Changes in histopathology and heteroplasmy rates over 8 years and effectiveness of taurine supplementation in a patient with mitochondrial nephropathy caused by mutation: A case report.

The m.3243A > G mutation in the () gene is known to cause mitochondrial nephropathy. However, its long-term effects of the m.3243A > G mutation on renal histopathology or heteroplasmy rates remain unknown. Here we present the case of a female patient who underwent renal biopsy at 34 years of age to investigate the reason for a low estimated glomerular filtration rate (eGFR) of 47.9 mL/min/1.73 m. Light microscopy revealed nephrosclerosis with granular swollen epithelial cells (GSECs) in the renal tubules. Genetic testing revealed the m.3243A > G mutation in the gene. Over a follow-up period of 8 years, the eGFR declined at a rate of 1.50 mL/min/1.73 m/year. A second renal biopsy was performed at the age of 42 years; the patient's glomerular sclerosis rate had increased from 45.5% to 63.2%, and the frequency of GSECs in the collecting ducts had increased from 5.8% to 20.8%. Furthermore, the heteroplasmy rate in blood cells and urinary sediment cells increased from 9% to 20% and 20% to 53%, respectively. Taurine therapy was initiated just after the second kidney biopsy. To date, after approximately 3 years of taurine administration, the rate of eGFR decline has markedly decreased to 0.26 mL/min/1.73 m/year. This experience suggests that an increased heteroplasmy rate may be associated with the progression of mitochondrial nephropathy caused by mutation. Furthermore, our case is the first to suggest the effectiveness of taurine for mitochondrial nephropathy caused by the m.3243A > G mutation in the gene.