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Kidney Week

Abstract: FR-PO800

Renal Lesions Associated with MYH9 Disorder (5773delG Mutation): Clinical and Pathological Analyses

Session Information

Category: Genetic Diseases of the Kidneys

  • 1002 Genetic Diseases of the Kidneys: Non-Cystic

Authors

  • Yoshikawa, Kazuhiro, Iwate Prefectural Central Hospital, Morioka-city Iwate, Japan
  • Kunishima, Shinji, Gifu University of Medical Science, Seki, Japan
  • Kurihara, Hidetake, Aino University, Ibaraki, Japan
  • Takahashi, Kei, Toho University Ohashi Medical Center, Tokyo, Japan
  • Nakaya, Izaya, Iwate Prefectural Central Hospital, Morioka-city Iwate, Japan
  • Soma, Jun, Iwate Prefectural Central Hospital, Morioka-city Iwate, Japan
Introduction

MYH9 mutations at C-terminal, such as exon 40, have not been reported to cause renal injuries. This is the first report of renal phenotype with MYH9 exon 40 5773delG mutation. Of note, focal segmental glomerulosclerosis (FSGS) could occur even in association with MYH9 exon 40 5773delG mutation. Accumulation of abnormal Non-muscle myosin heavy chain IIA (NMMHC-IIA) in podocytes may lead to podocyte injuries and development of FSGS lesions.

Case Description

A 37-year-old Japanese man with persistent urine abnormalities and gradually progressive renal dysfunction was admitted to hospital; his mother and two sons had giant platelets. Renal biopsy was postponed 8 years ago because he had thrombocytopenia. Laboratory data showed serum creatinine, 2.45 mg/dL; urine protein, 6 g/gCr; urine red blood cells, 36 /high-power field; and platelets, 47,000 /μL. May–Hegglin anomaly was suspected owing to macrothrombocytopenia and cytoplasmic Döhle-like inclusion bodies in granulocytes; he had bilateral cataracts and hearing loss in the 4000-Hz range. On renal biopsy, 13 glomeruli were microscopically examined: 6 showed global sclerosis and others showed mild mesangial proliferation with segmental glomerulosclerosis. On immunofluorescence examination, IgG, IgA, IgM, C1q, and C3 deposits were observed in the mesangium; α2, 5 chain staining in basement membranes showed normal pattern. Foot process effacements and intense bleb-like morphological changes in podocytes were observed via electron microscopy. Electron dense deposits in certain mesangial areas and no Alport’s basement membrane changes were found. NMMHC-IIA staining in spots pattern was observed via immunofluorescence examination of granulocytes. MYH9 5773delG (G1924fs) mutation was found via genomic DNA sequencing. These findings and ineffective steroid therapy led to the possible diagnosis of FSGS associated with MYH9 disorder.

Discussion

On further pathological analyses, double staining of vimentin and NMMHC-IIA showed decreased colocalization of NMMHC-IIA in cell bodies and primary processes of podocytes. Podocytes were significantly stained by an antibody specific to abnormal NMMHC-IIA produced by MYH9 5773delG mutation; this was not observed in glomeruli of patients without the mutation. We finally diagnosed the patient with FSGS associated with MYH9 disorder.