Pure Smooth Endoplasmic Reticulum (SER) Inclusions in Granulocytes of MYH9-Related Disorder Patients

MYH9-related disorders are a group of disorders (May-Hegglin anomaly, Fechtner syndrome, Sebastian syndrome) characterized by macrothrombocytopenia and ribosome inclusions in granulocytes. They are caused by mutations in the MYH9 gene and, depending on the location of the mutation, are associated with extrahematological pathologies (sensorineural hearing loss, progressive nephropathy, presenile cataracts) of variable intensity. The inclusions are formed by single and clustered ribosomes and are partially surrounded by segments of rough endoplasmic reticulum (RER). Typical inclusions in May-Hegglin anomaly are spindle-shaped, well-defined, and contain longitudinal filaments. Those found in Sebastian and Fechter syndromes are round or oval, have no filaments and, sometimes, show cross-striated arrangement of the ribosome aggregates. When reviewing the electron micrographs of the granulocyte inclusions of 10 patients with MYH9-related disorders previously published (Pujol-Moix et al. Haematologica 2004;89:330-337) we observed a special type of inclusion not described in the article. This inclusion has the typical appearance of smooth endoplasmic reticulum (SER) clusters, that is, a meshwork of branching tubules of SER without limiting membranes and no other structures such as ribosomes or RER. In 3 of the patients reviewed, in addition to the typical inclusions of MYH9-related disorder, some granulocytes with SER clusters were observed. These clusters were rounded or oval in shape and, when present, were 1 or 2 per cell (Fig. 1). The patients who presented granulocyte SER clusters are those identified as B4, C6 and D8 in the Haematologica article and are briefly described in Table 1. The patients presenting with SER clusters showed different characteristics such as age, bleeding, platelet counts, and proportion of giant platelets. Therefore, we cannot relate the presence of SER clusters to any clinical or biological characteristic of patients. It should be noticed that we did not find SER clusters in any patient with May-Hegglin anomaly. However, the small number of cases studied does not allow any conclusions to be drawn. SER clusters have been described in different types of cells such as hepatocytes or kidney tubular epitelial cells (Ghadially FN. Ultrastructural Pathology of the Cell and Matrix. Butterwords. London, 1988, pp 422-427). Normal granulocytes (neutrophils, eosinophils, and basophils) besides their own specific granules, also contain other general subcellular structures, including dispersed SER membranes. However, SER membranes forming clusters in these cells have not been previously described. In addition, SER clusters do not seem to correspond to evolved forms of typical MYH9 inclusions, for example by degranulation of the RER, based on the observations that typical inclusions show abundant ribosomes but few RER segments, no appreciable ribosomes are observed in the SER clusters, and the morphology of the tubules forming the SER and RER is different. We suggest that SER clusters could be considered a new type of inclusion in MYH9-related disorders. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

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.

A Novel Frameshift Mutation in a Case of Familial May-Hegglin Anomaly.

The May-Hegglin anomaly is a rare, autosomal dominant condition that is characterised by thrombocytopaenia, anisocytosis, and Dohlë-like inclusion bodies in leukocytes. The disorder generally results in a mild bleeding tendency. May-Hegglin anomaly results from defects in the MYH9 gene, which encodes the heavy chain of nonmuscle myosin IIA. The gene maps to chromosome 22q12.3-q13.2, comprises 40 exons, and produces a 5.8kb mRNA transcript. We present a case of familial May-Hegglin anomaly. This kindred was first identified, and published, in 1964; but no further analyses were carried out until recently. The proband, now aged 80 years, has a life long history of easy bruising and epistaxis, although the symptoms have improved with increasing age. Her sister (deceased) and daughter reported similar symptoms: the daughter requiring splenectomy for thrombocytopaenia at age 9 years. The proband has also suffered from deafness for in excess of 60 years. Recent investigations of the proband revealed a mild thrombocytopaenia, and the characteristic blood film of May -Hegglin anomaly. Platelet and neutrophil morphology were also consistent with the disorder. Karyotype analysis revealed good quality G banding throughout chromosome 22, and no gross alteration in the region 22q11.2., 22q13. Direct sequencing of the MYH9 gene identified a heterozygous deletion of a single base in a run of Gs at nucleotide positions 5818–5821 (codons 1940–1941). This frame shift mutation leads to the creation of a premature termination sequence at codon 1947, and the loss of the last fourteen amino acids. The deletion introduces a restriction site, and endonuclease digestion of a panel of normals failed to detect this change. Together with the fact that this is a conserved region across species (human, rat, rabbit, chicken), it is probable that this deletion is the causative mutation in this kindred. This novel mutation represents the second reported defect affecting the tail-piece domain in May-Hegglin anomaly. The protein’s two heavy chains homodimerise in this region to form a tail, and multiple polypeptides associate through this tail domain to form bipolar filaments. Therefore, a mutation in this domain may exert its effect by the inhibition of myosin filament assembly. To date, approximately 20 different mutations have been described in the MYH9 gene giving rise to not only May-Hegglin anomaly, but also the similar disorders of Fechtner syndrome, Sebastian syndrome and Epstein syndrome. In fact some mutations have been identified in patients with different diagnoses. The proband presented here has a long standing diagnosis of May-Hegglin anomaly, but does exhibit one symptom (deafness) more usually associated with Fechtner syndrome. The genetic, phenotypic and clinical overlap in these disorders suggest that these actually represent allelic variations of a single genetic disorder, which should more correctly be termed ‘MYHIIA syndrome’.