Mutations in tropomyosin 4 underlie a rare form of human macrothrombocytopenia
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
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
View: Text | PDF
Research Article Genetics Hematology

Mutations in tropomyosin 4 underlie a rare form of human macrothrombocytopenia

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

×

Figure 5

The function of human platelets is mildly affected by reduced TPM4 expression.

Options: View larger image (or click on image) Download as PowerPoint
The function of human platelets is mildly affected by reduced TPM4 expre...
(A) Platelet function testing measuring fibrinogen binding (top) and P-selectin expression (bottom) (percentage of positive platelets) after treatment with final concentrations of 0.0005 μM ADP, 0.3 μg/ml CRP-XL, or 0.8 μM TRAP-6. Depicted are the results obtained on 3 different days (2 technical replicates) for the day control and the patient (case 1-III-7). A bank of 20 controls is shown in white. (B and C) Thrombus formation on collagen under flow (shear rate 1,600/s). (B) Normalized thrombus number and coverage after blood perfusion through a collagen-coated chamber; 6 images captured per run, 2 runs per sample using 2 different samples. (C) Representative images of thrombi stained with P-selectin captured using fluorescence microscopy (EVOS system; Advanced Microscopy Group). Scale bars: 50 μm. Unpaired 2-tailed Student’s t test, ***P < 0.001.