Background and objectives: MYH9-related disorders are autosomal dominant hereditary macrothrombocytopenias caused by mutations in the MYH9 gene. This gene encodes the non-muscular myosin heavy chain type II A (MHCIIA). Among these disorders, May-Hegglin anomaly (MHA), Sebastian syndrome (SS), and Fechtner syndrome (FS) are associated with different types of ribosome inclusions in granulocytes. FS also exhibits Alport-like manifestations: nephropathy, neurosensory deafness, and cataracts. The aim of our study was to assess the granulocyte inclusion ultrastructure in genetically confirmed MYH9-related disorders.
Design and methods: Ten individuals were studied. All fulfilled the clinical and laboratory findings to be diagnosed as having an MYH9-related disorder. The ultrastructure of 50 granulocyte sections for each patient was examined, and the percentages of the different types of inclusion were established. Mutations of the MYH9 gene were also analyzed.
Results: The patients were classified as having MHA if the inclusions contained parallel longitudinal filaments. If not, they were classified as having SS or FS. FS patients also showed Alport-like manifestations. In all syndromes we observed a wide variability of the inclusion ultrastructure. Moreover, a small number of inclusions typical of other syndromes was observed. A new cross-striated inclusion variant was identified in SS. A significant number of pure ribosome aggregates were identified in all syndromes.
Interpretation and conclusions: Like other MYH9-related traits, the variation and partial overlap in the inclusion ultrastructure could be attributed to specific changes in the polymerization, assembly, or stability of the MHCIIA. These changes might be associated with MYH9 gene mutations as well as with its heterogeneous expression.