Novel RUNX1 mutations in families with inherited thrombocytopenia.

NORIS P.; DE ROCCO D.; MELAZZINI F.; MARCONI C.; PECCI A.; BOTTEGA R; GNAN C.; PALOMBO F.; GIORDANO P; COCCIOLI M; GLEMBOTSKY AC.; CIGALINI E.; HELLER PG.; SERI M.; SAVOIA A.

Congreso; 22nd Congress of the European Hematology Association; 2017

Background: Familial platelet disorder with propensity to acute myeloid leukemia (FPD/AML) is a rare autosomal dominantinherited thrombocytopenia (IT) caused by mutations in the hematopoietic transcription factor RUNX1; an important hallmark of thisIT is the increased risk of developing myeloid neoplasms, such as AML and myelodysplastic syndromes (MDS). FPD/AML is causedby different mutations of RUNX1 encoding the DNA binding subunit (known as core binding factor-alpha, CBF-alpha) of the CBFtranscription complex. The N-terminus domain of RUNX1 (runt-homologous domain) mediates DNA binding and heterodimerizationto CBF-beta, the other subunit of the CBF complex. The C-terminus of RUNX1 includes domains that are involved in transcriptionactivation and repression. This IT is characterized by impaired megakaryopoiesis and moderate thrombocytopenia, with normal-sizedand dysfunctional platelets.Aims: To unravel the molecular basis of ITs and to improve our knowledge on the molecular basis and clinical-laboratory picture ofFPD/AML.Methods: Whole exome sequencing (WES) was performed in 86 propositi with an unknown IT after the diagnostic workup based onthe most updated diagnostic algorithm for ITs (Clin Genet 2016;89:141). RUNX1 variants detected by WES were confirmed bySanger sequencing in the propositi and all available family members, which also undergo clinical-laboratory characterization. Thestudy was approved by the Institutional Review Board of the IRCCS Policlinico S. Matteo Foundation; all patients gave writteninformed consent.Results: We identified three pedigrees (families 1-3) with different RUNX1 heterozygous mutations, all segregating withthrombocytopenia in the respective families: the novel variants c.578T>A and c.967+2_5del, and the known c.351+1G>A. Thethirteen individuals carrying the RUNX1 mutations had mild thrombocytopenia (platelet count ranging from 70 to 130 x 109/L) withmild bleeding tendency. Platelet sizes were within the normal range in all the six patients analyzed, and the serum level ofthrombopoietin was normal or moderately increased. No specific morphological alteration of platelets was detected, except formoderate reduction in the alpha-granule content in family 1, confirmed by immunofluorescence analysis.The surface expression of the major platelet glycoprotein (GP) complexes GPIIb-IIIa and GPIb-IX-V was normal. In family 1 amoderate reduction of GPIa-IIa was detected, regardless of genotypes at the ITGA2 locus. A defective aggregation was detected afterplatelet stimulation with collagen 4 mcg/ml and ADP 2 mcM in the five patients investigated; normal responses were obtained usingcollagen 20 mcg/mL, ADP 20 mcM and ristocetin 1.5 mg/mL, suggesting mild functional platelets defects.Of note, three patients from two families developed AML, with a prevalence lower than reported in literature, probably because of adifferent criteria of enrolment (RUNX1 germline mutations are usually searched in ITs associated with AML). No solid/hematologicalcancer was reported in family 1.Summary/Conclusion: FPD/AML is an IT lacking pathognomonic laboratory criteria: it is characterized by a mild functionaldefect and, much more importantly, by a normal platelet size, similarly to the other ITs predisposing to hematological malignancies (ANKRD26 and ETV6-related thrombocytopenias). Given the importance of recognizing these diseases for patients counseling, followup,and therapeutic approach, we recommend a system