Abstract Number: PB1451
Meeting: ISTH 2020 Congress
Theme: Platelet Disorders and von Willebrand Disease » Inherited Thrombocytopenias
Background: Tubulin β1, expressed in megakaryocytes (Mks) and platelets, forms microtubules which mediate pro-platelet formation. Only 4 families with heterozygous, autosomal dominant variants in TUBB1 have been reported.
Aims: Characterization of a family with macrothrombocytopenia enrolled in the Spanish project “Functional/molecular characterization of patients with Inherited Platelet Disorder”.
Methods: Platelet phenotyping included: blood count/smear, platelet aggregation (LTA), glycoproteins (GP) and activation by flow cytometry; cytoskeleton proteins in resting/spreading platelets by immunofluorescence. Patient´s DNA was analyzed with a HTS-gene panel. Proplatelet formation was evaluated in Mks differentiated from CD34+ cells purified from blood. CHO cell transfection model was established to assess the pathogenicity of the candidate variant.
Results: The proband (52-year-old woman) and her brother displayed congenital macrothrombocytopenia (50×109/L) with 15% enlarged platelets (diameter:4.71µm). GPs expression, fibrinogen binding, granule secretion and LTA were normal. HTS analysis revealed the novel homozygous TUBB1 variant c.326G>A [p.Gly109Glu] in the proband and her brother. Unaffected family members were heterozygous carriers. Tubulin marginal band in resting platelets was undetectable in homozygous patients and normal in controls/heterozygotes. Platelet spreading on poli-L-lysine was unaltered in all cases. Tubulinβ1 formed aggregates in spread platelets/Mks in homozygous patients, while it was normally distributed in heterozygous carriers (FigureA&B). The localization of other cytoskeleton proteins (actin, actinin, DIAPH1, filamin and MYH9) was normal in all cases. Only homozygous patients displayed a defect in proplatelet formation (homozygous:< 5%; heterozygous/control:15% Mks forming proplatelets). p.Gly109Glu tubulinβ1-transfected CHO cells showed no incorporation of mutant tubulinβ1 into microtubules and the formation of punctuated aggregates similar to those observed in Mks/platelets from the homozygous patients (FigureC).
Conclusions: We report the first autosomal recessive variant in TUBB1 (p.Gly109Glu) associated with macrothrombocytopenia due to a defect in proplatelet formation. Tubulinβ1 is severely disorganized in platelets/Mks from homozygous carriers. However, platelet and Mk spreading is not impared, revealing that tubulinβ1 is not crucial for spreading. [PI17/01311-FMMAP172142019]
To cite this abstract in AMA style:
Palma-Barqueros V, Bury L, Bohdan N, Bastida JM, Rodriguez-Alen A, Ruiz-Pividal JF, Revilla N, Marin-Quilez A, Vicente V, Lozano ML, Gresele P, Rivera J. First Autosomal Recessive Variant in TUBB1 Impairs Proplatelet Formation and Results in Inherited Macrothrombocytopenia [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/first-autosomal-recessive-variant-in-tubb1-impairs-proplatelet-formation-and-results-in-inherited-macrothrombocytopenia/. Accessed March 21, 2024.« Back to ISTH 2020 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/first-autosomal-recessive-variant-in-tubb1-impairs-proplatelet-formation-and-results-in-inherited-macrothrombocytopenia/