P810: BONE MARROW FAILURE IN PATIENTS CARRYING VARIANTS ON CARD11 GENE.

Background: An accurate differential diagnosis in children with Marrow Failure (MF) is crucial for the clinical management of the disease. In addition to the classical congenital MF (cMF), the role of Inborn Errors of Immunity (IEI) have been recently highlighted as potential cause of the disease. CARD11 is a membrane protein acting as a key signaling scaffold which controls the antigen-induced lymphocyte activation during the adaptive immune response (NF-kB, JNK and mTOR pathway). Germline CARD11 mutations can result in gain/loss of function of the protein leading to different phenotypes (SCID, BENTA disease, atopy, CVID). Several heterozygous hypomorphic/dominant negative (DN) variants of CARD11 have demonstrated a loss of protein function, exhibiting high penetrance and variable expressivity. In particular, mutations in the GUK (Guanylate Kinase) domain seem to be involved in modulating the self-inactivating capacity of CARD11. No CARD11 variants have ever been described to be associated with MF. Herein, we report 4 patients with MF carrying variants on the CARD11 gene. Aims: To evaluate the clinical/immunological features and genetic profile of patients with MF carrying CARD11 variants and followed in our Centre. Methods: A restrospective review of clinical, immunological and genetic data was performed from patients’ records. Molecular analysis was conducted using Next-Generation Sequencing (NGS), targeted panels including genes involved in both cMF and IEI, or by Whole Exome Sequencing (WES). Filtering of variants was performed according to Mendelian disease segregation and zigosity (OMIM), in silico prediction of pathogenicity (ACMG criteria in “Varsome”), and minor allele frequency (reported in GnomAD). Results: Four children carrying variants in the CARD11 gene presented with MF as initial sign of the disease (n=2) or with immune cytopenias further evolving into MF (n=2). Their clinical/immunological features, genetic profile, treatment and follow-up are reported in Table1. Lymphocytes subsets analysis revealed a deficiency of B memory, Tregs and an increased of HLADR+ T cells in all patients. Two cases showed elevated CD4-CD8- TCR αβ+ T-cells (“double negatives T-cells”). All patients showed autoimmune stigmata and 2 of them also presented autoimmune hepatitis. No patients responded to first-line treatment. One responded to second-line treatment with Mychofenolate-mofetil (MMF) and periodic infusion of immunoglobulins. The remaining 3 patients underwent hematopoietic stem cell transplantation (SCT) from haploidentical-αβCD19 depleted transplant (n=2) or HLA-identical cousin (n=1) (Table1). Image:Summary/Conclusion: This report highlights novel phenotypic characteristics of patients carrying variants in CARD11 such as MF and autoimmune hepatitis, thus widening the clinical spectrum of the disease. This underlines the need for an enlarged molecular analysis in pediatric cases of MF and suggests that, in some patients, immune-mediated destruction of blood and marrow cells cooperate in generating the cytopenia. Three variants detected in our cohort are located in the GUK domain of the gene, close to other reported pathogenic dominant negative mutations leading to haploinsufficiency, suggesting interference with the CARD11’s ability to self-inactivate. Functional study will be necessary to confirm the pathogenic role of such variants. Although treatment with MMF may be considered, SCT represents the only curative option for such patients.