Acquired Gray Platelet Syndrome Associated with Primary Myelofibrosis.

A 53-year-old man presented with uncontrolled bleeding caused by acquired platelet dysfunction accompanied by calreticulin-mutated primary myelofibrosis. Based on the detection of abnormal platelets, including large gray platelets, under light microscopy and the loss of the second wave of aggregation observed by light transmission aggregometry, the patient was diagnosed with platelet dysfunction accompanied by myeloproliferative neoplasms (MPNs). In addition, the absence of platelet α-granules was confirmed by electron microscopy. Therefore, this condition may be termed "acquired gray platelet syndrome." Acquired platelet dysfunction must be ruled out when abnormal platelets are observed in patients with MPNs.

Correction of Severe Myelofibrosis, Impaired Platelet Functions and Abnormalities in a Patient with Gray Platelet Syndrome Successfully Treated by Stem Cell Transplantation.

Gray platelet syndrome (GPS) is an inherited disorder. Patients harboring GPS have thrombocytopenia with large platelets lacking α-granules. A long-term complication is myelofibrosis with pancytopenia. Hematopoietic stem cell transplant (HSCT) could be a curative treatment. We report a male GPS patient with severe pancytopenia, splenomegaly and a secondary myelofibrosis needing red blood cells transfusion. He received an HSCT from a 10/10 matched HLA-unrelated donor after a myeloablative conditioning regimen. Transfusion independence occurred at day+21, with a documented neutrophil engraftment. At day+ 180, we added ruxolitinib to cyclosporine and steroids for a moderate chronic graft versus host disease (GVHD) and persistent splenomegaly. At day+240 GVHD was controlled and splenomegaly reduced. Complete donor chimesrism was documented in blood and marrow and platelets functions and morphology normalized. At day+ 720, the spleen size normalized and there was no evidence of marrow fibrosis on the biopsy. In GPS, HSCT may be a curative treatment in selected patients with pancytopenia and myelofibrosis.

Platelet Releasate Proteome Profiling Reveals a Core Set of Proteins with Low Variance between Healthy Adults.

Upon activation, platelets release a powerful cocktail of soluble and vesicular signals, collectively termed the "platelet releasate" (PR). Although several studies have used qualitative/quantitative proteomic approaches to characterize PR; with debated content and significant inter-individual variability reported, confident, and reliable insights have been hindered. Using label-free quantitative (LFQ)-proteomics analysis, a reproducible, quantifiable investigation of the 1U mL-1 thrombin-induced PR from 32 healthy adults was conducted. MS proteomics data are available via ProteomeXchange, identifier PXD009310. Of the 894 proteins identified, 277 proteins were quantified across all donors and form a "core" PR. Bioinformatics and further LFQ-proteomic analysis revealed that the majority (84%) of "core" PR proteins overlapped with the protein composition of human platelet-derived exosomes. Vesicles in the exosomal-size range were confirmed in healthy-human PR and reduced numbers of similar-sized vesicles were observed in the PR of a mouse model of gray platelet syndrome, known to be deficient in platelet alpha-granules. Lastly, the variability of proteins in the PR was assessed, and reproducible secretion levels were found across all 32 healthy donors. Taken together, the PR contains valuable soluble and vesicular cargo and has low-population variance among healthy adults, rendering it a potentially useful platform for diagnostic fingerprinting of platelet-related disease.

Spontaneous 8bp Deletion in Nbeal2 Recapitulates the Gray Platelet Syndrome in Mice.

During the analysis of a whole genome ENU mutagenesis screen for thrombosis modifiers, a spontaneous 8 base pair (bp) deletion causing a frameshift in exon 27 of the Nbeal2 gene was identified. Though initially considered as a plausible thrombosis modifier, this Nbeal2 mutation failed to suppress the synthetic lethal thrombosis on which the original ENU screen was based. Mutations in NBEAL2 cause Gray Platelet Syndrome (GPS), an autosomal recessive bleeding disorder characterized by macrothrombocytopenia and gray-appearing platelets due to lack of platelet alpha granules. Mice homozygous for the Nbeal2 8 bp deletion (Nbeal2gps/gps) exhibit a phenotype similar to human GPS, with significantly reduced platelet counts compared to littermate controls (p = 1.63 x 10-7). Nbeal2gps/gps mice also have markedly reduced numbers of platelet alpha granules and an increased level of emperipolesis, consistent with previously characterized mice carrying targeted Nbeal2 null alleles. These findings confirm previous reports, provide an additional mouse model for GPS, and highlight the potentially confounding effect of background spontaneous mutation events in well-characterized mouse strains.

Gray platelet syndrome: natural history of a large patient cohort and locus assignment to chromosome 3p.

Gray platelet syndrome (GPS) is an inherited bleeding disorder characterized by macrothrombocytopenia and absence of platelet α-granules resulting in typical gray platelets on peripheral smears. GPS is associated with a bleeding tendency, myelofibrosis, and splenomegaly. Reports on GPS are limited to case presentations. The causative gene and underlying pathophysiology are largely unknown. We present the results of molecular genetic analysis of 116 individuals including 25 GPS patients from 14 independent families as well as novel clinical data on the natural history of the disease. The mode of inheritance was autosomal recessive (AR) in 11 and indeterminate in 3 families. Using genome-wide linkage analysis, we mapped the AR-GPS gene to a 9.4-Mb interval on 3p21.1-3p22.1, containing 197 protein-coding genes. Sequencing of 1423 (69%) of the 2075 exons in the interval did not identify the GPS gene. Long-term follow-up data demonstrated the progressive nature of the thrombocytopenia and myelofibrosis of GPS resulting in fatal hemorrhages in some patients. We identified high serum vitamin B(12) as a consistent, novel finding in GPS. Chromosome 3p21.1-3p22.1 has not been previously linked to a platelet disorder; identification of the GPS gene will likely lead to the discovery of novel components of platelet organelle biogenesis. This study is registered at www.clinicaltrials.gov as NCT00069680 and NCT00369421.