PLATELET PROPERTIES IN A PATIENT WITH STORMORKEN SYNDROME (STIM1 MUTATION) - ADHESION RECEPTOR LEVELS, CALCIUM HOMEOSTASIS AND PHOSPHATIDYLSERINE EXPOSURE
(Abstract release date: 05/19/16)
EHA Library. Cummins K. 06/12/16; 135317; S823
Dr. Katherine Cummins
Contributions
Contributions
Abstract
Abstract: S823
Type: Oral Presentation
Presentation during EHA21: On Sunday, June 12, 2016 from 08:00 - 08:15
Location: Room H4
Background
Stormorken syndrome is a rare monogenic disorder, recently attributed to a gain-of-function mutation of the stromal interaction molecule 1 (STIM1) gene, which is involved in calcium homeostasis. While this syndrome is associated with macrothrombocytopenia and a bleeding phenotype of variable severity, the pathophysiology underlying the platelet abnormalities is not fully described.
Aims
Evaluate parameters in platelets from a patient with Stormorken syndrome and assess the value of platelet flow cytometry in aiding differential diagnosis of Stormorken syndrome in patients with bleeding not fully explained by macrothrombocytopenia.
Methods
The presence of a p.R304W mutation in STIM1 exon 7 was confirmed after a Stormorken syndrome-like phenotype was recognised in a 21-year old male with long-standing thrombocytopenia, hyposplenism, pupillary miosis and tubular aggregate myopathy. Citrated blood was analysed by flow cytometry for platelet adhesion receptor levels, intracellular calcium levels (both at rest and flux in response to agonists, using Fluo-3-AM), microparticles and platelet phosphatidylserine (PS) exposure (annexin-V binding). Testing on two occasions compared samples from the patient, his unaffected mother, and healthy donors.
Results
Flow cytometry of platelet-rich plasma from the patient confirmed the morphological finding of macrothrombocytopenia, with altered forward and side scatter properties, and also increased numbers of CD41-positive microparticles. In comparison with the control samples, levels of metalloproteinase-sensitive adhesion receptors GPVI and GPIbα were present at the lowest end of normal ranges. The ratio of GPIbα:CD41 was significantly reduced, indicating that GPIbα receptor density was independent of mean platelet volume. Levels of sGPVI were within the normal range suggesting that aberrant metalloproteinase-mediated shedding was not responsible for reduction in GPVI levels. Resting intracellular calcium levels were elevated ~5-fold, and calcium flux in response to ionophore was significantly enhanced. Resting platelet PS exposure was at the upper end of the normal range.
Conclusion
Using flow cytometry, platelets from a patient with a confirmed gain-of-function mutation of STIM1 demonstrated altered physical properties, reduced adhesion receptor levels, enhanced PS exposure, significantly increased intracellular calcium at rest and an exaggerated calcium flux response to platelet agonists. Blood samples contained elevated levels of platelet-derived microparticles. Flow cytometric analyses of Stormorken syndrome platelets demonstrate reproducible abnormalities, which begin to inform the structural and functional differences in platelets that may contribute to the bleeding phenotype of this rare monogenic disorder, in particular with regards to surface receptor expression and calcium homeostasis.
Session topic: Platelet disorders 2
Keyword(s): Calcium, Genetic, Platelet function, Platelet microparticles
Type: Oral Presentation
Presentation during EHA21: On Sunday, June 12, 2016 from 08:00 - 08:15
Location: Room H4
Background
Stormorken syndrome is a rare monogenic disorder, recently attributed to a gain-of-function mutation of the stromal interaction molecule 1 (STIM1) gene, which is involved in calcium homeostasis. While this syndrome is associated with macrothrombocytopenia and a bleeding phenotype of variable severity, the pathophysiology underlying the platelet abnormalities is not fully described.
Aims
Evaluate parameters in platelets from a patient with Stormorken syndrome and assess the value of platelet flow cytometry in aiding differential diagnosis of Stormorken syndrome in patients with bleeding not fully explained by macrothrombocytopenia.
Methods
The presence of a p.R304W mutation in STIM1 exon 7 was confirmed after a Stormorken syndrome-like phenotype was recognised in a 21-year old male with long-standing thrombocytopenia, hyposplenism, pupillary miosis and tubular aggregate myopathy. Citrated blood was analysed by flow cytometry for platelet adhesion receptor levels, intracellular calcium levels (both at rest and flux in response to agonists, using Fluo-3-AM), microparticles and platelet phosphatidylserine (PS) exposure (annexin-V binding). Testing on two occasions compared samples from the patient, his unaffected mother, and healthy donors.
Results
Flow cytometry of platelet-rich plasma from the patient confirmed the morphological finding of macrothrombocytopenia, with altered forward and side scatter properties, and also increased numbers of CD41-positive microparticles. In comparison with the control samples, levels of metalloproteinase-sensitive adhesion receptors GPVI and GPIbα were present at the lowest end of normal ranges. The ratio of GPIbα:CD41 was significantly reduced, indicating that GPIbα receptor density was independent of mean platelet volume. Levels of sGPVI were within the normal range suggesting that aberrant metalloproteinase-mediated shedding was not responsible for reduction in GPVI levels. Resting intracellular calcium levels were elevated ~5-fold, and calcium flux in response to ionophore was significantly enhanced. Resting platelet PS exposure was at the upper end of the normal range.
Conclusion
Using flow cytometry, platelets from a patient with a confirmed gain-of-function mutation of STIM1 demonstrated altered physical properties, reduced adhesion receptor levels, enhanced PS exposure, significantly increased intracellular calcium at rest and an exaggerated calcium flux response to platelet agonists. Blood samples contained elevated levels of platelet-derived microparticles. Flow cytometric analyses of Stormorken syndrome platelets demonstrate reproducible abnormalities, which begin to inform the structural and functional differences in platelets that may contribute to the bleeding phenotype of this rare monogenic disorder, in particular with regards to surface receptor expression and calcium homeostasis.
Session topic: Platelet disorders 2
Keyword(s): Calcium, Genetic, Platelet function, Platelet microparticles
Abstract: S823
Type: Oral Presentation
Presentation during EHA21: On Sunday, June 12, 2016 from 08:00 - 08:15
Location: Room H4
Background
Stormorken syndrome is a rare monogenic disorder, recently attributed to a gain-of-function mutation of the stromal interaction molecule 1 (STIM1) gene, which is involved in calcium homeostasis. While this syndrome is associated with macrothrombocytopenia and a bleeding phenotype of variable severity, the pathophysiology underlying the platelet abnormalities is not fully described.
Aims
Evaluate parameters in platelets from a patient with Stormorken syndrome and assess the value of platelet flow cytometry in aiding differential diagnosis of Stormorken syndrome in patients with bleeding not fully explained by macrothrombocytopenia.
Methods
The presence of a p.R304W mutation in STIM1 exon 7 was confirmed after a Stormorken syndrome-like phenotype was recognised in a 21-year old male with long-standing thrombocytopenia, hyposplenism, pupillary miosis and tubular aggregate myopathy. Citrated blood was analysed by flow cytometry for platelet adhesion receptor levels, intracellular calcium levels (both at rest and flux in response to agonists, using Fluo-3-AM), microparticles and platelet phosphatidylserine (PS) exposure (annexin-V binding). Testing on two occasions compared samples from the patient, his unaffected mother, and healthy donors.
Results
Flow cytometry of platelet-rich plasma from the patient confirmed the morphological finding of macrothrombocytopenia, with altered forward and side scatter properties, and also increased numbers of CD41-positive microparticles. In comparison with the control samples, levels of metalloproteinase-sensitive adhesion receptors GPVI and GPIbα were present at the lowest end of normal ranges. The ratio of GPIbα:CD41 was significantly reduced, indicating that GPIbα receptor density was independent of mean platelet volume. Levels of sGPVI were within the normal range suggesting that aberrant metalloproteinase-mediated shedding was not responsible for reduction in GPVI levels. Resting intracellular calcium levels were elevated ~5-fold, and calcium flux in response to ionophore was significantly enhanced. Resting platelet PS exposure was at the upper end of the normal range.
Conclusion
Using flow cytometry, platelets from a patient with a confirmed gain-of-function mutation of STIM1 demonstrated altered physical properties, reduced adhesion receptor levels, enhanced PS exposure, significantly increased intracellular calcium at rest and an exaggerated calcium flux response to platelet agonists. Blood samples contained elevated levels of platelet-derived microparticles. Flow cytometric analyses of Stormorken syndrome platelets demonstrate reproducible abnormalities, which begin to inform the structural and functional differences in platelets that may contribute to the bleeding phenotype of this rare monogenic disorder, in particular with regards to surface receptor expression and calcium homeostasis.
Session topic: Platelet disorders 2
Keyword(s): Calcium, Genetic, Platelet function, Platelet microparticles
Type: Oral Presentation
Presentation during EHA21: On Sunday, June 12, 2016 from 08:00 - 08:15
Location: Room H4
Background
Stormorken syndrome is a rare monogenic disorder, recently attributed to a gain-of-function mutation of the stromal interaction molecule 1 (STIM1) gene, which is involved in calcium homeostasis. While this syndrome is associated with macrothrombocytopenia and a bleeding phenotype of variable severity, the pathophysiology underlying the platelet abnormalities is not fully described.
Aims
Evaluate parameters in platelets from a patient with Stormorken syndrome and assess the value of platelet flow cytometry in aiding differential diagnosis of Stormorken syndrome in patients with bleeding not fully explained by macrothrombocytopenia.
Methods
The presence of a p.R304W mutation in STIM1 exon 7 was confirmed after a Stormorken syndrome-like phenotype was recognised in a 21-year old male with long-standing thrombocytopenia, hyposplenism, pupillary miosis and tubular aggregate myopathy. Citrated blood was analysed by flow cytometry for platelet adhesion receptor levels, intracellular calcium levels (both at rest and flux in response to agonists, using Fluo-3-AM), microparticles and platelet phosphatidylserine (PS) exposure (annexin-V binding). Testing on two occasions compared samples from the patient, his unaffected mother, and healthy donors.
Results
Flow cytometry of platelet-rich plasma from the patient confirmed the morphological finding of macrothrombocytopenia, with altered forward and side scatter properties, and also increased numbers of CD41-positive microparticles. In comparison with the control samples, levels of metalloproteinase-sensitive adhesion receptors GPVI and GPIbα were present at the lowest end of normal ranges. The ratio of GPIbα:CD41 was significantly reduced, indicating that GPIbα receptor density was independent of mean platelet volume. Levels of sGPVI were within the normal range suggesting that aberrant metalloproteinase-mediated shedding was not responsible for reduction in GPVI levels. Resting intracellular calcium levels were elevated ~5-fold, and calcium flux in response to ionophore was significantly enhanced. Resting platelet PS exposure was at the upper end of the normal range.
Conclusion
Using flow cytometry, platelets from a patient with a confirmed gain-of-function mutation of STIM1 demonstrated altered physical properties, reduced adhesion receptor levels, enhanced PS exposure, significantly increased intracellular calcium at rest and an exaggerated calcium flux response to platelet agonists. Blood samples contained elevated levels of platelet-derived microparticles. Flow cytometric analyses of Stormorken syndrome platelets demonstrate reproducible abnormalities, which begin to inform the structural and functional differences in platelets that may contribute to the bleeding phenotype of this rare monogenic disorder, in particular with regards to surface receptor expression and calcium homeostasis.
Session topic: Platelet disorders 2
Keyword(s): Calcium, Genetic, Platelet function, Platelet microparticles
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