Background: Multiple investigators have described an increased incidence of thromboembolic events in SARS-CoV-2-infected individuals. Data concerning hemostatic complications in children hospitalized for COVID-19/multisystem inflammatory syndrome in children (MIS-C) are scant. Objectives: To share our experience in managing SARS-CoV-2-associated pro-coagulant state in hospitalized children. Methods: D-dimer values were recorded at diagnosis in children hospitalized for SARS-CoV-2-related manifestations. In moderately to critically ill patients and MIS-C cases, coagulation and inflammatory markers were checked at multiple time points and median results were compared. Pro-thrombotic risk factors were appraised for each child and thromboprophylaxis was started in selected cases. Results: Thirty-five patients were prospectively enrolled. D-dimer values did not discriminate COVID-19 of differing severity, whereas were markedly different between the COVID-19 and the MIS-C cohorts. In both cohorts, D-dimer and C-reactive protein levels increased upon clinical worsening but were not accompanied by decreased fibrinogen or platelet values, with all parameters returning to normal upon disease resolution. Six patients had multiple thrombotic risk factors and were started on pharmacological thromboprophylaxis. No deaths or thrombotic or bleeding complications occurred. Conclusions: COVID-19 pediatric patients show mildly altered coagulation and inflammatory parameters; on the other hand, MIS-C cases showed laboratory signs of an inflammatory driven pro-coagulant status. Universal anticoagulant prophylaxis in hospitalized children with SARS-CoV-2-related manifestations is not warranted, but may be offered to patients with other pro-thrombotic risk factors in the context of a multi-modal therapeutic approach.

PSTPIP1-associated myeloid-related proteinemia inflammatory (PAMI) syndrome is a rare early-onset autoinflammatory disease associated with various hematologic findings, including chronic neutropenia and pancytopenia. We report a unique case of PAMI syndrome in a toddler with transfusion-dependent hemolytic anemia, hepatosplenomegaly, failure to thrive, developmental delay, and multiple malformations. Because of acute inflammatory-driven decompensation, anakinra was started with dramatic improvement of both the hematologic and neurologic involvement. A customized next-generation sequencing panel later identified a de novo pathogenic variant in the PSTPIP1 gene, confirming the diagnosis. Our case illustrates the broad spectrum of phenotypes associated with PAMI syndrome, which should be considered in any case of unexplained cytopenias associated with autoinflammatory stigmata. It is also one of the few reports of neurologic involvement in PSTPIP1-associated inflammatory diseases. Increased awareness of this rare disease and early performance of genetic testing can correctly diagnose PAMI syndrome and prevent disease complications.

Abstracts Background Available diagnostics often fail to distinguish viral from bacterial causes of pediatric community‐acquired pneumonia (pCAP). Metabolomics, which aims at characterizing diseases based on their metabolic signatures, has been applied to expand pathophysiological understanding of many diseases. In this exploratory study, we used the untargeted metabolomic analysis to shed new light on the etiology of pCAP. Methods Liquid chromatography coupled with mass spectrometry was used to quantify the metabolite content of urine samples collected from children hospitalized for CAP of pneumococcal or viral etiology, ascertained using a conservative algorithm combining microbiological and biochemical data. Results Fifty‐nine children with CAP were enrolled over 16 months. Pneumococcal and viral cases were distinguished by means of a multivariate model based on 93 metabolites, 20 of which were identified and considered as putative biomarkers. Among these, six metabolites belonged to the adrenal steroid synthesis and degradation pathway. Conclusions This preliminary study suggests that viral and pneumococcal pneumonia differently affect the systemic metabolome, with a stronger disruption of the adrenal steroid pathway in pneumococcal pneumonia. This finding may lead to the discovery of novel diagnostic biomarkers and bring us closer to personalized therapy for pCAP.

Cartilage-hair hypoplasia (CHH) is a syndromic immunodeficiency characterized by metaphyseal dysplasia, cancer predisposition, and varying degrees of anemia. It may present as severe combined immunodeficiency in infancy, or slowly progress until fully manifesting in late adolescence/adulthood. No targeted treatment is currently available, and patients are usually managed with supportive measures, or are offered a bone marrow transplant if the clinical phenotype is severe and a suitable donor is available. We report the case of a young girl presenting with transfusion-dependent erythropoietic failure and immunological features resembling autoimmune lymphoproliferative syndrome who responded well to empirical sirolimus. She later developed a marked growth delay, which was ultimately attributed to metaphyseal dysplasia. A diagnosis of CHH was reached through whole-genome sequencing (WGS), after a less sensitive genetic diagnostic strategy failed. The patient eventually underwent a haploidentical bone marrow transplant due to progressive combined immunodeficiency manifested as cryptococcal meningoencephalitis. This case illustrates the potential role of sirolimus in correcting anemia and partially controlling the immune aberrations associated with CHH, and serves as a reminder of the invaluable role of WGS in diagnosing patients with complex and atypical presentations.

Venous thrombosis is a complication that mostly occurs in the paediatric patient with multiple comorbidities. In these cases, it is relatively simple for the paediatrician to suspect the presence of a thrombosis. On the contrary, due to the rarity of the pathology and the clinical presentation that can mimic other conditions, it could be difficult to recognize a thrombotic event in an extra-hospital context and in an "otherwise healthy" child. This article aims to examine how to diagnose and treat this rare paediatric condition promptly

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INTRODUCTION: Idiopathic neutropenia (IN) of childhood is a benign, self-limiting disorder usually occurring in the first 3 years of life that differs from primary autoimmune neutropenia (AIN) because anti neutrophil antibodies are not detected on repeated indirect testing over time(1). Chronic idiopathic neutropenia (CIN) is a well characterized disorder of elderly with a peculiar immunological pattern(2). Pediatric AIN patients, with atypical features represented by longer disease duration (Long Lasting) or diagnosed later (Late Onset), were recently shown by our group to display a different immune-hematological profile vs typical primary AIN(3). Atypical pediatric IN subjects, i.e. diagnosed later or with longer disease duration, though occasionally reported, were never systematically investigated. In the present study we analyzed a cohort of young patients with atypical IN and AIN, diagnosed after the age of 3 years or with longer disease duration, aiming to identify an immunological signature that might predict their different outcome from classical AIN and IN of infancy. PURPOSE OF THE STUDY: to analyze a cohort of patients affected with AIN and IN rising > 3 years of age and with duration >12 months or rising <3 years of age but persisting over 36 months. MATERIALS AND METHODS: Clinical, immunological and genetic data (NGS panel of 160 immunodeficiency/disimmunity genes) of eligible patients were collected from the database of the Italian Neutropenia Registry. RESULTS: From 2005 to 2020, data from 46 patients (24F, 24 autoimmune and 22 Idiopathic Neutropenia) were retrieved. Median age at onset was 11.2 years (IQR13.2-16.7), median follow-up was 4.3 years (IQR 3.2-6.8). Neither autoimmunity nor additional cytopenias to neutropenia were present at onset. Cumulative incidence at 5 years of autoimmune manifestations (thyroiditis, arthritis, vitiligo, recurrent skin rash) was 11.8% (CI 95% 4.3-30). Throughout the follow up, infections occurred in 32/46 (70%) subjects and in only 16% were severe (meningitis, recurrent pneumonia, sepsis and pericarditis). Infections sites were upper respiratory (in 84% of subjects mouth and gums (47%), and skin (40%) ear (25%), lung (19%) and urinary tract (12%). Fever of unknown origin was detected in 40% of patients. Recurrent infections (more than 3/y) involved mouth (85%) and ear (88%). White Blood Cell, Absolute Neutrophil and Lymphocyte counts retrieved at the beginning of the study, in the middle and at the end of follow up are shown in Table 1. Leucocytes and Lymphocytes at the end of follow up were significantly lower than values seen at diagnosis (p < 0.001) whereas neutrophil count remained stable (p=ns). One third of the cohort had lower values than normal of CD19+ and CD3-CD56+CD16+ cells. B switched memory CD27+/IgD-/IgM- (in 94%) were lower, while marginal zone B lymphocytes CD27+/IgD+/IgM+ (62%) and Tγδ cells (70%) were increased than the normal population according to a pattern comparable to that described in chronic idiopathic neutropenia (CIN). Immunoglobulin serum levels (IgA, IgG and IgM) were below the normal value in 7.5% of the population, but specularly a small subset (7.5%) of IN showed an increase of IgM was seen, similar to what already descibed in adult CIN. The genetic study carried out in 32 patients showed in 5 (16%) pathogenic variants: of immunodeficit/dysregulation (2 TACI, 1 TINF2, 1 CARD11) and in 9 cases (28%) VUS in genes of the same groups (1CARD11, 4CASP10,1DDX41/SOCS1, 1TSR2/DCLRE1c, 1PIK3D, 1TERT/TACI). CONCLUSIONS: Atypical IN and AIN (of longer duration or occurring in advanced pediatric age) are different from those appearing in early infancy. They seem to display dysimmune/autoimmune features that is some case is proven to rely on a genetic dysimmune background. They might represent an anticipation of more complex autoimmune disorders which may fully manifest later in life. Interstingly these patients seem to share some features with CIN of adults. Definitive conclusions will be drawn by applying more comprehensive genetic nalysis (WES and WGS) on larger group of subjects. References: 1. Farruggia et al, Am J Hematol. 2019, 94:216-222 2. Mavroudi I et al, Clin Immunol. 2017 Oct;183:75-84 3. Fioredda F et al, Blood Adv 2020 Nov 24;4:5644-5649 Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.