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Mutations in tropomyosin 4 underlie a rare form of human macrothrombocytopenia
Irina Pleines, … , Marloes R. Tijssen, Benjamin T. Kile
Irina Pleines, … , Marloes R. Tijssen, Benjamin T. Kile
Published January 30, 2017
Citation Information: J Clin Invest. 2017;127(3):814-829. https://doi.org/10.1172/JCI86154.
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Research Article Genetics Hematology

Mutations in tropomyosin 4 underlie a rare form of human macrothrombocytopenia

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Abstract

Platelets are anuclear cells that are essential for blood clotting. They are produced by large polyploid precursor cells called megakaryocytes. Previous genome-wide association studies in nearly 70,000 individuals indicated that single nucleotide variants (SNVs) in the gene encoding the actin cytoskeletal regulator tropomyosin 4 (TPM4) exert an effect on the count and volume of platelets. Platelet number and volume are independent risk factors for heart attack and stroke. Here, we have identified 2 unrelated families in the BRIDGE Bleeding and Platelet Disorders (BPD) collection who carry a TPM4 variant that causes truncation of the TPM4 protein and segregates with macrothrombocytopenia, a disorder characterized by low platelet count. N-Ethyl-N-nitrosourea–induced (ENU-induced) missense mutations in Tpm4 or targeted inactivation of the Tpm4 locus led to gene dosage–dependent macrothrombocytopenia in mice. All other blood cell counts in Tpm4-deficient mice were normal. Insufficient TPM4 expression in human and mouse megakaryocytes resulted in a defect in the terminal stages of platelet production and had a mild effect on platelet function. Together, our findings demonstrate a nonredundant role for TPM4 in platelet biogenesis in humans and mice and reveal that truncating variants in TPM4 cause a previously undescribed dominant Mendelian platelet disorder.

Authors

Irina Pleines, Joanne Woods, Stephane Chappaz, Verity Kew, Nicola Foad, José Ballester-Beltrán, Katja Aurbach, Chiara Lincetto, Rachael M. Lane, Galina Schevzov, Warren S. Alexander, Douglas J. Hilton, William J. Astle, Kate Downes, Paquita Nurden, Sarah K. Westbury, Andrew D. Mumford, Samya G. Obaji, Peter W. Collins, NIHR BioResource, Fabien Delerue, Lars M. Ittner, Nicole S. Bryce, Mira Holliday, Christine A. Lucas, Edna C. Hardeman, Willem H. Ouwehand, Peter W. Gunning, Ernest Turro, Marloes R. Tijssen, Benjamin T. Kile

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Figure 1

Tropomyosin expression in human and mouse.

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Tropomyosin expression in human and mouse.
(A) Multiple TPMs are express...
(A) Multiple TPMs are expressed in human megakaryocytes. Relative TPM mRNA expression of human cord blood–derived megakaryocytes was evaluated by real-time quantitative PCR. Data are presented as mean ± SD of 3 independent experiments. (B) Comparison of tropomyosin (TPM1–4) protein expression between human and WT mouse platelets. Top panel: The 30-kDa TPM4 protein isoform (TPM4.2) is the main isoform in both human and mouse platelets. Human platelets additionally express low amounts of the 38-kDa TPM4 isoform (TPM4.1). Bottom panel: β-Actin loading control.

Copyright © 2022 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)

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