Variants in CASP10, a diagnostic challenge: Single center experience and review of the literature.

Autoimmune lymphoproliferative syndrome is a primary immunodeficiency caused by variants in FAS-mediated apoptosis related genes and is characterized by lymphadenopathy, splenomegaly and autoimmunity. A total of six different variants in CASP10 have been described as potential causative of disease, although two of them have recently been considered polymorphisms. The high allele frequency of these variants in healthy population in addition to the broad clinical spectrum of the disease difficult the interpretation of their pathogenicity. Here, we describe the clinical and analytical findings of three new patients carrying variants in CASP10 and summarize 12 more cases from the literature. Autoimmune cytopenias, adenopathies and increment of TCRαß+CD4-CD8- cells have been the most common findings, being possibly the FAS-mediated apoptosis pathway the pathogenic mechanism of this disease. The clinical impact and the consequences of CASP10 variants are not fully elucidated, therefore the description of new cases will contribute to solve this issue.

ALPS-Like Phenotype Caused by ADA2 Deficiency Rescued by Allogeneic Hematopoietic Stem Cell Transplantation.

Adenosine deaminase 2 (ADA2) deficiency is an auto-inflammatory disease due to mutations in cat eye syndrome chromosome region candidate 1 (CECR1) gene, currently named ADA2. The disease has a wide clinical spectrum encompassing early-onset vasculopathy (targeting skin, gut and central nervous system), recurrent fever, immunodeficiency and bone marrow dysfunction. Different therapeutic options have been proposed in literature, but only steroids and anti-cytokine monoclonal antibodies (such as tumor necrosis factor inhibitor) proved to be effective. If a suitable donor is available, hematopoietic stem cell transplantation (HSCT) could be curative. Here we describe a case of ADA2 deficiency in a 4-year-old Caucasian girl. The patient was initially classified as autoimmune neutropenia and then she evolved toward an autoimmune lymphoproliferative syndrome (ALPS)-like phenotype. The diagnosis of ALPS became uncertain due to atypical clinical features and normal FAS-induced apoptosis test. She was treated with G-CSF first and subsequently with immunosuppressive drugs without improvement. Only HSCT from a 9/10 HLA-matched unrelated donor, following myeloablative conditioning, completely solved the clinical signs related to ADA2 deficiency. Early diagnosis in cases presenting with hematological manifestations, rather than classical vasculopathy, allows the patients to promptly undergo HSCT and avoid more severe evolution. Finally, in similar cases highly suspicious for genetic disease, it is desirable to obtain molecular diagnosis before performing HSCT, since it can influence the transplant procedure. However, if HSCT has to be performed without delay for clinical indication, related donors should be excluded to avoid the risk of relapse or partial benefit due to a hereditary genetic defect.

Deficiency of ADA2 mimicking autoimmune lymphoproliferative syndrome in the absence of livedo reticularis and vasculitis.

Adenosine deaminase-2 (ADA2) deficiency (DADA2) is associated with early onset polyarteritis nodosa and vasculopathy. Classic presentation includes livedo reticularis, vasculitis, and stroke. However, the phenotype and disease severity are variable. We present a 5-year-old female who presented with features that mimicked autoimmune lymphoproliferative syndrome (ALPS) in the absence of classic features of DADA2. Exome sequencing identified a novel homozygous splicing variant in ADA2 c.882-2A > G. Patient responded to anti- tumor necrosis factor medication and is in complete remission. Hematologists should be aware of various hematological presentations of DADA2, including ALPS-like disorder, that might lack vasculitis and livedo reticularis to prevent delay in initiating optimal therapy.