PLCG2-associated immune dysregulation (PLAID) comprises broad and distinct clinical presentations related to functional classes of genetic variants.

BACKGROUND: Pathogenic variants of phospholipase C gamma 2 (PLCG2) cause 2 related forms of autosomal-dominant immune dysregulation (ID), PLCγ2-associated antibody deficiency and immune dysregulation (PLAID) and autoinflammatory PLAID (APLAID). Since describing these conditions, many PLCG2 variants of uncertain significance have been identified by clinical sequencing of patients with diverse features of ID. OBJECTIVE: We sought to functionally classify PLCG2 variants and explore known and novel genotype-function-phenotype relationships. METHODS: Clinical data from patients with PLCG2 variants were obtained via standardized questionnaire. PLCG2 variants were generated by mutagenesis of enhanced green fluorescent protein (EGFP)-PLCG2 plasmid, which was overexpressed in Plcg2-deficient DT-40 B cells. B-cell receptor-induced calcium flux and extracellular signal-regulated kinase phosphorylation were assayed by flow cytometry. In some cases, stimulation-induced calcium flux was also measured in primary patient cells. RESULTS: Three-fourths of PLCG2 variants produced functional alteration of B-cell activation, in vitro. Thirteen variants led to gain of function (GOF); however, most functional variants defined a new class of PLCG2 mutation, monoallelic loss of function (LOF). Susceptibility to infection and autoinflammation were common with both GOF and LOF variants, whereas a new phenotypic cluster consisting of humoral immune deficiency, autoinflammation, susceptibility to herpesvirus infection, and natural killer cell dysfunction was observed in association with multiple heterozygous LOF variants detected in both familial and sporadic cases. In some cases, PLCG2 variants produced greater effects in natural killer cells than in B cells. CONCLUSIONS: This work expands the genotypic and phenotypic associations with functional variation in PLCG2, including a novel form of ID in carriers of heterozygous loss of PLCG2 function. It also demonstrates the need for more diverse assays for assessing the impact of PLCG2 variants on human disease.

Genetics of inborn errors of immunity: Diagnostic strategies and new approaches to CNV detection.

BACKGROUND: Genetic diagnosis of inborn errors of immunity (IEI) is complex due to the large number of genes involved and their molecular features. Missense variants have been reported as the most common cause of IEI. However, the frequency of copy number variants (CNVs) may be underestimated since their detection requires specific quantitative techniques. At this point, the use of Next Generation Sequencing (NGS) is acquiring relevance. METHODS: In this article, we present our experience in the genetic diagnosis of IEI based on three diagnostic algorithms that allowed the detection of single nucleotide variants (SNVs) and CNVs. Following this approximation, 703 index cases were evaluated between 2014 and 2021. Sanger sequencing, MLPA, CGH array, breakpoint spanning PCR or a customized NGS-based multigene-targeted panel were performed. RESULTS: A genetic diagnosis was reached in 142 of the 703 index cases (20%), 19 of them presented deletions as causal variants. Deletions were also detected in 5 affected relatives and 16 healthy carriers during the family studies. Additionally, we compile, characterize and present all the CNVs detected by our diagnostic algorithms, representing the largest cohort of deletions related to IEI to date. Furthermore, three bioinformatic tools (LACONv, XHMM, VarSeq™) based on NGS data were evaluated. VarSeq™ was the most sensitive and specific bioinformatic tool; detecting 21/23 (91%) deletions located in captured regions. CONCLUSION: Based on our results, we propose a strategy to guide the molecular diagnosis that can be followed by expert and non-expert centres in the field of IEI.

Characteristics of large granular lymphocyte leukemia associated with variable common immunodeficiency disorders: A study of 12 cases.

OBJECTIVES: Common Variable Immunodeficiency Disorders (CVID) and Large Granular Lymphocytes leukemia (LGLL) exhibit diverse clinical manifestations including infections, dysimmunity, and lymphoproliferation. Recent decades have seen the discovery of new genes in the lymphopoiesis pathway, such as JAK-STAT. This case series supplemented by a literature review aims to describe clinical and biological characteristics of patients with both CIVD and LGLL. METHODOLOGY: Patients were included through a call for comments to French and Belgian centers and through a literature review via PubMed. Clinical characteristics were compared to two large French cohort involving CVID and LGLL patients. RESULTS: Twelve patients were included. In all cases, CVID precedes LLGL (median diagnosis delay for LLGL was 7 years). Most cases presented with splenomegaly and autoimmune cytopenia. Ten out of 12 patients underwent splenectomy during follow up. CONCLUSIONS: Patients with LGLL and CVID differ from patients without immune deficiency in term of clinical presentation and prognosis. We suggest CVID may act as a trigger of LGL lymphocytosis, due to endogenous and exogenous antigenic pressure leading to the selection of a dominant LGL clone and stimulation of the JAK-STAT pathway. The role of splenomegaly and splenectomy in LGLL onset warrant further investigation in future studies.

Life quality, depression, and anxiety levels in parents of children with primary immunodeficiency.

BACKGROUND: Primary immune deficiencies (PID) encompasses genetic disorders that result in recurrent infections and immune dysregulation, often increasing the risk of malignancies. The aim of this study is to determine the quality of life, depression, and anxiety in parents of children with PID. METHODS: Various validated assessment tools, including the Beck Depression Inventory (BDI), State and Trait Anxiety Inventory (STAI), the 36-item Short Form Survey (SF-36), and a demographic form, were employed to gather data from 85 parents of 64 PID patients and 85 parents of 75 healthy children. RESULTS: The findings reveal that parents of PID patients exhibited higher BDI, STAI-S, STAI-T, and fatigue subdomain of SF-36 (p = .013, p = .013, p = .027, p = .000). Both parents had lower energy levels than the normal population, but mothers experienced higher levels of anxiety and depression. PID mothers' had higher scores than fathers of PID patients with healthy children in BDI, STAI-S, and STAI-T (p = .002, p = .010, p = .001). Mothers of PID patients reported lower scores in RLEP, E/F, EWB, P, and GH compared to fathers (p = .009, p = .005, p = .034, p = .001, p = .003). Additionally, the study found that STAI-T influenced all subdimensions of HRQOL. These results highlight the substantial emotional and psychological burden placed on parents caring for children with PID. CONCLUSION: The study underscores the importance of supporting caregivers to enhance the overall well-being of both parents and children with PID. Such support can potentially alleviate depression and anxiety levels among parents, ultimately improving their quality of life and aiding in the management of children with PID.

Neurological involvement in patients with primary immunodeficiency.

INTRODUCTION: Primary immunodeficiency diseases (PID) are defined by recurrent infections, allergies, autoimmunity, and malignancies. Neurologic symptoms are one of the major components of some immunodeficiency syndromes, such as Ataxia-Telangiectasia (AT), Nijmegen breakage syndrome (NBS), and Purine Nucleoside Phosphorylase (PNP) deficiency, which are considered as the primary involvement. Various pathological mechanisms, DNA repair disorders, metabolic abnormalities, and autoimmune phenomena have also been linked with neurological conditions. MATERIALS AND METHOD: We retrospectively assessed the neurological involvement in 108 patients out of 6000 with PID in this study. RESULTS: The female/male ratio of the cases was 49/59, and the median age was 13 years (min = 1; max = 60). Neurological problems were detected at a median age of 7 years (min = 0.5; max = 30). Di George Syndrome (DGS) and CVID (common variable immunodeficiency) were the most common diseases in our cohort (n = 31, 30% and n = 30, 27%, respectively). The most frequent outcomes were cognitive delay (n = 63, 58%), epilepsy (n = 25, 23%), and ataxia (n = 20, 18%). Central nervous system involvement was found in 99% of the patients (n = 107), and peripheral nervous system complication was found in only one patient with CVID and chronic inflammatory demyelinating polyneuropathy (CDIP). Cranial MRI was found to be abnormal in 74% (n = 80) of the patients. MRI findings included cerebellar atrophy (n = 33, 34%), white matter lesion (n = 27, 28.4%), cerebral atrophy (n = 21, 22.3%), gray matter lesion (n = 6, 6.3%), hydrocephalus (n = 5, 5,3%), and pituitary gland lesion (n = 3, 3.2%), intracranial hemorrhage (n = 3, 3%), intracranial vasculitis (n = 3, 2.7%), and arterio-venous malformation (n = 1, 0,9%). Primary involvement (a component of the disease) was 60% (n = 65), and secondary (infection or autoimmunity) and tertiary involvements (structural or incidental lesions) contributed 20% (n = 20) each in the patients. CONCLUSION: In this study, we describe the various neurologic findings of patients with PID. The neurologic presentation may represent the initial manifestation of certain types of PID. Early diagnosis and treatment are essential to prevent or reduce further neurologic damages.

Combined IFN-γ and JAK inhibition to treat hemophagocytic lymphohistiocytosis in mice.

BACKGROUND: Familial hemophagocytic lymphohistiocytosis is a life-threatening hyperinflammatory disease caused by genetic defects in the granule-mediated cytotoxic pathway. Success of hematopoietic cell transplantation, the only cure, is correlated with the extent of disease control before transplantation. Unfortunately, disease refractoriness and toxicities to standard chemotherapy-based regimens are fatal in a fraction of patients. Novel targeted immunotherapies, such as IFN-γ blocking antibodies or ruxolitinib, a Janus kinase (JAK) 1/2 inhibitor, are promising but only partially effective at controlling disease. OBJECTIVE: We asked whether combinations of cytokine-targeted therapies, using antibodies or JAK inhibitor, work synergistically to counteract HLH. METHODS: Genetically predisposed mice were infected and treated with distinct combinations of immunotherapies. Disease outcome was monitored and compared to monotherapies. RESULTS: We showed that inhibiting IL-6 or IL-18 signaling in combination with IFN-γ blockade or ruxolitinib did not increase disease control compared to anti-IFN-γ antibodies or ruxolitinib monotherapies. In contrast, clinically relevant doses of ruxolitinib combined with low doses of anti-IFN-γ blocking antibodies corrected cytopenias, prevented overt neutrophilia, limited cytokinemia, and resolved HLH immunopathology and symptomatology. CONCLUSIONS: Our findings demonstrate that IFN-γ blockade and ruxolitinib act synergistically to suppress HLH progression. This supports the use of combined cytokine-targeted therapies as a bridge to hematopoietic cell transplantation in severe familial hemophagocytic lymphohistiocytosis.

Pregnancy in primary immunodeficiency diseases: The PREPI study.

BACKGROUND: Primary immunodeficiencies (PID) are a heterogeneous group of rare inborn immunity defects. As management has greatly improved, morbidity and mortality are reduced in this population, while our knowledge on pregnancy's unfolding and outcome remains scarce. OBJECTIVE: We conducted a retrospective monocentric study to study pregnancy outcomes in women with PID. METHODS: The study cohort consisted of women over 18 included in the national registry for PID (CEREDIH), living in the greater Paris area, reporting ≥1 pregnancy. Data were collected through a standardized questionnaire and medical records. We analyzed PID features, pregnancy course and outcome, and neonatal features (NCT04581460). RESULTS: We studied 93 women with PID (27 combined immunodeficiencies, 51 predominantly antibody deficiencies, and 15 innate immunodeficiencies) and their 222 pregnancies (67, 119, and 36 in each group, respectively). One hundred fifty-four (69%) of 222 pregnancies led to 157 live births, including 4 severe preterm births (3%), in the range of pregnancy outcome in the French general population. In a multivariate model, poor obstetrical outcome (fetal loss or pregnancy termination) was associated with history of severe infection (adjusted odds ratio 0.28, 95% confidence interval 0.11-0.67, P = .005). Only 59% pregnancies were led with optimal anti-infective prophylaxis; severe infections were reported in only 2 pregnancies (1%). One infant died during the neonatal period. CONCLUSION: Pregnancy is achievable in women with a wide group of PID. Prematurity is increased and history of severe infection is associated with significant increase of fetal loss/pregnancy termination. Adjustment of care during pregnancy needs to be better delivered.

Intestinal microbiome and metabolome signatures in patients with chronic granulomatous disease.

BACKGROUND: Chronic granulomatous disease (CGD) is caused by defects in any 1 of the 6 subunits forming the nicotinamide adenine dinucleotide phosphate oxidase complex 2 (NOX2), leading to severely reduced or absent phagocyte-derived reactive oxygen species production. Almost 50% of patients with CGD have inflammatory bowel disease (CGD-IBD). While conventional IBD therapies can treat CGD-IBD, their benefits must be weighed against the risk of infection. Understanding the impact of NOX2 defects on the intestinal microbiota may lead to the identification of novel CGD-IBD treatments. OBJECTIVE: We sought to identify microbiome and metabolome signatures that can distinguish individuals with CGD and CGD-IBD. METHODS: We conducted a cross-sectional observational study of 79 patients with CGD, 8 pathogenic variant carriers, and 19 healthy controls followed at the National Institutes of Health Clinical Center. We profiled the intestinal microbiome (amplicon sequencing) and stool metabolome, and validated our findings in a second cohort of 36 patients with CGD recruited through the Primary Immune Deficiency Treatment Consortium. RESULTS: We identified distinct intestinal microbiome and metabolome profiles in patients with CGD compared to healthy individuals. We observed enrichment for Erysipelatoclostridium spp, Sellimonas spp, and Lachnoclostridium spp in CGD stool samples. Despite differences in bacterial alpha and beta diversity between the 2 cohorts, several taxa correlated significantly between both cohorts. We further demonstrated that patients with CGD-IBD have a distinct microbiome and metabolome profile compared to patients without CGD-IBD. CONCLUSION: Intestinal microbiome and metabolome signatures distinguished patients with CGD and CGD-IBD, and identified potential biomarkers and therapeutic targets.

Chronic Aichi Virus Infection As a Cause of Long-Lasting Multiorgan Involvement in Patients With Primary Immune Deficiencies.

BACKGROUND: Metagenomic next-generation sequencing (mNGS) was used to assess patients with primary or secondary immune deficiencies (PIDs and SIDs) who presented with immunopathological conditions related to immunodysregulation. METHODS: Thirty patients with PIDs or SIDs who presented with symptoms related to immunodysregulation and 59 asymptomatic patients with similar PIDs or SIDs were enrolled. mNGS was performed on organ biopsy. Specific Aichi virus (AiV) reverse-transcription polymerase chain reaction (RT-PCR) was used to confirm AiV infection and screen the other patients. In situ hybridization (ISH) assay was done on AiV-infected organs to identify infected cells. Virus genotype was determined by phylogenetic analysis. RESULTS: AiV sequences were detected using mNGS in tissue samples of 5 patients and by RT-PCR in peripheral samples of another patient, all of whom presented with PID and long-lasting multiorgan involvement, including hepatitis, splenomegaly, and nephritis in 4 patients. CD8+ T-cell infiltration was a hallmark of the disease. RT-PCR detected intermittent low viral loads in urine and plasma from infected patients but not from uninfected patients. Viral detection stopped after immune reconstitution obtained by hematopoietic stem cell transplantation. ISH demonstrated the presence of AiV RNA in hepatocytes (n = 1) and spleen tissue (n = 2). AiV belonged to genotype A (n = 2) or B (n = 3). CONCLUSIONS: The similarity of the clinical presentation, the detection of AiV in a subgroup of patients suffering from immunodysregulation, the absence of AiV in asymptomatic patients, the detection of viral genome in infected organs by ISH, and the reversibility of symptoms after treatment argue for AiV causality.

COVID-19 and Inborn Errors of Immunity.

Inborn errors of immunity (IEI) are a heterogeneous group of disorders affecting immune host defense and immunoregulation. Considering the predisposition to develop severe and chronic infections, it is crucial to understand the clinical evolution of COVID-19 in IEI patients. This review analyzes clinical outcomes following SARS-CoV-2 infection, as well as response to COVID-19 vaccines in patients with IEI.

Minimal dose of hematopoietic stem cell transplantation without myelosuppressive conditioning for T-B+NK- severe combined immunodeficiency.

We reviewed the medical records of five patients with T-B+NK- severe combined immunodeficiency (SCID) who received minimal dose allogeneic hematopoietic cell transplantation (HCT) (total nucleated cell count (TNC) lower than 1.0 × 108/kg). Patients were administered a median of 5.0 mL of bone marrow or peripheral blood without conditioning (in four) or with anti-thymocyte globulin alone (in one). Three patients received HCT from a matched sibling donor, one from unrelated donor, and one from familial mismatched donor. The median TNC and CD34+ cells were 0.54 (0.29-0.84) × 108/kg and 0.61 (0.35-0.84) × 106/kg, respectively. Engraftment was achieved in all. Total T cell, CD4+ cell, and CD8+ cell recovery was obtained within a year in four, and immunoglobulin replacement was discontinued in all. All patients survived, exhibiting stable donor chimerism. We obtained sufficient therapeutic effects with minimal dose transplantation without intensive conditioning in patients with T-B+NK- SCID.

Multiplexed Functional Assessment of Genetic Variants in CARD11.

Genetic testing has increased the number of variants identified in disease genes, but the diagnostic utility is limited by lack of understanding variant function. CARD11 encodes an adaptor protein that expresses dominant-negative and gain-of-function variants associated with distinct immunodeficiencies. Here, we used a "cloning-free" saturation genome editing approach in a diploid cell line to simultaneously score 2,542 variants for decreased or increased function in the region of CARD11 associated with immunodeficiency. We also described an exon-skipping mechanism for CARD11 dominant-negative activity. The classification of reported clinical variants was sensitive (94.6%) and specific (88.9%), which rendered the data immediately useful for interpretation of seven coding and splicing variants implicated in immunodeficiency found in our clinic. This approach is generalizable for variant interpretation in many other clinically actionable genes, in any relevant cell type.

Transplant for non-malignant disorders: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee report on the role of alternative donors, stem cell sources and graft engineering.

Hematopoietic stem cell transplantation (HSCT) is curative for many non-malignant disorders. As HSCT and supportive care technologies improve, this life-saving treatment may be offered to more and more patients. With the development of new preparative regimens, expanded alternative donor availability, and graft manipulation techniques, there are many options when choosing the best regimen for patients. Herein the authors review transplant considerations, transplant goals, conditioning regimens, donor choice, and graft manipulation strategies for patients with non-malignant disorders undergoing HSCT.

Real-life use of mTOR inhibitor-based therapy in adults with autoimmune cytopenia highlights strong efficacy in relapsing/refractory multi-lineage autoimmune cytopenia.

Data on mTOR inhibitors (mTORi) in autoimmune cytopenia (AIC), in adults are scarce. We retrospectively analysed 30 cases of refractory or relapsing AIC treated with an mTORi-based therapy. Eleven warm autoimmune hemolytic anaemia, 10 autoimmune thrombocytopenia, 6 acquired pure red cell aplasia, 3 autoimmune neutropenia were included. Twenty were multilineage AIC (67%) and 21 were secondary AIC (70%). mTORi were associated with other therapies in 23 AIC (77%). Twenty-two AIC (73%) responded to mTORi-based therapy: 5 reached a partial response (17%) and 17 a complete response (57%). Survival without unfavourable outcome (failure, requirement of a new therapy, or death) was longer in multilineage AIC compared to single-lineage AIC (p = 0.049) with a median event-free survival of 48 versus 12 months. Median event-free survival was 48 months in secondary AIC and 33 months in primary AIC (p = 0.79). mTORi were discontinued in 4 patients (15%) for safety reasons and in 3 patients for patient's choice (12%). In conclusion, mTORi could be considered as an alternative or an add-on therapy in refractory or relapsing AIC in adult patients, especially in multilineage AIC.

Chromosome 22q11.2 Deletion (DiGeorge Syndrome): Immunologic Features, Diagnosis, and Management.

PURPOSE OF REVIEW: This review focuses on immunologic findings, relationships among immunologic findings and associated conditions of autoimmunity and atopy, and management of immunologic disease in chromosome 22q11.2 deletion syndrome (22q11.2DS, historically known as DiGeorge syndrome). RECENT FINDINGS: The implementation of assessment of T cell receptor excision circles (TRECs) in newborn screening has led to increased detection of 22q11.2 deletion syndrome. While not yet applied in clinical practice, cell-free DNA screening for 22q11.2DS also has the potential to improve early detection, which may benefit prompt evaluation and management. Multiple studies have further elucidated phenotypic features and potential biomarkers associated with immunologic outcomes, including the development of autoimmune disease and atopy. The clinical presentation of 22q11.2DS is highly variable particularly with respect to immunologic manifestations. Time to recovery of immune system abnormalities is not well-defined in current literature. An understanding of the underlying causes of immunologic changes found in 22q11.2DS, and the progression and evolution of immunologic changes over the lifespan have expanded over time and with improved survival. An included case highlights the variability of presentation and potential severity of T cell lymphopenia in partial DiGeorge syndrome and demonstrates successful spontaneous immune reconstitution in partial DiGeorge syndrome despite initial severe T cell lymphopenia.

Evaluation of Psychiatric Symptomatology, Quality of Life, and Caregiver Burden in Mothers and Children with Primary Immunodeficiency.

BACKGROUND: The present study aimed to evaluate the quality of life, depression, and anxiety scores of children with primary immunodeficiency (PID) and depression, anxiety scores, and the caregiving burden of their mothers. METHODS: A total of 149 children aged 2-18 years and their mothers were included in the present study, along with 125 healthy children and their mothers as a control group. The Pediatric Quality of Life Inventory (PedsQL), Child Depression Inventory (CDI), and Screening for Child Anxiety-Related Emotional Disorders (SCARED) questionnaire were used based on the views of children and their mothers. The Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), Temperament Evaluation of Memphis, Pisa, Paris, San Diego Autoquestionnaire (TEMPS-A), and Zarit Caregiver Burden Scale (ZCB) were used for the mothers. RESULTS: According to children and their mothers, the scores of the PedsQL were lower than that of the control group (P < 0.05). In addition, according to the views of children and mothers, we found that PID children had higher depression and anxiety scores than healthy children (P < 0.05). The depression and anxiety levels of mothers in the patient group were also significantly higher than those in the control group (P = 0.05 and P = 0.001). CONCLUSION: Statistically, we found significantly lower psychosocial health summary scores and total scale score levels from the subclass of PedsQL in the patient group than in the control group. According to the views of both children and mothers, we observed that PID children had higher depression and anxiety scores than healthy children. It was also found that the BDI and BAI values in case of mothers in the patient group were significantly higher than those in the control group.

What did we learn from CTLA-4 insufficiency on the human immune system?

Cytotoxic-T-lymphocyte-antigen-4 (CTLA-4) is a negative immune regulator constitutively expressed on regulatory T (Treg) cells and upregulated on activated T cells. CTLA-4 inhibits T cell activation by various suppressive functions including competition with CD28, regulation of the inhibitory function of Treg cells, such as transendocytosis, and the control of adhesion and motility. Intrinsic CTLA-4 signaling has been controversially discussed, but so far no distinct signaling pathway has been identified. The CTLA-4-mediated Treg suppression plays an important role in the maintenance of peripheral tolerance and the prevention of autoimmune diseases. Human CTLA-4 insufficiency is caused by heterozygous germline mutations in CTLA4 and characterized by a complex immune dysregulation syndrome. Clinical studies on CTLA4 mutation carriers showed a reduced penetrance and variable expressivity, suggesting modifying factor(s). One hundred and forty-eight CTLA4 mutation carriers have been reported; patients showed hypogammaglobulinemia, recurrent infectious diseases, various autoimmune diseases, and lymphocytic infiltration into multiple organs. The CTLA-4 expression level in Treg cells was reduced, while the frequency of Treg cells was increased in CTLA-4-insufficient patients. The transendocytosis assay is a specific functional test for the assessment of newly identified CTLA4 gene variants. Immunoglobulin substitution, corticosteroids, immunosuppressive therapy, and targeted therapy such as with CTLA-4 fusion proteins and mechanistic target of rapamycin (mTOR) inhibitors were applied; patients with life-threatening, treatment-resistant symptoms underwent hematopoietic stem cell transplantation. The fact that in humans CTLA-4 insufficiency causes severe disease taught us that the amount of CTLA-4 molecules present in/on T cells matters for immune homeostasis. However, whether the pathology-causing activated T lymphocytes in CTLA-4-insufficient patients are antigen-specific is an unsolved question. CTLA-4, in addition, has a role in autoimmune diseases and cancer. Anti-CTLA-4 drugs are employed as checkpoint inhibitors to target various forms of cancer. Thus, clinical research on human CTLA-4 insufficiency might provide us a deeper understanding of the mechanism(s) of the CTLA-4 molecule and immune dysregulation disorders.

The 2022 Update of IUIS Phenotypical Classification for Human Inborn Errors of Immunity.

The International Union of Immunological Societies (IUIS) expert committee (EC) on Inborn Errors of Immunity (IEI) reports here the 2022 updated phenotypic classification, which accompanies and complements the most-recent genotypic classification. This phenotypic classification is aimed for clinicians at the bedside and focuses on clinical features and laboratory phenotypes of specific IEI. In this classification, 485 IEI underlying phenotypes as diverse as infection, malignancy, allergy, auto-immunity and auto-inflammation are described, including 55 novel monogenic defects and 1 autoimmune phenocopy. Therefore, all 485 diseases of the genetic classification are presented in this paper in the form of colored tables with essential clinical or immunological phenotype entries.

High Prevalence of Hemophagocytic Lymphohistiocytosis in Acute Liver Failure of Infancy.

OBJECTIVES: To investigate the prevalence of hemophagocytic lymphohistiocytosis (HLH) syndrome in pediatric acute liver failure (PALF) of infancy and assess the diagnostic role of rapid immunologic tests, genotype/phenotype correlations, and clinical outcomes. STUDY DESIGN: We retrospectively analyzed 78 children with PALF aged <24 months referred over almost 2 decades. The studied patients with a phenotype of HLH syndrome had a comprehensive immunologic workup, including additional genetic analysis for primary immunologic causes. RESULTS: Thirty of the 78 children had the HLH phenotype and underwent genetic assessment, which demonstrated positive findings in 19 (63.3%), including 9 (30%) with biallelic primary HLH mutations and 10 (33.3%) with heterozygous mutations and/or polymorphisms. The most common form of primary HLH was familial hemophagocytic lymphohistiocytosis (FHL)-2, diagnosed in 6 children, 4 of whom had a c.50delT (p.Leu17ArgfsTer34) mutation in the PRF1 gene. Three patients with primary HLH received genetic diagnoses of FHL-3, Griscelli syndrome, and LRBA (lipopolysaccharide-responsive vesicle trafficking, beach- and anchor-containing) protein deficiency. Overall mortality in the series was 52.6% (10 of 19), and mortality in children with a documented biallelic pathogenic HLH mutation (ie, primary HLH) was 66.6% (6 of 9). Two children underwent liver transplantation, and 4 children underwent emergency hematopoietic stem cell transplantation; all but 1 child survived medium term. CONCLUSIONS: Primary HLH can be diagnosed retrospectively in approximately one-third of infants with indeterminate PALF (iPALF) who meet the clinical criteria for HLH, often leading to their death. The most common HLH type in iPALF is FHL-2, caused by biallelic mutations in PRF-1. The clinical relevance of observed heterozygous mutations and variants of uncertain significance requires further investigation. Prompt hematopoietic stem cell transplantation could be life-saving in infants who survive the liver injury.

Determining T and B Cell development by TREC/KREC analysis in primary immunodeficiency patients and healthy controls.

T cell receptor excision circles (TRECs) and kappa-deleting excision circles (KRECs) are DNA fragments potentially indicative of T and B cell development, respectively. Recent thymic emigrants (RTEs) are a subset of peripheral cells that may also represent thymic function. Here, we investigated TREC/KREC copy numbers by quantitative real-time PCR in the peripheral blood of patients with primary immunodeficiencies (PIDs, n = 145) and that of healthy controls (HCs, n = 86) and assessed the correlation between RTEs and TREC copy numbers. We found that TREC copy numbers were significantly lower in children and adults with PIDs (P < .0001 and P < .002, respectively) as compared with their respective age-matched HCs. A moderate correlation was observed between TREC copies and RTE numbers among children with PID (r = .5114, P < .01), whereas no significant correlation was detected between RTE values and TREC content in the HCs (r = .0205, P = .9208). Additionally, we determined TREC and KREC copy numbers in DNA isolated from the Guthrie cards of 200 newborns and showed that this method is applicable to DNA isolated from both peripheral blood samples and dried blood spots, with the two sample types showing comparable TREC and KREC values. We further showed that RTE values are not always reliable markers of T cell output. Although additional confirmatory studies with larger cohorts are needed, our results provide thresholds for TREC/KREC copy numbers for different age groups.