Advances in the understanding of MYH9 disorders:

Comprehensive genetic analysis for identification of monogenic disorders and selection of appropriate treatments in pediatric patients with persistent thrombocytopenia

Persistent thrombocytopenia is caused by various diseases, including immune thrombocytopenia, inherited thrombocytopenia, and inherited bone marrow failure syndromes. Considering the large number of genes responsible for inherited disorders, comprehensive genetic analysis is required to diagnose monogenic disorders. In this study, we enrolled 53 pediatric patients with persistent thrombocytopenia exhibiting visually small or normal-sized platelets. We performed whole-exome sequencing, including 56 genes responsible for inherited thrombocytopenia, and evaluated clinical parameters according to disease type. Among 53 patients, 12 patients (22.6%) were diagnosed with monogenic disorders. Nine patients had a family history of thrombocytopenia. Pathogenic or novel variants of genes responsible for inherited thrombocytopenia were identified in three and six patients, respectively. The variants in genes for inherited thrombocytopenia with large or giant platelets were unexpectedly identified in six patients. Pathogenic variants in genes for inherited bone marrow failure syndromes with systemic features were identified in three patients with atypical symptoms. Since the definitive diagnostic methods for immune thrombocytopenia are limited, and a substantial number of patients with inherited thrombocytopenia are at a high risk of developing malignancies, comprehensive genetic analysis is indispensable for selecting appropriate therapies, avoidance of unnecessary treatments for immune thrombocytopenia, and long-term follow-up of patients with inherited thrombocytopenia.

MYH9-related inherited thrombocytopenia: the genetic spectrum, underlying mechanisms, clinical phenotypes, diagnosis, and management approaches

Inherited thrombocytopenias have been considered exceedingly rare for a long time, but recent advances have facilitated diagnosis and greatly enabled the discovery of new causative genes. MYH9-related disease (MYH9-RD) represents one of the most frequent forms of inherited thrombocytopenia, usually presenting with nonspecific clinical manifestations, which renders it difficult to establish an accurate diagnosis. MYH9-RD is an autosomal dominant-inherited thrombocytopenia caused by deleterious variants in the MYH9 gene encoding the heavy chain of nonmuscle myosin IIA. Patients with MYH9-RD usually present with thrombocytopenia and platelet macrocytosis at birth or in infancy, and most of them may develop one or more extrahematologic manifestations of progressive nephritis, sensorial hearing loss, presenile cataracts, and elevated liver enzymatic levels during childhood and adult life. Here, we have reviewed recent advances in the study of MYH9-RD, which aims to provide an updated and comprehensive summary of the current knowledge and improve our understanding of the genetic spectrum, underlying mechanisms, clinical phenotypes, diagnosis, and management approaches of this rare disease. Importantly, our goal is to enable physicians to better understand this rare disease and highlight the critical role of genetic etiologic analysis in ensuring accurate diagnosis, clinical management, and genetic counseling while avoiding ineffective and potentially harmful therapies for MYH9-RD patients.

The genetics of spontaneous coronary artery dissection: a scoping review

BACKGROUND

Spontaneous coronary artery dissection (SCAD) is a multifactorial process that involves predisposing factors and precipitating stressors. Genetic abnormality has been implicated to play a mechanistic role in the development of SCAD. This systematic review aims to summarize the current evidence concerning the link between SCAD and genetic abnormalities.

METHODS

We reviewed original studies published until May 2023 that reported SCAD patients with a genetic mutation by searching PubMed, Embase Ovid, and Google Scholar. Registries, cohort studies, and case reports were included if a definitive SCAD diagnosis was reported, and the genetic analysis was performed. Exclusion criteria included editorials, reviews, letters or commentaries, animal studies, meeting papers, and studies from which we were unable to extract data. Data were extracted from published reports.

RESULTS

A total of 595 studies were screened and 55 studies were identified. Among 116 SCAD patients with genetic abnormalities, 20% had mutations in the COL gene, 13.70% TLN1 gene, and 8.42% TSR1 gene. Mutations affecting the genes encoding COL and TLN1 were most frequently reported (20 and 13.7%, respectively). Interestingly, 15 genes of this collection were also reported in patients with thoracic aortic diseases as well. The genetic commonality between fibromuscular dysplasia (FMD) and SCAD was also included.

CONCLUSION

In this review, the inherited conditions and reported genes of undetermined significance from case reports associated with SCAD are collected. A brief description of the encoded protein and the clinical features associated with pathologic genes is provided. Current data suggested that the diagnostic yield of genetic studies for patients with SCAD would be low and routine genetic screening of such patients with no clinical features indicative of associated disorders remains debatable. This review can be used as a guide for clinicians to recognize inherited syndromic and nonsyndromic disorders associated with SCAD.

Diagnostic delay of MYH9-related disorder in Japan

MYH9-related disorder (MYH9-RD) is characterized by congenital macrothrombocytopenia and granulocyte inclusion bodies. MYH9-RD is often misdiagnosed as chronic immune thrombocytopenia. In this study, we investigated age at definitive diagnosis and indicative thrombocytopenia in 41 patients with MYH9-RD from the congenital thrombocytopenia registry in Japan. Our cohort comprises 54.8% adults over 18 years at confirmed diagnosis. We found a significant difference (p < 0.0001) between the median age at definitive diagnosis of 25.0 years and for indicative thrombocytopenia it was 9.0 years. Our findings strongly suggest diagnostic delay of MYH9-RD in Japan. Our registry system will continue to contribute to this issue.

Disease-related non-muscle myosin IIA D1424N rod domain mutation, but not R702C motor domain mutation, disrupts mouse ocular lens fiber cell alignment and hexagonal packing

The mouse ocular lens is an excellent vertebrate model system for studying hexagonal cell packing and shape changes during tissue morphogenesis and differentiation. The lens is composed of two types of cells, epithelial and fiber cells. During the initiation of fiber cell differentiation, lens epithelial cells transform from randomly packed cells to hexagonally shaped and packed cells to form meridional row cells. The meridional row cells further differentiate and elongate into newly formed fiber cells that maintain hexagonal cell shape and ordered packing. In other tissues, actomyosin contractility regulates cell hexagonal packing geometry during epithelial tissue morphogenesis. Here, we use the mouse lens as a model to study the effect of two human disease-related non-muscle myosin IIA (NMIIA) mutations on lens cellular organization during fiber cell morphogenesis and differentiation. We studied genetic knock-in heterozygous mice with NMIIA-R702C motor domain or NMIIA-D1424N rod domain mutations. We observed that while one allele of NMIIA-R702C has no impact on lens meridional row epithelial cell shape and packing, one allele of the NMIIA-D1424N mutation can cause localized defects in cell hexagonal packing. Similarly, one allele of NMIIA-R702C motor domain mutation does not affect lens fiber cell organization while the NMIIA-D1424N mutant proteins disrupt fiber cell organization and packing. Our work demonstrates that disease-related NMIIA rod domain mutations (D1424N or E1841K) disrupt mouse lens fiber cell morphogenesis and differentiation.

Successful administration of eltrombopag in preparation for peritoneal dialysis catheter placement in a girl with MYH9-related disease

MYH9-related disease is an autosomal dominant disorder characterized by macrothrombocytopenia, nephropathy, inclusion bodies in leukocytes, sensorineural hearing loss, and cataract. Severe cases require kidney replacement therapy in the patient's second decade of life; thrombocytopenia constitutes a major risk factor for hemorrhagic complications during dialysis initiation or kidney transplantation. Prophylactic platelet transfusion prior to surgery is commonly administered to affected patients in these cases. However, transfusion in such patients has limitations other than the general risk of allergic reactions and blood-borne infections; it may also trigger alloimmunization, leading to platelet transfusion resistance or the development of anti-donor antibodies in potential kidney transplant recipients. Here, we describe prophylactic administration of eltrombopag, an oral thrombopoietin receptor agonist, prior to laparoscopic peritoneal dialysis catheter placement in a 15-year-old girl with MYH9-related disease. Her platelet count was approximately 30 × 103/μL at baseline; it increased to 61 × 103/μL on the day before surgery, thereby avoiding the need for platelet transfusions. There were no major bleeding or adverse events associated with eltrombopag administration. Thus, eltrombopag may be a safe and effective alternative to prophylactic platelet transfusions in patients with MYH9-related disease.

Nonmuscle Myosin IIA Regulates the Precise Alignment of Hexagonal Eye Lens Epithelial Cells During Fiber Cell Formation and Differentiation

Purpose

Epithelial cells in the equatorial region of the ocular lens undergo a remarkable transition from randomly packed cells into precisely aligned and hexagon-shaped cells organized into meridional rows. We investigated the function of nonmuscle myosin IIA (encoded by Myh9) in regulating equatorial epithelial cell alignment to form meridional rows during secondary fiber cell morphogenesis.

Methods

We used genetic knock-in mice to study a common human Myh9 mutation, E1841K, in the rod domain. The E1841K mutation disrupts bipolar filament assembly. Lens shape, clarity, and stiffness were evaluated, and Western blots were used to determine the level of normal and mutant myosins. Cryosections and lens whole mounts were stained and imaged by confocal microscopy to investigate cell shape and organization.

Results

We observed no obvious changes in lens size, shape, and biomechanical properties (stiffness and resilience) between the control and nonmuscle myosin IIA-E1841K mutant mice at 2 months of age. Surprisingly, we found misalignment and disorder of fiber cells in heterozygous and homozygous mutant lenses. Further analysis revealed misshapen equatorial epithelial cells that cause disorientation of the meridional rows before fiber cell differentiation in homozygous mutant lenses.

Conclusions

Our data indicate that nonmuscle myosin IIA bipolar filament assembly is required for the precise alignment of the meridional rows at the lens equator and that the organization of lens fiber cells depends on the proper patterning of meridional row epithelial cells. These data also suggest that lens fiber cell organization and a hexagonal shape are not required for normal lens size, shape transparency, or biomechanical properties.

Systematic identification of intron retention associated variants from massive publicly available transcriptome sequencing data

Many disease-associated genomic variants disrupt gene function through abnormal splicing. With the advancement of genomic medicine, identifying disease-associated splicing associated variants has become more important than ever. Most bioinformatics approaches to detect splicing associated variants require both genome and transcriptomic data. However, there are not many datasets where both of them are available. In this study, we develop a methodology to detect genomic variants that cause splicing changes (more specifically, intron retention), using transcriptome sequencing data alone. After evaluating its sensitivity and precision, we apply it to 230,988 transcriptome sequencing data from the publicly available repository and identified 27,049 intron retention associated variants (IRAVs). In addition, by exploring positional relationships with variants registered in existing disease databases, we extract 3,000 putative disease-associated IRAVs, which range from cancer drivers to variants linked with autosomal recessive disorders. The in-silico screening framework demonstrates the possibility of near-automatically acquiring medical knowledge, making the most of massively accumulated publicly available sequencing data. Collections of IRAVs identified in this study are available through IRAVDB ( https://iravdb.io/ ).

“MYH9 mutation and squamous cell cancer of the tongue in a young adult: a novel case report”

Background

The incidence of tongue cancer in young adults is on the rise. This trend is more pronounced in females. Although the aetiology is still unclear, there is mounting evidence that genetic syndromes can play a key role in development of oral cancers in this patient group. We report the first case of oral squamous cell carcinoma (oSCC) in a young adult with an MYH9-related disorder (MYH9-RD).

Case presentation

A 19-year-old female with a germline MYH9 variant (missense variant in exon 2: c.287C > T, (p.Ser96Leu)) was referred to the head and neck surgery department for investigation of a painful, thick right tongue ulcer. She was diagnosed with Epstein syndrome, an MYH9-RD, at 12 years of age. Her main phenotypic features were profound thrombocytopenia and marked renal impairment. The tongue biopsy confirmed SCC. Preoperative positron emission tomography (PET) revealed avidity in the right tongue and ipsilateral level 2A neck lymph node. With substantial preoperative multidisciplinary input, she underwent cancer ablation and microvascular free flap reconstruction. Her pathology showed a 35 mm diameter, 14 mm thick moderately differentiated SCC with perineural and lymphovascular invasion. Two out of 38 right neck nodes were positive for metastasis with extranodal extension. None of the 34 left neck nodes was involved.

She had an uneventful recovery and was discharged home on day 6 postoperative day. On day 15 postoperative day, she had catastrophic bleeding in the neck with a respiratory arrest after a forceful cough. She required an emergency tracheostomy and returned to the theatre for haemostasis. Following a short inpatient stay, she was again discharged home and underwent adjuvant therapy consisting of external beam radiotherapy of 60Gy in 30 fractions. On clinical examination and PET at 6 months after surgery, she had no evidence of disease recurrence.

Conclusions

MYH9-RD can present with advanced locoregional oral cavity malignancy at an early age. The combination of profound thrombocytopenia and marked renal impairment can impact heavily on routine major head and neck cancer surgery and adjuvant treatment. This rare and challenging condition underlines the importance of early detection of cancer and multidisciplinary team input.

Essential role of zyxin in platelet biogenesis and glycoprotein Ib-IX surface expression

Platelets are generated from the cytoplasm of megakaryocytes (MKs) via actin cytoskeleton reorganization. Zyxin is a focal adhesion protein and wildly expressed in eukaryotes to regulate actin remodeling. Zyxin is upregulated during megakaryocytic differentiation; however, the role of zyxin in thrombopoiesis is unknown. Here we show that zyxin ablation results in profound macrothrombocytopenia. Platelet lifespan and thrombopoietin level were comparable between wild-type and zyxin-deficient mice, but MK maturation, demarcation membrane system formation, and proplatelet generation were obviously impaired in the absence of zyxin. Differential proteomic analysis of proteins associated with macrothrombocytopenia revealed that glycoprotein (GP) Ib-IX was significantly reduced in zyxin-deficient platelets. Moreover, GPIb-IX surface level was decreased in zyxin-deficient MKs. Knockdown of zyxin in a human megakaryocytic cell line resulted in GPIbα degradation by lysosomes leading to the reduction of GPIb-IX surface level. We further found that zyxin was colocalized with vasodilator-stimulated phosphoprotein (VASP), and loss of zyxin caused diffuse distribution of VASP and actin cytoskeleton disorganization in both platelets and MKs. Reconstitution of zyxin with VASP binding site in zyxin-deficient hematopoietic progenitor cell-derived MKs restored GPIb-IX surface expression and proplatelet generation. Taken together, our findings identify zyxin as a regulator of platelet biogenesis and GPIb-IX surface expression through VASP-mediated cytoskeleton reorganization, suggesting possible pathogenesis of macrothrombocytopenia.

Renal Biopsy-induced Hematoma and Infection in a Patient with Asymptomatic May-Hegglin Anomaly

The May-Hegglin anomaly is characterized by inherited thrombocytopenia, giant platelets, and leukocyte cytoplasmic inclusion bodies. The Fechtner, Sebastian, and Epstein syndromes are associated with mutations of the MYH9-coding nonmuscle myosin heavy chain ⅡA, similar to the May-Hegglin anomaly, and are together classified as MYH9 disorders. MYH9 disorders may include symptoms of Alport syndrome, including nephritis and auditory and ocular disorders. A 6-year-old boy was diagnosed with an MYH9 disorder after incidental discovery of hematuria and proteinuria. Focal segmental glomerulosclerosis was detected on renal biopsy. However, despite no prior bleeding diatheses, he developed a large post-biopsy hematoma despite a preprocedural platelet transfusion calculated to increase the platelet count from 54,000/μL to >150,000/μL. Idiopathic thrombocytopenic purpura is a major cause of pediatric thrombocytopenia following acute infection or vaccination, and patients with MYH9 disorders may be misdiagnosed with idiopathic thrombocytopenic purpura and inappropriately treated with corticosteroids. Careful differential diagnosis is important in thrombocytopenic patients with hematuria and proteinuria for the early detection of thrombocytopenia. Patients with MYH9 disorders require close follow-up and treatment with angiotensin Ⅱ receptor blockers to prevent the onset of progressive nephritis, which may necessitate hemodialysis or renal transplantation. The need for renal biopsy in patients with MYH9 disorders should be carefully considered because there could be adverse outcomes even after platelet transfusion.

A De Novo Mutation in MYH9 in a Child With Severe and Prolonged Macrothrombocytopenia

Congenital macrothrombocytopenia is a diverse group of hereditary disorders caused by mutations in the MYH9 gene, which encodes the nonmuscle myosin heavy chain-A, an important motor protein in hemopoietic cells. Thus, the term MYH9-related disease has been proposed, but the clinicopathologic basis of MYH9 mutations has been poorly investigated. Here, we report a sporadic case of Epstein syndrome, an MYH9 disorder, in a 4-year-old Chinese boy who presented with macrothrombocytopenia. He had no family history of thrombocytopenia, hearing loss, or renal failure. A de novo heterozygous MYH9 mutation, c.287C>T; p. (Ser96Leu), was found in this patient. Genotype-phenotype analysis of all reported mutations suggested a domain-specific relationship between the location of the MYH9 mutation and the penetrance of the nonhematologic characteristics of MYH9-related disorders. Our study highlights the importance of suspecting MYH9-related disease even in cases of chronic macrothrombocytopenia without a family history or extrahematologic symptoms.

Two Cases of the MYH9 Disorder Fechtner Syndrome Diagnosed from Observation of Peripheral Blood Cells before End-Stage Renal Failure

As a MYH9 disorder, Fechtner syndrome is characterized by nephritis, giant platelets, granulocyte inclusion bodies (Döhle-like bodies), cataract, and sensorineural deafness. Observation of peripheral blood smear for the presence of thrombocytopenia, giant platelets, and granulocyte inclusion bodies (Döhle-like bodies) is highly important for the early diagnosis of MYH9 disorders. In our two cases, sequencing analysis of the MYH9 gene indicated mutations in exon 24. Both cases were diagnosed as the MYH9 disorders Fechtner syndrome before end-stage renal failure on the basis of the observation of peripheral blood smear.

MYH9-related disease mutations cause abnormal red blood cell morphology through increased myosin-actin binding at the membrane

MYH9-related disease (MYH9-RD) is a rare, autosomal dominant disorder caused by mutations in MYH9, the gene encoding the actin-activated motor protein non-muscle myosin IIA (NMIIA). MYH9-RD patients suffer from bleeding syndromes, progressive kidney disease, deafness, and/or cataracts, but the impact of MYH9 mutations on other NMIIA-expressing tissues remains unknown. In human red blood cells (RBCs), NMIIA assembles into bipolar filaments and binds to actin filaments (F-actin) in the spectrin-F-actin membrane skeleton to control RBC biconcave disk shape and deformability. Here, we tested the effects of MYH9 mutations in different NMIIA domains (motor, coiled-coil rod, or non-helical tail) on RBC NMIIA function. We found that MYH9-RD does not cause clinically significant anemia and that patient RBCs have normal osmotic deformability as well as normal membrane skeleton composition and micron-scale distribution. However, analysis of complete blood count data and peripheral blood smears revealed reduced hemoglobin content and elongated shapes, respectively, of MYH9-RD RBCs. Patients with mutations in the NMIIA motor domain had the highest numbers of elongated RBCs. Patients with mutations in the motor domain also had elevated association of NMIIA with F-actin at the RBC membrane. Our findings support a central role for motor domain activity in NMIIA regulation of RBC shape and define a new sub-clinical phenotype of MYH9-RD.

Blood clot contraction differentially modulates internal and external fibrinolysis

Essentials Clot contraction influences the rate of fibrinolysis in vitro. Internal fibrinolysis is enhanced ∼2-fold in contracted vs. uncontracted blood clots. External fibrinolysis is ∼4-fold slower in contracted vs. uncontracted blood clots. Contraction can modulate lytic resistance and potentially the clinical outcome of thrombosis. SUMMARY: Background Fibrinolysis involves dissolution of polymeric fibrin networks that is required to restore blood flow through vessels obstructed by thrombi. The efficiency of lysis depends in part on the susceptibility of fibrin to enzymatic digestion, which is governed by the structure and spatial organization of fibrin fibers. How platelet-driven clot contraction affects the efficacy of fibrinolysis has received relatively little study. Objective Here, we examined the effects of clot contraction on the rate of internal fibrinolysis emanating from within the clot to simulate (patho)physiological conditions and external fibrinolysis initiated from the clot exterior to simulate therapeutic thrombolysis. Methods Clot contraction was prevented by inhibiting platelet myosin IIa activity, actin polymerization or platelet-fibrin(ogen) binding. Internal fibrinolysis was measured by optical tracking of clot size. External fibrinolysis was determined by the release of radioactive fibrin degradation products. Results and Conclusions Clot contraction enhanced the rate of internal fibrinolysis ∼2-fold. In contrast, external fibrinolysis was ~4-fold slower in contracted clots. This dichotomy in the susceptibility of contracted and uncontracted clots to internal vs. external lysis suggests that the rate of lysis is dependent upon the interplay between accessibility of fibrin fibers to fibrinolytic agents, including clot permeability, and the spatial proximity of the fibrin fibers that modulate the effects of the fibrinolytic enzymes. Understanding how compaction of blood clots influences clot lysis might have important implications for prevention and treatment of thrombotic disorders.

MYH9-macrothrombocytopenia caused by a novel variant (E1421K) initially presenting as apparent neonatal alloimmune thrombocytopenia

MYH9-related disease is a rare cause of thrombocytopenia. We report an infant girl who presented with severe thrombocytopenia at birth and was initially diagnosed with and treated for neonatal alloimmune thrombocytopenia. However, persistent thrombocytopenia led to the suspicion of congenital thrombocytopenia and subsequent identification of a novel variant in MYH9 (E1421K). In silico analysis strongly predicts that this is a disruptive substitution. Immunofluorescent analysis of neutrophils demonstrates abnormal aggregates of MYH9 protein. This case also suggests that a very high immature platelet fraction (≥40%) may be useful for rapidly differentiating MYH9-related disease from other causes of neonatal thrombocytopenia.

Macrothrombocytopenia With Congenital Bilateral Cataracts: A Phenotype of MYH9 Disorder With Exon 24 Indel Mutations

MYH9 disorder is characterized by large platelets and granulocyte inclusion bodies, and can be complicated with young-adult onsets of nephropathy, sensorineural hearing loss, and cataracts. Congenital cataracts in patients with MYH9 disorder is rare, and their etiology has not been elucidated. We report a 3-year-old patient with MYH9 disorder who had a p.E1066_A1072del mutation and developed cataracts congenitally. A review of the literature reveals that patients with an MYH9 exon 24 indel mutation, including p.E1066_A1072del, are susceptible to developing congenital cataracts and should be followed closely for other nonhematological complications.

Myosin IIa is critical for cAMP-mediated endothelial secretion of von Willebrand factor

Nonmuscle myosin II has been implicated in regulation of von Willebrand factor (VWF) release from endothelial Weibel-Palade bodies (WPBs), but the specific role of myosin IIa isoform is poorly defined. Here, we report that myosin IIa is expressed both in primary human endothelial cells and intact mouse vessels, essential for cyclic adenosine monophosphate (cAMP)-mediated endothelial VWF secretion. Downregulation of myosin IIa by shRNAs significantly suppressed both forskolin- and epinephrine-induced VWF secretion. Endothelium-specific myosin IIa knockout mice exhibited impaired epinephrine-stimulated VWF release, prolonged bleeding time, and thrombosis. Further study showed that in resting cells, myosin IIa deficiency disrupted the peripheral localization of Rab27-positive WPBs along stress fibers; on stimulation by cAMP agonists, myosin IIa in synergy with zyxin promotes the formation of a functional actin framework, which is derived from preexisting cortical actin filaments, around WPBs, facilitating fusion and subsequent exocytosis. In summary, our findings not only identify new functions of myosin IIa in regulation of WPB positioning and the interaction between preexisting cortical actin filaments and exocytosing vesicles before fusion but also reveal myosin IIa as a physiological regulator of endothelial VWF secretion in stress-induced hemostasis and thrombosis.

Mutations responsible for MYH9-related thrombocytopenia impair SDF-1-driven migration of megakaryoblastic cells

MYH9-related disease (MYH9-RD) is an autosomal-dominant thrombocytopenia caused by mutations in the gene for the heavy chain of nonmuscle myosin-IIA (NMMHC-IIA). Recent in vitro studies led to the hypothesis that thrombocytopenia of MYH9-RD derives from an ectopic platelet release by megakaryocytes in the osteoblastic areas of bone marrow (BM), which are enriched in type I collagen, rather than in vascular spaces. SDF-1-driven migration of megakaryocytes within BM to reach the vascular spaces is a key mechanism for platelet biogenesis. Since myosin-IIA is implicated in polarised migration of different cell types, we hypothesised that MYH9 mutations could interfere with this mechanism. We therefore investigated the SDF-1-driven migration of a megakaryoblastic cell line, Dami cells, on type I collagen or fibrinogen by a modified transwell assay. Inhibition of myosin-IIA ATPase activity suppressed the SDF-1-driven migration of Dami cells, while over-expression of NMMHC-IIA increased the efficiency of chemotaxis, indicat- ing a role for NMMHC-IIA in this mechanism. Transfection of cells with three MYH9 mutations frequently responsible for MYH9-RD (p.R702C, p.D1424H, or p.R1933X) resulted in a defective SDF-1-driven migration with respect to the wild-type counterpart and in increased cell spreading onto collagen. Analysis of differential localisation of wild-type and mutant proteins suggested that mutant NMMHC-IIAs had an impaired cytoplasmic re-organisation in functional cytoskeletal structures after cell adhesion to collagen. These findings support the hypothesis that a defect of SDF-1-driven migration of megakaryocytes induced by MYH9 mutations contributes to ectopic platelet release in the BM osteoblastic areas, resulting in ineffective platelet production.

Subarachnoid Hemorrhage Revealing Moyamoya Syndrome in a Patient With May-Hegglin Anomaly

INTRODUCTION

Moyamoya syndrome is a rare progressive cerebrovascular occlusive disease for which several associated conditions have been described.

CASE REPORT

We report the case of a 76-year-old woman with a history of May-Hegglin anomaly who presented with an isolated unusual diffuse headache. Initial laboratory investigations showed only thrombocytopenia (platelet count 95000/μL). Unenhanced brain computed tomography scan revealed a small subarachnoid hemorrhage in the left frontal lobe. Computed tomography angiography showed occlusion of the terminal portion of the left internal carotid artery (ICA) and narrowing of the terminal portion of the right ICA with abnormal collateral vessels. Conventional angiography confirmed the tight stenosis of the extremity of the right ICA, and the occlusion of the left ICA, associated with an extensive collateral network consistent with moyamoya syndrome. No aneurysm was identified.

CONCLUSIONS

The rarity of these 2 diseases makes a fortuitous association very unlikely. We thus concluded that this observation could be the first reported case of May-Hegglin anomaly as a cause of moyamoya syndrome.

Severe to profound deafness may be associated with MYH9-related disease: report of 4 patients

MYH9-related disease (MYH9-RD) is a rare genetic syndromic disorder characterised by congenital thrombocytopenia and is associated with the risk of developing progressive sensorineural hearing loss, nephropathy and presenile cataracts during childhood or adult life. All consecutive patients enrolled in the Italian Registry for MYH9-RD with severe to profound deafness were included in a retrospective study. The study population involved 147 Italian patients with MYH9-RD: hearing loss was identified in 52% of cases and only 4 patients (6%) presented severe to profound deafness at a mean age of 33 years. Deafness was associated with mild spontaneous bleeding in all patients and with kidney involvement in 3 cases. Cochlear implantation was carried out in 3 cases with benefit, and no major complications were observed. Diagnosis was performed about 28 years after the first clinical manifestation of MYH9-RD, which was never suspected by an otolaryngologist. The clinical and diagnostic aspects of 4 patients with severe to profound deafness are discussed with a focus on therapeutic implications.

Diagnosis of inherited platelet disorders on a blood smear: a tool to facilitate worldwide diagnosis of platelet disorders

Essentials There are many hereditary platelet disorders (HPD) but diagnosing these is challenging. We provide a method to diagnose several HPDs using standard blood smears requiring < 100 µL blood. By this approach, the underlying cause of HPD was characterized in ~25-30% of referred individuals. The method facilitates diagnosis of HPD for patients of all ages around the world.

SUMMARY

Background Many hereditary thrombocytopenias and/or platelet function disorders have been identified, but diagnosis of these conditions remains challenging. Diagnostic laboratory techniques are available only in a few specialized centers and, using fresh blood, often require the patient to travel long distances. For the same reasons, patients living in developing countries usually have limited access to diagnosis. Further, the required amount of blood is often prohibitive for pediatric patients. Objectives By a collaborative international approach of four centers, we aimed to overcome these limitations by developing a method using blood smears prepared from less than 100 μL blood, for a systematic diagnostic approach to characterize the platelet phenotype. Methods We applied immunofluorescence labelling (performed centrally) to standard air-dried peripheral blood smears (prepared locally, shipped by regular mail), using antibodies specific for proteins known to be affected in specific hereditary platelet disorders. Results By immunofluorescence labelling of blood smears we characterized the underlying cause in 877/3217 (27%) patients with suspected hereditary platelet disorders (HPD). Currently about 50 genetic causes for HPD are identified. Among those, the blood smear method was especially helpful to identify MYH9 disorders/MYH9-related disease, biallelic Bernard-Soulier syndrome, Glanzmann thrombasthenia and gray platelet syndrome. Diagnosis could be established for GATA1 macrothrombocytopenia, GFI1B macrothrombocytopenia, ß1-tubulin macrothrombocytopenia, filamin A-related thrombocytopenia and Wiskott-Aldrich syndrome. Conclusion Combining basic and widely available preanalytical methods with the immunomorphological techniques presented here, allows detailed characterization of the platelet phenotype. This supports genetic testing and facilitates diagnosis of hereditary platelet disorders for patients of all ages around the world.

Harris Platelet Syndrome in Patients of Non-Indian Origin

Inherited giant platelet disorders are a subgroup of congenital thrombocytopenias characterized by decreased platelet counts along with macroplatelets and variable bleeding symptoms. Harris platelet syndrome, a newly described rare entity, is a subtype of inherited giant platelet disorders and is characterized by mild-to-severe thrombocytopenia, macroplatelets, and no bleeding manifestations. This entity was observed incidentally in healthy blood donors from India in the early 2000s, and the reported cases to date have without exception originated from the same region of the Indian subcontinent. We herein report the occurrence of Harris platelet syndrome in patients from a different ethnogeographic origin.

Perinatal Management for a Pregnant Woman with an MYH9 Disorder

We diagnosed a primipara woman with an MYH9 disorder during her pregnancy. A peripheral blood smear with an immunofluorescence analysis is the established method of diagnosing MYH9 disorders. We provided genetic counseling, as required, which included apprising the woman of the inheritance pattern, the importance of a genetic analysis, and the potential delivery risks for the patient and her offspring. Given that the potential delivery risks are reportedly low, special perinatal management is not necessary for patients with an MYH9 disorder whose platelet count is above 5.0 × 10(4)/μL, except for rapid blood access.

Macrothrombocytopenia With Döhle Body-Like Granulocyte Inclusions: A Case Report of May-Hegglin Anomaly in a 33-Year-Old White Woman With an Update on the Molecular Findings of MYH9-Related Disease

A 33-year-old white woman arrived at the hospital to undergo a hysterectomy due to uterine fibroids. Blood smear review identified macrothrombocytopenia and Döhle body-like cytoplasmic leukocyte inclusions. Genetic testing identified a mutation in exon 39 of the myosin heavy chain gene (MHY9; OMIM 160775), which confirmed the diagnosis of May-Hegglin anomaly. May-Hegglin anomaly is one of a spectrum of MYH9 disorders that also includes Sebastian, Epstein, and Fechtner syndromes. Herein, we describe the clinical and laboratory presentation of a patient with May-Hegglin anomaly and provide an update on the molecular findings and a discussion of the genotypic-phenotypic correlations in this potentially underdiagnosed disorder.

What Is the Biological and Clinical Relevance of Fibrin?

As our knowledge of the structure and functions of fibrinogen and fibrin has increased tremendously, several key findings have given some people a superficial impression that the biological and clinical significance of these clotting proteins may be less than earlier thought. Most strikingly, studies of fibrinogen knockout mice demonstrated that many of these mice survive to weaning and beyond, suggesting that fibrin(ogen) may not be entirely necessary. Humans with afibrinogenemia also survive. Furthermore, in recent years, the major emphasis in the treatment of arterial thrombosis has been on inhibition of platelets, rather than fibrin. In contrast to the initially apparent conclusions from these results, it has become increasingly clear that fibrin is essential for hemostasis; is a key factor in thrombosis; and plays an important biological role in infection, inflammation, immunology, and wound healing. In addition, fibrinogen replacement therapy has become a preferred, major treatment for severe bleeding in trauma and surgery. Finally, fibrin is a unique biomaterial and is used as a sealant or glue, a matrix for cells, a scaffold for tissue engineering, and a carrier and/or a vector for targeted drug delivery.

Late onset and high-frequency dominant hearing loss in a family with MYH9 disorder

MYH9 disorder is a rare autosomal-dominant disorder. We previously reported that it is caused by mutations in the gene for nonmuscle myosin heavy chain IIA (NMMHC-IIA). MYH9 disorder causes congenital macrothrombocytopenia accompanied by progressive sensorineural hearing loss, nephropathy, and cataract. However, there are few reports that describe the audiological features of MYH9 disorder. The objective of this study was to characterize auditory and other phenotypes of patients with MYH9 disorder. We examined nine subjects from one Japanese family. Audiological, ophthalmological, hematological, and imaging examinations were used to assess clinical features. We carried out genetic analysis of the causative gene, MYH9. Five subjects exhibited macrothrombocytopenia and neutrophil cytoplasmic inclusion bodies. Immunofluorescence analysis of neutrophil NMMHC-IIA revealed abnormal type II localization. Two subjects had high-frequency dominant hearing loss, which was adult onset and progressive. Only one subject had cataract. MYH9 sequencing analysis of all thrombocytopenic subjects revealed a heterozygous c.4270G>A mutation in exon 30 (p.D1424N). We identified five patients with MYH9 disorder from the family. The hearing impairment associated with MYH9 disorder in this family was characterized as adult onset, progressive, and high-frequency dominant. Hematological manifestations of MYH9 disorder show complete penetrance, whereas extra-hematological manifestations show incomplete penetrance and variable expressivity in this family.

Translational control mediated by hnRNP K links NMHC IIA to erythroid enucleation

Post-transcriptional regulation is crucial for structural and functional alterations in erythropoiesis. Enucleation of erythroid progenitors precedes reticulocyte release into circulation. In enucleated cells, reticulocyte 15-lipoxygenase (r15-LOX, also known as ALOX15) initiates mitochondria degradation. Regulation of r15-LOX mRNA translation by hnRNP K determines timely r15-LOX synthesis in terminal maturation. K562 cells induced for erythroid maturation recapitulate enucleation and mitochondria degradation. HnRNP K depletion from maturing K562 cells results in enhanced enucleation, which even occurs independently of maturation. We performed RIP-Chip analysis to identify hnRNP K-interacting RNAs comprehensively. Non-muscle myosin heavy chain (NMHC) IIA (also known as MYH9) mRNA co-purified with hnRNP K from non-induced K562 cells, but not from mature cells. NMHC IIA protein increase in erythroid maturation at constant NMHC IIA mRNA levels indicates post-transcriptional regulation. We demonstrate that binding of hnRNP K KH domain 3 to a specific sequence element in the NMHC IIA mRNA 3'UTR mediates translation regulation in vitro Importantly, elevated NMHC IIA expression results in erythroid-maturation-independent enucleation as shown for hnRNP K depletion. Our data provide evidence that hnRNP-K-mediated regulation of NMHC IIA mRNA translation contributes to the control of enucleation in erythropoiesis.

Linkage between the mechanisms of thrombocytopenia and thrombopoiesis

Thrombocytopenia is defined as a status in which platelet numbers are reduced. Imbalance between the homeostatic regulation of platelet generation and destruction is 1 potential cause of thrombocytopenia. In adults, platelet generation is a 2-stage process entailing the differentiation of hematopoietic stem cells into mature megakaryocytes (MKs; known as megakaryopoiesis) and release of platelets from MKs (known as thrombopoiesis or platelet biogenesis). Until recently, information about the genetic defects responsible for congenital thrombocytopenia was only available for a few forms of the disease. However, investigations over the past 15 years have identified mutations in genes encoding >20 different proteins that are responsible for these disorders, which has advanced our understanding of megakaryopoiesis and thrombopoiesis. The underlying pathogenic mechanisms can be categorized as (1) defects in MK lineage commitment and differentiation, (2) defects in MK maturation, and (3) defect in platelet release. Using these developmental stage categories, we here update recently described mechanisms underlying megakaryopoiesis and thrombopoiesis and discuss the association between platelet generation systems and thrombocytopenia.

Homoharringtonine binds to and increases myosin-9 in myeloid leukaemia

BACKGROUND AND PURPOSE

Homoharringtonine (HHT) is a natural alkaloid isolated from various Cephalotaxus species. HHT has been used to treat acute myeloid leukaemia (AML), chronic myeloid leukaemia (CML), chronic lymphocyte leukaemia and myelodysplastic syndromes. Although HHT inhibits protein synthesis and promotes apoptosis of leukaemia cells in preclinical studies, its molecular target proteins remain unknown. The aim of this study was to identify target proteins of HHT.

EXPERIMENTAL APPROACH

We have synthesized a biotinylated affinity column and used it to identify targets of HHT and confirmed the results by MS and Western blots. We also examined the effects of HHT on the target protein and determined roles of the target protein in anti-leukaemia activities of HHT through Western blots, flow cytometry and retrovirus transfection.

KEY RESULTS

Myosin-9, a member of the myosin super-family, was identified as a direct interactor of HHT. Furthermore, HHT up-regulated the expression level of myosin-9 in both AML and CML cell lines in a time-dependent manner. Thus, HHT-induced apoptosis of leukaemia cells begins in 6 h and continues to increase for 24 h. There is a positive correlation between up-regulated myosin-9 expression level and increased percentage of apoptotic cells mediated by HHT. Overexpression of myosin-9 could increase the sensitivity of the leukaemia cells to the cytotoxicity of HHT and arrest cells in S and G2/M phases.

CONCLUSIONS AND IMPLICATIONS

Our results indicated that myosin-9 was the target protein of HHT and played an important role in the HHT-induced apoptosis of leukaemia cells.

Sporadic Epstein syndrome with macrothrombocytopenia, sensorineural hearing loss and renal failure

We report here a sporadic case of Epstein syndrome, one of the MYH9 disorders. A Japanese boy was first noted to have thrombocytopenia at 3 years of age. Blood smear showed giant platelets but no Döhle-like bodies in the neutrophils. He had no family history of thrombocytopenia, hearing loss, and/or renal failure. Thrombocytopenia took a chronic course and platelet count fluctuated in the range 18 000-46 000/μL, not responding to i.v. immunoglobulin or prednisolone treatment. The patient had episodes of gross nasal bleeding at 7 and 18 years of age. Mild hearing loss was suspected at 6, and proteinuria was first noted at 14 years of age. At the development of renal failure at 24 years of age, he was identified to have de novo R702H MYH9 mutation. This case illustrates the importance of suspecting MYH9 disorder even in cases of chronic macrothrombocytopenia without family history.

Genotype-phenotype Correlation of the p.R1165C Mutation in the MYH9 Disorder: Report of a Japanese Pedigree

MYH9 disorder is a rare autosomal dominant disease characterized by congenital thrombocytopenia with giant platelets and leukocyte inclusion bodies and is often associated with Alport-like symptoms, such as glomerulonephritis, sensorineural hearing loss, and cataracts. We report a Japanese pedigree wherein the MYH9 p.R1165C mutation was present in over 4 generations. Three individuals were misdiagnosed as Bernard-Soulier syndrome carriers. Among the 12 patients with abnormal hematological features, the proband's mother, aunt, and grandaunt presented with sensorineural hearing impairment, and the mother presented with presenile cataract, and nephritis. This case report confirms the previously established genotype-phenotype correlations of the MYH9 disorder that p.R1165C is associated with variable expression of nonhematological manifestations. Careful detection of leukocyte inclusion bodies in peripheral blood smears is necessary to prevent misdiagnosis.

Macrothrombocytopenia in north India: role of automated platelet data in the detection of an under diagnosed entity

Congenital macrothrombocytopenia is being increasingly recognised because of the increasing availability of automated platelet counts during routine complete blood count. If not recognised, these patients may be unnecessarily investigated or treated. The study was done to assess the occurrence of macrothrombocytopenia in the North Indian population and the role of automated platelet parameters in its detection. This prospective study was done on patients whose blood samples were sent for CBC to the hematology laboratory of a tertiary care hospital. Samples were run on Advia-120, a 5-part differential automated analyzer. Routine blood parameters including platelet count, mean platelet volume (MPV), platelet cytogram pattern and platelet flagging was studied along with peripheral blood smear examination. ANOVA was used to compare difference in mean MPV in patients with macrothrombocytopenia, and those with secondary thrombocytopenia and ITP. Seventy five (0.6 %) patients with CBC evaluation were detected to have macrothrombocytopenia, majority (96 %) of North Indian origin. The MPV (fl) in the 75 patients ranged from 10.9 to 23.3 (mean 15.1 ± 3.1 fl) with a dispersed cytogram pattern distinct from that seen in patients with normal platelet count, raised platelet count or low platelets due to secondary thrombocytopenia (MPV-10.9 ± 2.6) or ITP (10.8 ± 3.5). The difference in mean MPV in these patients was statistically significant (p < 0.00001). Macrothrombocytopenia is an under diagnosed condition and may be initially suspected on automated blood counts. Along with a blood smear examination, automated data (MPV and platelet cytogram pattern) aids the diagnosis and can avoid unnecessary investigations and interventions for these patients.

The collagen receptor DDR1 co-localizes with the non-muscle myosin IIA in mice inner ear and contributes to the cytoarchitecture and stability of motile cells

Discoidin domain receptor 1 (DDR1) is a tyrosine kinase receptor activated by native collagen. DDRs regulate cell adhesion, migration and various other cell functions. Deletion of the DDR1 gene in mice is associated with a severe decrease in auditory function and substantial structural alterations in a heterogeneous group of cells, including cells containing actin/myosin contractile elements, e.g., outer hair cells (OHCs) (Meyer zum Gottesberge et al. Lab Invest, 88: 27-37, 2008). The non-muscle myosin heavy chain isoform IIA (NM-IIA), encoded by MYH9, is implicated in the regulation of cell spreading, cellular reshaping and movement and cell migration and adhesion. In this study, we identify DDR1 and NM-IIA co-localization in the type III fibrocytes (tension fibrocytes) of the spiral ligament, the OHCs and the stereocilia of both OHCs and inner hair cells. We show for the first time that DDR1 malfunction causes OHC deformation and the separation of the lateral wall, the location of the cellular motor responsible for the electromotile property, explicitly in those regions showing DDR1 and NM-IIA co-localization. On the basis of our results, we propose that DDR1 acts in concert with proteins of the actin/myosin complex to maintain mechanical forces in the inner ear and to stabilize OHC cellular shape for proper auditory signal transduction.

The formin DIAPH1 (mDia1) regulates megakaryocyte proplatelet formation by remodeling the actin and microtubule cytoskeletons

Megakaryocytes are highly specialized precursor cells that produce platelets via cytoplasmic extensions called proplatelets. Proplatelet formation (PPF) requires profound changes in microtubule and actin organization. In this work, we demonstrated that DIAPH1 (mDia1), a mammalian homolog of Drosophila diaphanous that works as an effector of the small GTPase Rho, negatively regulates PPF by controlling the dynamics of the actin and microtubule cytoskeletons. Moreover, we showed that inhibition of both DIAPH1 and the Rho-associated protein kinase (Rock)/myosin pathway increased PPF via coordination of both cytoskeletons. We provide evidence that 2 major effectors of the Rho GTPase pathway (DIAPH1 and Rock/myosin II) are involved not only in Rho-mediated stress fibers assembly, but also in the regulation of microtubule stability and dynamics during PPF.

R705H mutation of MYH9 is associated with MYH9-related disease and not only with non-syndromic deafness DFNA17

MYH9-related disease (MYH9-RD) is a rare autosomal dominant disease caused by mutation of MYH9, the gene encoding for the heavy chain of non-muscle myosin IIA (NMMHC-IIA). MYH9-RD patients have macrothrombocytopenia and granulocyte inclusions (pathognomonic sign of the disease) containing wild-type and mutant NMMHC-IIA. During life they might develop sensorineural hearing loss, cataract, glomerulonephritis, and elevation of liver enzymes. One of the MYH9 mutations, p.R705H, was previously reported to be associated with DFNA17, an autosomal dominant non-syndromic sensorineural hearing loss without any other features associated. We identified the same mutation in two unrelated families, whose four affected individuals had not only hearing impairment but also thrombocytopenia, giant platelets, leukocyte inclusions, as well as mild to moderate elevation of some liver enzymes. Our data suggest that DFNA17 should not be a separate genetic entity but part of the wide phenotypic spectrum of MYH9-RD characterized by congenital hematological manifestations and variable penetrance and expressivity of the extra-hematological features.

Spectrum of the mutations in Bernard-Soulier syndrome

Bernard-Soulier syndrome (BSS) is a rare autosomal recessive bleeding disorder characterized by defects of the GPIb-IX-V complex, a platelet receptor for von Willebrand factor (VWF). Most of the mutations identified in the genes encoding for the GP1BA (GPIbα), GP1BB (GPIbβ), and GP9 (GPIX) subunits prevent expression of the complex at the platelet membrane or more rarely its interaction with VWF. As a consequence, platelets are unable to adhere to the vascular subendothelium and agglutinate in response to ristocetin. In order to collect information on BSS patients, we established an International Consortium for the study of BSS, allowing us to enrol and genotype 132 families (56 previously unreported). With 79 additional families for which molecular data were gleaned from the literature, the 211 families characterized so far have mutations in the GP1BA (28%), GP1BB (28%), or GP9 (44%) genes. There is a wide spectrum of mutations with 112 different variants, including 22 novel alterations. Consistent with the rarity of the disease, 85% of the probands carry homozygous mutations with evidence of founder effects in some geographical areas. This overview provides the first global picture of the molecular basis of BSS and will lead to improve patient diagnosis and management.

Cochlear implantation is safe and effective in patients with MYH9-related disease

BACKGROUND

MYH9-related disease (MYH9-RD) is a rare syndromic disorder deriving from mutations in MYH9, the gene for the heavy chain of non-muscle myosin IIA. Patients present with congenital thrombocytopenia and giant platelets and have a variable risk of developing sensorineural deafness, kidney damage, presenile cataract, and liver abnormalities. Almost all MYH9-RD patients develop the hearing defect, which, in many individuals, progresses to severe to profound deafness with high impact on quality of life. These patients are potential candidates for cochlear implantation (CI), however, no consistent data are available about the risk to benefit ratio of CI in MYH9-RD. The only reported patient who received CI experienced perisurgery complications that have been attributed to concurrent platelet defects and/or MYH9 protein dysfunction.

METHODS

By international co-operative study, we report the clinical outcome of 10 patients with MYH9-RD and severe to profound deafness who received a CI at 8 institutions.

RESULTS

Nine patients benefited from CI: in particular, eight of them obtained excellent performances with restoration of a practically normal hearing function and verbal communication abilities. One patient had a slightly worse performance that could be explained by the very long duration of severe deafness before CI. Finally, one patient did not significantly benefit from CI. No adverse events attributable to MYH9-RD syndrome were observed, in particular no perisurgery bleeding complications due to the platelet defects were seen. Patients' perioperative management is described and discussed.

CONCLUSIONS

CI is safe and effective in most patients with MYH9-RD and severe to profound deafness and should be offered to these subjects, possibly as soon as they develop the criteria for candidacy.

MYH9-related disease: description of a large Chinese pedigree and a survey of reported mutations

We describe a large four-generational Chinese pedigree segregating MYH9 -related disease caused by a V1516L mutation. The clinical findings supported previously established genotype-phenotype correlations, and also demonstrated interindividual variability of disease manifestations even within the same family. The same mutation was previously reported in another Chinese pedigree but resulting from a different DNA substitution. Analyzing the patterns of previously reported mutations revealed a limited spectrum of pathogenic variants. The implications of this finding are discussed.