Aberrant maturation of mutant perforin underlies the clinical diversity of hemophagocytic lymphohistiocytosis

Genetic background of primary and familial HLH in Qatar: registry data and population study

Background

Familial hemophagocytic lymphohistiocytosis (FHLH) is an inherited life-threatening disease. Five types are identified, with the addition of congenital immunodeficiency syndromes in which HLH is a typical manifestation. The literature on this disease is very scarce in the Middle East, with only a few scattered reports.

Methods

We report detailed demographic, clinical, and genomic data from 28 patients diagnosed with primary and familial HLH over the last decade in Qatar. An evaluation was performed of allele frequencies of deleterious variants from 12 primary and familial HLH causative genes on the Qatar Genome Programme (QGP) cohort of 14,669 Qatari individuals.

Results

The genetic diagnosis was obtained in 15 patients, and four novel mutations in Perforin 1 (PRF1), UNC13D, LYST, and RAB27A genes were found. We identified 22,945 low/high/moderate/modifier impact variants significantly enriched in the QGP in those 12 genes. The variants rs1271079313 in PRF1 and rs753966933 in RAB27A found in our patient cohort were significantly more prevalent in the QGP compared to the Genome Aggregation Database (gnomAD) database, with a high carrier frequency in the Qatari population.

Conclusions

We established the first primary and familial HLH Registry in the Gulf Region and identified novel possibly pathogenic variants present at higher frequency in the Qatari population, which could be used for screening purposes. Raising awareness about primary and familial HLH and implementing screening activities in the Qatari highly inbred population could stem into more comprehensive premarital and prenatal evaluations and faster diagnosis.

Unraveling the dynamic mechanisms of natural killer cells in viral infections: insights and implications

Viruses pose a constant threat to human well-being, necessitating the immune system to develop robust defenses. Natural killer (NK) cells, which play a crucial role in the immune system, have become recognized as vital participants in protecting the body against viral infections. These remarkable innate immune cells possess the unique ability to directly recognize and eliminate infected cells, thereby contributing to the early control and containment of viral pathogens. However, recent research has uncovered an intriguing phenomenon: the alteration of NK cells during viral infections. In addition to their well-established role in antiviral defense, NK cells undergo dynamic changes in their phenotype, function, and regulatory mechanisms upon encountering viral pathogens. These alterations can significantly impact the effectiveness of NK cell responses during viral infections. This review explores the multifaceted role of NK cells in antiviral immunity, highlighting their conventional effector functions as well as the emerging concept of NK cell alteration in the context of viral infections. Understanding the intricate interplay between NK cells and viral infections is crucial for advancing our knowledge of antiviral immune responses and could offer valuable information for the creation of innovative therapeutic approaches to combat viral diseases.

Hemophagocytic Lymphohistiocytosis in Adolescents and Young Adults: Genetic Predisposition and Secondary Disease

Hemophagocytic lymphohistiocytosis (HLH) is a disorder of impaired immune regulation resulting in hyperinflammation that is ultimately fatal if not treated. HLH is categorized into familial disease, caused by genetic mutations affecting the function of cytotoxic T lymphocytes and natural killer cells, and secondary disease, triggered by infections, malignancies, rheumatologic disorders, or immune deficiency. Adolescent and young adults with HLH represent a unique population with specific diagnostic challenges. Here we review the diagnostic criteria, possible etiologies, pathophysiology, and management of HLH with focus on the adolescent population.

Dengue Fever Complicated with Hemophagocytic Lymphohistiocytosis: A Case Report of Resolution with Steroid-Sparing Supportive Care

Dengue fever (DF) can be complicated by hemophagocytic lymphohistiocytosis (HLH). Steroid administration is markedly effective for this hematologic complication, and for other viral infections. We present a rare case of DF-associated HLH that improved with steroid-sparing supportive care. A 47-year-old Japanese male with diabetes mellitus and no history of DF traveled to the Philippines 10 days before his hospitalization. Three days before emergency admission, he experienced fever and joint pain and was referred to our hospital for suspected DF, after blood tests indicated liver damage and thrombocytopenia. Erythema of the extremities and trunk appeared on day 2, and the next day neutrophils were 550 cells/μL, platelets 29,000 cells/μL, ferritin 9840 ng/mL, and fibrinogen 141 mg/dL. Bone marrow aspirate revealed hemophagocytic lymphohistiocytosis, and he was diagnosed with HLH. On day 4, the symptoms and findings improved; only supportive care without steroids was continued. He tested positive for dengue virus antigen on admission. He was discharged on day 9 of hospitalization in good general condition with no vascular leakage or bleeding and recovery of blood cells. Although steroid administration is markedly effective in cases of DF complicated by HLH, this case suggests that such cases can resolve with steroid-sparing supportive care.

[Clinical characteristics of primary hemophagocytic lymphohistiocytosis associated with perforin gene deficiency: a single-center retrospective study]

Objective: This study aimed to investigate the clinical characteristics of patients diagnosed with primary hemophagocytic lymphohistiocytosis (pHLH) associated with perforin gene deficiency. Methods: We retrospectively analyzed the clinical data of 16 pHLH patients associated with perforin gene deficiency at Beijing Friendship Hospital, Capital Medical University, from April 2014 to August 2021. The mutation sites, mutation types, family history, clinical characteristics, and prognosis of the patients were assessed. Results: A total of 16 patients, including ten males and six females, with a median onset age of 17.5 years (range: 4-42 years), were enrolled in this study. Sixteen different mutations were identified, consisting of 11 missense mutations, one nonsense mutation, two frameshift mutations, and two in-frame mutations. All patients harbored at least one deleterious missense mutation, with the most common mutation sites being c.1349C>T (p.T450M) and c.503G>A (p.S168N). Decreased natural killer (NK) cell activity was observed in 11 patients, reduced perforin protein expression in ten patients, concurrent Epstein-Barr virus (EBV) infection at onset in eight patients, a family history in two patients, and central nervous system involvement in four patients. Eleven cases underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT), with eight cases surviving. The median survival time of non-transplanted patients was eight months (range: 4-18 months), while that of transplanted patients was reported as "not reached". Conclusions: Emphasizing the diagnosis of pHLH in adults with perforin gene deficiency. In addition, it should be noted that EBV infection can potentially act as a triggering factor in such disease, and allo-HSCT exerts a substantial effect on the prognosis of patients.

The Multifaceted Immunology of Cytokine Storm Syndrome

Cytokine storm syndromes (CSSs) are potentially fatal hyperinflammatory states that share the underpinnings of persistent immune cell activation and uninhibited cytokine production. CSSs can be genetically determined by inborn errors of immunity (i.e., familial hemophagocytic lymphohistiocytosis) or develop as a complication of infections, chronic inflammatory diseases (e.g., Still disease), or malignancies (e.g., T cell lymphoma). Therapeutic interventions that activate the immune system such as chimeric Ag receptor T cell therapy and immune checkpoint inhibition can also trigger CSSs in the setting of cancer treatment. In this review, the biology of different types of CSSs is explored, and the current knowledge on the involvement of immune pathways and the contribution of host genetics is discussed. The use of animal models to study CSSs is reviewed, and their relevance for human diseases is discussed. Lastly, treatment approaches for CSSs are discussed with a focus on interventions that target immune cells and cytokines.

Hyperinflammatory syndrome, natural killer cell function and genetic polymorphisms in the pathogenesis of severe dengue

BACKGROUND

Severe dengue, characterized by shock and organ dysfunction is driven by an excessive host immune response. We investigated the role of hyperinflammation in dengue pathogenesis.

METHODS

Patients recruited into an observational study were divided into three plasma leak severity grades. Hyperinflammatory biomarkers were measured at 4 time-points. Frequencies, activation and cytotoxic potential of NK cells were analysed by flow cytometry. RNA was extracted from sorted CD56+ NK cells and libraries prepared using SMART-Seq and sequenced using HiSeq3000 (Illumina).

RESULTS

69 patients were included (grade 0: 42, grade 1: 19, grade 2: 8 patients). Patients with grade 2 leakage had higher biomarkers than grade 0, including higher peak ferritin levels (83.3% vs 45.2%) and H scores (median 148.5 vs 105.5). NK cells from grade 2 patients exhibited decreased expression of perforin and granzyme B and activation markers. RNA sequencing revealed three SNPs in NK cell functional genes associated with more severe leakage; NK cell lectin-like receptor K1 gene (KLRK1) and PRF1 gene.

CONCLUSIONS

Features of hyperinflammation are associated with dengue severity, including higher biomarkers, impaired NK cell function and polymorphisms in genes NK cell cytolyitc function genes (KLRK1 and PRF-1). Trials of immunomodulatory therapy in these patients is now warranted.

Hemophagocytic Lymphohistiocytosis Gene Variants in Multisystem Inflammatory Syndrome in Children

Simple Summary

Children with a COVID-19 infection are at risk of developing a novel syndrome called multisystem inflammatory syndrome in children (MIS-C). This disease state is characterized by a high level of inflammation. It is unclear why only some children infected with SARS-CoV-2 later develop MIS-C. There may be genetic risk factors for MIS-C development, but none have previously been reported. We report genetic findings in a group of children with MIS-C.

Abstract

Multisystem inflammatory syndrome in children (MIS-C) affects few children previously infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In 2020, 45 children admitted to our hospital for MIS-C underwent genetic screening with a commercial 109-immune-gene panel. Thirty-nine children were diagnosed with MIS-C, and 25.4% of the 39 MIS-C patients harbored rare heterozygous missense mutations either in primary hemophagocytic lymphohistiocytosis (pHLH) genes (LYST, STXBP2, PRF1, UNC13D, AP3B1) or the HLH-associated gene DOCK8 (four variants). We demonstrate that foamy virus introduction of cDNA for the four DOCK8 variants into human NK-92 natural killer (NK) cells led to decreased CD107a expression (degranulation) and decreased NK cell lytic function in vitro for each variant. Heterozygous carriers of missense mutations in pHLH genes and DOCK8 may serve as risk factors for development of MIS-C among children previously infected with SARS-CoV-2.

The pore conformation of lymphocyte perforin

Perforin is a pore-forming protein that facilitates rapid killing of pathogen-infected or cancerous cells by the immune system. Perforin is released from cytotoxic lymphocytes, together with proapoptotic granzymes, to bind to a target cell membrane where it oligomerizes and forms pores. The pores allow granzyme entry, which rapidly triggers the apoptotic death of the target cell. Here, we present a 4-Å resolution cryo-electron microscopy structure of the perforin pore, revealing previously unidentified inter- and intramolecular interactions stabilizing the assembly. During pore formation, the helix-turn-helix motif moves away from the bend in the central β sheet to form an intermolecular contact. Cryo-electron tomography shows that prepores form on the membrane surface with minimal conformational changes. Our findings suggest the sequence of conformational changes underlying oligomerization and membrane insertion, and explain how several pathogenic mutations affect function.

Carrier frequency and incidence estimation of familial hemophagocytic lymphohistiocytosis in East Asian populations by genome aggregation database (gnomAD) based analysis

OBJECTIVES

Hemophagocytic lymphohistiocytosis (HLH) is a clinical syndrome characterized by a life-threatening condition caused by severe hypercytokinemia. The hereditary forms of HLH, also called familial HLH (fHLH), have 4 different genes (PRF1, UNC13D, STX11, and STXBP2) and have been identified as being causative for fHLH. This study aimed to analyze the carrier frequency and expected incidence of fHLH in East Asians and Koreans using exome data from the Genome Aggregation Database (gnomAD).

METHODS

We analyzed 9,197 exomes for East Asian populations from gnomAD with 1,909 Korean for four fHLH genes. All identified variants were classified according to 2015 American College of Medical Genetics and Genomics and the Association for Molecular Pathology guideline.

RESULTS

19 pathogenic variant/likely pathogenic variants (PV/LPVs) were identified in 30 East Asian individuals (0.33%). Among them, 7 PV/LPVs were identified in 17 Korean individuals (0.63%). The estimated incidence of fHLH was 1 in 1,105,652 for East Asians and l in 235,128 for Koreans.

CONCLUSIONS

This study is the first to identify carrier frequencies in East Asian and Korean populations for fHLH using gnomAD. It was confirmed that the carrier frequency of fHLH patients was high in Koreans among East Asians and the incidence was also predicted to be higher than that of other East Asians. The variant spectrum of fHLH genes in East Asian and Korean populations differed greatly from those of other ethnic groups.

A rare cause of acute liver failure due to haemophagocytic lymphohistiocytosis secondary to diffuse large B-cell lymphoma

Acute liver failure is a life-threatening condition commonly caused by drug-induced hepatotoxicity or viral hepatitides. However, there are a number of rarer causes such as haemophagocytic lymphohistiocytosis. Haemophagocytic lymphohistiocytosis is a syndrome of uncontrolled immune cell activation, triggered by infection or malignancy, which carries a high mortality. Whilst mild to moderate liver injury is commonly seen with haemophagocytic lymphohistiocytosis, acute liver failure has rarely been reported in adults. We present a case of a 74-year-old man with acute liver failure secondary to haemophagocytic lymphohistiocytosis triggered by undiagnosed large B-cell lymphoma. Initially treated for biliary sepsis, there was a delay in the diagnosis of haemophagocytic lymphohistiocytosis and despite initiating chemotherapy, he died soon after. This case highlights the importance of considering haemophagocytic lymphohistiocytosis as a rare cause of acute liver failure, as given the life-threatening potential of haemophagocytic lymphohistiocytosis, a prompt diagnosis may allow early initiation of chemotherapy for any chance of survival.

Associations between PRF1 Ala91Val polymorphism and risk of hemophagocytic lymphohistiocytosis: a meta-analysis based on 1366 subjects

BACKGROUND

Perforin (PRF1) gene mutation can cause the onset of hemophagocytic lymphohistiocytosis (HLH). It has reported that PRF1 Ala91Val polymorphism was related with HLH risk. In the meta-analysis, we aim to evaluate the association between PRF1 Ala91Val polymorphism and HLH risk.

METHODS

We accomplished a meta-analysis of six published case-control studies including 391 patients with HLH and 975 controls. We evaluated the quality of each study through Newcastle-Ottawa Scale (NOS). Data analysis was performed with Stata software.

RESULTS

In general, all studies were of high quality (NOS score higher than 7). There were statistically significant between the PRF1 Ala91Val polymorphism and HLH risk though the pooled analysis [for Ala/Val vs. Ala/Ala: pooled odds ratio (OR) = 3.22, 95% confidence interval (CI) 1.08-9.56, P = 0.035, random model; for Ala/Val + Val/Val vs. Ala/Ala: pooled OR = 2.96, 95% CI 1.14-7.69, P = 0.025, random model]. Furthermore, sensitivity analysis also revealed a relationship between PRF1 Ala91Val polymorphism and HLH risk (for Ala/Val vs. Ala/Ala: pooled OR = 5.236, 95% CI 2.72-10.08, P < 0.000, I² = 12.1%, P_{heterogeneity} = 0.332; for Ala/Val + Val/Val vs. Ala/Ala, pooled OR = 4.856, 95% CI 2.66-8.85, P < 0.000, I² = 5.9%, P_{heterogeneity} = 0.373). Funnel plot and Egger's test did not indicate obvious published bias (P = 0.841 for Ala/Val vs. Ala/Ala; P = 0.284 for Ala/Val + Val/Val vs. Ala/Ala).

CONCLUSION

This meta-analysis indicated that PRF1 Ala91Val polymorphism affects the factor for developing HLH and future studies of PRF1 Ala91Val on the onset of HLH will be guaranteed.

The genetics of macrophage activation syndrome

Macrophage activation syndrome (MAS), or secondary hemophagocytic lymphohistiocytosis (HLH), is a cytokine storm syndrome associated with multi-organ system dysfunction and high mortality rates. Laboratory and clinical features resemble primary HLH, which arises in infancy (1 in 50,000 live births) from homozygous mutations in various genes critical to the perforin-mediated cytolytic pathway employed by NK cells and cytotoxic CD8 T lymphocytes. MAS/secondary HLH is about ten times more common and typically presents beyond infancy extending into adulthood. The genetics of MAS are far less defined than for familial HLH. However, the distinction between familial HLH and MAS/secondary HLH is blurred by the finding of heterozygous perforin-pathway mutations in MAS patients, which may function as hypomorphic or partial dominant-negative alleles and contribute to disease pathogenesis. In addition, mutations in a variety of other pathogenic pathways have been noted in patients with MAS/secondary HLH. Many of these genetically disrupted pathways result in a similar cytokine storm syndrome, and can be broadly categorized as impaired viral control (e.g., SH2P1A), dysregulated inflammasome activity (e.g., NLRC4), other immune defects (e.g., IKBKG), and dysregulated metabolism (e.g., LIPA). Collectively these genetic lesions likely combine with states of chronic inflammation, as seen in various rheumatic diseases (e.g., still disease), with or without identified infections, to result in MAS pathology as explained by the threshold model of disease. This emerging paradigm may ultimately support genetic risk stratification for high-risk chronic and even acute inflammatory disorders. Moving forward, continued whole-exome and -genome sequencing will likely identify novel MAS gene associations, as well as noncoding mutations altering levels of gene expression.

Emerging insights into human health and NK cell biology from the study of NK cell deficiencies

Human NK cells are innate immune effectors that play a critical roles in the control of viral infection and malignancy. The importance of their homeostasis and function can be demonstrated by the study of patients with primary immunodeficiencies (PIDs), which are part of the family of diseases known as inborn defects of immunity. While NK cells are affected in many PIDs in ways that may contribute to a patient's clinical phenotype, a small number of PIDs have an NK cell abnormality as their major immunological defect. These PIDs can be collectively referred to as NK cell deficiency (NKD) disorders and include effects upon NK cell numbers, subsets, and/or functions. The clinical impact of NKD can be severe including fatal viral infection, with particular susceptibility to herpesviral infections, such as cytomegalovirus, varicella zoster virus, and Epstein-Barr virus. While NKD is rare, studies of these diseases are important for defining specific requirements for human NK cell development and homeostasis. New themes in NK cell biology are emerging through the study of both known and novel NKD, particularly those affecting cell cycle and DNA damage repair, as well as broader PIDs having substantive impact upon NK cells. In addition, the discovery of NKD that affects other innate lymphoid cell (ILC) subsets opens new doors for better understanding the relationship between conventional NK cells and other ILC subsets. Here, we describe the biology underlying human NKD, particularly in the context of new insights into innate immune cell function, including a discussion of recently described NKD with accompanying effects on ILC subsets. Given the impact of these disorders upon human immunity with a common focus upon NK cells, the unifying message of a critical role for NK cells in human host defense singularly emerges.

Flow Cytometry as a Diagnostic Tool in Primary and Secondary Immune Deficiencies

Flow cytometry is an incredibly powerful diagnostic tool in the evaluation of primary and secondary immune deficiencies. Assay design and setup involves a methodological consideration of specimen collection, marker and fluorochrome selection, antibody titration, instrumentation, compensation, gating, reference range development, and cross validation. Commonly used analyses for lymphocytes are the lymphocyte subset, T-cell subset, B-cell and T-cell naive/memory, double-negative T-cell, and plasmablast panels. Flow cytometry has direct clinical applicability to the workup of severe forms of primary immune deficiency disorders and is used diagnostically and for therapeutic monitoring in the context of secondary immune deficiency disorders.

Type 2 familial hemophagocytic lymphohistiocytosis in half brothers: A case report

RATIONALE

We describe a novel case of half-brothers suffering from type 2 familial hemophagocytic lymphohistiocytosis (FHL).

PATIENT CONCERNS

A 15-year-old Chinese child was admitted to the hematology department. PRF1 gene coding revealed that he was c.282C>A/p.N94K heterozygous and had a c.1349C>T/p.T450M heterozygous mutation. One year later, his younger halfbrother suffered from the same disease. PRF1 gene coding revealed that the younger brother was c.282C>A/p.T450M heterozygous with a c.1349C>T/p.T450M heterozygous mutation. His mother and grandfather were confirmed to have c.1349C>T/p.T450M heterozygous mutations in exon 3.

DIAGNOSES

Half-brothers were diagnosed for type 2 familial hemophagocytic lymphohistiocytosis INTERVENTIONS:: To our knowledge, this is a possible FHL and the children's mother may be a pathogenic gene carrier.

OUTCOMES

After being treated with the HLH-04 schedule, the symptoms of half-brothers were all improved.

LESSONS SUBSECTIONS

Therefore, once FHL is diagnosed, HSCT needs to be done early, even if no perfect match is found.

Primary hemophagocytic lymphohistiocytosis in adults: the utility of family surveys in a single-center study from China

Background

This study investigated the clinical characteristics of primary hemophagocytic lymphohistiocytosis (HLH) in adults, including immunological markers, pedigree findings, and conditions of allogeneic hematopoietic stem cell transplantation (Allo-HSCT).

Methods

The study included clinical data of 18 adult patients with primary HLH treated in our center from June 2010 to January 2017.

Results

Of these 18 cases, pathogenic variants were found in the following genes: PRF1 (n = 11), UNC13D (n = 5), SH2D1A (n = 2), RAB27a (n = 1), and LYST (n = 2). One patient had pathogenic variants in both PRF1 and UNC13D genes, one patient had pathogenic variants in both LYST and UNC13D genes and another patient had pathogenic variants in both PRF1 and SH2D1A genes. Additionally, 3 of the 18 cases involved homozygous pathogenic variants, while 2 cases involved hemizygous pathogenic variants. The remaining 13 cases involved compound heterozygous pathogenic variants. The natural killer (NK) cell activity test was conducted in all 18 cases where 14(77.8%)patients showed reduction in NK cell activity. Furthermore, this article presents 3 representative results of the pedigree findings from 12 patients who underwent family surveys. The 8 patients who underwent Allo-HSCT had a median survival of 27.2 months, as compared with the median survival of 7 months for the10 patients who did not undergo Allo-HSCT, a significant difference between the two groups of patients (p = 0.006).

Conclusion

PRF1 was one of the most commonly mutated gene in adult patients with primary HLH. Family surveys and immunological markers were important for the HLH diagnosis and the selection of an appropriate donor. Allo-HSCT was an effective therapy for adult primary HLH.

Human perforin gene variation is geographically distributed

Background

Deleterious mutations in PRF1 result in lethal, childhood disease, familial hemophagocytic lymphohistiocytosis type 2 (FHL 2). However, not all mutations in PRF1 are deleterious and result in FHL 2. Currently, these nondeleterious mutations are being investigated in the onset of numerous disorders, such as lymphomas and diabetes. Yet, there is still an overwhelmingly large amount of PRF1 mutations that are not associated with disease.

Methods

We conducted a post hoc analysis of the PRF1 mutations in the coding region using the recently published Exome Aggregation Consortium genomes, Leiden Open Variation Database, NCBI SNP database, and primary literature to better understand PRF1 variation in the human population.

Results

This study catalogs 460 PRF1 mutations in the coding region, and demonstrates PRF1 is more variant then previously predicted. We identify key PRF1 mutations with high allelic frequency and are only found in certain populations. Additionally, we define PRF1SNVs are geographically distributed.

Conclusions

This study concludes with a novel hypothesis that nondeleterious mutation in PRF1, which decreases perforin expression and/or activity, may be an example of selective advantage in the context of environmental stressors prevalent near the equator. Our studies illustrate how perforin deficiency can be protective from injuries resulting in blood–brain barrier (BBB) disruption.

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.

Finding a Balance between Protection and Pathology: The Dual Role of Perforin in Human Disease

Perforin is critical for controlling viral infection and tumor surveillance. Clinically, mutations in perforin are viewed as unfavorable, as lack of this pore-forming protein results in lethal, childhood disease, familial hemophagocytic lymphohistiocytosis type 2 (FHL 2). However, many mutations in the coding region of PRF1 are not yet associated with disease. Animal models of viral-associated blood–brain barrier (BBB) disruption and experimental cerebral malaria (ECM) have identified perforin as critical for inducing pathologic central nervous system CNS vascular permeability. This review focuses on the role of perforin in both protecting and promoting human disease. It concludes with a novel hypothesis that diversity observed in the PRF1 gene may be an example of selective advantage that protects an individual from perforin-mediated pathology, such as BBB disruption.

Dengue-associated hemophagocytic lymphohistiocytosis in an adult: A case report and literature review

BACKGROUND

Infection-associated hemophagocytic syndrome (IAHS) is potentially a fatal disease caused by systemic infection complicated by hemophagocyticlymphohistiocytosis (HLH). Here, we report a case of HLH associated with dengue hemorrhagic fever (DHF) after a trip to Thailand.

CASE SUMMARY

A 33-year-old healthy female patient presented with 3 days of fever, myalgia, and skin rash. Serotype 3 dengue virus was isolated. Clinical and laboratory findings fulfilled the criteria of HLH. After the initiation of corticosteroid therapy, the patient recovered and laboratory findings were normalized.

CONCLUSION

It would be important to differentially diagnose dengue-associated HLH from severe DHF. Early recognition and initiation of steroid treatment would be crucial for the successful treatment of dengue fever complicated by HLH.

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.

Whole-Exome Sequencing Reveals Mutations in Genes Linked to Hemophagocytic Lymphohistiocytosis and Macrophage Activation Syndrome in Fatal Cases of H1N1 Influenza

BACKGROUND

Severe H1N1 influenza can be lethal in otherwise healthy individuals and can have features of reactive hemophagocytic lymphohistiocytosis (HLH). HLH is associated with mutations in lymphocyte cytolytic pathway genes, which have not been previously explored in H1N1 influenza.

METHODS

Sixteen cases of fatal influenza A(H1N1) infection, 81% with histopathologic hemophagocytosis, were identified and analyzed for clinical and laboratory features of HLH, using modified HLH-2004 and macrophage activation syndrome (MAS) criteria. Fourteen specimens were subject to whole-exome sequencing. Sequence alignment and variant filtering detected HLH gene mutations and potential disease-causing variants. Cytolytic function of the PRF1 p.A91V mutation was tested in lentiviral-transduced NK-92 natural killer (NK) cells.

RESULTS

Despite several lacking variables, cases of influenza A(H1N1) infection met 44% and 81% of modified HLH-2004 and MAS criteria, respectively. Five subjects (36%) carried one of 3 heterozygous LYST mutations, 2 of whom also possessed the p.A91V PRF1 mutation, which was shown to decrease NK cell cytolytic function. Several patients also carried rare variants in other genes previously observed in MAS.

CONCLUSIONS

This cohort of fatal influenza A(H1N1) infections confirms the presence of hemophagocytosis and HLH pathology. Moreover, the high percentage of HLH gene mutations suggests they are risk factors for mortality among individuals with influenza A(H1N1) infection.

[Expression of porforin and granzyme B in familial hemophagocytic lymphohistiocytosis]

OBJECTIVE

To analyze the correlation between genetic variants of PRF1 and expression level of perforin and granzyme B protein, and further determine the relationship between PRF1 gene variants and cytotoxic T lymphocyte/natural killer (CTL/NK) cell function in famililal hemophagocytic lymphohistiocytosis (FHL2).

METHODS

Eight children of FHL2 (P1-P8) after treatment, as well as parents and siblings of P1-P5 were included, and thirty healthy children came for physical examination were designated as controls. PRF1, Unc13D, STX11, STXBP2, RAB27A, LYST, SH2D1A, BIRC4 exons were amplified by PCR and followed by direct sequencing. Bioinformatics analysis of mutant PRF1 was performed by ExPASy online system. Perforin and granzyme B expression on cytotoxic lymphocyte was detected by flow cytometry.

RESULTS

① Three of eight FHL2 children harbored heterozygous missense of PRF1 exons: P1 had compound heterozygous missense mutations (R4C and R33H) and P2 had heterozygous mutations (V50L), P3 had heterozygous mutations (R489W), which confirmed the diagnosis of FHL2. The father (F1) and younger brother (B1) of P1 also had compound heterozygous missense mutation (R4C/R33H), the mother (M2) and younger brother (B2) of P2 had V50L mutation, the father (F3) of P3 had no R489W mutation and the mother of P3 did not participate in this research, so mutation of R4C/R33H of P1 inherited from paternal line, and V50L mutation of P2 came from maternal line, R489W mutation of P3 came from maternal line. ② Comparing to control group, perforin expression of CD8(+) T cells and natural killer (NK) cells of P1, F1, B1, P2, M2 and B2 decreased significantly, but there was no significant difference between two groups in terms of granzyme B expression.

CONCLUSIONS

R4C/R33H compound heterozygous mutation and V50L heterozygous mutation all cause lower expression of perforin on CTL/NK cells, and may be causative mutations for familial hemophagocytic lymphohistiocytosis.

A Heterozygous RAB27A Mutation Associated with Delayed Cytolytic Granule Polarization and Hemophagocytic Lymphohistiocytosis

Frequently fatal, primary hemophagocytic lymphohistiocytosis (HLH) occurs in infancy resulting from homozygous mutations in NK and CD8 T cell cytolytic pathway genes. Secondary HLH presents after infancy and may be associated with heterozygous mutations in HLH genes. We report two unrelated teenagers with HLH and an identical heterozygous RAB27A mutation (c.259G→C). We explore the contribution of this Rab27A missense (p.A87P) mutation on NK cell cytolytic function by cloning it into a lentiviral expression vector prior to introduction into the human NK-92 cell line. NK cell degranulation (CD107a expression), target cell conjugation, and K562 target cell lysis was compared between mutant- and wild-type-transduced NK-92 cells. Polarization of granzyme B to the immunologic synapse and interaction of mutant Rab27A (p.A87P) with Munc13-4 were explored by confocal microscopy and proximity ligation assay, respectively. Overexpression of the RAB27A mutation had no effect on cell conjugate formation between the NK and target cells but decreased NK cell cytolytic activity and degranulation. Moreover, the mutant Rab27A protein decreased binding to Munc13-4 and delayed granzyme B polarization toward the immunologic synapse. This heterozygous RAB27A mutation blurs the genetic distinction between primary and secondary HLH by contributing to HLH via a partial dominant-negative effect.

Practical NK cell phenotyping and variability in healthy adults

Human natural killer (NK) cells display a wide array of surface and intracellular markers that indicate various states of differentiation and/or levels of effector function. These NK cell subsets exist simultaneously in peripheral blood and may vary among individuals. We examined variety among selected NK cell receptors expressed by NK cells from normal donors, as well as the distribution of select NK cell subsets and NK cell receptor expression over time in several individual donors. Peripheral blood mononuclear cells were evaluated using flow cytometry via fluorochrome-conjugated antibodies against a number of NK cell receptors. Results were analyzed for both mean fluorescence intensity (MFI) and the percent positive cells for each receptor. CD56(bright) and CD56(dim) NK cell subsets were also considered separately, as was variation in receptor expression in NK cell subsets over time in selected individuals. Through this effort, we provide ranges of NK cell surface receptor expression for a local adult population as well as provide insight into intra-individual variation.

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.

Variations of the perforin gene in patients with chronic inflammatory demyelinating polyradiculoneuropathy

Perforin (PRF) has a key role in the function of cytotoxic T and natural killer cells. Rare variations of PRF1 predispose to autoimmunity. Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an autoimmune disease of the peripheral nervous system, involving defective lymphocyte apoptosis. The aim of this study was to investigate the role of PRF1 in CIDP. The entire coding region of PRF1 was sequenced in 94 patients and 158 controls. We found three missense variations leading to amino acid substitutions and one nonsense variation resulting in a premature stop codon. All variations would decrease PRF activity. Their overall frequency was significantly higher in patients than in controls (odds ratio (OR)=4.47). The most frequent variation was p.Ala91Val (OR=3.92) previously associated with other autoimmune diseases. Clinical analysis showed that PRF1 variations were more frequent in relapsing patients and in patients displaying axonal damage. These data suggest that PRF1 variations may influence CIDP development and course.

Hemophagocytic lymphohistiocytosis: review of etiologies and management

Hemophagocytic lymphohistiocytosis (HLH) covers a wide array of related life-threatening conditions featuring ineffective immunity characterized by an uncontrolled hyperinflammatory response. HLH is often triggered by infection. Familial forms result from genetic defects in natural killer cells and cytotoxic T-cells, typically affecting perforin and intracellular vesicles. HLH is likely under-recognized, which contributes to its high morbidity and mortality. Early recognition is crucial for any reasonable attempt at curative therapy to be made. Current treatment regimens include immunosuppression, immune modulation, chemotherapy, and biological response modification, followed by hematopoietic stem-cell transplant (bone marrow transplant). A number of recent studies have contributed to the understanding of HLH pathophysiology, leading to alternate treatment options; however, much work remains to raise awareness and improve the high morbidity and mortality of these complex conditions.

An A91V SNP in the perforin gene is frequently found in NK/T-cell lymphomas

NK/T-cell lymphoma (NKTCL) is the most frequent EBV-related NK/T-cell disease. Its clinical manifestations overlap with those of familial haemophagocytic lymphohistiocytosis (FHLH). Since PERFORIN (PRF1) mutations are present in FHLH, we analysed its role in a series of 12 nasal and 12 extranasal-NKTCLs. 12.5% of the tumours and 25% of the nasal-origin cases had the well-known g.272C>T(p.Ala91Val) pathogenic SNP, which confers a poor prognosis. Two of these cases had a double-CD4/CD8-positive immunophenotype, although no correlation was found with perforin protein expression. p53 was overexpressed in 20% of the tumoral samples, 80% of which were of extranasal origin, while none showed PRF1 SNVs. These results suggest that nasal and extranasal NKTCLs have different biological backgrounds, although this requires validation.

Human immunodeficiency syndromes affecting human natural killer cell cytolytic activity

Natural killer (NK) cells are lymphocytes of the innate immune system that secrete cytokines upon activation and mediate the killing of tumor cells and virus-infected cells, especially those that escape the adaptive T cell response caused by the down regulation of MHC-I. The induction of cytotoxicity requires that NK cells contact target cells through adhesion receptors, and initiate activation signaling leading to increased adhesion and accumulation of F-actin at the NK cell cytotoxic synapse. Concurrently, lytic granules undergo minus-end directed movement and accumulate at the microtubule-organizing center through the interaction with microtubule motor proteins, followed by polarization of the lethal cargo toward the target cell. Ultimately, myosin-dependent movement of the lytic granules toward the NK cell plasma membrane through F-actin channels, along with soluble N-ethylmaleimide-sensitive factor attachment protein receptor-dependent fusion, promotes the release of the lytic granule contents into the cleft between the NK cell and target cell resulting in target cell killing. Herein, we will discuss several disease-causing mutations in primary immunodeficiency syndromes and how they impact NK cell-mediated killing by disrupting distinct steps of this tightly regulated process.

Structural and functional analysis of perforin mutations in association with clinical data of familial hemophagocytic lymphohistiocytosis type 2 (FHL2) patients

Perforin plays a key role in the immune system via pore formation at the target cell membrane in the elimination of virus-infected and transformed cells. A vast number of observed mutations in perforin impair this mechanism resulting in a rare but fatal disease, familial hemophagocytic lymphohistiocytosis type 2 (FHL2). Here we report a comprehensive in silico structural analysis of a collection of 76 missense perforin mutations based on a proposed pore model. In our model, perforin monomers oligomerize having cyclic symmetry in consistent with previously found experimental constraints yet having flexibility in the size of the pore and the number of monomers involved. Clusters of the mutations on the model map to three distinct functional regions of the perforin. Calculated stability (free energy) changes show that the mutations mainly destabilize the protein structure, interestingly however, A91V polymorphism, leads to a more stable one. Structural characteristics of mutations help explain the severe functional consequences on perforin deficient patients. Our study provides a structural approach to the mutation effects on the perforin oligomerization and impaired cytotoxic function in FHL2 patients.

Natural killer cell deficiency

Natural killer (NK) cells are part of the innate immune defense against infection and cancer and are especially useful in combating certain viral pathogens. The utility of NK cells in human health has been underscored by a growing number of persons who are deficient in NK cells and/or their functions. This can be in the context of a broader genetically defined congenital immunodeficiency, of which there are more than 40 presently known to impair NK cells. However, the abnormality of NK cells in certain cases represents the majority immunologic defect. In aggregate, these conditions are termed NK cell deficiency. Recent advances have added clarity to this diagnosis and identified defects in 3 genes that can cause NK cell deficiency, as well as some of the underlying biology. Appropriate consideration of these diagnoses and patients raises the potential for rational therapeutic options and further innovation.

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.

Gene-expression signatures differ between different clinical forms of familial hemophagocytic lymphohistiocytosis

We performed gene-expression profiling of PBMCs obtained from patients with familial hemophagocytic lymphohistiocytosis (FHL) to screen for biologic correlates with the genetic and/or clinical forms of this disease. Unsupervised hierarchical clustering of 167 differentially expressed probe sets, representing 143 genes, identified 3 groups of patients corresponding to the genetic forms and clinical presentations of the disease. Two clusters of up- and down-regulated genes separated patients with perforin-deficient FHL from those with unidentified genetic cause(s) of the disease. The clusterscomprised genes involved in defense/immune responses, apoptosis, zinc homeostasis, and systemic inflammation. Unsupervised hierarchical clustering partitioned patients with unknown genetic cause(s) of FHL into 2 well-distinguished subgroups. Patterns of up- and down-regulated genes separated patients with “late-onset” and “relapsing” forms of FHL from patients with an “early onset and rapidly evolving” form of the disease. A cluster was identified in patients with “late onset and relapsing” form of FHL related to B- and T-cell differentiation/survival, T-cell activation, and vesicular transport. The resulting data suggest that unique gene-expression signatures can distinguish between genetic and clinical subtypes of FHL. These differentially expressed genes may represent biomarkers that can be used as predictors of disease progression.

Familial Hemophagocytic Lymphohistiocytosis with A665G Perforin Gene Mutation: A Case Report

Familial hemophagocytic lymphohistiocytosis (FHL) is a genetically heterogeneous disease. Presentation of the disease such as primarily fever, hepatosplenomegaly, and cytopenia, which are the results of functional degradation in cytotoxic T-lymphocytes and natural killer cells, activation of macrophages and T-lymphocytes, over production of proinflammatory cytokines, and hemophagocytosis. In all, 5 genetic loci have been identified in FHL, and all known affected genes encode critical components of the granule exocytosis pathway, which is essential for the release of cytotoxic granules and proteases that are necessary for targeted cell death. Herein we present an FHL patient with a severe clinical course and a very rare perforin gene mutation. The patient was homozygous for A665G mutation. However, the child died in a short period of time. Prenatal diagnosis was performed in the family and the fetus was found to be heterozygous for the mutation.

A novel Dutch mutation in UNC13D reveals an essential role of the C2B domain in munc13-4 function

BACKGROUND

UNC13D, encoding the protein munc13-4, is essential in intracellular trafficking and exocytosis of lytic granules. Mutations in this gene are associated with familial hemophagocytic lymphohistiocytosis type 3 (FHL3), a genetically heterogeneous, rare autosomal recessive immune disorder. How mutations affect function of munc13-4 is poorly understood. Since 2006 we genetically identified seven FHL patients with mutations in UNC13D.

PROCEDURES

Here, we report for the first time a c.2695C>T (p.Arg899X) mutation in exon 28 of UNC13D in three young unrelated Dutch patients. The mutation causes a premature stop codon and encodes munc13-4(1-899), which lacks the C-terminal C2 domain. Genealogical research and haplotyping of the patient families demonstrated that a single ancestral founder introduced the mutation in the Netherlands. We then characterized the mutant protein phenotypically in cell biological and immunological assays.

RESULTS

Munc13-4(1-899) was correctly targeted to CD63-positive secretory lysosomes, although its stability was reduced and dynamic turnover on the granule membrane became uncoupled from receptor signaling. In accord, and in contrast to wild-type munc13-4, ectopically expressed mutant failed to rescue degranulation in cells with silenced endogenous munc13-4.

CONCLUSIONS

The functional and clinical data showed that this novel Dutch founder mutation leads to severe early onset of FHL3 due to misfolding and degradation of munc13-4(1-899).

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.

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.

Gene expression profiling of peripheral blood mononuclear cells from children with active hemophagocytic lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (FHL) is a rare, genetically heterogeneous autosomal recessive immune disorder that results when the critical regulatory pathways that mediate immune defense mechanisms and the natural termination of immune/inflammatory responses are disrupted or overwhelmed. To advance the understanding of FHL, we performed gene expression profiling of peripheral blood mononuclear cells from 11 children with untreated FHL. Total RNA was isolated and gene expression levels were determined using microarray analysis. Comparisons between patients with FHL and normal pediatric controls (n = 30) identified 915 down-regulated and 550 up-regulated genes with more than or equal to 2.5-fold difference in expression (P ≤ .05). The expression of genes associated with natural killer cell functions, innate and adaptive immune responses, proapoptotic proteins, and B- and T-cell differentiation were down-regulated in patients with FHL. Genes associated with the canonical pathways of interleukin-6 (IL-6), IL-10 IL-1, IL-8, TREM1, LXR/RXR activation, and PPAR signaling and genes encoding of antiapoptotic proteins were overexpressed in patients with FHL. This first study of genome-wide expression profiling in children with FHL demonstrates the complexity of gene expression patterns, which underlie the immunobiology of FHL.

Genotype-phenotype study of familial haemophagocytic lymphohistiocytosis type 3

BACKGROUND

Mutations of UNC13D are causative for familial haemophagocytic lymphohistiocytosis type 3 (FHL3; OMIM 608898).

OBJECTIVE

To carry out a genotype-phenotype study of patients with FHL3.

METHODS

A consortium of three countries pooled data on presenting features and mutations from individual patients with biallelic UNC13D mutations in a common database.

RESULTS

84 patients with FHL3 (median age 4.1 months) were reported from Florence, Italy (n=54), Hamburg, Germany (n=18), Stockholm, Sweden (n=12). Their ethnic origin was Caucasian (n=57), Turkish (n=10), Asian (n=7), Hispanic (n=4), African (n=3) (not reported (n=3)). Thrombocytopenia was present in 94%, splenomegaly in 96%, fever in 89%. The central nervous system (CNS) was involved in 49/81 (60%) patients versus 36% in patients with FHL2 (p=0.001). A combination of fever, splenomegaly, thrombocytopenia and hyperferritinaemia was present in 71%. CD107a expression, NK activity and Munc 13-4 protein expression were absent or reduced in all but one of the evaluated patients. 54 different mutations were observed, including 15 new ones: 19 missense, 14 deletions or insertions, 12 nonsense, nine splice errors. None was specific for ethnic groups. Patients with two disruptive mutations were younger than patients with two missense mutations (p<0.001), but older than comparable patients with FHL2 (p=0.001).

CONCLUSION

UNC13D mutations are scattered over the gene. Ethnic-specific mutations were not identified. CNS involvement is more common than in FHL2; in patients with FHL3 and disruptive mutations, age at diagnosis is significantly higher than in FHL2. The combination of fever, splenomegaly, thrombocytopenia and hyperferritinaemia appears to be the most easily and frequently recognised clinical pattern and their association with defective granule release assay may herald FHL3.

Contemporary diagnostic methods for hemophagocytic lymphohistiocytic disorders

Hemophagocytic lymphohistiocytosis is a life-threatening multi-system hyperinflammatory disorder characterized by dysfunctional cytolytic lymphocyte responses, hypercytokinemia, and widespread lymphohistiocytic tissue infiltration and destruction. Diagnosis and definitive therapy are often delayed as clinical efforts are directed toward treatment of presumed overwhelming infection. Sporadic cases occur in association with underlying immune dysfunction related to autoimmune disease, malignancy, or severe infection. However, familial cases predominate with remarkable associations between underlying genetic defects and dysregulation of immune responses. Here, we review the genetic and immunologic basis of contemporary diagnostic methods for hemophagocytic lymphohistiocytosis.

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.

Mutations of perforin gene in Chinese patients with acute lymphoblastic leukemia

To address whether mutations and single nucleotide polymorphisms (SNPs) in perforin gene (PRF1) are correlated with acute lymphoblastic leukemia (ALL) in Chinese, we screened mutations in codon region of PRF1 in 111 ALL patients, and correlated the results with patients' immunophenotype, karyotype and fusion genes. Four novel monoallelic missense and two novel monoallelic synonymous mutations (G198R, R225Q, D486G, R509K, S388S and Q540Q) were identified in 9 B-ALL, of whom 7 cases carried BCR-ABL gene, one carried MLL-AF4 fusion gene, and one lost two chromosomes. Our results suggest that mutations in PRF1 may play a role in the pathogenesis of B-ALL.