Platelet Pathology in GATA-1 Dyserythropoietic Macrothrombocytopenia.
Authors: White James G. , Steensma David P. , Nichols William L. 
Published: April 2020

Abstract
Germline mutations in the X-linked hematopoietic transcription factor, GATA-1, have been associated with dyserythropoietic anemia (DEA), macrothrombocytopenia (MTP), and congenital erythropoietic porphyria. Recently, morphological features suggestive of the Gray Platelet Syndrome (GPS) were described in a pedigree with a germline R216Q GATA-1 mutation (Blood106:6a, 2005). The present study has evaluated platelets (Pl) in the electron microscope from members of a previously described pedigree (Blood98:2681–2688, 2001) with GATA-1 G208S, MTP, and dyserythropoiesis without anemia, for whom detailed platelet morphology studies have not been reported. The presence of a hemizygous GATA-1 mutation was confirmed by conventional fluorescent dye chemistry sequencing of DNA from patient peripheral blood mononuclear cells. Their Pl revealed wide variations in size, shape, internal and external structure. Some normal sized and giant Pl contained usual numbers of alpha granules and dense bodies, while most of the large cells were hypogranular. Some contained no membrane systems or organelles. Others were filled with masses of dense tubular system (DTS) channels, and others contained the tubular inclusions found in the Medich Giant Platelets Disorder (Platelets15:345–353, 2004). Many of the hypogranular cells contained small vacuoles that may have been enclosing membranes of alpha granules. Except for the tubular inclusions, all of these structural variations are observed in GPS Pl (Am. J. Pathol.95:445–462, 1979). However, additional striking abnormalities were seen in GATA-1 Pl that are not characteristic of GPS Pl. Many GATA-1 Pl contained unusual, closely associated dense double membranes differing from normal elements of rough endoplasmic reticulum, smooth endoplasmic reticulum, DTS or surface connected open canalicular system (OCS), but resembling channels of the OCS after exposure to EDTA. They were observed previously only in megakaryocytes (Mk) from one family with GATA-1 DEA-MTP (Nat. Genet, 24:266–270, 2000). The dense double membranes were often found in parallel association and, in some examples, isolating areas of cytoplasm. However, the isolated areas were not undergoing autophagic degradation as such areas enclosed by elements of the DTS do in White Platelet Syndrome Pl (Platelets 15:173,2004). Instead, they proved to be another unique feature of GATA-1 platelets, the presence of Pl within Pl. The sequestered cells were usually mature in appearance and often discoid in form with circumferential coils of microtubules. In some GATA-1 Pl there were two Pl within the same cell, and on rare occasions, a Pl within a Pl within a Pl. Pl within Pl have never been observed previously in any human platelet disorder. Another unique feature, related to Pl within Pl, was the frequent Pl to Pl surface attachment of non-activated cells forming large macrothrombocytes with no similarity to aggregates of stimulated normal platelets.
Conclusion: The substructural abnormalities of Pl from patients with germline GATA-1 mutations share some overlap with those seen in GPS Pl, but are distinct and unique. The MTP, Pl within Pl and surface Pl to Pl attachments suggest a major defect in the formation and separation of GATA-1 Pl from pro-Pl of the parent Mk, resulting in the MTP characteristic of the disorder.