosphoglucomutase 3 mutations. We did also report a novel form of autoimmune lymphoproliferative syndrome caused by homozygous FAS mutations with normal or residual protein expression as well as a novel AR transcription factor 3 deficiency. Finally, we identified several founder effects for specific AR mutations. This did facilitate the implementation of preventive approaches through genetic counseling in affected consanguineous families. All together, these findings highlight the specific nature of highly consanguineous populations and confirm the importance of unraveling the molecular basis of genetic diseases in this context. Besides providing a better fundamental knowledge of novel pathways, their study is improving diagnosis strategies and appropriate care.

Lymphadenopathy driven by TCR-Vγ8Vδ1 T-cell expansion in FAS-related autoimmune lymphoproliferative syndrome

FAS-dependent apoptosis in V_δ1 T cells makes the latter possible culprits for the lymphadenopathy observed in patients with FAS mutations.Rapamycin and methylprednisolone resistance should prompt clinicians to look for V_δ1 T cell proliferation in ALPS-FAS patients.

Biomarkers and Algorithms for the Diagnosis of Vitamin B12 Deficiency

Vitamin B12 (cobalamin, Cbl, B12) is an indispensable water-soluble micronutrient that serves as a coenzyme for cytosolic methionine synthase (MS) and mitochondrial methylmalonyl-CoA mutase (MCM). Deficiency of Cbl, whether nutritional or due to inborn errors of Cbl metabolism, inactivate MS and MCM leading to the accumulation of homocysteine (Hcy) and methylmalonic acid (MMA), respectively. In conjunction with total B12 and its bioactive protein-bound form, holo-transcobalamin (holo-TC), Hcy, and MMA are the preferred serum biomarkers utilized to determine B12 status. Clinically, vitamin B12 deficiency leads to neurological deterioration and megaloblastic anemia, and, if left untreated, to death. Subclinical vitamin B12 deficiency (usually defined as a total serum B12 of <200 pmol/L) presents asymptomatically or with rather subtle generic symptoms that oftentimes are mistakenly ascribed to unrelated disorders. Numerous studies have now established that serum vitamin B12 has limited diagnostic value as a stand-alone marker. Low serum levels of vitamin B12 not always represent deficiency, and likewise, severe functional deficiency of the micronutrient has been documented in the presence of normal and even high levels of serum vitamin B12. This review discusses the usefulness and limitations of current biomarkers of B12 status in newborn screening, infant and adult diagnostics, the algorithms utilized to diagnose B12 deficiency and unusual findings of vitamin B12 status in various human disorders.

Rare autoimmune disorders with Mendelian inheritance

Autoimmune diseases represent a heterogeneous group of common disorders defined by complex trait genetics and environmental effects. The genetic variants usually align in immune and metabolic pathways that affect cell survival or apoptosis and modulate leukocyte function. Nevertheless, the exact triggers of disease development remain poorly understood and the current therapeutic interventions only modify the disease course. Both the prevention and the cure of autoimmune disorders are beyond our present medical capabilities. In contrast, a growing number of single gene autoimmune disorders have also been identified and characterized in the last few decades. Mutations and other gene alterations exert significant effects in these conditions, and often affect genes involved in central or peripheral immunologic tolerance induction. Even though a single genetic abnormality may be the disease trigger, it usually upsets a number of interactions among immune cells, and the biological developments of these monogenic disorders are also complex. Nevertheless, identification of the triggering molecular abnormalities greatly contributes to our understanding of the pathogenesis of autoimmunity and facilitates the development of newer and more effective treatment strategies.

A Novel and Likely Inherited Lymphoproliferative Disease in British Shorthair Kittens

An unusual lymphoproliferative disease was identified in multiple closely related British Shorthair (BSH) kittens, suggesting an inherited predisposition to disease. Affected kittens typically developed rapidly progressive and marked generalized lymphadenopathy, moderate splenomegaly, and regenerative and likely hemolytic anemia from 6 weeks of age. Microscopic findings were suggestive of multicentric T-cell lymphoma, but additional testing revealed a polyclonal population of CD3+/CD4–/CD8– “double negative” T cells (DNT cells). This is a novel disease presentation with similarities to the human disorder autoimmune lymphoproliferative syndrome (ALPS), a rare inherited disease causing lymphoproliferation and variable manifestations of autoimmunity. The human disease is most commonly due to the presence of Fas gene mutations causing defective lymphocyte apoptosis, and further investigations of both the mode of inheritance and genetic basis for disease in affected cats are currently in progress.

Approaches to Managing Autoimmune Cytopenias in Novel Immunological Disorders with Genetic Underpinnings Like Autoimmune Lymphoproliferative Syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is a rare disorder of apoptosis. It is frequently caused by mutations in FAS (TNFRSF6) gene. Unlike most of the self-limiting autoimmune cytopenias sporadically seen in childhood, multi lineage cytopenias due to ALPS are often refractory, as their inherited genetic defect is not going to go away. Historically, more ALPS patients have died due to overwhelming sepsis following splenectomy to manage their chronic cytopenias than due to any other cause, including malignancies. Hence, current recommendations underscore the importance of avoiding splenectomy in ALPS, by long-term use of corticosteroid-sparing immunosuppressive agents like mycophenolate mofetil and sirolimus. Paradigms learnt from managing ALPS patients in recent years is highlighted here and can be extrapolated to manage refractory cytopenias in patients with as yet undetermined genetic bases for their ailments. It is also desirable to develop international registries for children with rare and complex immune problems associated with chronic multilineage cytopenias in order to elucidate their natural history and long-term comorbidities due to the disease and its treatments.

IL-10/Janus kinase/signal transducer and activator of transcription 3 signaling dysregulates Bim expression in autoimmune lymphoproliferative syndrome

BACKGROUND

Autoimmune lymphoproliferative syndrome (ALPS) is a human disorder of T cell homeostasis caused by mutations that impair FAS-mediated apoptosis. A defining characteristic of ALPS is the expansion of double negative T cells (DNTC). Relatively little is known about how defective FAS-driven cell death and the Bcl-2 apoptotic pathway intersect in ALPS patients.

OBJECTIVE

We studied changes in Bcl-2 family member expression in ALPS to determine whether the Bcl-2 pathway might provide a therapeutic target.

METHODS

We used flow cytometry to analyze the expression of pro- and anti-apoptotic Bcl-2 family members in T cells from 12 ALPS patients and determined the in vitro sensitivity of ALPS DNTC to the pro-apoptotic BH3 mimetic, ABT-737.

RESULTS

The pro-apoptotic molecule, Bim, was significantly elevated in DNTC. Although no general pattern of individual anti-apoptotic Bcl-2 family members emerged, increased expression of Bim was always accompanied by increased expression of at least 1 anti-apoptotic Bcl-2 family member. Strikingly, Bim levels in DNTC correlated significantly with serum IL-10 in ALPS patients, and IL-10 was sufficient to mildly induce Bim in normal and ALPS T cells via a Janus kinase/signal transducer and activator of transcription 3-dependent mechanism. Finally, ABT-737 preferentially killed ALPS DNTC in vitro.

CONCLUSION

Combined, these data show that an IL-10/Janus kinase/signal transducer and activator of transcription 3 pathway drives Bim expression in ALPS DNTC, which renders them sensitive to BH3 mimetics, uncovering a potentially novel therapeutic approach to ALPS.

The expanding spectrum of the autoimmune lymphoproliferative syndromes

PURPOSE OF REVIEW

Several autoimmune lymphoproliferative syndromes have been described lately. We review here the main clinical and laboratory findings of these new disorders.

RECENT FINDINGS

The prototypical autoimmune lymphoproliferative syndrome (ALPS) has had its diagnostic criteria modified, somatic mutations in RAS genes were found to cause an ALPS-like syndrome in humans, and mutations in a gene encoding a protein kinase C (PRKCD) were discovered to cause a syndrome of lymphoproliferation, autoimmunity and natural killer cell defect.

SUMMARY

The recent discoveries shed light on the molecular pathways governing lymphocyte death, proliferation and immune tolerance in humans.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

The role of B lymphocyte stimulator in B cell biology: implications for the treatment of lupus

B lymphocyte stimulator (BLyS; also known as B cell activating factor (BAFF)) plays a key role in peripheral B cell tolerance. Mounting evidence indicates that B cell tolerance can be either broken or modulated by deliberately manipulating BLyS levels, and belimumab, a BLyS-neutralizing antibody, was recently approved for the treatment of systemic lupus erythematosus (SLE). Thus, intense investigation has focused on understanding how therapeutics targeting BLyS may work, and accumulating evidence suggests multiple points of action. BLyS signaling, in conjunction with B cell receptor (BCR) signaling, determines the size and quality of the mature primary B cell compartment. Moreover, BLyS family members play roles in antigen-experienced B cell selection and differentiation. Together, these findings have implications for the continued development of novel therapeutics that target BLyS.

Causes and consequences of the autoimmune lymphoproliferative syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is the first autoimmune hematological disease whose genetic basis has been defined. It is a disorder of apoptosis in which the inability of lymphocytes to die leads to lymphadenopathy, hypersplenism, and autoimmune cytopenias of childhood onset. More than 200 ALPS patients have been studied over the last 15 years and followed by our colleagues and ourselves at the Clinical Center of the National Institutes of Health. Based upon this experience we have determined that patients with germline mutations of the intracellular domain of Fas protein, the most frequent single genetic cause of ALPS, have a significantly increased risk of developing Hodgkin and non-Hodgkin lymphoma (NHL), underscoring the critical role played by cell surface receptor-mediated apoptosis in eliminating redundant proliferating lymphocytes with autoreactive and oncogenic potential. The major determinants of morbidity and mortality in ALPS are the severity of the autoimmune disease, hypersplenism, asplenia-related sepsis, and the risk of lymphoma, which in itself requires long-term surveillance. Though most episodes of cytopenias respond to courses of conventional immunomodulatory agents, some ALPS patients, especially those with massive splenomegaly and hypersplenism, may require splenectomy and/or ongoing immunosuppressive treatment. Thus, ALPS highlights the importance of cell death pathways in health and disease.

Variations of the UNC13D gene in patients with autoimmune lymphoproliferative syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is caused by genetic defects decreasing Fas function and is characterized by lymphadenopathy/splenomegaly and expansion of CD4/CD8 double-negative T cells. This latter expansion is absent in the ALPS variant named Dianzani Autoimmune/lymphoproliferative Disease (DALD). In addition to the causative mutations, the genetic background influences ALPS and DALD development. We previously suggested a disease-modifying role for the perforin gene involved in familial hemophagocytic lymphohistiocytosis (FHL). The UNC13D gene codes for Munc13-4, which is involved in perforin secretion and FHL development, and thus, another candidate for a disease-modifying role in ALPS and DALD. In this work, we sequenced UNC13D in 21 ALPS and 20 DALD patients and compared these results with sequences obtained from 61 healthy subjects and 38 multiple sclerosis (MS) patients. We detected four rare missense variations in three heterozygous ALPS patients carrying p.Cys112Ser, p.Val781Ile, and a haplotype comprising both p.Ile848Leu and p.Ala995Pro. Transfection of the mutant cDNAs into HMC-1 cells showed that they decreased granule exocytosis, compared to the wild-type construct. An additional rare missense variation, p.Pro271Ser, was detected in a healthy subject, but this variation did not decrease Munc13-4 function. These data suggest that rare loss-of-function variations of UND13D are risk factors for ALPS development.

Monogenic defects in lymphocyte apoptosis

PURPOSE OF REVIEW

The recognition that apoptosis - programmed cell death - is an important mechanism in immune homeostasis has led to the identification of human disorders associated with defects in the critical control mechanism.

RECENT FINDINGS

Patients have been identified with defects affecting the extrinsic apoptotic pathway mediated by the protein receptor FAS which results in the autoimmune lymphoproliferative syndrome and more recently in defects affecting the intrinsic apoptotic pathway mediated by RAS proteins resulting in the RAS-associated autoimmune leukoproliferative disorder. This review summarizes the immunopathogenesis, clinical features and diagnostic approaches to these human disorders.

SUMMARY

Apoptotic pathways are critical in the maintenance of leukocyte homeostasis, and genetic defects impacting these can result in clinical disease manifested as expansion of selected leukocyte populations, autoimmunity, increased risk for malignancy and in some situations defects in host defense.

Somatic loss of heterozygosity, but not haploinsufficiency alone, leads to full-blown autoimmune lymphoproliferative syndrome in 1 of 12 family members with FAS start codon mutation

We describe a family with 12 members carrying a heterozygous germline FAS c.3G>T start codon mutation leading to FAS haploinsufficiency. One patient had autoimmune lymphoproliferative syndrome (ALPS), one had recovered from ALPS, and ten mutation-positive relatives (MPRs) were healthy. FAS-mediated apoptosis and surface expression of FAS in single-positive T cells were lower for MPRs but did not discriminate between them and the ALPS patient. However, double-negative (DN) T cells of the ALPS patient had no FAS expression due to somatic loss of heterozygosity. Our results in this kindred suggest that FAS haploinsufficiency does not cause ALPS-FAS, but that modifying genetic events are crucial for its pathogenesis. FAS surface expression on DN T cells should be assessed routinely and FAS haploinsufficient patients should be followed as its potential for lymphomagenesis is not well defined and a second hit might occur later on.

A rapid ex vivo clinical diagnostic assay for fas receptor-induced T lymphocyte apoptosis

Deleterious mutations in genes involved in the Fas apoptosis pathway lead to Autoimmune Lymphoproliferative Syndrome (ALPS). Demonstration of an apoptosis defect is critical for the diagnosis and study of ALPS. The traditional in vitro apoptosis assay, however, requires a week of experimental procedures. Here, we show that defects in Fas-induced apoptosis in PBMCs can be evaluated directly ex vivo using multicolor flow cytometry to analyze the apoptosis of effector memory T cells, a Fas-sensitive subset of PBMCs. This method allowed us to sensitively quantify defective apoptosis in ALPS patients within a few hours. Some ALPS patients (ALPS-sFAS) without germline mutations have somatic mutations in Fas specifically in double-negative αβ T cells (DNTs), an unusual lymphocyte population that is characteristically expanded in ALPS. Since DNTs have been notoriously difficult to culture, defective apoptosis has not been previously demonstrated for ALPS-sFAS patients. Using our novel ex vivo apoptosis assay, we measured Fas-induced apoptosis of DNTs for the first time and found that ALPS-sFAS patients had significant apoptosis defects in these cells compared to healthy controls. Hence, this rapid apoptosis assay can expedite the diagnosis of new ALPS patients, including those with somatic mutations, and facilitate clinical and molecular investigation of these diseases.

Precise mapping of the CD95 pre-ligand assembly domain

Pre-association of CD95 at the plasma membrane is mandatory for efficient death receptor signaling. This homotrimerization occurs through self-association of an extracellular domain called the pre-ligand assembly domain (PLAD). Using novel molecular and cellular tools, we confirmed that CD95-PLAD is necessary to promote CD95 multimerization and plays a pivotal role in the transmission of apoptotic signals. However, while a human CD95 mutant deleted of the previously described PLAD domain (amino acids 1 to 66) fails to interact with its wild-type counterpart and trigger autonomous cell death, deletion of amino acids 1 to 42 does not prevent homo- or hetero (human/mouse)-oligomerization of CD95, and thus does not alter transmission of the apoptotic signal. Overall, these findings indicate that the region between amino acids 43 to 66 corresponds to the minimal motif involved in CD95 homotypic interaction and is necessary to convey an efficient apoptotic signal. Interfering with this PLAD may represent a new therapeutic strategy for altering CD95-induced apoptotic and non-apoptotic signals.

Autoimmune lymphoproliferative syndrome caused by a homozygous null FAS ligand (FASLG) mutation

BACKGROUND

Autoimmune lymphoproliferative syndrome (ALPS) is characterized by chronic nonmalignant lymphoproliferation, accumulation of double-negative T cells, hypergammaglobulinemia G and A, and autoimmune cytopenia.

OBJECTIVES

Although mostly associated with FAS mutations, different genetic defects leading to impaired apoptosis have been described in patients with ALPS, including the FAS ligand gene (FASLG) in rare cases. Here we report on the first case of complete FAS ligand deficiency caused by a homozygous null mutant.

METHODS

Double-negative T-cell counts and plasma IL-10 and FAS ligand concentrations were determined as ALPS markers. The FASLG gene was sequenced, and its expression was analyzed by means of Western blotting. FAS ligand function was assessed based on reactivation-induced cell death.

RESULTS

We describe a patient born to consanguineous parents who presented with a severe form of ALPS caused by FASLG deficiency. Although the clinical presentation was compatible with a homozygous FAS mutation, FAS-induced apoptosis was normal, and plasma FAS ligand levels were not detectable. This patient carries a homozygous, germline, single-base-pair deletion in FASLG exon 1, leading to a premature stop codon (F87fs x95) and a complete defect in FASLG expression. The healthy parents were each heterozygous for the mutation, confirming its recessive trait.

CONCLUSION

FAS ligand deficiency should be screened in patients presenting with ALPS features but lacking the usual markers, including plasma soluble FAS ligand and an in vitro apoptotic defect. An activation-induced cell death test could help in discrimination.

CD95-mediated cell signaling in cancer: mutations and post-translational modulations

Apoptosis has emerged as a fundamental process important in tissue homeostasis, immune response, and during development. CD95 (also known as Fas), a member of the tumor necrosis factor receptor (TNF-R) superfamily, has been initially cloned as a death receptor. Its cognate ligand, CD95L, is mainly found at the plasma membrane of activated T-lymphocytes and natural killer cells where it contributes to the elimination of transformed and infected cells. According to its implication in the immune homeostasis and immune surveillance, and since several malignant cells of various histological origins exhibit loss-of-function mutations, which cause resistance towards the CD95-mediated apoptotic signal, CD95 has been classified as a tumor suppressor gene. Nevertheless, this assumption has been recently challenged, as in certain pathophysiological contexts, CD95 engagement transmits non-apoptotic signals that promote inflammation, carcinogenesis or liver/peripheral nerve regeneration. The focus of this review is to discuss these apparent contradictions of the known function(s) of CD95.

The -346T polymorphism of the SH2D1A gene is a risk factor for development of autoimmunity/lymphoproliferation in males with defective Fas function

Inherited defects decreasing function of the Fas death receptor cause autoimmune lymphoproliferative syndrome (ALPS) and its variant Dianzani autoimmune lymphoproliferative disease (DALD). Since a deleterious mutation of the SH2D1A gene protects MRLlpr/lpr mice from ALPS development, we investigated the role of SH2D1A, located in the X chromosome, in 51 patients with ALPS or DALD by mutational screening of coding and regulative sequences. Allelic frequency of the -346C>T polymorphism was different in male patients and controls (-346T: 61% vs 36%, p = 0.01), with similar frequencies in ALPS and DALD. By contrast, no differences were found among females or between the controls and patients with multiple sclerosis (229 males, 157 females). Further analyses showed that -346C was a methylation site in CD8(+) T and natural killer cells, and SH2D1A expression was higher in -346T than in -346C males. Finally, in vitro-activated T cells from -346T males produced lower amounts of interferon-γ than those from -346C males. These data suggest that -346T is a predisposing factor for ALPS and DALD in males possibly because of its effect on SAP expression influencing the T-cell response.

New advances in the diagnosis and treatment of autoimmune lymphoproliferative syndrome

PURPOSE OF REVIEW

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of disrupted lymphocyte homeostasis, resulting from mutations in the Fas apoptotic pathway. Clinical manifestations include lymphadenopathy, splenomegaly, and autoimmune cytopenias. A number of new insights have improved the understanding of the genetics and biology of ALPS. These will be discussed in this review.

RECENT FINDINGS

A number of key observations have been made recently that better define the pathophysiology of ALPS, including the characterization of somatic FAS variant ALPS, the identification of haploinsufficiency as a mechanism of decreased Fas expression, and the description of multiple genetic hits in FAS in some families that may explain the variable penetrance of the disease. In addition, ALPS has been shown to be a more common condition, as patients diagnosed with other disorders, including Evans syndrome and common variable immune deficiency, have been found to have ALPS. Finally, the treatment of the disease has changed as splenectomy and rituximab have been shown to have unexpected ALPS-specific toxicities, and mycophenolate mofetil and sirolimus have been demonstrated to have marked activity against the disease.

SUMMARY

On the basis of novel advances, the diagnostic algorithm and recommended treatment for ALPS have changed significantly, improving quality of life for many patients.