GFI1B mutation causes a bleeding disorder with abnormal platelet function

Abstract

Summary. Background: GFI1B is a transcription factor important for erythropoiesis and megakaryocyte development but previously unknown to be associated with human disease. Methods: A family with a novel bleeding disorder was identified and characterized. Genetic linkage analysis and massively parallel sequencing were used to localize the mutation causing the disease phenotype on chromosome 9. Functional studies were then performed in megakaryocytic cell lines to determine the biological effects of the mutant transcript. Results: We have identified a family with an autosomal dominant bleeding disorder associated with macrothrombocytopenia, red cell anisopoikilocytosis, and platelet dysfunction. The severity of bleeding is variable with some affected individuals experiencing spontaneous bleeding while other family members exhibit only abnormal bleeding with surgery. A single nucleotide insertion was identified in GFI1B that predicts a frameshift mutation in the fifth zinc finger DNA-binding domain. This mutation alters the transcriptional activity of the protein, resulting in a reduction in platelet a-granule content and aberrant expression of key platelet proteins. Conclusions: GFI1B mutation represents a novel human bleeding disorder, and the described phenotype identifies GFI1B as a critical regulator of platelet shape, number, and function.

Should any genetic defect affecting α‐granules in platelets be classified as gray platelet syndrome?

“…2). A premature stop codon at p.Q287* gave a truncated protein lacking 44 carboxyterminal amino acids, slightly more than for the truncation identified by Stevenson et al [27]. Analysis of cDNA from CD341 progenitor cells revealed the co-expression of wild type and mutated GFI1B transcripts.…”

“…This caused a loss of invariant histidine residues required for zinc ion stabilization and folding within the DNA-binding domain. Both wildtype and truncated GFI1B transcripts were present in platelets and CD341 cells from an affected family member while expression studies in the Mag01 leukemia cell line showed the mutant protein to cause reversal of transcriptional repression of the TGFBR3 gene, encoding transforming growth factor beta receptor III, a known target for GFI1B [27]. This study was quickly followed by the report of another truncating mutation in GFI1B in a European family with MTP and a moderate to severe bleeding diathesis [28].…”

“…Stevenson et al [27] were the first to identify an autosomal dominant form of MTP with platelet dysfunction and "gray" platelets that segregated to a heterozygous stop codon in GFI1B. While some affected members of a four-generation Australian Caucasian family showed lifelong spontaneous mucocutaneous-type bleeding (epistaxis, easy bruising, and prolonged blood loss from superficial cuts); for others excessive bleeding only occurred after surgery or trauma.…”

“…We show the full-length GFI1B protein, a shorter splice form lacking ZNF2 and parts of ZNF1 and 3 may also be found in hematopoietic tissue. The mutations or non-synonymous SNPs identified by Chen et al [25] are in black and occur along the protein; the truncating mutations within exon 6 characterized by Stevenson et al [27] and by Monteferrario et al [28] and affecting ZNF5 and 6 are in red. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]…”

Linkage between the mechanisms of thrombocytopenia and thrombopoiesis

“…75 Two null GFI1B mutations that disrupt DNA binding were identified in patients with autosomal-dominant macrothrombocytopenia, a decrease in a-granules, and red cell anisopoikilocytosis. 76,77 The 2 mutants exert dominant-negative effects when coexpressed with the wild-type form. Monteferrario et al 77 described the condition as gray platelet syndrome, though the platelets reported by Stevenson et al 76 were not gray.…”