In
X-linked thrombocytopenia with
thalassemia (XLTT; OMIM 314050), caused by the mutation p.R216Q in exon 4 of the GATA1 gene, male hemizygous patients display macrothrombocytopenia,
bleeding diathesis and a β-
thalassemia trait. Herein, we describe findings in two unrelated Swedish XLTT families with a
bleeding tendency exceeding what is expected from the
thrombocytopenia. Blood tests revealed low P-PAI-1 and P-
factor 5, and elevated S-
thrombopoietin levels. Transmission electron microscopy showed diminished numbers of platelet α- and dense granules. The
proteomes of isolated blood platelets from 5 male XLTT patients, compared to 5 gender- and age matched controls, were explored. Quantitative mass spectrometry showed alterations of 83
proteins (fold change ≥±1.2, q< .05). Of 46 downregulated
proteins, 39 were previously reported to be associated with platelet granules. Reduced
protein levels of PTGS1 and SLC35D3 were validated in megakaryocytes of XLTT bone marrow biopsies by immunohistochemistry. Platelet function testing by flow cytometry revealed low dense- and α-granule release and
fibrinogen binding in response to
ligation of receptors for
ADP, the
thrombin receptor PAR4 and the
collagen receptor GPVI. Significant reductions of a number of α-granule
proteins overlapped with a previous platelet proteomics investigation in the inherited macrothrombocytopenia
gray platelet syndrome (GPS). In contrast, Ca2+ transporter
proteins that facilitate dense granule release were downregulated in XLTT but upregulated in GPS. Ingenuity Pathway Analysis showed altered Coagulation System and
Protein Ubiquitination pathways in the XLTT platelets. Collectively, the results revealed
protein and functional alterations affecting platelet α- and dense granules in XLTT, probably contributing to
bleeding.