Inherited thrombocytopenias (ITs) encompass a group of rare disorders characterized by diminished platelet count. Recent advancements have unveiled various forms of IT, with inherited thrombocytopenia 2 (THC2) emerging as a prevalent subtype associated with germline variants in the critical 5' untranslated region of the ANKRD26 gene. This region is crucial in regulating the gene expression of ANKRD26, particularly in megakaryocytes. THC2 is an autosomal dominant disorder presenting as mild-to-moderate thrombocytopenia with minimal symptoms, with an increased risk of myeloproliferative malignancies. In our study of a family with suspected IT, three affected individuals harbored the c.-118C>T ANKRD26 variant, while four healthy members carried the c.-140C>G ANKRD26 variant. We performed a functional analysis by studying platelet-specific ANKRD26 gene expression levels using quantitative real-time polymerase-chain reaction. Functional analysis of the c.-118C>T variant showed a significant increase in ANKRD26 expression in affected individuals, supporting its pathogenicity. On the contrary, carriers of the c.-140C>G variant exhibited normal platelet counts and no significant elevation in the ANKRD26 expression, indicating the likely benign nature of this variant. Our findings provide evidence confirming the pathogenicity of the c.-118C>T ANKRD26 variant in THC2 and suggest the likely benign nature of the c.-140C>G variant.

What is the context?Inherited thrombocytopenias (ITs) are rare conditions characterized by low platelet counts. Inherited thrombocytopenia 2 (THC2) is caused by ANKRD26 gene changes leading to increased ANKRD26 expression as the main reason for subsequent thrombocytopenia. THC2 results in a mild-to-moderate decrease in platelet count and increases blood cancer risk. We focused on understanding two ANKRD26 variants in a family with a history of thrombocytopenia.What is new?We conducted functional analysis to understand the effect of variants on platelet function and gene expression. We identified three thrombocytopenic family members as carriers of ANKRD26 variant c.-118C>T. This variant is linked to increased expression of the ANKRD26 gene and confirmed as the likely cause of THC2. Another variant, c.-140C>G, was present in four healthy family members. Although it was considered causal for THC2 in the past, our study suggests that the c.-140C>G variant does not elevate ANKRD26 expression and does not cause thrombocytopenia.What is the impact?Understanding the genetic and functional implications of ANKRD26 gene variants is crucial for THC2 diagnosis and management. Our study emphasizes the necessity of conducting functional analyses to precisely evaluate the clinical significance of variants linked to inherited blood disorders. Carriers of the c.-118C>T variant should undergo vigilant monitoring for THC2 and potential cancer development. Conversely, the c.-140C>G variant does not pose a risk of THC2 or heightened cancer susceptibility.

Centre of Molecular Medicine Central European Institute of Technology Masaryk University Brno Czech Republic

Department of Clinical Haematology and Haematooncology Hospital Havířov Havířov Czech Republic

Department of Clinical Haematology University Hospital Brno Masaryk University Brno Czech Republic

Department of Internal Medicine Haematology and Oncology University Hospital Brno and Faculty of Medicine Masaryk University and ERN EuroBloodNet Centre Brno Czech Republic

Department of Laboratory Methods Faculty of Medicine Masaryk University Brno Czech Republicand

Institute of Medical Genetics and Genomics University Hospital Brno and Faculty of Medicine Masaryk University Brno Czech Republic

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