Late-onset cases of familial hemophagocytic lymphohistiocytosis with missense perforin gene mutations

Hemophagocytic lymphohistiocytosis after solid organ transplantation: A challenge for clinicians

Hemophagocytic lymphohistiocytosis (HLH) is a rare inflammatory disorder with a high mortality rate and a wide range of symptoms. Solid organ transplantation, which provides patients with a unique immunosuppressive state, is a less common predisposing factor for HLH. HLH after solid organ transplantation (HLH-SOT) is very rare and fatal. It is hard to diagnose and treat and extremely understudied. The use of immunosuppressants makes the situation of HLH-SOT more complex. This review summarizes the existing literature on HLH after solid organ transplantation and describes its triggers and symptoms, focusing on its diagnosis and treatment. We performed a literature search of case reports, case series, letters to the editor, and clinical quizzes describing patients with HLH after solid organ transplantation (HLH-SOT). We provide recommendations on the diagnosis protocol and treatment strategy based on the existing evidence.

Hemophagocytic lymphohistiocytosis with a hemizygous PRF1 c.674G>A mutation

Hemophagocytic lymphohistiocytosis(HLH) is a rare highly-fatal disease presenting with fever, hepatosplenomegaly, and pancytopenia and has a poor prognosis. Homozygous or semi-zygous or complex heterozygous variants can cause familial HLH and heterozygous carriers are frequently seen in secondary HLH. A 42-year-old male patient was admitted to the hospital for persistent fever, fatigue, and splenomegaly. Investigations revealed hypertriglyceridemia, hyperlactatemia dehydrogenaseemia, hyperferritinemia, and elevated levels of soluble cluster of differentiation 25. We found a heterozygous mutation of PRF1: c.674G>A (p.R225Q) through next-generation sequencing technology of hemophagocytic-lymphohistiocytosis-related genes. After a brief remission with dexamethasone and etoposide-based therapy, the disease relapsed quickly, and an allogeneic hematopoietic stem cell transplant was performed to achieve complete remission. To date, the patient's condition was in complete remission. Our study detected a rare missense mutation in the PRF1 gene in a patient with HLH disease and the c.674G>A mutation may be rated as a possible pathogenic variant.

Natural Killer Cells in Multiple Sclerosis: Entering the Stage

Studies investigating the immunopathology of multiple sclerosis (MS) have largely focused on adaptive T and B lymphocytes. However, in recent years there has been an increased interest in the contribution of innate immune cells, amongst which the natural killer (NK) cells. Apart from their canonical role of controlling viral infections, cell stress and malignancies, NK cells are increasingly being recognized for their modulating effect on the adaptive immune system, both in health and autoimmune disease. From different lines of research there is now evidence that NK cells contribute to MS immunopathology. In this review, we provide an overview of studies that have investigated the role of NK cells in the pathogenesis of MS by use of the experimental autoimmune encephalomyelitis (EAE) animal model, MS genetics or through ex vivo and in vitro work into the immunology of MS patients. With the advent of modern hypothesis-free technologies such as single-cell transcriptomics, we are exposing an unexpected NK cell heterogeneity, increasingly blurring the boundaries between adaptive and innate immunity. We conclude that unravelling this heterogeneity, as well as the mechanistic link between innate and adaptive immune cell functions will lay the foundation for the use of NK cells as prognostic tools and therapeutic targets in MS and a myriad of other currently uncurable autoimmune disorders.

Lupus Erythematosus Tumidus Associated With Hemophagocytosis

ABSTRACT

A case of lupus erythematosus tumidus (LET), a subtype of chronic cutaneous lupus erythematosus, in an 85-year-old woman who presented with discrete indurated erythematous plaques over the face and upper chest is described. A skin biopsy showed features in keeping with a diagnosis of LET. Unusually however, the lymphocytic infiltrate contained frequent macrophages that demonstrated hemophagocytosis. Most of the phagocytosed cells were lymphocytes, but there was also evidence of erythrophagocytosis. The presence of conspicuous hemophagocytosis has only rarely been reported in skin biopsies of patients with autoimmune conditions. These include systemic lupus, neonatal lupus and dermatomyositis, and on 2 occasions in cases of nonspecified cutaneous lupus erythematosus. To the best of our knowledge, hemophagocytosis as a feature of LET has not been previously described in the literature.

Neuroinflammation Associated With Inborn Errors of Immunity

The advent of high-throughput sequencing has facilitated genotype-phenotype correlations in congenital diseases. This has provided molecular diagnosis and benefited patient management but has also revealed substantial phenotypic heterogeneity. Although distinct neuroinflammatory diseases are scarce among the several thousands of established congenital diseases, elements of neuroinflammation are increasingly recognized in a substantial proportion of inborn errors of immunity, where it may even dominate the clinical picture at initial presentation. Although each disease entity is rare, they collectively can constitute a significant proportion of neuropediatric patients in tertiary care and may occasionally also explain adult neurology patients. We focus this review on the signs and symptoms of neuroinflammation that have been reported in association with established pathogenic variants in immune genes and suggest the following subdivision based on proposed underlying mechanisms: autoinflammatory disorders, tolerance defects, and immunodeficiency disorders. The large group of autoinflammatory disorders is further subdivided into IL-1β-mediated disorders, NF-κB dysregulation, type I interferonopathies, and hemophagocytic syndromes. We delineate emerging pathogenic themes underlying neuroinflammation in monogenic diseases and describe the breadth of the clinical spectrum to support decisions to screen for a genetic diagnosis and encourage further research on a neglected phenomenon.

Co-Occurrence of Familial Hemophagocytic Lymphohistiocytosis Type 2 and Chronic Active Epstein-Barr Virus in Adulthood

We report, to the best of our best knowledge, the oldest individual to ever be diagnosed with Familial Hemophagocytic Lymphohistiocytosis (FHL) Type 2 from homozygous c.1349C>T (p.T450M) missense variants in the PRF1 gene. This rare case advanced in complexity with a simultaneous diagnosis of Chronic Active Epstein-Barr Virus (CAEBV) - a distinct clinical entity from acute EBV infections and a well-described trigger of Hemophagocytic Lymphohistiocytosis (HLH). This is, to the best of our knowledge, the only individual to ever be diagnosed with CAEBV in the setting of this specific variant and the oldest to be diagnosed with a coexisting perforin variant. This case provides understanding of EBV, human genetics, and lymphoproliferative disorders while adding a unique differential diagnosis to adults who present with fever of unknown origin and diffuse lymphadenopathy without evidence of malignancy. This report explores the diagnosis and treatment of both HLH and CAEBV, encouraging discussion regarding current clinical management and future research needs.

Genotype characteristics and immunological indicator evaluation of 311 hemophagocytic lymphohistiocytosis cases in China

Background

Primary hemophagocytic lymphohistiocytosis (pHLH) is a genetic disorder that is classically diagnosed by genetic testing. Secondary HLH (sHLH) is usually caused by infections, malignancies, or autoimmune disorders, but may display some mutations or polymorphisms. Rapid immunological assays examining natural killer (NK) cell activity, degranulation function (CD107a), and protein expression related to genetic deficiencies have been recommended for early pHLH identification.

Methods

A retrospective analysis of 311 HLH patients from a Chinese population was performed to evaluate the potential correlations between genetic testing and rapid immunological assays; genotyping characteristics, age of onset, and etiology were examined.

Results

Among the 128 (128/311) patients who were positive in the genetic screening, the most frequently detected mutant gene was UNC13D (29%), followed by LYST (21%), PRF1 (17%), and STXBP2 (10%). Among pHLH patients (n = 39), the majority (67%) had PRF1 and UNC13D defects. FHL-2 was predominant (12/27, 44%) in patients aged under 18, while FHL-3 was the most common (6/12, 50%) in adults. Differences in genetic variant types and etiological components were noted in HLH patients based on the age of onset. NK cell activity and CD107a were observed to show a consistent trend (P_trend < 0.001) when grouping patients according to the severity of the genetic variant type. Moreover, NK cell activity was generally consistent within a certain range of ΔCD107a values (P_trend < 0.001). The PPV for bi-allelic degranulation gene mutations in patients with CD107a < 5% was 38.9% (7/18), while the PPV in patients with CD107a ≤10% was 16.7% (13/78). The PPV for pHLH was 41.4% (29/70) with NK cell activity ≤13%. To further evaluate the diagnostic efficacy of NK cell activity assay in pHLH, a receiver operating characteristic (ROC) curve was generated and showed an area under the curve (AUC) of 0.872, and the optimal cutoff value was determined to be 13.425% with a sensitivity of 84.21% and specificity of 80.67% when the corresponding Youden index was maximized. Flow cytometry screening for deficient proteins, including perforin, SAP, and XIAP, showed a relatively high sensitivity (83.33–93.33%). The positive predictive values (PPVs) of perforin and XIAP were relatively low (20.83–26.92%), but the negative predictive values (NPVs) for all three were excellent (all > 98%).

Conclusions

Various immunological indicators have different clinical prediction and application values for the diagnosis of pHLH. The degree of reduction of immunological indicators also needs attention, and choosing appropriate cutoff value may be of important significance in guiding clinical judgment for pHLH.

Neurologic Manifestations as Initial Clinical Presentation of Familial Hemophagocytic Lymphohistiocytosis Type2 Due to PRF1 Mutation in Chinese Pediatric Patients

Familial hemophagocytic lymphohistiocytosis Type 2 (FHL2) associated central nervous system (CNS) involvement is less understood in children, especially when considering neurologic manifestations as part of the initial presentation. We conducted a retrospective review of the clinical manifestations and genetic abnormality of four Han Chinese children with FHL2 who were patients at the neurology department of Beijing Children’s Hospital from November 2015 to October 2018. These four patients initially manifested CNS symptoms in their disease presentation, and all four patients were misdiagnosed as having ademyelinating disease, such as acute disseminated encephalomyelitis and multiple sclerosis. Given these misdiagnoses, it is important that general physicians and pediatricians maintain awareness of the possibility of FHL2 as a differential diagnosis. These four cases included neurologic manifestations including seizures, ataxia, spasticity, gait disorder, and coma. Bilateral abnormal signals in the cerebrum, including in white matter, gray matter, and junctions were discovered. Enhanced magnetic resonance imaging (MRI) in these patients showed spot or ring enhancement and/or hemorrhage. These patients all possessed a compound heterozygote mutation PRF1 gene. Whole exome sequencing analysis revealed seven different mutations (three novel mutations) spread over the PRF1 gene and a heterozygous missense mutation c.1349C > T [p.T450M] that was present in two patients. Three novel mutations, c.634T > C[p.Y212H], c.1083_1094del[p.361_364del], and c.1306G > T [p.D436Y], were discovered and through in silico analysis were discovered to be deleterious. Neurologic manifestations were the initial symptoms of FHL2 in these patients in addition to the expected leukopenia and hepatosplenomegaly. Whole exome sequencing of PRF1 for patients with similar presentations would facilitate prompt and accurate diagnosis and treatment.

To Transplant or Not to Transplant? Late-Onset Primary HLH in a Patient: A Case Report and Review of Literature

Primary, or familial, hemophagocytic lymphohistiocytosis (P-HLH) is a rare inherited autosomal-recessive immune deficiency which generally manifests during infancy or early childhood. Recent literature suggests an increased number of reports of late-onset P-HLH, especially in association with infection and underlying malignancy. The authors describe a case of subcutaneous T-cell lymphoma in a 8-year-old child that was complicated by primary, perforin-deficient HLH. In contrast, we examined retrospective data for 19 cases of late-onset P-HLH with available treatment data and compared the results of conservative medical therapy with hematopoietic stem cell transplant (HSCT) postremission therapy. Our patient displayed compound heterozygous mutations in PRF1 that have not been described in the literature previously: allele 1 [c.786_801del(p.Gln263fs)] and allele 2 [c.886T>C(p.Tyr296His)]. Of the 19 cases analyzed, 14 achieved remission. Postremission, 7 of 14 (50%) received HSCT and were reported alive at a median time of 24 months, 5 of 14 (36%) received medical therapy and were reported alive at a median time of 24 months, and 2 of 14 (14%) received medical therapy and died at a median of 73 months postremission. Our retrospective literature review suggests that some patients can survive late-onset, perforin-deficient, P-HLH without the potential lifelong risks of HSCT when in the first remission.

Fatal familial hemophagocytic lymphohistiocytosis with perforin gene (PRF1) mutation and EBV-associated T-cell lymphoproliferative disorder of the thyroid

Familial hemophagocytic lymphohistiocytosis (FHL) is a rare fatal autosomal recessive disorder of immune dysregulation. The disease presents most commonly in the first year of life; however, symptomatic presentation throughout childhood and adulthood has also been identified. Biallelic mutation in the perforin gene is present in 20%–50% of all cases of FHL. Secondary hemophagocytic lymphohistiocytosis (HLH) in association with hematological malignancies is known; however, whether mutations in HLH-associated genes can be associated with FHL and hematolymphoid neoplasms is not well documented. Also, Epstein–Barr-virus- (EBV) positive systemic T-cell lymphoproliferative disease (SE-LPD) in the setting of FHL is not clearly understood. Here, we present the case of a young boy who presented with typical features of childhood FHL harboring the perforin gene (PRF1) mutation, and had SE-LPD diagnosed on autopsy, along with evidence of recent EBV infection. The patient expired due to progressive disease. Five siblings died in the second or third decade of life with undiagnosed disease. Genetic counseling was provided to the two surviving siblings and parents, but they could not afford genetic testing. One surviving sibling has intermittent fever and is on close follow-up for possible bone marrow transplantation.

Hemophagocytic lymphohistiocytosis followed by an episode of peritoneal dialysis associated peritonitis: a case report

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is characterized by excessive activation of the immune system due to infection, autoimmune diseases, or malignancy. As an aggressive and life-threatening clinical syndrome, HLH secondary to peritoneal dialysis associated peritonitis (PDAP) has never been reported.

CASE PRESENTATION

A 34-year-old female peritoneal dialysis (PD) patient was hospitalized for fever, progressively multi-organ damage (including cytopenias, abnormalities of coagulation and liver enzyme) after an episode of organism-specific peritonitis. She was refractory to the broad-spectrum antimicrobial agent. Further tests found hemophagocytosis on the bone marrow examination, and extremely high level of sIL2-R and impaired activity of NK cell. The diagnosis of HLH was eventually established. After HLH-specific therapy, this patient recovered and discharged.

CONCLUSIONS

The present case suggests that clinicians should to be aware of HLH in those patients apparently suspected with refractory or relapsing peritonitis, especially those accompanied with persist fever, hyperferritinemia, and cytopenias. HLH-specific therapy and supportive care should be applied without delay.

A Case of Recurrent Pregnancy-Induced Adult Onset Familial Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a rare and potentially fatal disease primarily of children, characterized by a severe hyperinflammatory state. We describe a case of adult onset familial HLH with a novel exon 19, c.1607G>T (p.Arg536Leu) heterozygous mutation of the UNC13D gene in a 40-year-old woman who developed HLH during her first and second pregnancies, both episodes occurring during the first trimester. Our patient was treated successfully both times with HLH-94 protocol following spontaneous abortions and is currently in the process of getting a bone marrow transplant. We also discuss pregnancy as a potential trigger for late onset familial HLH.

Macrophage Activation Syndrome

Hemophagocytic lymphohistiocytosis (HLH), or termed macrophage activation syndrome (MAS) when associated with rheumatic disorders, is a frequently fatal complication of infections, rheumatic disorders, and hematopoietic malignancies. Clinically, HLH/MAS is a life-threatening condition that is usually diagnosed among febrile hospitalized patients (children and adults) who commonly present with unremitting fever and a shock-like multiorgan dysfunction scenario. Laboratory studies reveal pancytopenia, elevated liver enzymes, elevated markers of inflammation (ESR, CRP), hyperferritinemia, and features of coagulopathy. In about 60% of cases, excess hemophagocytosis (macrophages/histiocytes engulfing other hematopoietic cell types) is noted on biopsy specimens from the bone marrow, liver, lymph nodes, and other organs. HLH/MAS has been hypothesized to occur when a threshold level of inflammation has been achieved, and genetic and environmental risk factors are believed to contribute to the hyperinflammatory state. A broad variety of infections, from viruses to fungi to bacteria, have been identified as triggers of HLH/MAS, either in isolation or in addition to an underlying inflammatory disease state. Certain infections, particularly by members of the herpesvirus family, are the most notorious triggers of HLH/MAS. Treatment for infection-triggered MAS requires therapy for both the underlying infection and dampening of the hyperactive immune response.

Late-onset hemophagocytic lymphohistiocytosis with neurological presentation

Missense mutations in genes involved in familial hemophagocytic lymphohistiocytosis can delay the onset of this life-threatening disease. In children and adults, early recognition of aspecific features as neurological symptoms is crucial as urgent treatment is required.

Germline heterozygous variants in genes associated with familial hemophagocytic lymphohistiocytosis as a cause of increased bleeding

Familial hemophagocytic lymphohistiocytosis (FHL) is caused by biallelic variants in genes regulating granule secretion in cytotoxic lymphocytes. In FHL3-5, the affected genes UNC13D, STX11 and STXBP2 have further been shown to regulate the secretion of platelet granules, giving rise to compromised platelet function. Therefore, we aimed to investigate platelet degranulation in patients heterozygous for variants in UNC13D, STX11 and STXBP2. During the work-up of patients referred to the Coagulation Unit, Skåne University Hospital, Malmö, Sweden and the Department of Hematology, Rigshospitalet, Copenhagen, Denmark due to bleeding tendencies, 12 patients harboring heterozygous variants in UNC13D, STX11 or STXBP2 were identified using targeted whole exome sequencing. Transmission electron microscopy (TEM) was used to assess the secretion of platelet dense granules following thrombin stimulation. Platelet degranulation, activation and aggregation were further assessed by flow cytometry (FC) and light transmission aggregometry (LTA) with lumi-aggregometry. In total, eight out of twelve (67%) patients showed impaired degranulation by at least one of the assays (TEM, FC and LTA). In the 12 patients, eight different heterozygous variants were identified. One variant was strongly associated with impaired degranulation, while four of the variants were associated with impaired granule secretion to a slightly lesser extent. One additional variant was found in six out of the twelve patients, and was associated with varying degrees of degranulation impairment. Accordingly, six out of the eight (75%) identified variants were associated with impaired platelet degranulation. Our results suggest that heterozygous variants in UNC13D, STX11 and STXBP2 are sufficient to cause platelet secretion defects resulting in increased bleeding.

Exome sequencing for simultaneous mutation screening in children with hemophagocytic lymphohistiocytosis

In the present study, we used exome sequencing to analyze PRF1, UNC13D, STX11, and STXBP2, as well as genes associated with primary immunodeficiency disease (RAB27A, LYST, AP3B1, SH2D1A, ITK, CD27, XIAP, and MAGT1) in Thai children with hemophagocytic lymphohistiocytosis (HLH). We performed mutation analysis of HLH-associated genes in 25 Thai children using an exome sequencing method. Genetic variations found within these target genes were compared to exome sequencing data from 133 healthy individuals. Variants identified with minor allele frequencies <5% and novel mutations were confirmed using Sanger sequencing. Exome sequencing data revealed 101 non-synonymous single nucleotide polymorphisms (SNPs) in all subjects. These SNPs were classified as pathogenic (n = 1), likely pathogenic (n = 16), variant of unknown significance (n = 12), or benign variant (n = 72). Homozygous, compound heterozygous, and double-gene heterozygous variants, involving mutations in PRF1 (n = 3), UNC13D (n = 2), STXBP2 (n = 3), LYST (n = 3), XIAP (n = 2), AP3B1 (n = 1), RAB27A (n = 1), and MAGT1 (n = 1), were demonstrated in 12 patients. Novel mutations were found in most patients in this study. In conclusion, exome sequencing demonstrated the ability to identify rare genetic variants in HLH patients. This method is useful in the detection of mutations in multi-gene associated diseases.

[The significance of pedigree genetic screening and rapid immunological parameters in the diagnosis of primary hemophagocytic lymphohistiocytosis]

目的

探讨家系基因筛查及快速免疫学指标检测在原发性噬血细胞综合征（HLH）诊断中的意义。

方法

通过对伴有PRF1、UNC13D及SH2D1A基因突变的4例原发性HLH患者展开家系调查，分别完成基因筛查及各项免疫学指标检测（包括NK细胞活性、CD107a检测及HLH相关缺陷蛋白表达测定），评价各项检测指标在原发性HLH诊断中的意义并探讨各项指标间的相关性。

结果

4个家系基因突变分别为PRF1基因错义突变c.T172C（p.S58P）和非框架移码突变c.1083_1094del (p.361_365del）；PRF1基因错义突变c.C1349T（p.T450M）和框架移码突变c.1090_1091delCT (p.T364fsX93）；UNC13D基因错义突变c.G2588A（p.G863D）；SH2D1A基因半合子错义突变c.32T>G (p.I11S）。先证者及家系成员分别存在不同程度的NK细胞活性降低，其中PRF1基因及SH2D1A基因突变家系HLH相关基因编码穿孔素蛋白、信号淋巴细胞活化分子相关蛋白（SAP）表达水平下降，UNC13D基因突变先证者及与其存在完全相同突变位点的家系成员细胞毒脱颗粒功能（CD107a表达）显著减低。

结论

开展家系基因筛查及快速免疫学指标检测对诊断原发性HLH具有重要意义，两者具有较好的一致性，其中快速免疫学指标检测作为一种高效的检测手段，可为原发性HLH的早期诊断提供可靠依据。

Hemophagocytic lymphohistiocytosis: Pathogenesis, diagnosis, and management

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome that is classified into primary and secondary HLH. Primary HLH consists of monogenic disorders that mainly affect the perforin-mediated cytotoxicity of cytotoxic T lymphocytes and natural killer cells. Secondary HLH occurs as a complication in various settings such as infection, malignancy, autoimmune disease, and post-allogeneic hematopoietic stem cell transplantation. Both primary and secondary HLH are characterized by uncontrolled hypercytokinemia that results in myelosuppression and vascular endothelium damage. More than 10% of patients with HLH die within 2 months of diagnosis due to bleeding in the visceral organs, opportunistic infection due to neutropenia, or multiple organ failure. The most obvious presentations of HLH are persistent fever refractory to antimicrobial agents and hyperferritinemia due to hypersecretion of various cytokines. The first rule is not to overlook signs of hypercytokinemia and to settle the hyperactivated immunological state as soon as possible. In addition, to improve outcome, it is essential to identify the disorders underlying HLH and provide disorder-appropriate treatment.

Familial Hemophagocytic Lymphohistiocytosis due to Mutation of UNC13D Gene

Hemophagocytic lymphohistiocytosis (HLH) are basically a heterogenous group of clinical syndromes, characterised by activation and non-malignant proliferation of benign histiocytes i.e. lymphocytes and macrophages, leading to a cytokine storm that accounts for the fever, organomegaly and multi-organ dysfunction. Two types of HLH are described, either due to known genetic defect (familial HLH/FHL) or due to some acquired cause either infection or rheumatological diseases. Here we present a case of a 3 months old baby, admitted with fever, hepatosplenomegaly and cytopenia and ultimately was diagnosed to be a case of Familial HLH type 3 due to defect in UNC13D gene as a result of compound heterozygous for two nonsense mutation resulting in the Munc13-4 protein defect.

Search for the potential "second-hit" mechanism underlying the onset of familial hemophagocytic lymphohistiocytosis type 2 by whole-exome sequencing analysis

Familial hemophagocytic lymphohistiocytosis type 2 (FHL2), caused by perforin 1 (PRF1), is a genetic disorder of lymphocyte cytotoxicity that usually presents in the first 2 years of life and has a poor prognosis. Late onset of FHL2 has been sporadically reported, and the mechanism is largely unknown. A newly diagnosed FHL2 patient was detected to have compound mutations in both PRF1 alleles and positive Epstein-Barr virus (EBV) infection. Her brother carried the same mutations and EBV infection status but kept healthy. To search the potential unknown mechanisms, we performed whole-exome sequencing analysis. The patient and her asymptomatic brother carried the same heterozygous missense (c.916G>A) and frameshift mutation (c.65delC) in PRF1. Germline mutation analysis demonstrated that only the proband was exclusively detected with a homozygous missense mutation (S1006L) in the PCDH18 gene, whereas others were found to have a heterozygous mutation (S1006L) of PCDH18. The calculated stability (free energy) changes showed that the mutation of PCDH18 mainly destabilized the protein structure. Furthermore, the mutation (S1006L) could lessen the PCDH18-induced inhibition of target cell activation and reduce the apoptosis of T lymphocytes. This study is the first to perform whole-exome sequencing analysis to search the potential "second-hit" mechanism that underlies the onset of FHL2. A novel type of compound heterozygous mutation has been found in PRF1. The detection of the homozygous germline mutation in PCDH18 strongly argues that the presence of a "second" germline mutation besides the PRF1 gene might be potentially an important mechanism for triggering the onset of FHL2.

Hemophagocytic Lymphohistiocytosis in Children: Pathogenesis and Treatment

Hemophagocytic lymphohistiocytosis (HLH) is a rare disorder in children that is characterized by persistent fever, splenomegaly with cytopenia, hypertriglyceridemia, and hypofibrinogenemia. Increased levels of various cytokines and soluble interleukin-2 receptor are biological markers of HLH. HLH can be classified into two major forms: primary and secondary. Familial hemophagocytic lymphohistiocytosis (FHL), a type of primary HLH, is an autosomal recessive disorder that typically occurs in infancy and can be classified into five different subtypes (FHL types 1-5). In Japan, >80% of patients with FHL have either PRF1 (FHL type 2) or UNC13D (FHL type 3) defects. FHL is considered to be a disorder of T-cell function because the activity of NK cells or cytotoxic T lymphocytes as target cells is usually impaired. Moreover, Epstein-Barr virus-associated HLH (EBV-HLH) is considered a major subtype of secondary HLH. Any genetic background could have an effect on the pathogenesis of secondary HLH because EBV-HLH is considered to be particularly prevalent in Asian countries. For primary HLH, hematopoietic stem cell transplantation is the only accepted curative therapy, although cord blood transplantation with a reduced-conditioning regimen has been used with superior outcomes. For secondary HLH, including EBV-HLH, immunochemotherapy based on the HLH-2004 protocol has been used. In the near future, the entire mechanism of HLH should be clarified to establish less toxic therapies, including cell therapy and gene targeting therapy.

Targeted high-throughput sequencing for genetic diagnostics of hemophagocytic lymphohistiocytosis

Background

Hemophagocytic lymphohistiocytosis (HLH) is a rapid-onset, potentially fatal hyperinflammatory syndrome. A prompt molecular diagnosis is crucial for appropriate clinical management. Here, we validated and prospectively evaluated a targeted high-throughput sequencing approach for HLH diagnostics.

Methods

A high-throughput sequencing strategy of 12 genes linked to HLH was validated in 13 patients with previously identified HLH-associated mutations and prospectively evaluated in 58 HLH patients. Moreover, 2504 healthy individuals from the 1000 Genomes project were analyzed in silico for variants in the same genes.

Results

Analyses revealed a mutation detection sensitivity of 97.3 %, an average coverage per gene of 98.0 %, and adequate coverage over 98.6 % of sites previously reported as mutated in these genes. In the prospective cohort, we achieved a diagnosis in 22 out of 58 patients (38 %). Genetically undiagnosed HLH patients had a later age at onset and manifested higher frequencies of known secondary HLH triggers. Rare, putatively pathogenic monoallelic variants were identified in nine patients. However, such monoallelic variants were not enriched compared with healthy individuals.

Conclusions

We have established a comprehensive high-throughput platform for genetic screening of patients with HLH. Almost all cases with reduced natural killer cell function received a diagnosis, but the majority of the prospective cases remain genetically unexplained, highlighting genetic heterogeneity and environmental impact within HLH. Moreover, in silico analyses of the genetic variation affecting HLH-related genes in the general population suggest caution with respect to interpreting causality between monoallelic mutations and HLH. A complete understanding of the genetic susceptibility to HLH thus requires further in-depth investigations, including genome sequencing and detailed immunological characterization.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-015-0244-1) contains supplementary material, which is available to authorized users.

Spectrum of Atypical Clinical Presentations in Patients with Biallelic PRF1 Missense Mutations

BACKGROUND

Perforin, encoded by PRF1, is a pore-forming protein crucial for lymphocyte cytotoxicity. Biallelic PRF1 nonsense mutations invariably result in early-onset hemophagocytic lymphohistiocytosis (HLH), termed familial HLH type 2 (FHL2). In contrast, biallelic PRF1 missense mutations may give rise to later-onset disease and more variable manifestations.

PROCEDURE

We retrospectively searched our database for patients from families with siblings carrying biallelic PRF1 missense mutations where at least one sibling did not develop HLH, and for patients with biallelic PRF1 missense mutations and an atypical presentation of disease. We reviewed their clinical, genetic, and immunological characteristics.

RESULTS

In all, we identified 10 such patients, including three sibling pairs with discordant manifestations. Interestingly, in two families, siblings of late-onset HLH patients developed Hodgkin lymphoma but no HLH. In a third family, one sibling presented with recurrent HLH episodes, whereas the other remains healthy. Of note, the affected sibling also suffered from systemic lupus erythematosus. Additional unrelated patients with biallelic PRF1 missense mutations were affected by neurological disease without classical signs of HLH, gastrointestinal inflammation as initial presentation of disease, as well as a hematological malignancy. Compared to early-onset FHL2 patients, the patients with an atypical presentation displayed a partial recovery of NK cell cytotoxicity upon IL-2 stimulation in vitro.

CONCLUSIONS

Our findings substantiate and expand the spectrum of clinical presentations of perforin deficiency, linking PRF1 missense mutations to lymphoma susceptibility and highlighting clinical variability within families. PRF1 mutations should, therefore, be considered as a cause of several diseases disparate to HLH.

Hypertrophic Obstructive Cardiomyopathy in An Infant With Hemophagocytic Lymphohistiocytosis; Answer to a Riddle

Familial hemophagocytic lymphohistiocytosis (FHLH) is a hereditary hyperinflammatory condition with T-cell and macrophage activation. Treatment consists of immunosuppressive therapy plus bone marrow transplantation. Cardiac manifestations of FHLH were scarcely mentioned in the literature with conflicting pathophysiological explanations. We report a case of hypertrophic obstructive cardiomyopathy associated with FHLH. Guided by such a case, a clear vision regarding the real cause is thought to be obtained in the cloudy landscape of pathophysiology.

Prognostic Factors and Outcomes of Adult-Onset Hemophagocytic Lymphohistiocytosis: A Retrospective Analysis of 34 Cases

Adult-onset hemophagocytic lymphohistiocytosis (HLH) has features that are distinct from that of HLH in pediatric patients. The clinical records at the Japanese Red Cross Kumamoto Hospital were reviewed. We retrospectively analyzed 34 patients who fulfilled the diagnostic criteria of HLH-2004. The median age of patients was 60.0 (range 15-86). Underlying diseases were diagnosed in 17 patients. They consisted of malignant lymphoma (n=3), other neoplastic disease (n=3), viral infection (n=4), collagen vascular disease (n=3), Kikuchi’s disease (n=3) and drug (n=1). Underlying diseases were not diagnosed in 17 patients despite examination. The treatments were steroids (n=18), dexamethasone + cyclosporine A (CSA) + etoposide (n=4), multidrug chemotherapy (n=2), steroids and CSA (n=3). Eleven patients died during observation. In a multivariate analysis, the significant predictor for death was age at onset (hazard ratio, 1.22; 95%CI, 1.02-1.44; P=0.027). Autopsy was performed in 4 cases, but the underlying disease remained unknown in 3 of those cases. Adult-onset HLH has high diversity and various outcomes. The mechanism of adult-onset HLH is not fully understood and further research is required.

A novel pathogenic variant in PRF1 associated with hemophagocytic lymphohistiocytosis

Familial Hemophagocytic Lymphohistiocytosis type 2 (FHL2) results from mutations in PRF1. We described two unrelated individuals who presented with FHL, in whom severely impaired NK cytotoxicity and decrease perforin expression was observed. DNA sequencing of PRF1 demonstrated that both were not only heterozygous for the p.54R > C/91A > V haplotype but also presented with the novel variant p.47G > V at the perforin protein. Perforin mRNA was found to be increased in a individual with that genotype. A carrier of the novel variant also demonstrated altered perforin mRNA and protein expression. Phylogenetic analysis and multiple alignments with perforin orthologous demonstrated a high level of conservation at Gly47. PolyPhen-2 and PROVEAN predicted p.47G > V to be "probably damaging" and "deleterious", respectively. A thermodynamic analysis showed that this variant was highly stabilizing, decreasing the protein internal energy. The ab initio perforin molecular modeling indicated that Gly47 is buried inside the hydrophobic core of the MACPF domain, which is crucial for the lytic pore formation and protein oligomerization. After the in silico induction of the p.47G > V mutation, Val47 increased the interactions with the surrounding amino acids due to its size and physical properties, avoiding a proper conformational change of the domain. To our knowledge, this is the first description supporting that p.47G > V is a pathogenic variant that in conjunction with p.54R > C/91A > V might result in the clinical phenotype of FHL2.

Hemophagocytic lymphohistiocytosis: Recent progress in the pathogenesis, diagnosis and treatment

Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory syndrome that develops as a primary (familial/hereditary) or secondary (non-familial/hereditary) disease characterized in the majority of the cases by hereditary or acquired impaired cytotoxic T-cell (CTL) and natural killer responses. The molecular mechanisms underlying impaired immune homeostasis have been clarified, particularly for primary diseases. Familial HLH (familial hemophagocytic lymphohistiocytosis type 2-5, Chediak-Higashi syndrome, Griscelli syndrome type 2, Hermansky-Pudlak syndrome type 2) develops due to a defect in lytic granule exocytosis, impairment of (signaling lymphocytic activation molecule)-associated protein, which plays a key role in CTL activity [e.g., X-linked lymphoproliferative syndrome (XLP) 1], or impairment of X-linked inhibitor of apoptosis, a potent regulator of lymphocyte homeostasis (e.g., XLP2). The development of primary HLH is often triggered by infections, but not in all. Secondary HLH develops in association with infection, autoimmune diseases/rheumatological conditions and malignancy. The molecular mechanisms involved in secondary HLH cases remain unknown and the pathophysiology is not the same as primary HLH. For either primary or secondary HLH cases, immunosuppressive therapy should be given to control the hypercytokinemia with steroids, cyclosporine A, or intravenous immune globulin, and if primary HLH is diagnosed, immunochemotherapy with a regimen containing etoposide or anti-thymocyte globulin should be started. Thereafter, allogeneic hematopoietic stem-cell transplantation is recommended for primary HLH or secondary refractory disease (especially EBV-HLH).

Familial hemophagocytic lymphohistiocytosis: when rare diseases shed light on immune system functioning

The human immune system depends on the activity of cytotoxic T lymphocytes (CTL), natural killer (NK) cells, and NKT cells in order to fight off a viral infection. Understanding the molecular mechanisms during this process and the role of individual proteins was greatly improved by the study of familial hemophagocytic lymphohistiocytosis (FHL). Since 1999, genetic sequencing is the gold standard to classify patients into different subgroups of FHL. The diagnosis, once based on a clinical constellation of abnormalities, is now strongly supported by the results of a functional flow-cytometry screening, which directs the genetic study. A few additional congenital immune deficiencies can also cause a resembling or even identical clinical picture to FHL. As in many other rare human disorders, the collection and analysis of a relatively large number of cases in registries is crucial to draw a complete picture of the disease. The conduction of prospective therapeutic trials allows investigators to increase the awareness of the disease and to speed up the diagnostic process, but also provides important functional and genetic confirmations. Children with confirmed diagnosis may undergo hematopoietic stem cell transplantation, which is the only cure known to date. Moreover, detailed characterization of these rare patients helped to understand the function of individual proteins within the exocytic machinery of CTL, NK, and NKT cells. Moreover, identification of these genotypes also provides valuable information on variant phenotypes, other than FHL, associated with biallelic and monoallelic mutations in the FHL-related genes. In this review, we describe how detailed characterization of patients with genetic hemophagocytic lymphohistiocytosis has resulted in improvement in knowledge regarding contribution of individual proteins to the functional machinery of cytotoxic T- and NK-cells. The review also details how identification of these genotypes has provided valuable information on variant phenotypes.

Advances in understanding the pathogenesis of HLH

Haemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory disorder resulting from immune dysfunction reflecting either primary immune deficiency or acquired failure of normal immune homeostasis. Familial HLH includes autosomal recessive and X-linked disorders characterized by uncontrolled activation of T cells and macrophages and overproduction of inflammatory cytokines, secondary to defects in genes encoding proteins involved in granule-dependent cytolytic pathways. In older children and adults, HLH is associated more often with infections, malignancies, autoimmune diseases, and acquired immune deficiencies. HLH, macrophage activation syndrome, sepsis, and systemic inflammatory response syndrome are different clinical entities that probably represent a common immunopathological state, termed cytokine storm. These conditions may be clinically indistinguishable; all include massive inflammatory response, elevated serum cytokine levels, multi-organ involvement, haemophagocytic macrophages, and often death. Tissues of haematopoietic and lymphoid function are directly involved; other organs are secondarily damaged by circulating cytokines and chemokines. Haemophagocytic disorders are now increasingly diagnosed in the context of severe inflammatory reactions to viruses, malignancies and systemic connective tissue diseases. Many of these cases may reflect underlying genetic predispositions to HLH. The detection of gene defects has contributed considerably to our understanding of HLH, but the mechanisms leading to acquired HLH have yet to be fully determined.

Diagnostic evaluation of patients with suspected haemophagocytic lymphohistiocytosis

Haemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome characterized by severely disturbed immune homeostasis. It can affect all age groups. Diagnostic evaluation of the patient with suspected HLH has to address three main questions: (i) does the patient have HLH? There is no simple diagnostic test, but a number of clinical and laboratory criteria define this clinical syndrome. (ii) Can a trigger be identified? A variety of infections, malignant or autoimmune diseases can contribute to the disturbed immune homeostasis with important consequences for treatment. (iii) Does the patient suffer from a genetic disease predisposing to HLH? Recent advances in the understanding of the genetic and pathophysiological basis of HLH have enabled a better and more rapid answer to this question, which is relevant for prognosis and the decision to perform haematopoietic stem cell transplantation. This review summarizes the current diagnostic approach to the patient with HLH.

Familial hemophagocytic lymphohistiocytosis may present during adulthood: clinical and genetic features of a small series

Familial Hemophagocytic lymphohistiocytosis (FHL) is a rare immune deficiency with defective cytotoxic function. The age at onset is usually young and the natural course is rapidly fatal if untreated. A later onset of the disease has been sporadically reported even in adolescents and adults. We report the results of our retrospective data collection of all cases diagnosed with FHL at an age of 18 years or older and enrolled in the Italian Registry of HLH. All cases were diagnosed with FHL based on evidence of genetic defect in one FHL-related gene. A total of 11 patients were diagnosed with FHL. They were 9 males and 2 females, from 10 unrelated families; their age ranged between 18 and 43 years (median, 23 years). Family history was unremarkable in eight families at the time of the diagnosis. Their genetic diagnoses are: FHL2 (n = 6), FHL3 (n = 2), FHL5 (n = 1), XLP1 (n = 2). Clinical, molecular and functional data are described. These data confirm that FHL may present beyond the pediatric age and up to the fifth decade. FHL2 due to perforin defect is the most frequently reported subtype. Adult specialists should consider FHL in the differential diagnosis of patients with cytopenia and liver or central nervous system disorders, especially when a lymphoproliferative disease is suspected but eventually not confirmed. FHL may turn to be fatal within a short time course even in adults. This risk, together with the continuous improvement in the transplant technique, especially in the area of transplant from matched unrelated donor, resulting in reduced treatment related mortality, might suggest a wider use of SCT in this population. Current diagnostic approach allows prompt identification of patients by flow-cytometry screening, then confirmed by the genetic study, and treatment with chemo-immunotherapy followed by stem cell transplantation.

Hemophagocytic lymphohistiocytosis associated with necrotizing enterocolitis in premature newborns

Hemophagocytic lymphohistiocytosis (HLH) is a systemic disease resulting from the excessive release of inflammatory cytokines by macrophages under prolonged antigenic stimulation. If untreated, it leads to multiorgan failure and death. Necrotizing enterocolitis (NEC) has not previously been associated with HLH. Here we report four preterm infants who were diagnosed with HLH associated with NEC. Two patients received chemotherapy and one survived. The other two infants succumbed to multiorgan failure. These results suggest that NEC may be a common clinical manifestation of HLH in premature neonates.

Epitope specificity of memory CD8+ T cells dictates vaccination-induced mortality in LCMV-infected perforin-deficient mice

Perforin-deficient (PKO) mice serve as models for familial hemophagocytic lympho-histiocytosis, a uniformly fatal disease associated with viral infection of perforin-deficient humans. Naïve perforin-deficient BALB/c mice survive while vaccinated PKO mice containing virus-specific memory CD8(+) T cells rapidly succumb to lymphocytic choriomeningitis virus (LCMV) infection. Thus, vaccination converts a nonlethal persistent infection into a fatal disease mediated by virus-specific memory CD8(+) T cells. Here, we determine the extent to which vaccination-induced mortality in PKO mice following LCMV challenge is due to differences in vaccine modalities, the quantity or epitope specificity of memory CD8(+) T cells. We show that LCMV-induced mortality in immune PKO mice is independent of vaccine modalities and that the starting number of memory CD8(+) T cells specific to the immunodominant epitope NP(118-126) dictates the magnitude of secondary CD8(+) T-cell expansion, the inability to regulate production of CD8(+) T-cell-derived IFN-γ, and mortality in the vaccinated PKO mice. Importantly, mortality is determined by the epitope specificity of memory CD8(+) T cells and the associated degree of functional exhaustion and cytokine dysregulation but not the absolute magnitude of CD8(+) T-cell expansion. These data suggest that deeper understanding of the parameters that influence the outcome of vaccine-induced diseases would aid rational vaccine design to minimize adverse outcomes after infection.

Familial and acquired hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening syndrome in which an uncontrolled and ineffective immune response, triggered in most cases by infectious agents, leads to severe hyperinflammation. Familial forms of HLH (FHL), which are increasingly found also in adolescents and adults, are due to genetic defects leading to impaired function of natural killer cells and cytotoxic T cells. These mutations occur either in the perforin gene or in genes important for the exocytosis of cytotoxic granules. Cytotoxic granules contain perforin and granzymes, which induce apoptosis upon entering (infected) target cells. Additionally, perforin is important for the downregulation of the immune response. Acquired forms of HLH are encountered in association with (usually) viral infections, autoinflammatory/autoimmune diseases, malignant diseases, and acquired immune deficiency states (e.g., after organ transplantation). Treatment of HLH includes immune-suppressive and immune-modulatory agents, cytostatic drugs, and biological response modifiers. For patients with FHL, stem cell transplantation is indicated and can be curative.

Analyses of the PRF1 gene in individuals with hemophagocytic lymphohystiocytosis reveal the common haplotype R54C/A91V in Colombian unrelated families associated with late onset disease

Familial hemophagocytic lymphohistiocytosis (FHL), is a rare autosomal recessive disorder characterized by an impairment of cytotoxic cells and uncontrolled activation of macrophages. This study presents the first description of four patients with FHL type 2 in Latin America. Patient 1 fulfilled the disease diagnostic criteria since 2 months of age, whereas patients 2, 3 and 4 exhibited the typical manifestations of the disease only later in their childhood. The PRF1 genetic analysis in these patients revealed two previously reported mutations: L17fsx50 and R54C. Interestingly, seven out of the 8 alleles evaluated here in patients carried the haplotype R54C/A91V, suggesting that this is a highly frequent FHL type 2 allele in Colombia. This haplotype confers residual cytotoxic function leading to late onset disease. Therefore, this report highlights the remarkable complexity of FHL diagnostic, emphasizing the importance of the genetic characterization of the disease.

Chemoimmunotherapy for hemophagocytic lymphohistiocytosis: long-term results of the HLH-94 treatment protocol

Hemophagocytic lymphohistiocytosis (HLH) used to have a dismal prognosis. We report the final results of HLH-94, the largest prospective diagnostic/therapeutic HLH study so far. The treatment includes immunosuppressive and cytotoxic therapy aiming at clinical remission, followed by HSCT in patients with familial, persistent, or recurrent disease. Altogether, 249 patients fulfilled inclusion criteria and started HLH-94 therapy (July 1994-December 2003); 227 (91%) were followed-up for ≥ 5 years. At 6.2 years median follow-up, estimated 5-year probability of survival was 54% ± 6%. Seventy-two patients (29%) died before HSCT, 64 within 1 year, 97% of whom had active disease. In 124 patients who underwent HSCT, 5-year survival was 66 ± 8%; tendency to increased survival (P = .064) in patients with nonactive disease at HSCT. Patients with familial disease had a 5-year survival of 50% ± 13%; none survived without HSCT. Patients deceased during the first 2 months more often had jaundice, edema, and elevated creatinine. Forty-nine patients (20%) were alive without signs of HLH activity and off-therapy > 1-year without HSCT; they presented at older age (P < .001), were more often female (P = .011), and less often had CNS disease (P < .001) or hepatomegaly (P = .007). To conclude, HLH-94 chemoimmunotherapy has considerably improved outcome in HLH. Collaborative efforts are needed to further reduce early mortality, HSCT-related mortality, and neurologic late effects.

Hypomorphic mutations in PRF1, MUNC13-4, and STXBP2 are associated with adult-onset familial HLH

Familial hemophagocytic lymphohistiocytosis (HLH) is a rare primary immunodeficiency disorder characterized by defects in cell-mediated cytotoxicity that results in fever, hepatosplenomegaly, and cytopenias. Familial HLH is well recognized in children but rarely diagnosed in adults. We conducted a retrospective review of genetic and immunologic test results in patients who developed HLH in adulthood. Included in our study were 1531 patients with a clinical diagnosis of HLH; 175 patients were 18 years or older. Missense and splice-site sequence variants in PRF1, MUNC13-4, and STXBP2 were found in 25 (14%) of the adult patients. The A91V-PRF1 genotype was found in 12 of these patients (48%). The preponderance of hypomorphic mutations in familial HLH-causing genes correlates with the later-onset clinical symptoms and the more indolent course in adult patients. We conclude that late-onset familial HLH occurs more commonly than was suspected previously.

Familial haemophagocytic lymphohistiocytosis: advances in the genetic basis, diagnosis and management

Familial haemophagocytic lymphohistiocytosis (FHL) is a rare autosomal recessive disorder of immune dysregulation associated with uncontrolled T cell and macrophage activation and hypercytokinaemia. The incidence of FHL is 0·12/100·000 children born per year, with a male to female ratio of 1:1. The disease is classified into six different types based on genetic linkage analysis and chromosomal localization; five specific genetic defects have been identified, which account for approximately 90% of all patients. Type 1 is due to an as yet unidentified gene defect located on chromosome nine. Type 2 is caused by mutations in the perforin (PRF1) gene, type 3 by mutations in the Munc-13-4 (UNC13D) gene, type 4 by mutations in the syntaxin 11 (STX11) gene and the recently described type 5 due to mutations in the gene encoding syntaxin binding protein 2 (STXBP-2). The incidence of the five types varies in different ethnic groups. The most common presenting features are pyrexia of unknown origin, pronounced hepatosplenomegaly and cytopenias. Neurological features tend to present later and are associated with poor prognosis. Absent or decreased lymphocyte cytotoxicity is the cellular hallmark of FHL. Biochemical features such as hyperferritinaemia, hypertriglyceridaemia and hypofibrinogenaemia are usually present, along with high levels of soluble interleukin 2 receptor in the blood and cerebrospinal fluid. Bone marrow aspirate may demonstrate the characteristic haemophagocytes, but initially is non-diagnostic in two-thirds of patients. Established international clinical, haematological and biochemical criteria now facilitate accurate clinical diagnosis. The disease is fatal unless a haematopoietic stem cell transplant (HSCT) is performed. The introduction of HSCT has dramatically improved the prognosis of the disease. However, the mortality of the disease is still significantly high and a number of challenges remain to be addressed. Active disease at the time of the transplant is the major significant poor prognostic factor. Delayed diagnosis, after irreversible organ damage has occurred, especially neurological damage, disease reoccurrence and pre-transplant mortality, remain a concern.

Development of secondary T-cell acute lymphoblastic leukemia in a child with hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a severe life-threatening disorder, characterized by hyperactivation of macrophages. A 12-year-old female was referred to our center; the diagnosis of HLH was made for the patient and immunosuppressive regimen was started. After a 2-year follow-up, the patient developed secondary T-cell acute lymphoblastic leukemia (T-ALL), confirmed by flow cytometric studies. Treatment was started based on T-ALL protocol, but the patient died because of relapse and sepsis. This case highlights the issue of secondary malignancy following HLH and demonstrates the need for continued follow-up in such patients.

Atypical familial hemophagocytic lymphohistiocytosis due to mutations in UNC13D and STXBP2 overlaps with primary immunodeficiency diseases

BACKGROUND

Familial hemophagocytic lymphohistiocytosis is a genetic disorder of lymphocyte cytotoxicity that usually presents in the first two years of life and has a poor prognosis unless treated by hematopoietic stem cell transplantation. Atypical courses with later onset and prolonged survival have been described, but no detailed analysis of immunological parameters associated with typical versus atypical forms of familial hemophagocytic lymphohistiocytosis has been performed.

DESIGN AND METHODS

We analyzed disease manifestations, NK-cell and T-cell cytotoxicity and degranulation, markers of T-cell activation and B-cell differentiation as well as Natural Killer T cells in 8 patients with atypical familial hemophagocytic lymphohistiocytosis due to mutations in UNC13D and STXBP2.

RESULTS

All but one patient with atypical familial hemophagocytic lymphohistiocytosis carried at least one splice-site mutation in UNC13D or STXBP2. In most patients episodes of hemophagocytic lymphohistiocytosis were preceded or followed by clinical features typically associated with immunodeficiency, such as chronic active Epstein Barr virus infection, increased susceptibility to bacterial infections, granulomatous lung or liver disease, encephalitis or lymphoma. Five of 8 patients had hypogammaglobulinemia and reduced memory B cells. Most patients had a predominance of activated CD8(+) T cells and low numbers of Natural Killer T cells. When compared to patients with typical familial hemophagocytic lymphohistiocytosis, NK-cell cytotoxicity and NK-cell and CTL degranulation were impaired to a similar extent. However, in patients with an atypical course NK-cell degranulation could be partially reconstituted by interleukin-2 and cytotoxic T-cell cytotoxicity in vitro was normal.

CONCLUSIONS

Clinical and immunological features of atypical familial hemophagocytic lymphohistiocytosis show an important overlap to primary immunodeficiency diseases (particularly common variable immunodeficiency and X-linked lymphoproliferative syndrome) and must, therefore, be considered in a variety of clinical presentations. We show that degranulation assays are helpful screening tests for the identification of such patients.

Perforin: structure, function, and role in human immunopathology

The secretory granule-mediated cell death pathway is the key mechanism for elimination of virus-infected and transformed target cells by cytotoxic lymphocytes. The formation of the immunological synapse between an effector and a target cell leads to exocytic trafficking of the secretory granules and the release of their contents, which include pro-apoptotic serine proteases, granzymes, and pore-forming perforin into the synapse. There, perforin polymerizes and forms a transmembrane pore that allows the delivery of granzymes into the cytosol, where they initiate various apoptotic death pathways. Unlike relatively redundant individual granzymes, functional perforin is absolutely essential for cytotoxic lymphocyte function and immune regulation in the host. Nevertheless, perforin is still the least studied and understood cytotoxic molecule in the immune system. In this review, we discuss the current state of affairs in the perforin field: the protein's structure and function as well as its role in immune-mediated diseases.