Immunological Aspects of Kabuki Syndrome: A Retrospective Multicenter Study of the Italian Primary Immunodeficiency Network (IPINet).

Kabuki Syndrome (KS) is a multisystemic genetic disorder. A portion of patients has immunological manifestations characterized by increased susceptibility to infections and autoimmunity. Aiming to describe the clinical and laboratory immunological aspects of KS, we conducted a retrospective multicenter observational study on patients with KS treated in centers affiliated to the Italian Primary Immunodeficiency Network.Thirty-nine patients were enrolled, with a median age at evaluation of 10 years (range: 3 m-21y). All individuals had organ malformations of variable severity. Congenital heart defect (CHD) was present in 19/39 patients (49%) and required surgical correction in 9/39 (23%), with associated thymectomy in 7/39 (18%). Autoimmune cytopenia occurred in 6/39 patients (15%) and was significantly correlated with thymectomy (p < 0.002), but not CHD. Individuals with cytopenia treated with mycophenolate as long-term immunomodulatory treatment (n = 4) showed complete response. Increased susceptibility to infections was observed in 22/32 patients (69%). IgG, IgA, and IgM were low in 13/29 (45%), 13/30 (43%) and 4/29 (14%) patients, respectively. Immunoglobulin substitution was required in three patients. Lymphocyte subsets were normal in all patients except for reduced naïve T-cells in 3/15 patients (20%) and reduced memory switched B-cells in 3/17 patients (18%). Elevated CD3 + TCRαß + CD4-CD8-T-cells were present in 5/17 individuals (23%) and were correlated with hematological and overall autoimmunity (p < 0.05).In conclusion, immunological manifestations of KS in our cohort include susceptibility to infections, antibody deficiency, and autoimmunity. Autoimmune cytopenia is correlated with thymectomy and elevated CD3 + TCRαß + CD4-CD8-T-cells, and benefits from treatment with mycophenolate.

Convergence and divergence in Kawasaki disease and multisystem inflammatory syndrome in children: results from the COVASAKI survey.

OBJECTIVES: To compare Kawasaki disease (KD) and multisystem inflammatory syndrome (MIS-C) in children. METHODS: Prospective collection of demographics, clinical and treatment data. Assessment of type 1 interferon (IFN) score, CXCL9, CXCL10, Interleukin (IL)18, IFNγ, IL6, IL1b at disease onset and at recovery. RESULTS: 87 patients (43 KD, 44 MIS-C) were included. Age was higher in MIS-C compared to KD group (mean 31±23 vs. 94±50 months, p<0.001). Extremities abnormalities (p=0.027), mucosal involvement (p<0.001), irritability (p<0.001), gallbladder hydrops (p=0.01) and lymphadenopathy (p=0.07) were more often recorded in KD. Neurological findings (p=0.002), gastrointestinal symptoms (p=0.013), respiratory involvement (p=0.019) and splenomegaly (p=0.026) were more frequently observed in MIS-C. Cardiac manifestations were higher in MIS-C (p<0.001), although coronary aneurisms were more frequent in KD (p=0.012). In the MIS-C group, the multiple linear regression analysis revealed that a higher IFN score at onset was related to myocardial disfunction (p<0.001), lymphadenopathy (p=<0.001) and need of ventilation (p=0.024). Both CXCL9 and CXCL10 were related to myocardial disfunction (p<0.001 and p=0.029). IL18 was positively associated to PICU admission (0.030) and ventilation (p=004) and negatively associated to lymphadenopathy (0.004). IFNγ values were related to neurological involvement and lymphadenopathy (p<0.001), IL1b to hearth involvement (0.006). A negative correlation has been observed between IL6 values, heart involvement (p=0.013) and PICU admission (p<0.001). CONCLUSIONS: The demographic and clinical differences between KD e MIS-C cohorts confirm previous reported data. The assessment of biomarkers levels at MIS-C onset could be useful to predict a more severe disease course and the development of cardiac complications.

Clinical features, treatment and outcomes of Italian children with enthesitis-related arthritis and juvenile psoriatic arthritis: a cross-sectional cohort study.

OBJECTIVES: Limited information is available on the clinical features, treatment modalities and outcomes of the juvenile idiopathic arthritis (JIA) categories of enthesitis-related arthritis (ERA) and juvenile psoriatic arthritis (JPsA). This study was aimed to describe the characteristics of Italian children with ERA and JPsA and to compare them with those of patients with the other categories of JIA. METHODS: Patients were part of a multinational sample included in a study aimed to investigate the prevalence of disease categories, treatment approaches, and disease status in patients from across different geographical areas (EPOCA Study). All patients underwent a retrospective assessment, based on the review of clinical chart, and a cross-sectional evaluation, which included assessment of physician- and parent-reported outcomes and laboratory tests, and recording of ongoing therapies. RESULTS: Of the 9081 children with JIA enrolled in the EPOCA Study, 1300 were recruited at 18 paediatric rheumatology centres in Italy. 45 (3.5%) had ERA and 49 (3.8%) had JPsA. Several remarkable differences in demographic features and frequency of articular and extra-articular manifestations, disease damage, impairment in physical function and health-related quality of life, school-related problems, comorbidities, and ongoing treatments were observed between ERA and JPsA and the other JIA categories. CONCLUSIONS: We described the characteristics of Italian children with ERA and JPsA and highlighted their peculiarities and their differences from the other JIA subsets. These data provide useful insights for future revisions of JIA classification and a benchmarking against which the features from other cohorts may be compared.

Revising the value of Antistreptolysin O titre in childhood and its interpretation in the diagnostic approach of rheumatic diseases.

The burden of group A streptococcus (GAS) infection and its rheumatic sequelae remains dramatically high, especially in low-income countries. Recently, an increased number of Acute Rheumatic Fever (ARF) cases was documented in many regions of Italy. The diagnosis of rheumatic sequelae relies on clinical signs and on the evaluation of the Antistreptolysin O titre (ASO), whose variations are globally reported. To re-examine the standard reference value of ASO titre, by measuring either its upper limit of normal (ULN) in a population of healthy children (HC) or comparing these values with streptococcal antibodies registered in a cohort of patients affected by the rheumatic sequelae of GAS infection. We performed a multicenter retrospective study. We enrolled 125 HC, aged 2-17 years, and a total of 181 patients affected by ARF, acute streptococcal pharyngitis, post-streptococcal arthritis, Henoch-Schönlein purpura and erythema nodosum, divided into four groups. The levels of ASO and anti-deoxyribonuclease B (anti-DNase B) titres were analyzed and compared among the various groups. Moreover, the 80th percentile value was calculated and established as the ULN for ASO titre in HC group. The ULN for ASO titre in overall HC group was 515 IU/mL, resulting in higher than used in the routine investigation. The ASO titre was significantly higher in patients with rheumatic sequelae compared with HC group, with a peak in the age between 5 and 15 years.    Conclusion: Our study established a new ULN normal value of streptococcal serology in a childhood and adolescent population of Italy, suggesting the need to extend this revaluation to the critical areas, in order to avoid underestimating ARF diagnosis. The correct interpretation of ASO and anti-DNase B values in the context of rheumatic diseases has been discussed. What is Known: • The global burden of disease caused by group A streptococcus is not known and remains an important cause of morbidity and mortality. Acute rheumatic fever continues to be a serious worldwide public health problem and a recent recurrence of group A streptococcus infection cases is observed. • The streptococcal sequelae requires evidence of preceding streptococcal infection, commonly elevated streptococcal antibody titre, but the upper limit for these titres varies considerably based on age group, region, and origin. What is New: • This study provides population-specific values for streptococcal antibody titres in Italy. • Interpret the results of group A streptococcal antibody tests within the clinical context.

Pediatric Recurrent Pericarditis: Appropriateness of the Standard of Care and Response to IL-1 Blockade.

OBJECTIVE: To analyze, in a cohort of pediatric patients with recurrent pericarditis undergoing anti-interleukin (IL)-1 treatment: the agent and dosing used as first-line treatment, the long-term efficacy of IL-1 blockers, the percentage of patients achieving a drug-free remission, and the presence of variables associated with drug-free remission. STUDY DESIGN: Data were collected from patients' charts. The annualized relapse rate (ARR) was used for evaluation of treatment efficacy, and bivariate logistic regression analysis was used for variables associated with drug-free remission. RESULTS: Fifty-eight patients, treated between 2008 and 2018, were included in the study (mean follow-up. 2.6 years). Of the 56 patients treated with first-line drugs, 14 not responsive patients were underdosed. Fifty-seven patients were treated with anakinra: the ARR before and during daily treatment was 3.05 and 0.28, respectively (P < .0001); an increase to 0.83 was observed after the reduction/withdrawal of treatment (P < .0001). The switch from anakinra to canakinumab (5 patients) was associated to an increase of the ARR (0.49 vs 1.46), but without statistical significance (P = .215). At last follow-up, only 9 of the 58 patients had withdrawn all treatments. With the limits of a retrospective study and the heterogeneity between the patients enrolled in the study, a shorter duration of treatment with anakinra was the only variable associated with drug-free remission. CONCLUSIONS: This study shows that most pediatric patients with recurrent pericarditis needing IL-1 blockade received an inadequate treatment with first-line agents. The effectiveness of anakinra is supported by this study, but few patients achieved drug-free remission. The different rate of response to anakinra and canakinumab may suggest a possible role of IL-1α in the pathogenesis of recurrent pericarditis.

Neurovisual Manifestations in Children with Mild COVID-19: An Association to Remember.

Neurovisual involvement has been reported in a number of patients with severe SARS-CoV-2 disease (COVID-19), mainly among adult patients. In children, such involvement has been reported in rare cases, often in those presenting with severe forms of COVID-19. The aim of this work is to explore the association between mild COVID-19 and neurovisual manifestations. We report the cases of three previously healthy children who developed neurovisual manifestations following mild acute COVID-19, analysing the clinical phenotype, the latency between the onset of acute COVID-19 and neurovisual involvement, and the kinetic of resolution. Our patients developed different clinical patterns, including visual impairment and ophthalmoplegia. In two cases, these clinical features occurred during acute COVID-19, while in the third patient their development was delayed after 10 days from disease onset. Furthermore, the dynamics of resolution were different, with one patient showing remission after 24 hours, the second after 30 days, and the third showing persistence of the strabismus after 2 months of follow-up. The spreading of COVID-19 among the paediatric population will probably lead to an increase of atypical disease forms, including those presenting with neurovisual involvement. Therefore, a better knowledge of the pathogenic and clinical features of these manifestations is warranted.

Progressive Depletion of B and T Lymphocytes in Patients with Ataxia Telangiectasia: Results of the Italian Primary Immunodeficiency Network.

Ataxia telangiectasia (AT) is a rare neurodegenerative genetic disorder due to bi-allelic mutations in the Ataxia Telangiectasia Mutated (ATM) gene. The aim of this paper is to better define the immunological profile over time, the clinical immune-related manifestations at diagnosis and during follow-up, and to attempt a genotype-phenotype correlation of an Italian cohort of AT patients. Retrospective data of 69 AT patients diagnosed between December 1984 and November 2019 were collected from the database of the Italian Primary Immunodeficiency Network. Patients were classified at diagnosis as lymphopenic (Group A) or non-lymphopenic (Group B). Fifty eight out of 69 AT patients (84%) were genetically characterized and distinguished according to the type of mutations in truncating/truncating (TT; 27 patients), non-truncating (NT)/T (28 patients), and NT/NT (5 patients). In 3 patients, only one mutation was detected. Data on age at onset and at diagnosis, cellular and humoral compartment at diagnosis and follow-up, infectious diseases, signs of immune dysregulation, cancer, and survival were analyzed and compared to the genotype. Lymphopenia at diagnosis was related per se to earlier age at onset. Progressive reduction of cellular compartment occurred during the follow-up with a gradual reduction of T and B cell number. Most patients of Group A carried bi-allelic truncating mutations, had a more severe B cell lymphopenia, and a reduced life expectancy. A trend to higher frequency of interstitial lung disease, immune dysregulation, and malignancy was noted in Group B patients. Lymphopenia at the onset and the T/T genotype are associated with a worst clinical course. Several mechanisms may underlie the premature and progressive immune decline in AT subjects.

OBSIDIAN - real-world evidence of originator to biosimilar drug switch in juvenile idiopathic arthritis.

OBJECTIVES: Limited data about use of biosimilars (BIOs) are available in children with JIA. This study therefore aimed to evaluate long-term efficacy and safety of switching from etanercept (ETA) and adalimumab (ADA) originators to their biosimilars (BIOs), in children with JIA, in a real-world setting. METHODS: This is a retro-prospective non-interventional multicentre Italian comparative cohort study. Medical charts of JIA children treated with biosimilars of ETA or ADA were included. Efficacy and safety of TNF-inhibitors therapy was evaluated at last follow-up during originator and at 3, 6 and 12 months following the switch to biosimilar. RESULTS: A total of 59 children (42 female, median age at onset 88 months) were treated with biosimilar of ETA (21) and ADA (38). Forty-five switched from the originator to the BIO (17 ETA, 28 ADA). At time of switch, 12/17 patients on ETA and 18/28 on ADA were in remission. No significant difference has been found at 3, 6 and 12 months after the switch. Ten patients discontinued biosimilars due to disease remission (4 ETA, 3 ADA), family willing (1 ETA), occurrence of burning at injection site (1 ETA) and persistent activity (1 ADA). No statistically significant difference was observed between originator and BIOs, nor between originator and BIOs, and between ADA and ETA in time to disease remission achievement, time to relapse and number of patients who experienced adverse event (AE). CONCLUSION: Our real-life results seem to confirm the efficacy and safety profile of switching from originator of ADA and ETA to their respective BIOs, also in paediatric patients with JIA.

Lymphadenopathy at the crossroad between immunodeficiency and autoinflammation: An intriguing challenge.

Lymphadenopathies can be part of the clinical spectrum of several primary immunodeficiencies, including diseases with immune dysregulation and autoinflammatory disorders, as the clinical expression of benign polyclonal lymphoproliferation, granulomatous disease or lymphoid malignancy. Lymphadenopathy poses a significant diagnostic dilemma when it represents the first sign of a disorder of the immune system, leading to a consequently delayed diagnosis. Additionally, the finding of lymphadenopathy in a patient with diagnosed immunodeficiency raises the question of the differential diagnosis between benign lymphoproliferation and malignancies. Lymphadenopathies are evidenced in 15-20% of the patients with common variable immunodeficiency, while in other antibody deficiencies the prevalence is lower. They are also evidenced in different combined immunodeficiency disorders, including Omenn syndrome, which presents in the first months of life. Interestingly, in the activated phosphoinositide 3-kinase delta syndrome, autoimmune lymphoproliferative syndrome, Epstein-Barr virus (EBV)-related lymphoproliferative disorders and regulatory T cell disorders, lymphadenopathy is one of the leading signs of the entire clinical picture. Among autoinflammatory diseases, the highest prevalence of lymphadenopathies is observed in patients with periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis (PFAPA) and hyper-immunoglobulin (Ig)D syndrome. The mechanisms underlying lymphoproliferation in the different disorders of the immune system are multiple and not completely elucidated. The advances in genetic techniques provide the opportunity of identifying new monogenic disorders, allowing genotype-phenotype correlations to be made and to provide adequate follow-up and treatment in the single diseases. In this work, we provide an overview of the most relevant immune disorders associated with lymphadenopathy, focusing on their diagnostic and prognostic implications.

Long-term follow-up of 168 patients with X-linked agammaglobulinemia reveals increased morbidity and mortality.

BACKGROUND: X-linked agammaglobulinemia (XLA) is the prototype of primary humoral immunodeficiencies. Long-term follow-up studies regarding disease-related complications and outcome are scarce. OBJECTIVE: Our aim was to describe the natural history of XLA. METHODS: A nationwide multicenter study based on the Italian Primary Immunodeficiency Network registry was established in 2000 in Italy. Affected patients were enrolled by documenting centers, and the patients' laboratory, clinical, and imaging data were recorded on an annual base. RESULTS: Data on the patients (N = 168) were derived from a cumulative follow-up of 1370 patient-years, with a mean follow-up of 8.35 years per patient. The mean age at diagnosis decreased after establishment of the Italian Primary Immunodeficiency Network registry (84 months before vs 23 months after). Respiratory, skin, and gastrointestinal manifestations were the most frequent clinical symptoms at diagnosis and during long-term follow-up. Regular immunoglobulin replacement treatment reduced the incidence of invasive infections. Affected patients developed chronic lung disease over time (47% after 40 years of follow-up) in the presence of chronic sinusitis (84%). Malignancies were documented in a minority of cases (3.7%). Overall survival for affected patients was significantly reduced when compared with that for the healthy male Italian population, and it further deteriorated in the presence of chronic lung disease. CONCLUSIONS: This is the first detailed long-term follow-up study for patients with XLA, revealing that although immunoglobulin replacement treatment reduces the incidence of invasive infections, it does not appear to influence the development of chronic lung disease. The overall survival of affected patients is reduced. Further studies are warranted to improve patients' clinical management and increase awareness among physicians.

The Italian Registry for Primary Immunodeficiencies (Italian Primary Immunodeficiency Network; IPINet): Twenty Years of Experience (1999-2019).

Primary immunodeficiencies (PIDs) are heterogeneous disorders, characterized by variable clinical and immunological features. National PID registries offer useful insights on the epidemiology, diagnosis, and natural history of these disorders. In 1999, the Italian network for primary immunodeficiencies (IPINet) was established. We report on data collected from the IPINet registry after 20 years of activity. A total of 3352 pediatric and adult patients affected with PIDs are registered in the database. In Italy, a regional distribution trend of PID diagnosis was observed. Based on the updated IUIS classification of 2019, PID distribution in Italy showed that predominantly antibody deficiencies account for the majority of cases (63%), followed by combined immunodeficiencies with associated or syndromic features (22.5%). The overall age at diagnosis was younger for male patients. The minimal prevalence of PIDs in Italy resulted in 5.1 per 100.000 habitants. Mortality was similar to other European registries (4.2%). Immunoglobulin replacement treatment was prescribed to less than one third of the patient cohort. Collectively, this is the first comprehensive description of the PID epidemiology in Italy.

Correction to: The Italian version of the Juvenile Arthritis Multidimensional Assessment Report (JAMAR).

The family name of author Francesco La Torre was incorrect in the published article. The correct family name should read as La Torre F.

The Italian version of the Juvenile Arthritis Multidimensional Assessment Report (JAMAR).

The Juvenile Arthritis Multidimensional Assessment Report (JAMAR) is a new parent/patient reported outcome measure that enables a thorough assessment of the disease status in children with juvenile idiopathic arthritis (JIA). We report the results of the cross-cultural adaptation and validation of the parent and patient versions of the JAMAR in the Italian language.The reading comprehension of the questionnaire was tested in 10 JIA parents and patients. Each participating centre was asked to collect demographic, clinical data and the JAMAR in 100 consecutive JIA patients or all consecutive patients seen in a 6-month period and to administer the JAMAR to 100 healthy children and their parents.The statistical validation phase explored descriptive statistics and the psychometric issues of the JAMAR: the 3 Likert assumptions, floor/ceiling effects, internal consistency, Cronbach's alpha, interscale correlations, test-retest reliability, and construct validity (convergent and discriminant validity).A total of 1296 JIA patients (7.2% systemic, 59.5% oligoarticular, 21.4% RF negative polyarthritis, 11.9% other categories) and 100 healthy children, were enrolled in 18 centres. The JAMAR components discriminated well healthy subjects from JIA patients except for the Health Related Quality of Life (HRQoL) Psychosocial Health (PsH) subscales. All JAMAR components revealed good psychometric performances.In conclusion, the Italian version of the JAMAR is a valid tool for the assessment of children with JIA and is suitable for use both in routine clinical practice and clinical research.

Osteoid osteoma mimicking monoarticular juvenile idiopathic arthritis in a girl.

Osteoid osteoma (OO) is a benign osteogenic neoplasm, usually affecting children and young adults, that is typically characterized by nocturnal pain and response to non-steroidal anti-inflammatory drugs. OO is frequently misdiagnosed because it mimics juvenile idiopathic arthritis (JIA), bone infection or malignancy. Herein we report the case of a girl who presented with chronic monoarthritis of the knee mimicking JIA. After 1 year, OO of the femoral distal metaphysis was diagnosed. OO was treated with computed tomography-guided radiofrequency ablation with disappearance of the symptoms and resolution of the neoplasm. No recurrences have been observed 3 years after the treatment. This case highlights that intra-articular or juxta-articular OO should be suspected in the case of misleading symptoms and signs, such as swelling, lack of typical pain and synovial thickening on ultrasound; needle biopsy of the lesion is necessary in the case of confusing imaging.

Intergenerational and intrafamilial phenotypic variability in 22q11.2 deletion syndrome subjects.

BACKGROUND: 22q11.2 deletion syndrome (22q11.2DS) is a common microdeletion syndrome, which occurs in approximately 1:4000 births. Familial autosomal dominant recurrence of the syndrome is detected in about 8-28% of the cases. Aim of this study is to evaluate the intergenerational and intrafamilial phenotypic variability in a cohort of familial cases carrying a 22q11.2 deletion. METHODS: Thirty-two 22q11.2DS subjects among 26 families were enrolled. RESULTS: Second generation subjects showed a significantly higher number of features than their transmitting parents (212 vs 129, P = 0.0015). Congenital heart defect, calcium-phosphorus metabolism abnormalities, developmental and speech delay were more represented in the second generation (P < 0.05). Ocular disorders were more frequent in the parent group. No significant difference was observed for the other clinical variables. Intrafamilial phenotypic heterogeneity was identified in the pedigrees. In 23/32 families, a higher number of features were found in individuals from the second generation and a more severe phenotype was observed in almost all of them, indicating the worsening of the phenotype over generations. Both genetic and epigenetic mechanisms may be involved in the phenotypic variability. CONCLUSIONS: Second generation subjects showed a more complex phenotype in comparison to those from the first generation. Both ascertainment bias related to patient selection or to the low rate of reproductive fitness of adults with a more severe phenotype, and several not well defined molecular mechanism, could explain intergenerational and intrafamilial phenotypic variability in this syndrome.

Clinical features and follow-up in patients with 22q11.2 deletion syndrome.

OBJECTIVE: To investigate the clinical manifestations at diagnosis and during follow-up in patients with 22q11.2 deletion syndrome to better define the natural history of the disease. STUDY DESIGN: A retrospective and prospective multicenter study was conducted with 228 patients in the context of the Italian Network for Primary Immunodeficiencies. Clinical diagnosis was confirmed by cytogenetic or molecular analysis. RESULTS: The cohort consisted of 112 males and 116 females; median age at diagnosis was 4 months (range 0 to 36 years 10 months). The diagnosis was made before 2 years of age in 71% of patients, predominantly related to the presence of heart anomalies and neonatal hypocalcemia. In patients diagnosed after 2 years of age, clinical features such as speech and language impairment, developmental delay, minor cardiac defects, recurrent infections, and facial features were the main elements leading to diagnosis. During follow-up (available for 172 patients), the frequency of autoimmune manifestations (P = .015) and speech disorders (P = .002) increased. After a median follow-up of 43 months, the survival probability was 0.92 at 15 years from diagnosis. CONCLUSIONS: Our data show a delay in the diagnosis of 22q11.2 deletion syndrome with noncardiac symptoms. This study provides guidelines for pediatricians and specialists for early identification of cases that can be confirmed by genetic testing, which would permit the provision of appropriate clinical management.

Case Report: Efficacy, safety, and favorable long-term outcome of early treatment with IL-1 inhibitors in a patient with chronic infantile neurological cutaneous articular (CINCA) syndrome caused by NLRP3 mosaicism.

Chronic infantile neurological cutaneous articular (CINCA) syndrome is an autoinflammatory disease encompassed in the group of cryopyrin-associated periodic syndromes (CAPS). Patients suffering from CINCA have an elevated risk of developing chronic sequelae, including deforming arthropathy, chronic meningitis, neurodevelopmental delay, and neurosensorial hearing loss. The diagnosis of CINCA presents several difficulties, as the clinical phenotype could be difficult to recognize, and almost half of the patients have negative genetic testing. In this paper, we describe the case of a patient presenting with the typical phenotype of neonatal-onset CINCA who resulted negative for NLRP3 mutations. Based on the clinical judgment, the patient underwent treatment with anti-interleukin-1 (IL-1) agents (anakinra and, later, canakinumab) resulting in a complete clinical and laboratory response that allowed confirmation of the diagnosis. Additional genetic investigations performed after the introduction of anti-IL-1 therapy revealed a pathogenic mosaicism in the NLRP3 gene. After a 12-year follow-up, the patient has not experienced chronic complications. Although genetics is rapidly progressing, this case highlights the importance of early diagnosis of CINCA patients when the clinical and laboratory picture is highly suggestive in order to start the appropriate anti-cytokine treatment even in the absence of a genetic confirmation.

The Etiologic Landscape of Lymphoproliferation in Childhood: Proposal for a Diagnostic Approach Exploring from Infections to Inborn Errors of Immunity and Metabolic Diseases.

Lymphoproliferation is defined by lymphadenopathy, splenomegaly, hepatomegaly, or lymphocytic organ and tissue infiltration. The most common etiologies of lymphoproliferation are represented by infectious diseases and lymphoid malignancies. However, it is increasingly recognized that lymphoproliferative features can be the presenting sign of rare conditions, including inborn errors of immunity (IEI) and inborn errors of metabolism (IEM). Among IEI, lymphoproliferation is frequently observed in autoimmune lymphoproliferative syndrome (ALPS) and related disorders, common variable immunodeficiency (CVID), activated phosphoinositide 3-kinase δ syndrome, and Epstein-Barr virus (EBV)-related disorders. Gaucher disease and Niemann-Pick disease are the most common IEMs that can present with isolated lymphoproliferative features. Notably, other rare conditions, such as sarcoidosis, Castleman disease, systemic autoimmune diseases, and autoinflammatory disorders, should be considered in the differential diagnosis of patients with persistent lymphoproliferation when infectious and malignant diseases have been reasonably ruled out. The clinical features of lymphoproliferative diseases, as well as the associated clinical findings and data deriving from imaging and first-level laboratory investigations, could significantly help in providing the correct diagnostic suspicion for the underlying etiology. This paper reviews the most relevant diseases associated with lymphoproliferation, including infectious diseases, hematological malignancies, IEI, and IEM. Moreover, some practical indications to orient the initial diagnostic process are provided, and two diagnostic algorithms are proposed for the first-level assessment and the approach to persistent lymphoproliferation, respectively.