Targeted high-throughput sequencing for genetic diagnostics of hemophagocytic lymphohistiocytosis

Genetics of Familial Hemophagocytic Lymphohistiocytosis (HLH)

Familial hemophagocytic lymphohistiocytosis (fHLH) represents a group of rare, inherited immune system disorders characterized by uncontrolled inflammatory responses. fHLH results from genetic mutations that impair CD8 T cell and natural killer cell cytotoxicity. Without treatment, fHLH is commonly fatal, but early diagnosis and treatment, including immunosuppressive therapy, and in many cases, an allogeneic hematopoietic stem cell transplant (HSCT), can improve overall outcomes. Genetic testing is critical for confirming the diagnosis, identifying specific gene mutations, assessing family members for carrier status or disease risk, and informing donor selection for HSCT.

Clinical Characteristics and Treatment of Familial Hemophagocytic Lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (fHLH) comprises a group of autosomal recessive disorders characterized by germline loss-of-function variants that negatively impact lymphocyte cytotoxicity. These disorders exhibit variable clinical presentations, most often in association with severe hyperinflammation. fHLH is diagnosed through clinical and laboratory assessments as well as genetic testing and immunologic assays. In the absence of therapy to control the hyperactive immune system, fHLH is generally fatal. Treatment has historically taken the form of cytotoxic chemotherapy and/or immunosuppressive therapy, although targeted inhibitors of inflammatory cytokines and their downstream signaling are increasingly being utilized. Definitive treatment requires allogeneic hematopoietic cell transplantation.

Clinical spectrum of primary hemophagocytic lymphohistiocytosis: experience of reference centers in Central and Southeast Anatolia

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening disease, with a high mortality if left untreated. In addition, the disease has unique diagnostic challenges. Therefore, despite the existing guidelines on management, current clinical practice data is informative on the course and outcome. Herein, a retrospective chart review study was conducted through the collaboration of six centers, located in central and southeastern Türkiye. The demographical data, laboratory results, and treatment outcomes were evaluated. Eighty-three patients were enrolled in the study. The mean age was 2 years, whereas the median age was 8 months with a range of a minimum of 1 week and a maximum of 12.6 years. Consanguineous marriage, history of sibling death, and familial history of similar disease were determined in 72.2% (n:60), 34.9% (n:29), and 39.8% (n:33) of the patients, respectively. The most common presentation was fever, followed by hepatosplenomegaly on admission. Disease-causing familial HLH variants were identified in 60.2% (n:50) of the patients. Hematopoietic stem cell transplantation (HSCT) was performed in 39.7% (n:33) of the cohort. The 2-year overall survival (OS) rate was 62.4% for the whole group. Comparing the patients who received HSCT and those who did not; the HSCT group had a 2-year OS of 84.7%, which was significantly better than patients who did not receive HSCT had a 2-year OS of 47.1% (p:0.001). Despite the improvement in HLH diagnostics and treatment options over the last decade, early death remains a leading problem for the survival of these patients. Therefore, appropriate assessment of the patients in experienced centers and HSCT are pivotal for better outcomes.

Spectrum of LYST mutations in Chediak-Higashi syndrome: a report of novel variants and a comprehensive review of the literature

INTRODUCTION

Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disorder characterised by partial oculocutaneous albinism, a bleeding diathesis, immunological dysfunction and neurological impairment. Bi-allelic loss-of-function variants in LYST cause CHS. LYST encodes the lysosomal trafficking regulator, a highly conserved 429 kDa cytoplasmic protein with an unknown function.

METHODS

To further our understanding of the pathogenesis of CHS, we conducted clinical evaluations on individuals with CHS enrolled in our natural history study. Using genomic DNA Sanger sequencing, we identified novel pathogenic LYST variants. Additionally, we performed an extensive literature review to curate reported LYST variants and classified these novel and reported variants according to the American College of Medical Genetics/Association for Molecular Pathology variant interpretation guidelines.

RESULTS

Our investigation unveiled 11 novel pathogenic LYST variants in eight patients with a clinical diagnosis of CHS, substantiated by the presence of pathognomonic giant intracellular granules. From these novel variants, together with a comprehensive review of the literature, we compiled a total of 147 variants in LYST, including 61 frameshift variants (41%), 44 nonsense variants (30%), 23 missense variants (16%), 13 splice site variants or small genomic deletions for which the coding effect is unknown (9%), 5 in-frame variants (3%) and 1 start-loss variant (1%). Notably, a genotype-phenotype correlation emerged, whereby individuals harbouring at least one missense or in-frame variant generally resulted in milder disease, while those with two nonsense or frameshift variants generally had more severe disease.

CONCLUSION

The identification of novel pathogenic LYST variants and improvements in variant classification will provide earlier diagnoses and improved care to individuals with CHS.

Detection of a novel gross deletion in the UNC13D gene ends the diagnostic odyssey for a family with familial hemophagocytic lymphohistiocytosis 3

BACKGROUND

Familial hemophagocytic lymphohistiocytosis (FHL) is an immunological disorder characterized by overactivation of macrophages and T lymphocytes. This autosomal recessive condition has been characterized into multiple types depending on the genetic etiology. FHL type 3 is associated with bi-allelic pathogenic variants in the UNC13D gene.

CASE PRESENTATION

We present a 12-year diagnostic odyssey for a family with FHL that signifies the advances of FHL genetic testing in a clinical genetic diagnostic laboratory setting. We describe the first case of a large UNC13D gross deletion in trans to a nonsense variant in a family with FHL3, which may have been mediated by Alu elements within introns 12 and 25 of the UNC13D gene.

CONCLUSIONS

This case highlights the importance of re-evaluating past genetic testing for a patient and family as test technology evolves in order to end a diagnostic odyssey.

CD8+ T Cell Biology in Cytokine Storm Syndromes

Familial forms of hemophagocytic lymphohistiocytosis (HLH) are caused by loss-of-function mutations in genes encoding perforin as well as those required for release of perforin-containing cytotoxic granule constituent. Perforin is expressed by subsets of CD8+ T cells and NK cells, representing lymphocytes that share mechanism of target cell killing yet display distinct modes of target cell recognition. Here, we highlight recent findings concerning the genetics of familial HLH that implicate CD8+ T cells in the pathogenesis of HLH and discuss mechanistic insights from animal models as well as patients that reveal how CD8+ T cells may contribute to or drive disease, at least in part through release of IFN-γ. Intriguingly, CD8+ T cells and NK cells may act differentially in severe hyperinflammatory diseases such as HLH. We also discuss how CD8+ T cells may promote or drive pathology in other cytokine release syndromes (CSS). Moreover, we review the molecular mechanisms underpinning CD8+ T cell-mediated lymphocyte cytotoxicity, key to the development of familial HLH. Together, recent insights to the pathophysiology of CSS in general and HLH in particular are providing promising new therapeutic targets.

Safety and efficacy of canakinumab treatment for undifferentiated autoinflammatory diseases: the data of a retrospective cohort two-centered study

Introduction

The blockade of interleukine-1 (anakinra and canakinumab) is a well-known highly effective tool for monogenic autoinflammatory diseases (AIDs), such as familial Mediterranean fever, tumor necrosis factor receptor-associated periodic syndrome, hyperimmunoglobulinaemia D syndrome, and cryopyrin-associated periodic syndrome, but this treatment has not been assessed for patients with undifferentiated AIDs (uAIDs). Our study aimed to assess the safety and efficacy of canakinumab for patients with uAIDs.

Methods

Information on 32 patients with uAIDs was retrospectively collected and analyzed. Next-generation sequencing and Federici criteria were used for the exclusion of the known monogenic AID.

Results

The median age of the first episode was 2.5 years (IQR: 1.3; 5.5), that of the disease diagnosis was 5.7 years (IQR: 2.5;12.7), and that of diagnostic delay was 1.1 years (IQR: 0.4; 6.1). Patients had variations in the following genes: IL10, NLRP12, STAT2, C8B, LPIN2, NLRC4, PSMB8, PRF1, CARD14, IFIH1, LYST, NFAT5, PLCG2, COPA, IL23R, STXBP2, IL36RN, JAK1, DDX58, LACC1, LRBA, TNFRSF11A, PTHR1, STAT4, TNFRSF1B, TNFAIP3, TREX1, and SLC7A7. The main clinical features were fever (100%), rash (91%; maculopapular predominantly), joint involvement (72%), splenomegaly (66%), hepatomegaly (59%), lymphadenopathy (50%), myalgia (28%), heart involvement (31%), intestinal involvement (19%); eye involvement (9%), pleuritis (16%), ascites (6%), deafness, hydrocephalia (3%), and failure to thrive (25%). Initial treatment before canakinumab consisted of non-biologic therapies: non-steroidal anti-inflammatory drugs (NSAID) (91%), corticosteroids (88%), methotrexate (38%), intravenous immunoglobulin (IVIG) (34%), cyclosporine A (25%), colchicine (6%) cyclophosphamide (6%), sulfasalazine (3%), mycophenolate mofetil (3%), hydroxychloroquine (3%), and biologic drugs: tocilizumab (62%), sarilumab, etanercept, adalimumab, rituximab, and infliximab (all 3%). Canakinumab induced complete remission in 27 patients (84%) and partial remission in one patient (3%). Two patients (6%) were primary non-responders, and two patients (6%) further developed secondary inefficacy. All patients with partial efficacy or inefficacy were switched to tocilizumab (n = 4) and sarilumab (n = 1). The total duration of canakinumab treatment was 3.6 (0.1; 8.7) years. During the study, there were no reported Serious Adverse Events (SAEs). The patients experienced non-frequent mild respiratory infections at a rate that is similar as before canakinumab is administered. Additionally, one patient developed leucopenia, but it was not necessary to stop canakinumab for this patient.

Conclusion

The treatment of patients with uAIDs using canakinumab was safe and effective. Further randomized clinical trials are required to confirm the efficacy and safety.

Approaching hemophagocytic lymphohistiocytosis

Hemophagocytic Lymphohistiocytosis (HLH) is a rare clinical condition characterized by sustained but ineffective immune system activation, leading to severe and systemic hyperinflammation. It may occur as a genetic or sporadic condition, often triggered by an infection. The multifaceted pathogenesis results in a wide range of non-specific signs and symptoms, hampering early recognition. Despite a great improvement in terms of survival in the last decades, a considerable proportion of patients with HLH still die from progressive disease. Thus, prompt diagnosis and treatment are crucial for survival. Faced with the complexity and the heterogeneity of syndrome, expert consultation is recommended to correctly interpret clinical, functional and genetic findings and address therapeutic decisions. Cytofluorimetric and genetic analysis should be performed in reference laboratories. Genetic analysis is mandatory to confirm familial hemophagocytic lymphohistiocytosis (FHL) and Next Generation Sequencing is increasingly adopted to extend the spectrum of genetic predisposition to HLH, though its results should be critically discussed with specialists. In this review, we critically revise the reported laboratory tools for the diagnosis of HLH, in order to outline a comprehensive and widely available workup that allows to reduce the time between the clinical suspicion of HLH and its final diagnosis.

Treatment Strategies for Central Nervous System Effects in Primary and Secondary Haemophagocytic Lymphohistiocytosis in Children

Purpose of Review

This review presents an appraisal of current therapeutic options for the treatment of central nervous system haemophagocytic lymphohistiocytosis (CNS-HLH) in the context of systemic disease, as well as when CNS features occur in isolation. We present the reader with a diagnostic approach to CNS-HLH and commonly used treatment protocols. We discuss and evaluate newer treatments on the horizon.

Recent Findings

Mortality is high in patients who do not undergo HSCT, and while larger studies are required to establish benefit in many treatments, a number of new treatments are currently being evaluated. Alemtuzumab is being used as a first-line treatment for CNS-HLH in a phase I/II multicentre prospective clinical trial as an alternative to traditional HLH-1994 and 2004 protocols. It has also been used successfully as a second-line agent for the treatment of isolated CNS-HLH that is refractory to standard treatment. Ruxolitinib and emapalumab are new immunotherapies that block the Janus kinase—Signal Transducer and Activator of Transcription (JAK-STAT) pathway that have shown efficacy in refractory HLH, including for CNS-HLH disease.

Summary

Treatment of CNS-HLH often requires HLH-94 or 2004 protocols followed by haematopoietic stem cell transplantation (HSCT) to maintain remission, although relapse can occur, particularly with reduced intensity conditioning if donor chimerism falls. CNS features have been shown to improve or stabilise following HSCT in CNS-HLH in the context of systemic disease and in isolated CNS-HLH. Encouraging reports of early cohort studies suggest alemtuzumab and the Janus kinase (JAK) inhibitor ruxolitinib offer potential salvage therapy for relapsed and refractory CNS-HLH. Newer immunotherapies such as tocilizumab and natalizumab have been shown to be beneficial in sporadic cases. CNS-HLH due to primary gene defects may be amenable to gene therapy in the future.

Identification of germline variants in adults with hemophagocytic lymphohistiocytosis

Some germline variants are predicted to disrupt protein function in HLH-associated genes. Such variants are neither enriched in adult-onset HLH nor associated with specific clinical or laboratory features of HLH.

The Spectrum of Clinical, Immunological, and Molecular Findings in Familial Hemophagocytic Lymphohistiocytosis: Experience From India

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of immune dysregulation characterized by hyperactivation of the immune system, excessive cytokine secretion and severe systemic inflammation. HLH is classified as familial (FHL) when associated with mutations in PRF1, UNC13D, STX11, and STXBP2 genes. There is limited information available about the clinical and mutational spectrum of FHL patients in Indian population. This study is a retrospective analysis of 101 molecularly characterized FHL patients over the last 10 years from 20 different referral centers in India. FHL2 and FHL3 together accounted for 84% of cases of FHL in our cohort. Patients belonging to different FHL subtypes were indistinguishable based on clinical and biochemical parameters. However, flow cytometry-based assays viz. perforin expression and degranulation assay were found to be specific and sensitive in diagnosis and classification of FHL patients. Molecular characterization of respective genes revealed 76 different disease-causing mutations including 39 (51%) novel mutations in PRF1, UNC13D, STX11, and STXBP2 genes. Overall, survival was poor (28%) irrespective of the age of onset or the type of mutation in our cohort. Altogether, this article sheds light on the current scenario of FHL in India. Our data reveal a wide genetic heterogeneity of FHL in the Indian population and confirms the poor prognosis of FHL. This study also emphasizes that though mutational analysis is important for diagnostic confirmation of FHL, flow cytometry based assays help significantly in rapid diagnosis and functional validation of novel variants identified.

Outcomes and prognostic factors associated with 180-day mortality in Taiwanese pediatric patients with Hemophagocytic Lymphohistiocytosis

BACKGROUND/PURPOSE

Hemophagocytic lymphohistiocytosis (HLH), a rarely occurring syndrome with various triggers, is associated with early mortality. Owing to a lack of sufficient corresponding data in Taiwan, this study aimed to identify the outcome and potential factors associated with 180-day mortality in pediatric HLH.

METHODS

This retrospective study analyzed clinical and laboratory data on pediatric patients diagnosed with HLH at our institute (1995-2019). Logistic regression analysis was conducted to determine the associations between various factors and 180-day mortality.

RESULTS

Overall, 48 patients had HLH; their median age at diagnosis was 5 years (interquartile range: 2-11 years). Clinical presentations and laboratory parameters required for diagnosis included fever (98%), splenomegaly (79%), hyperferritinemia (98%), hemophagocytosis (94%), thrombocytopenia (90%), anemia (63%), hypertriglyceridemia (68%), and neutropenia (57%). The 5-year overall survival (OS) rate was 49%. Of 22 patients who had died at the last follow-up, 15 (68%) died within 180 days after diagnosis. In the multivariate analysis, hemoglobin (odds ratio [OR]: 0.564, p = 0.024) and triglyceride (OR: 1.004, p = 0.049) were significantly associated with 180-day mortality. Higher triglyceride levels at diagnosis were related to significantly lower 180-day OS rates (52.9% vs. 86.1%, p = 0.018).

CONCLUSION

The overall outcome in our cohort was similar to that reported in some of the largest international cohorts. Hypertriglyceridemia and anemia may be indicative of poor prognoses in pediatric HLH patients independently and may be used to guide treatment strategy formulations for better outcomes.

Different Clinical Presentation of 3 Children With Familial Hemophagocytic Lymphohistiocytosis With 2 Novel Mutations

Although familial hemophagocytic lymphohistiocytosis (FHL) generally manifest with a combination of unremitting fever, hepatosplenomegaly, and pancytopenia; unusual presentations should also be taken into account. Herein, we present 3 FHL cases with 2 novel mutations with different initial presentations. The first patient bearing a homozygous truncation mutation in UNC13D (c.2650C>T.p.Gln884Ter) presented with central nervous system involvement and skin rash. The patient responded to the HLH-2004 protocol, and allogenic hematopoietic stem cell transplantation was performed from her healthy sister. The second and third patients with homozygous splice site mutation (c.430-1G>A) in STXBP2 were siblings who presented at birth with fevers, elevated aspartate aminotransferase, alanine aminotransferase, and hyperferritinemia but did not fulfill FHL criteria. The last 2 infants died despite intervention. Hematologists should be vigilant about the different presentation of FHL in children.

Human Adenovirus 7-Associated Hemophagocytic Lymphohistiocytosis-Like Illness: Clinical and Virological Characteristics in a Cluster of Five Pediatric Cases

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening condition of immune dysregulation. Children often suffer from primary genetic forms of HLH, which can be triggered by infection. Others suffer from secondary HLH as a complication of infection, malignancy, or rheumatologic disease. Identifying the exact cause of HLH is crucial, as definitive treatment for primary disease is hematopoietic stem cell transplant. Adenoviruses have been associated with HLH but molecular epidemiology data are lacking.

METHODS

We describe the clinical and virologic characteristics of 5 children admitted with adenovirus infection during 2018-2019 who developed HLH or HLH-like illness. Detailed virologic studies, including virus isolation and comprehensive molecular typing were performed.

RESULTS

All patients recovered; clinical management varied but included immunomodulating and antiviral therapies. A genetic predisposition for HLH was not identified in any patient. Adenovirus isolates were recovered from 4/5 cases; all were identified as genomic variant 7d. Adenovirus type 7 DNA was detected in the fifth case. Phylogenetic analysis of genome sequences identified two clusters - one related to strains implicated in 2016-2017 outbreaks in Pennsylvania and New Jersey, the other related to a 2009 Chinese strain.

CONCLUSIONS

It can be challenging to determine whether HLH is the result of an infectious pathogen alone or genetic predisposition triggered by an infection. We describe 5 children from the same center presenting with an HLH-like illness after onset of adenovirus type 7 infection. None of the patients were found to have a genetic predisposition to HLH. These findings suggest that adenovirus 7 infection alone can result in HLH.

[A genetic analysis of children with Epstein-Barr virus-positive hemophagocytic lymphohistiocytosis and its association with T-helper type 1/T-helper type 2 cytokines]

OBJECTIVE

To study the effect of genetic variation on the prognosis of children with Epstein-Barr virus (EBV)-positive hemophagocytic lymphohistiocytosis (HLH) and its association with cytokines.

METHODS

A total of 81 EBV-positive HLH children who received the sequencing of related genes were enrolled. According to the results of gene detection, they were divided into a non-mutation group and a mutation group. According to the pattern of gene mutation, the mutation group was further divided into three subgroups: single heterozygous mutation (SHM), double heterozygous mutation (DHM), and homozygous or compound heterozygous mutation (H-CHM). The serum levels of cytokines were measured and their association with HLH gene mutations was analyzed.

RESULTS

UNC13D gene mutation had the highest frequency (13/46, 28%). The STXBP2 c.575G>A(p.R192H) and UNC13D c.604C>A(p.L202M) mutations (likely pathogenic) were reported for the first time. The mutation group had a significantly higher level of tumor necrosis factor alpha (TNF-α) than the non-mutation group, while it had a significantly lower level of interferon gamma (IFN-γ) than the non-mutation group (P<0.05). The IL-4 level of the DHM subgroup was higher than that of the non-mutation group, while the IL-4 level of the H-CHM subgroup was lower than that of the DHM group (P<0.0083). The H-CHM subgroup had a significantly lower 1-year overall survival rate than the non-mutation group, the SHM subgroup, and the DHM subgroup (39%±15% vs 85%±6%/86%±7%/91%±9%, P=0.001).

CONCLUSIONS

There is a significant reduction in IFN-γ level in the mutation group. Children with homozygous or compound heterozygous mutation tend to have poorer prognosis, while other mutations do not have a significant impact on prognosis.

A Rare Case of Activated Phosphoinositide 3-Kinase Delta Syndrome (APDS) Presenting With Hemophagocytosis Complicated With Hodgkin Lymphoma

Gain of function mutations in the p110δ catalytic subunit of the phosphatidylinositol-3-OH kinase (PIK3CD) classified as activated phosphoinositide 3-kinase delta syndrome (APDS) are the cause of a primary immunodeficiency characterized by recurrent sinopulmonary infections, and lymphoproliferation. Previously, autoimmunity and Epstein-Barr virus-related B-cell lymphoma have been documented for patients with APDS; here, we present a case that extends the picture, as the patient shows the full diagnostic criteria of hemophagocytic lymphohistiocytosis at 6 months of age. He experienced Hodgkin lymphoma as a 2.5-year-old baby. Next-generation sequencing returned a de novo heterozygous missense variant in PIK3CD (LRG_191t1: c.3061G>A; p.Glu1021Lys), confirming the primary immunodeficiency. After 2 courses of ifosfamide, cisplatin, and etoposide combined with brentuximab, the patient successfully underwent allogeneic hematopoietic stem cell transplantation from his HLA full matched sister, and he has been well for 18 months after that. The hematologist treating Hodgkin lymphoma and/or hemophagocytic lymphohistiocytosis should be vigilant about the possible underlying immune deficiency, and they should consider APDS in their differential diagnosis.

FHLdb: A Comprehensive Database on the Molecular Basis of Familial Hemophagocytic Lymphohistiocytosis

Background: Primary immunodeficiencies (PIDs) are a heterogeneous group of disorders. The lack of comprehensive disease-specific mutation databases may hinder or delay classification of the genetic variants found in samples from these patients. This is especially true for familial hemophagocytic lymphohistiocytosis (FHL), a life-threatening PID classically considered an autosomal recessive condition, but with increasingly demonstrated genetic heterogeneity.

Objective: The aim of this study was to build an open-access repository to collect detailed information on the known genetic variants reported in FHL.

Methods: We manually reviewed more than 120 articles to identify all reported variants related to FHL. We retrieved relevant information about the allelic status, the number of patients with the same variant, and whether functional assays were done. We stored all the data retrieved in a PostgreSQL database and then built a website on top of it, using the Django framework.

Results: The database designed (FHLdb) (https://www.biotoclin.org/FHLdb) contains comprehensive information on reported variants in the 4 genes related to FHL (PRF1, UNC13D, STXBP2, STX11). It comprises 240 missense, 69 frameshift, 51 nonsense, 51 splicing, 10 in-frame indel, 7 deep intronic, and 5 large rearrangement variants together with their allelic status, carrier(s) information, and functional evidence. All genetic variants have been classified as pathogenic, likely pathogenic, uncertain significance, likely benign or benign, according to the American College of Medical Genetics guidelines. Additionally, it integrates information from other relevant databases: clinical evidence from ClinVar and UniProt, population allele frequency from ExAC and gnomAD, and pathogenicity predictions from well-recognized tools (e.g., PolyPhen-2, SIFT). Finally, a diagram depicts the location of the variant relative to the gene exon and protein domain structures.

Conclusion: FHLdb includes a broad range of data on the reported genetic variants in familial HLH genes. It is a free-access and easy-to-use resource that will facilitate the interpretation of molecular results of FHL patients, and it illustrates the potential value of disease-specific databases for other PIDs.

Hermansky-Pudlak syndrome: Mutation update

Hermansky-Pudlak syndrome (HPS) is a group of 10 autosomal recessive multisystem disorders, each defined by the deficiency of a specific gene. HPS-associated genes encode components of four ubiquitously expressed protein complexes: Adaptor protein-3 (AP-3) and biogenesis of lysosome-related organelles complex-1 (BLOC-1) through -3. All individuals with HPS exhibit albinism and a bleeding diathesis; additional features occur depending on the defective protein complex. Pulmonary fibrosis is associated with AP-3 and BLOC-3 deficiency, immunodeficiency with AP-3 defects, and gastrointestinal symptoms are more prevalent and severe in BLOC-3 deficiency. Therefore, identification of the HPS subtype is valuable for prognosis, clinical management, and treatment options. The prevalence of HPS is estimated at 1-9 per 1,000,000. Here we summarize 264 reported and novel variants in 10 HPS genes and estimate that ~333 Puerto Rican HPS subjects and ~385 with other ethnicities are reported to date. We provide pathogenicity predictions for missense and splice site variants and list variants with high minor allele frequencies. Current cellular and clinical aspects of HPS are also summarized. This review can serve as a manifest for molecular diagnostics and genetic counseling aspects of HPS.

Natural Killer Cells in Systemic Autoinflammatory Diseases: A Focus on Systemic Juvenile Idiopathic Arthritis and Macrophage Activation Syndrome

Natural killer (NK) cells are innate immune lymphocytes with potent cytolytic and immune-regulatory activities. NK cells are well-known for their ability to kill infected and malignant cells in a fast and non-specific way without prior sensitization. For this purpose, NK cells are equipped with a set of cytotoxic molecules such as perforin and apoptosis-inducing proteins. NK cells also have the capacity to produce large amounts of cytokines and chemokines that synergize with their cytotoxic function and that ensure interaction with other immune cells. A less known feature of NK cells is their capacity to kill non-infected autologous cells, such as immature dendritic cells and activated T cells and monocytes. Via the release of large amounts of TNF-α and IFN-γ, NK cells may contribute to disease pathology. Conversely they may exert a regulatory role through secretion of immuno-regulatory cytokines such as GM-CSF, IL-13, and IL-10. Thus, NK cells may be important target and effector cells in the pathogenesis of autoinflammatory diseases, in particular in those disorders associated with a cytokine storm or in conditions where immune cells are highly activated. Key examples of such diseases are systemic juvenile idiopathic arthritis (sJIA) and its well-associated complication, macrophage activation syndrome (MAS). sJIA is a chronic childhood immune disorder of unknown etiology, characterized by arthritis and systemic inflammation, including a daily spiking fever and evanescent rash. MAS is a potentially fatal complication of autoimmune and autoinflammatory diseases, and most prevalently associated with sJIA. MAS is considered as a subtype of hemophagocytic lymphohistiocytosis (HLH), a systemic hyperinflammatory disorder characterized by defective cytotoxic pathways of cytotoxic T and NK cells. In this review, we describe the established features of NK cells and provide the results of a literature survey on the reported NK cell abnormalities in monogenic and multifactorial autoinflammatory disorders. Finally, we discuss the role of NK cells in the pathogenesis of sJIA and MAS.

Hemophagocytic Lymphohistiocytosis and Other Culture Negative Sepsis-Like Syndromes in the ICU

There are many sepsis-like inflammatory syndromes that may be encountered by critical care practitioners. Clinically, these syndromes may imitate sepsis and are often identified after an extensive, but unrevealing evaluation for infection. In some instances, these syndromes are anticipated complications of advanced therapies for malignancy. It is vitally important to identify these disorders and treat them with specific chemotherapeutic or immunomodulating therapies. This chapter will focus on hemophagocytic lympho-histiocytosis (HLH), a rare disorder of pathologic immune system activation that presents as a sepsis-like illness in the critically ill. While treatment of HLH with chemotherapy and immunosuppression should be guided by an expert hematologist, the diagnosis is often made by the critical care medicine practitioner. We present a case illustrating the challenges of defining this syndrome in a patient with recurrent critical illness, and review the evidence underlying diagnostic and prognostic criteria for this protean syndrome. We also review several of the more common sepsis-like inflammatory syndromes that are encountered in the critical care unit along with their specific treatments.

Application of blood and immunodeficiency gene detection in the diagnosis of hemophagocytic lymphohistiocytosis patients

To investigate the value of genetic mutations in the pathogenesis and differential diagnosis of hemophagocytic lymphohistiocytosis (HLH), mutations related to blood and immune deficiency genes were analyzed in patients with HLH. Peripheral blood samples from 33 children diagnosed with HLH on the basis of the 2004 diagnostic criteria were collected, and 317 genes related to blood system diseases and 562 genes related to immunodeficiency were detected by second-generation targeted sequencing technology, bioinformatic analysis, and parental verification analysis. A total of 159 mutations related to blood system diseases and immunodeficiency were found in 33 patients, including 7 HLH-related gene mutations (UNC13D, XIAP, LYST, STX11, ITK, PRF1, and SRGN) in 12 patients. UNC13D was found in 6 patients, with the highest frequency. Two cases (6.1%, 2/33) were diagnosed as primary hemophagocytic lymphohistiocytosis (pHLH), and 6 cases (18.2%, 6/33) were diagnosed as primary immunodeficiency disease (PID) or hereditary hematopathy; the remainder were diagnosed as secondary hemophagocytic lymphohistiocytosis (sHLH). It is necessary to detect blood and immunodeficiency genes to exclude the possibility of pHLH, PID, or hereditary hematopathy associated with HLH for children.

Current Flow Cytometric Assays for the Screening and Diagnosis of Primary HLH

Advances in flow cytometry have led to greatly improved primary immunodeficiency (PID) diagnostics. This is due to the fact that patient blood cells in suspension do not require further processing for analysis by flow cytometry, and many PIDs lead to alterations in leukocyte numbers, phenotype, and function. A large portion of current PID assays can be classified as “phenotyping” assays, where absolute numbers, frequencies, and markers are investigated using specific antibodies. Inherent drawbacks of antibody technology are the main limitation to this type of testing. On the other hand, “functional” assays measure cellular responses to certain stimuli. While these latter assays are powerful tools that can be used to detect defects in entire pathways and distinguish variants of significance, it requires samples with robust viability and also skilled processing. In this review, we concentrate on hemophagocytic lymphohistiocytosis (HLH), describing the principles and accuracies of flow cytometric assays that have been proven to assist in the screening diagnosis of primary HLH.

Genetic and mechanistic diversity in pediatric hemophagocytic lymphohistiocytosis

The HLH-2004 criteria are used to diagnose hemophagocytic lymphohistiocytosis (HLH), yet concern exists for their misapplication, resulting in suboptimal treatment of some patients. We sought to define the genomic spectrum and associated outcomes of a diverse cohort of children who met the HLH-2004 criteria. Genetic testing was performed clinically or through research-based whole-exome sequencing. Clinical metrics were analyzed with respect to genomic results. Of 122 subjects enrolled over the course of 17 years, 101 subjects received genetic testing. Biallelic familial HLH (fHLH) gene defects were identified in only 19 (19%) and correlated with presentation at younger than 1 year of age (P < .0001). Digenic fHLH variants were observed but lacked statistical support for disease association. In 28 (58%) of 48 subjects, research whole-exome sequencing analyses successfully identified likely molecular explanations, including underlying primary immunodeficiency diseases, dysregulated immune activation and proliferation disorders, and potentially novel genetic conditions. Two-thirds of patients identified by the HLH-2004 criteria had underlying etiologies for HLH, including genetic defects, autoimmunity, and malignancy. Overall survival was 45%, and increased mortality correlated with HLH triggered by infection or malignancy (P < .05). Differences in survival did not correlate with genetic profile or extent of therapy. HLH should be conceptualized as a phenotype of critical illness characterized by toxic activation of immune cells from different underlying mechanisms. In most patients with HLH, targeted sequencing of fHLH genes remains insufficient for identifying pathogenic mechanisms. Whole-exome sequencing, however, may identify specific therapeutic opportunities and affect hematopoietic stem cell transplantation options for these patients.

Identification of a novel nonsense mutation in the UNC13D gene from a patient with hemophagocytic lymphohistiocytosis: a case report

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a heterogeneous and potentially fatal disease that presents symptoms of persistent fever, splenomegaly and cytopenia. Primary HLH is identified as an autosomal recessive disorder with causative genes including HPLH1, PRF1, UNC13D, STX11 and STXBP2.

CASE PRESENTATION

Here, we reported an 8-month-old female patient with compound heterozygosity in the UNC13D gene. The patient, who presented typical symptoms, was diagnosed with HLH based on HLH-2004 guidelines. High-throughput amplicon sequencing for the full-length exon, including a 5 bp padding region and 6 HLH-related genes, was performed to identify the pathogenic mutations in this patient. In all, 9 heterozygous variations were detected, namely, 7 nonpathogenic SNPs, one nonsense mutation (NM_199242.2:c.2206C > T, p.Gln736X), and one splicing mutation (NM_199242.2:c.2709 + 1G > A). These two mutations were considered pathogenic according to previous studies and functional prediction. A two-generation pedigree analysis based on Sanger sequencing was performed to confirm the result.

CONCLUSION

Compound heterozygosity in the UNC13D gene was identified in trans and considered a causative mutation in a female patient with HLH. The nonsense mutation (NM_199242.2:c.2206C > T, p.Gln736X) was novel in cases of HLH. Our data expand the spectrum of HLH-related mutations in China and demonstrate the potential of high-throughput amplicon sequencing in the diagnosis of HLH.

A Newborn With Familial Hemophagocytic Lymphohistiocytosis Complicated With Transfusion Associated Graft Versus Host Disease

Hemophagocytic lymphohistiocytosis (HLH) is characterized by activation of cytotoxic T and natural killer (NK) cells, and macrophages related to a spectrum of hyperinflammatory disorders. The clinical findings mainly include high fever, cytopenia, splenomegaly, phagocytosis, and proliferation of histiocytes in lymphoreticular tissue. To the best of our knowledge, transfusion-associated graft versus host disease (TA-GVHD) in a 13-day old male newborn with HLH is being reported first time in the literature. The aim of this report was to emphasize the importance of blood products irradiation in the prevention of the development of graft versus host disease especially among high-risk subjects such as newborns with HLH.

Proliferation through activation: hemophagocytic lymphohistiocytosis in hematologic malignancy

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of cytokine-driven immune activation. Cardinal features include fever, hemophagocytosis, hepatosplenomegaly, lymphocytic infiltration, and hypercytokinemia that result in multisystem organ dysfunction and failure. Familial HLH is genetically driven, whereas secondary HLH (SHL) is caused by drugs, autoimmune disease, infection, or cancer. SHL is associated with worse outcomes, with a median overall survival typically of less than 1 year. This reflects difficulty in both diagnostic accuracy and in establishing reliable treatments, especially in cases of malignancy-induced SHL, which have significantly worse outcomes. Malignancy-induced HLH is seen almost exclusively with hematologic malignancies, constituting 97% of cases in the literature over the past 2 years. In these situations, the native immune response driven by CD8 T cells produces an overabundance of T helper 1 cytokines, notably interferon-γ, tumor necrosis factor-α, and interleukin-6, which establish a positive feedback loop of inflammation, enhancing replication of hematologic malignancies while leaving the host immune system in disarray. In this paper, we present 2 case studies of secondary HLH driven by HM, followed by a review of the literature discussing the cytokines driving HLH, diagnostic criteria, and current treatments used or undergoing investigation.

Differences in Granule Morphology yet Equally Impaired Exocytosis among Cytotoxic T Cells and NK Cells from Chediak-Higashi Syndrome Patients

Chediak–Higashi syndrome (CHS) is caused by autosomal recessive mutations in LYST, resulting in enlarged lysosomal compartments in multiple cell types. CHS patients display oculocutaneous albinism and may develop life-threatening hemophagocytic lymphohistiocytosis (HLH). While NK cell-mediated cytotoxicity has been reported to be uniformly defective, variable defects in T cell-mediated cytotoxicity has been observed. The latter has been linked to the degree of HLH susceptibility. Since the discrepancies in NK cell- and T cell-mediated cellular cytotoxicity might result from differences in regulation of cytotoxic granule release, we here evaluated perforin-containing secretory lysosome size and number in freshly isolated lymphocytes from CHS patients and furthermore compared their exocytic capacities. Whereas NK cells from CHS patients generally contained a single, gigantic perforin-containing granule, cytotoxic T cells predominantly contained several smaller granules. Nonetheless, in a cohort of 21 CHS patients, cytotoxic T cell and NK cell granule exocytosis were similarly impaired upon activating receptor stimulation. Mechanistically, polarization of cytotoxic granules was defective in cytotoxic lymphocytes from CHS patients, with EEA1, a marker of early endosomes, mislocalizing to lysosomal structures. The results leads to the conclusion that lysosome enlargement corresponds to loss of distinct organelle identity in the endocytic pathway, which on a subcellular level more adversely affects NK cells than T cells. Hence, vesicular size or numbers do not per se dictate the impairment of lysosomal exocytosis in the two cell types studied.

Usual and Unusual Manifestations of Familial Hemophagocytic Lymphohistiocytosis and Langerhans Cell Histiocytosis

Familial hemophagocytic lymphohistiocytosis (FHL) and Langerhans cell histiocytosis (LCH) are histiocytic diseases that occur most commonly in young children. Improvements in recognition and treatment have been substantial for both diseases in the past decade, although early and late morbidity continue to be major concerns. These two diagnoses behave differently, although the clinical spectra for both diseases are diverse and can lead to confusion and delays in diagnosis and treatment. This article focuses on the clinical and genetic spectrum of FHL as well as the clinical and treatment variations of LCH.

Primary and secondary hemophagocytic lymphohistiocytosis have different patterns of T-cell activation, differentiation and repertoire

Hemophagocytic lymphohistiocytosis (HLH) is a life‐threatening inflammatory syndrome characterized by hyperactivation of lymphocytes and histiocytes. T cells play a key role in HLH pathogenesis, but their differentiation pattern is not well characterized in patients with active HLH. We compared T‐cell activation patterns between patients with familial HLH (1°HLH), 2°HLH without apparent infectious trigger (2°HLH) and 2°HLH induced by a viral infection (2°V‐HLH). Polyclonal CD8⁺ T cells are highly activated in 1°HLH and 2°V‐HLH, but less in 2°HLH as assessed by HLA‐DR expression and marker combination with CD45RA, CCR7, CD127, PD‐1 and CD57. Absence of increased HLA‐DR expression on T cells excluded active 1° HLH with high sensitivity and specificity. A high proportion of polyclonal CD127⁻CD4⁺ T cells expressing HLA‐DR, CD57, and perforin is a signature of infants with 1°HLH, much less prominent in virus‐associated 2°HLH. The similar pattern and extent of CD8⁺ T‐cell activation compared to 2° V‐HLH is compatible with a viral trigger of 1°HLH. However, in most 1°HLH patients no triggering infection was documented and the unique activation of cytotoxic CD4⁺ T cells indicates that the overall T‐cell response in 1°HLH is different. This may reflect different pathways of pathogenesis of these two HLH variants.

Advances in the pathogenesis of primary and secondary haemophagocytic lymphohistiocytosis: differences and similarities

Haemophagocytic lymphohistiocytosis (HLH) comprises a heterogeneous spectrum of hyperinflammatory conditions that are inherited (primary HLH) or acquired in a context of infections, malignancies or autoimmune/autoinflammatory disorders (secondary HLH). Genetic defects in the cytotoxic machinery of natural killer and CD8(+) T cells underlie primary HLH, with residual cytotoxicity determining disease severity. Improved sequencing techniques have expanded the range of causal mutations and have redefined many cases of secondary HLH as primary HLH and vice versa, blurring the distinction between both subtypes. These insights allow HLH to be conceptualized as a threshold disease, in which interplay between various genetic and environmental factors causes progressive inflammation into a critical point, beyond which uncontrolled activation of immune cells and excessive cytokine production give rise to the cardinal symptoms of HLH. Various pathogenic pathways may thus converge to a common end stage of fulminant HLH.

Polygenic mutations in the cytotoxicity pathway increase susceptibility to develop HLH immunopathology in mice

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory disease. Inherited forms of HLH are caused by biallelic mutations in several effectors of granule-dependent lymphocyte-mediated cytotoxicity. A small proportion of patients with a so-called "secondary" form of HLH, which develops in the aftermath of infection, autoimmunity, or cancer, carry a monoallelic mutation in one or more HLH-associated genes. Although this observation suggests that HLH may have a polygenic mode of inheritance, the latter is very difficult to prove in humans. In order to determine whether the accumulation of partial genetic defects in lymphocyte-mediated cytotoxicity can contribute to the development of HLH, we generated mice that were doubly or triply heterozygous for mutations in HLH-associated genes, those coding for perforin, Rab27a, and syntaxin-11. We found that the accumulation of monoallelic mutations did indeed increase the risk of developing HLH immunopathology after lymphocytic choriomeningitis virus infection. In mechanistic terms, the accumulation of heterozygous mutations in the two degranulation genes Rab27a and syntaxin-11, impaired the dynamics and secretion of cytotoxic granules at the immune synapse of T lymphocytes. In addition, the accumulation of heterozygous mutations within the three genes impaired natural killer lymphocyte cytotoxicity in vivo. The genetic defects can be ranked in terms of the severity of the resulting HLH manifestations. Our results form the basis of a polygenic model of the occurrence of secondary HLH.