Novel GATA1 mutation in residue D218 leads to macrothrombocytopenia and clinical bleeding problems

We studied two related patients (III.4 and III.10) with spontaneous clinical bleeding problems and a family history suggestive of X-linked inherited thrombocytopenia (Figure 1A). Both patients presented with hematomas, ecchymosis, epistaxis, and gingival bleeding symptoms since childhood and developed splenomegaly. Hematological investigations (after the patient was splenectomized) showed the presence of macrothrombocytopenia combined with mild features of dyserythropoiesis including poikilocytosis, anisocytosis, and schizocytes, Howell–Jolly bodies in erythrocytes and stomatocytes but no anemia (Table I). Both patients did not respond to immune thrombocytopenic purpura-specific therapy such as intravenous immunoglobulins, steroids, or splenectomy. Bone marrow analysis showed hypermegakaryopoiesis with an increased number of immature megakaryoblasts but no features of dysmyelopoiesis. Platelet functional studies for patient III:4 showed normal aggregations for collagen and ristocetin (amplitudes of 84% and 86%, respectively) and mildly reduced for ADP (amplitude of 40%). The PFA100 closure time with collagen/epinephrine for patient III:4 was prolonged (4300 s; nl: 82–142 s) while normal with collagen/ADP. X-linked macrothrombocytopenia with platelet dysfunction has been described by others and us for patients with mutations in the gene for the transcription factor GATA1 [1–10]. The GATA family of nuclear regulatory proteins serves as a prototype for the action of lineage-restricted transcription factors. The GATA1 protein is typically present in the more differentiated cells of the erythroid, megakaryocytic, mast, and eosinophilic lineages, whereas GATA2 expression is limited to HSCs and early haematopoietic progenitors [11]. Remarkably since its first description in 2001, still only a limited number of families are presently reported with germline GATA1 missense mutations and these presented with closely related but still somewhat altered hematological disorders. They comprise severe dyserythropoietic anemia with macrothrombocytopenia (V205M, G208R, and D218Y), macrothrombocytopenia with mild dyserythropoietic features (G208S, D218G), macrothrombocytopenia with mild b-thalassemia (R216Q), and congenital erythropoietic porphyria (R216W) [1–10]. Figure 1(B) shows the position of these mutations that are all present in the N-terminal zinc finger of GATA1. Males with these mutations have enlarged platelets with a paucity of alpha granules and a reduced function. Some patients also present with splenomegaly [7, 9] or myelodysplasia with marked organomegaly [10], likely due to ineffective and consequential extramedullary hematopoiesis. Genotype–phenotype correlations are hampered by the low numbers of families with a GATA1 mutation to date, with only two mutations (R216Q [6–8] and G208R [5, 10]) being identified in more than one family. Sanger sequencing of the different GATA1 exons using leukocyte gDNA of patient III:4 showed the presence of a missense mutation gac (D) to aac (N) at codon 218 (Figure 1C). Interestingly, we already have described two other missense mutations in this residue for two unrelated families for which patients presented with mild macrothrombocytopenia with dyserythropoiesis (D218G) [2] and severe macrothrombocytopenia with anemia (D218Y) [3]. A genomic DNA sample was not available from subject III:10 to confirm the presence to the GATA1 D218N variant. The D218N GATA1 variant was not present in the dbSNP or 1000 genomes databases (www.1000genomes.org). In addition, SIFT (sift.jcvi.org) predicted GATA1 variants D218G/Y and N to be damaging. The platelet defect for propositus III:4 and his relative III:10 seems milder than found for subjects with the D218G or D218Y mutations as the degree of thrombocytopenia is less severe and especially their platelets are large but not giant (Table I and Figure 1D). Actually, without having evidence of an X-linked inheritance patterns in this family, a single patient with this type of platelet defect might escape the genetic diagnosis of GATA1. This could be a reason why still only few patients have been described with GATA1 mutations still giving us no idea about the Correspondence: Kathleen Freson, Center for Molecular and Vascular Biology, University of Leuven, Herestraat 49, B-3000 Leuven, Belgium. Tel: +32-16346017. Fax: +32-16345990. E-mail: kathleen.freson@ med.kuleuven.be Keywords