CXCR4 signaling controls dendritic cell location and activation at steady state and in inflammation.

Dendritic cells (DCs) encompass several cell subsets that collaborate to initiate and regulate immune responses. Proper DC localization determines their function and requires the tightly controlled action of chemokine receptors. All DC subsets express CXCR4, but the genuine contribution of this receptor to their biology has been overlooked. We addressed this question using natural CXCR4 mutants resistant to CXCL12-induced desensitization and harboring a gain of function that cause the warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome (WS), a rare immunodeficiency associated with high susceptibility to the pathogenesis of human papillomavirus (HPV). We report a reduction in the number of circulating plasmacytoid DCs (pDCs) in WHIM patients, whereas that of conventional DCs is preserved. This pattern was reproduced in an original mouse model of WS, enabling us to show that the circulating pDC defect can be corrected upon CXCR4 blockade and that pDC differentiation and function are preserved, despite CXCR4 dysfunction. We further identified proper CXCR4 signaling as a critical checkpoint for Langerhans cell and DC migration from the skin to lymph nodes, with corollary alterations of their activation state and tissue inflammation in a model of HPV-induced dysplasia. Beyond providing new hypotheses to explain the susceptibility of WHIM patients to HPV pathogenesis, this study shows that proper CXCR4 signaling establishes a migration threshold that controls DC egress from CXCL12-containing environments and highlights the critical and subset-specific contribution of CXCR4 signal termination to DC biology.

A patient with Silver-Russell syndrome with multilocus imprinting disturbance, and Schimke immuno-osseous dysplasia unmasked by uniparental isodisomy of chromosome 2.

Silver-Russell syndrome (SRS) is a congenital disorder characterized by prenatal and postnatal growth failure and craniofacial features. Hypomethylation of the H19/IGF2:IG-differential methylated region (H19LOM) is observed in 50% of SRS patients, and 15% of SRS patients with H19LOM had multilocus imprinting disturbance (MLID). Schimke immuno-osseous dysplasia (SIOD), characterized by spondyloepiphyseal dysplasia and nephropathy, is an autosomal recessive disorder caused by mutations in SMARCAL1 on chromosome 2. We report a patient with typical SRS-related features, spondyloepiphyseal dysplasia, and severe nephropathy. Molecular analyses showed H19LOM, paternal uniparental isodisomy of chromosome 2 (iUPD(2)pat), and a paternally inherited homozygous frameshift variant in SMARCAL1. Genome-wide methylation analysis showed MLID in this patient, although it showed no MLID in another patient with SIOD without SRS phenotype. These results suggest that iUPD(2)pat unmasked the recessive mutation in SMARCAL1 and that the SMARCAL1 gene mutation may have no direct effect on the patient's methylation defects.

Assessment of weight and height of patients with primary immunodeficiency disorders and group of children with recurrent respiratory tract infections.

BACKGROUND: Primary immunodeficiences (PIDs) are a group of chronic, serious disorders in which the immune response is insufficient. In consequence, it leads to an increased susceptibility to infections. Up to date, there are about 350 different disorders classified in that group. There are also patients suffering from recurrent respiratory tract infections (RRTI), however that group doesn't present any abnormalities in terms of conducted immunological tests. Many factors, including medical, can have an impact on physical development of a child. Data such as birth weight and length, also weight, height, BMI during admission to the hospital were collected from 195 patients' medical histories from their hospitalization at Clinical Immunology and Paediatrics Ward of J. Gromkowski Hospital in Wroclaw. Investigated groups included patients with PIDs, RRTI and a control group of healthy children. Our purpose was to evaluate the physical growth of children with PID and children with RRTI by assessment of their height and weight. All of parameters were evaluated using centile charts, suitable best for the Polish population. RESULTS: The lowest mean birth weight and height was found among the PIDs patients group. Children with PIDs during hospitalization had statistically relevant lower mean weight than the control group and almost 18% of them had their height situated below 3rd percentile. The statistically relevant differences have been found between them and RRTI group in terms of weight, height and nutritional status. The statistically significant difference was detected between the nutritional status of PID and control group. CONCLUSIONS: There is a higher percentage of PID patients with physical growth abnormalities in comparison to healthy children. Our findings indicate a need for further investigation of immune system irregularities and their influence on physical growth of children.

Immunodeficiency in cartilage-hair hypoplasia: Pathogenesis, clinical course and management.

Cartilage-hair hypoplasia (CHH) is an autosomal recessive syndromic immunodeficiency with skeletal dysplasia, short stature, hypotrichosis, variable degree of immune dysfunction and increased incidence of anaemia, Hirschsprung disease and malignancy. CHH is caused by variants in the RMRP gene, encoding the untranslated RNA molecule of the mitochondrial RNA-processing endoribonuclease, which participates in for example cell cycle regulation and telomere maintenance. Recent studies have expanded our understanding of the complex pathogenesis of CHH. Immune dysfunction has a major impact on clinical course and prognosis. Clinical features of immune dysfunction are highly variable, progressive and include infections, lung disease, immune dysregulation and malignancy. Mortality is increased compared with the general population, due to infections, malignancy and pulmonary disease. Several risk factors for early mortality have been reported in the Finnish CHH cohort and can be used to guide management. Newborn screening for severe combined immunodeficiency can possibly be of prognostic value in CHH. Regular follow-up by a multidisciplinary team should be implemented to address immune dysfunction in all patients with CHH, also in asymptomatic cases. Haematopoietic stem cell transplantation can cure immune dysfunction, but its benefits in mildly symptomatic patients with CHH remain debatable. Further research is needed to understand the mechanisms behind the variability of clinical features, to search for potential molecular treatment targets, to examine and validate risk factors for early mortality outside the Finnish CHH cohort and to develop management guidelines. This review focuses on the pathogenesis, clinical course and management of CHH.

Rheumatological manifestations in inborn errors of immunity.

Rare monogenetic diseases serve as natural models to dissect the molecular pathophysiology of the complex disease traits. Rheumatologic disorders by their nature are considered complex diseases with partially genetic origin, as illustrated by their heterogeneous genetic background and variable phenotypic presentation. Recent advances in genetic technologies have helped uncover multiple variants associated with disease susceptibility; however, a precise understanding of genotype-phenotype relationships is still missing. Inborn errors of immunity (IEIs), in addition to recurrent infections, may also present with autoimmune and autoinflammatory rheumatologic manifestations and have provided insights for understanding the underlying the principles of immune system homeostasis and mechanisms of immune dysregulation. This review discusses the rheumatologic manifestations in IEIs with overlapping and differentiating features in immunodeficiencies and rheumatologic disorders.

Human inborn errors of the actin cytoskeleton affecting immunity: way beyond WAS and WIP.

Inherited defects in genes encoding for proteins that are involved in the assembly and dynamics of the actin skeleton have increasingly been identified in patients presenting with primary immunodeficiencies. In this review, we summarize a subset of the recently described conditions, emphasizing the clinical features as well as the immunophenotype and pathophysiology.

Gynecologic health in cartilage-hair hypoplasia: A survey of 26 adult females.

Cartilage-hair hypoplasia (CHH) is a rare metaphyseal chondrodysplasia significantly affecting adult height and quality of life. Immunodeficiency and increased risk for malignancies contribute to significant morbidity. Little is known about gynecologic health in CHH. We performed a questionnaire study of 26 women (mean age 42.3 years) with genetically confirmed CHH, inquiring about pubertal development, menstrual cycle, use of contraception, pregnancies, gynecologic infections, and gynecologic cancers. Mean age at menarche and menopause was 12.7 and 46.1 years, respectively. Mean length of menstrual cycle was 27 days. Contraception was used by 76%, most commonly condom (60%), and combined contraception (60%). Despite significant short stature (mean height 121 cm) and potentially small pelvic diameters, 10 CHH women (38%) had been pregnant. Six of these women reported miscarriages and three had, induced pregnancy terminations. Eight women had in total, 19 deliveries. Abnormal Pap smear was reported in five patients and cervical cancer once. Our findings of normal timing of puberty and menopause suggest a fairly normal length of the fertility period in women with CHH. However, many patients expressed concerns regarding the safety of pregnancy and lack of prepregnancy counseling. Immunodeficiency may predispose CHH women to prolonged HPV infections. This study highlights the importance of careful gynecologic follow-up for these patients.

Mesenchymal Stem/Stromal Cells Overexpressing CXCR4R334X Revealed Enhanced Migration: A Lesson Learned from the Pathogenesis of WHIM Syndrome.

C-X-C chemokine receptor type 4 (CXCR4), initially recognized as a co-receptor for HIV, contributes to several disorders, including the WHIM (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis) syndrome. CXCR4 binds to its ligand SDF-1 to make an axis involved in the homing property of stem cells. This study aimed to employ WHIM syndrome pathogenesis as an inspirational approach to reinforce cell therapies. Wild type and WHIM-type variants of the CXCR4 gene were chemically synthesized and cloned in the pCDH-513B-1 lentiviral vector. Molecular cloning of the synthetic genes was confirmed by DNA sequencing, and expression of both types of CXCR4 at the protein level was confirmed by western blotting in HEK293T cells. Human adipose-derived mesenchymal stem cells (Ad-MSCs) were isolated, characterized, and subjected to lentiviral transduction with Wild type and WHIM-type variants of CXCR4. The presence of copGFP-positive MSCs confirmed the high efficiency of transduction. The migration ability of both groups of transduced cells was then assessed by transwell migration assay in the presence or absence of a CXCR4-blocking agent. Our qRT-PCR results showed overexpression of CXCR4 at mRNA level in both groups of transduced MSCs, and expression of WHIM-type CXCR4 was significantly higher than Wild type CXCR4 (P<0.05). Our results indicated that the migration of genetically modified MSCs expressing WHIM-type CXCR4 had significantly enhanced towards SDF1 in comparison with Wild type CXCR4 (P<0.05), while it was reduced after treatment with CXCR4 antagonist. These data suggest that overexpression of WHIM-type CXCR4 could lead to enhanced and sustained expression of CXCR4 on human MSCs, which would increase their homing capability; hence it might be an appropriate strategy to improve the efficiency of cell-based therapies.

Biallelic mutations in calcium release activated channel regulator 2A (CRACR2A) cause a primary immunodeficiency disorder.

CRAC channel regulator 2 A (CRACR2A) is a large Rab GTPase that is expressed abundantly in T cells and acts as a signal transmitter between T cell receptor stimulation and activation of the Ca2+-NFAT and JNK-AP1 pathways. CRACR2A has been linked to human diseases in numerous genome-wide association studies, however, to date no patient with damaging variants in CRACR2A has been identified. In this study, we describe a patient harboring biallelic variants in CRACR2A [paternal allele c.834 gaG> gaT (p.E278D) and maternal alelle c.430 Aga > Gga (p.R144G) c.898 Gag> Tag (p.E300*)], the gene encoding CRACR2A. The 33-year-old patient of East-Asian origin exhibited late onset combined immunodeficiency characterised by recurrent chest infections, panhypogammaglobulinemia and CD4+ T cell lymphopenia. In vitro exposure of patient B cells to a T-dependent stimulus resulted in normal generation of antibody-secreting cells, however the patient's T cells showed pronounced reduction in CRACR2A protein levels and reduced proximal TCR signaling, including dampened SOCE and reduced JNK phosphorylation, that contributed to a defect in proliferation and cytokine production. Expression of individual allelic mutants in CRACR2A-deleted T cells showed that the CRACR2AE278D mutant did not affect JNK phosphorylation, but impaired SOCE which resulted in reduced cytokine production. The truncated double mutant CRACR2AR144G/E300* showed a pronounced defect in JNK phosphorylation as well as SOCE and strong impairment in cytokine production. Thus, we have identified variants in CRACR2A that led to late-stage combined immunodeficiency characterized by loss of function in T cells.

Immunodeficiency in a patient with microcephalic osteodysplastic primordial dwarfism type I as compared to Roifman syndrome.

BACKGROUND: Microcephalic osteodysplastic primordial dwarfism type I (MOPD I, also known as Taybi-Linder syndrome) is a rare genetic disorder associated with severe intrauterine growth retardation, short stature, microcephaly, brain anomalies, stunted limbs, and early mortality. RNU4ATAC, the gene responsible for this disorder, does not encode a protein but instead the U4atac small nuclear RNA (snRNA), a crucial component of the minor spliceosome. Roifman syndrome is an allelic disorder of MOPD I that is characterized by immunodeficiency complications. CASE REPORT: The patient described herein is an 18-year-old woman exhibiting congenital dwarfism and microcephaly with structural brain anomaly. She suffered human herpesvirus 6 (HHV-6)-associated acute necrotizing encephalopathy at the age of one, thereafter resulting in severe psychomotor disabilities. Genetic analysis using gene microarray and whole-exome sequencing could not identify the cause of her congenital anomalies. However, Sanger sequencing revealed a compound heterozygous mutation within RNU4ATAC (NR_023343.1:n.[50G > A];[55G > A]). Immunological findings showed decreases in total lymphocytes, CD4+ T cells, and T cell regenerative activity. Furthermore, antibodies against varicella-zoster, rubella, measles, mumps, and influenza were very low or negative despite having received vaccinations for these viruses. HHV-6 IgG antibodies were also undetected. DISCUSSION: The patient here exhibited a marked MOPD I phenotype complicated by various immunodeficiencies. Previous studies have not demonstrated immunodeficiency comorbidities within MOPD I subjects, but this report suggests an evident immunodeficiency in MOPD I. Patients with MOPD I should be treated with one of the immunodeficiency syndromes.

DL4-µbeads induce T cell lineage differentiation from stem cells in a stromal cell-free system.

T cells are pivotal effectors of the immune system and can be harnessed as therapeutics for regenerative medicine and cancer immunotherapy. An unmet challenge in the field is the development of a clinically relevant system that is readily scalable to generate large numbers of T-lineage cells from hematopoietic stem/progenitor cells (HSPCs). Here, we report a stromal cell-free, microbead-based approach that supports the efficient in vitro development of both human progenitor T (proT) cells and T-lineage cells from CD34+cells sourced from cord blood, GCSF-mobilized peripheral blood, and pluripotent stem cells (PSCs). DL4-µbeads, along with lymphopoietic cytokines, induce an ordered sequence of differentiation from CD34+ cells to CD34+CD7+CD5+ proT cells to CD3+αß T cells. Single-cell RNA sequencing of human PSC-derived proT cells reveals a transcriptional profile similar to the earliest thymocytes found in the embryonic and fetal thymus. Furthermore, the adoptive transfer of CD34+CD7+ proT cells into immunodeficient mice demonstrates efficient thymic engraftment and functional maturation of peripheral T cells. DL4-µbeads provide a simple and robust platform to both study human T cell development and facilitate the development of engineered T cell therapies from renewable sources.

The development of a quality improvement project to improve infection prevention and management in patients with asplenia or hyposplenia.

Asplenia and hyposplenia (a/hyposplenia) are associated with increased morbidity and mortality from complications including infection. The recommended measures to reduce the risks associated with infection include patient education, vaccination and early initiation of antibiotic therapy for fever. Despite these recommendations, there is poor adherence to best practice management of patients with asplenia or hyposplenia (PWA/H). We present the development methodology and pilot data of a quality improvement project that explored whether a programme involving a novel medical alert card together with a patient and healthcare provider educational booklet increased vaccination rates and improved awareness and understanding of the infectious implications of a/hyposplenia. Our aim was to increase the proportion of those appropriately vaccinated and the proportion of patients with proper understanding of fever management by twofold in 18 months. Questionnaires were used locally as a root-cause-analysis to confirm the need for education and evaluate the effectiveness of the programme, as well as patient satisfaction. An interdisciplinary team developed a toolkit composed of a medical alert card and booklet. The toolkit was distributed to PWA/H who presented for a haematology clinic visit at a tertiary care centre. A separate set of questionnaires was then used to evaluate satisfaction and obtain feedback from patients and practitioners receiving the toolkit for the first time. Changes suggested by patients and practitioners with unanimous agreement among study investigators were made to the toolkit. The pilot study showed an increase in vaccination rates and awareness of vaccination status and appropriate fever management. The majority of the patients and practitioners found the information provided by the toolkit helpful. Given these promising single-centre findings, the intervention is being extended to another tertiary care centre with a large red blood cell disorders programme to evaluate its generalisability. The next step will be to expand the scope to paediatric PWA/H.

Schimke immuno-osseous dysplasia, two new cases with peculiar EEG pattern.

INTRODUCTION: Schimke Immuno-Osseous Dysplasia (SIOD) is an autosomal recessive multisystem disorder caused by pathogenic variants in the gene SMARCAL1. The clinical picture is characterized by spondyloepiphyseal dysplasia resulting in growth failure, nephropathy and T-cell deficiency. Neurologic manifestations include microcephaly, cognitive impairment, migraine-like headaches and cerebrovascular manifestations such as cerebral atherosclerotic vascular disease and reversible cerebral vasoconstriction. The role of SMARCAL1 deficiency in non-vascular neurological complications is still under debate. Epilepsy has been reported in a few patients, even in the absence of brain abnormalities. Data regarding electroencephalographic (EEG) patterns in SIOD are scarce METHODS: We describe the clinical, neuroradiological and EEG findings in two unrelated patients with SIOD showing a peculiar pseudo-periodic EEG pattern apparently not related to the cerebrovascular complications, since it was recognized both before and after cerebrovascular events CONCLUSION: Our observations support the hypothesis that SMARCAL1plays an important role in neurodevelopment and brain function and expand the spectrum of neurological abnormalities related to SIOD.

Pulmonary function evaluation in pediatric patients with primary immunodeficiency complicated by bronchiectasis.

BACKGROUND: Primary immunodeficiency (PID) accompanying with recurrent respiratory infections is thought to have a devastating effect on lung function. However, the associations between the airway structural abnormalities on chest computed tomography (CT), severity of dyspnea, and deterioration of pulmonary function test (PFT) have not been fully addressed. METHODS: Children diagnosed with PID in a tertiary referred center in northern Taiwan were enrolled. Demographic and clinical data including age, sex, age at diagnosis of PID, and follow-up period were collected. Chest CT images (modified Reiff scores), parameters of PFT, and life quality questionnaires (mMRC dyspnea scale) were analyzed and correlated using Spearman's rank correlation test. RESULTS: A total of nineteen children with PID were enrolled and thirteen patients were diagnosed as having bronchiectasis based on chest CT scans. Modified Reiff scores of chest CT scan were negatively correlated with FEV1 (% predicted) and FEV1/FVC ratio (P < 0.05). A strongly negative correlation was found between the mMRC dyspnea scale and FEV1 (% predicted) and FVC (% predicted), but positively correlated with RV (% predicted) and RV/TLC ratio (P < 0.05). Furthermore, there was a negative correlation between FVC (% predicted) with increasing follow-up period (P < 0.05). CONCLUSIONS: In pediatric patients with PID, chest CT scan appears to be a good tool for not only the diagnosis of bronchiectasis, but also the degree of pulmonary function impairment. Further quality of life impairments could be particularly due to the airflow obstruction and air trapping related to bronchiectasis.

Alpha-1 Antitrypsin Deficiency and Pulmonary Morbidity in Patients with Primary Immunodeficiency Disease: A Single-Center Experience.

Background: Alpha-1 antitrypsin deficiency (AATD) is of importance in the pathogenesis of pulmonary emphysema, chronic obstructive pulmonary diseases (COPD), and bronchiectasis. Various pulmonary disorders are a typical feature of primary immunodeficiency disease (PID). This includes recurrent pulmonary infections, immunodysregulation, and autoinflammatory diseases. As a result, incidence of acute and chronic pulmonary diseases is higher. Interestingly, pulmonary morbidity in PID and AATD share similar features. To study the coexistence of AATD in patients suffering from PID, we performed the underlying investigation. Methods: We evaluated a study group of 149 patients (n = 149) with PID. In total, serum AAT concentrations were available for 110 patients (n = 110). For the identified patients, we analyzed both clinical associations and interactions. Results: Among the investigated patients, reduced serum AAT levels were detected in 7 patients. With regard to the genotype, PI∗ZZ was found in 2 patients, whereas PI∗MZ was observed in 5 patients. Independent of the underlying phenotype, obstructive lung diseases were found in 2 patients with PI∗ZZ and 2 patients with PI∗MZ. Conclusions: In Germany, the estimated percentage for PI∗ZZ and PI∗MZ is 0.01% and 1.9%, respectively. As demonstrated, the ratio in our study group was even higher. We identified seven patients with AATD. Since AATD contributes to pulmonary morbidity in PID patients, systematic underdiagnosis of the coexistence might yield a strong clinical impact. Hence, AAT analysis should be offered to all patients with confirmed PID diagnoses. To strengthen this finding, we suggest the investigation of larger databases.

DNA methylation in satellite repeats disorders.

Despite the tremendous progress made in recent years in assembling the human genome, tandemly repeated DNA elements remain poorly characterized. These sequences account for the vast majority of methylated sites in the human genome and their methylated state is necessary for this repetitive DNA to function properly and to maintain genome integrity. Furthermore, recent advances highlight the emerging role of these sequences in regulating the functions of the human genome and its variability during evolution, among individuals, or in disease susceptibility. In addition, a number of inherited rare diseases are directly linked to the alteration of some of these repetitive DNA sequences, either through changes in the organization or size of the tandem repeat arrays or through mutations in genes encoding chromatin modifiers involved in the epigenetic regulation of these elements. Although largely overlooked so far in the functional annotation of the human genome, satellite elements play key roles in its architectural and topological organization. This includes functions as boundary elements delimitating functional domains or assembly of repressive nuclear compartments, with local or distal impact on gene expression. Thus, the consideration of satellite repeats organization and their associated epigenetic landmarks, including DNA methylation (DNAme), will become unavoidable in the near future to fully decipher human phenotypes and associated diseases.

DNA methylation in disease: Immunodeficiency, Centromeric instability, Facial anomalies syndrome.

DNA methylation is an epigenetic modification essential for normal mammalian development. Initially associated with gene silencing, more diverse roles for DNA methylation in the regulation of gene expression patterns are increasingly being recognized. Some of these insights come from studying the function of genes that are mutated in human diseases characterized by abnormal DNA methylation landscapes. The first disorder to be associated with congenital defects in DNA methylation was Immunodeficiency, Centromeric instability, Facial anomalies syndrome (ICF). The hallmark of this syndrome is hypomethylation of pericentromeric satellite repeats, with mutations in four genes: DNMT3B, ZBTB24, CDCA7 and HELLS, being linked to the disease. Here, we discuss recent progress in understanding the molecular interactions between these genes and consider current evidence for how aberrant DNA methylation may contribute to the abnormal phenotype present in ICF syndrome patients.

Primary Immunodeficiency and Cancer in Children; A Review of the Literature.

The life span of patients with primary and secondary immunodeficiencies has increased due to recent advances in diagnostic and therapeutic strategies. Primary immune deficiencies (PIDs) are genetic disorders that predispose patients to frequent infections, autoimmunity and malignancies. Genomic instability due to defective DNA repair processes and other unknown mechanisms in patients with PID leads to an enhanced risk of cancer. PIDs were originally described as rare diseases occurring only in infants and young children, which are associated with severe clinical symptoms. However, advances in gene sequencing technologies, have revealed that they are much more common than originally appreciated and are present in older children, adolescents, and adults. After infection, malignancy is the most prevalent cause of death in both children and adults with PIDs. The overall risk of developing cancer in patients with PID is estimated to range from 4.7 to 5.7 percent. A 1.4 to 1.6-fold excess relative risk of cancer has been reported for PIDs. Increasing awareness among physicians regarding PID and cancer may lead to earlier diagnosis which may decrease morbidity and mortality. In this paper, we review the various categories of PIDs in children and highlight their association with various malignancies. MEDLINE was searched to identify articles for inclusion. Three authors have independently screened literature search results from MEDLINE and abstracted data from studies dealing with cancers of children among primary immune deficiencies.

Mutations in topoisomerase IIß result in a B cell immunodeficiency.

B cell development is a highly regulated process involving multiple differentiation steps, yet many details regarding this pathway remain unknown. Sequencing of patients with B cell-restricted immunodeficiency reveals autosomal dominant mutations in TOP2B. TOP2B encodes a type II topoisomerase, an essential gene required to alleviate topological stress during DNA replication and gene transcription, with no previously known role in B cell development. We use Saccharomyces cerevisiae, and knockin and knockout murine models, to demonstrate that patient mutations in TOP2B have a dominant negative effect on enzyme function, resulting in defective proliferation, survival of B-2 cells, causing a block in B cell development, and impair humoral function in response to immunization.

Primary Immunodeficiency Disorders Among North Indian Children.

OBJECTIVES: To report the distribution pattern of various categories of primary immunodeficiency disorders (PIDs) in children from North India, frequency of warning signs and critical parameters for evaluation. METHODS: In this retrospective study, 528 children below 18 y of age after clinical assessment and presentation suggestive of PID were further screened by immunophenotyping for immune cell markers by flow cytometry. RESULTS: A total of 120 (23%) children were diagnosed with PID with median age at diagnosis being 2.5 y in males and 3.5 y in females and an average delay in diagnosis from onset of symptoms being approximately 5 y. Chronic lower respiratory tract infections, gastrointestinal symptoms like persistent diarrhea and failure to thrive were amongst the most common warning signs in these patients. PIDs were classified according to the International Union of Immunological Societies' (IUIS) criteria. The diagnosis of index study subjects included combined humoral and cellular immunodeficiency (29%), phagocytic defects (29%), followed by predominantly antibody deficiency (18%), innate immunity and dysregulation (17%) and other well-defined syndromes (7%). A family history of PID (23%), consanguineous marriage (8%) and previous sibling death (23%) were observed as major clinical predictors/clues for underlying PID. All children received prophylactic antibiotics and/or antifungals in addition to specific therapy for underlying immune deficiency. CONCLUSIONS: The field of PIDs in India remains largely unexplored and we are faced with various challenges in the diagnosis of PIDs due to lack of awareness as well as absence of equipped immunological laboratory support. The authors propose a methodical step-wise laboratory diagnostic approach that can facilitate early diagnosis and timely intervention of these mis/underdiagnosed disorders.