A case of mitochondrial disease with an A3243G mutation diagnosis based on progressive proteinuria

Abstract

A 9-year-old girl visited our hospital complaining of proteinuria, which was identified during her school urinary screening. She had mild proteinuria (1+, 29 mg/dl, protein/creatinine ratio =0.9 g/gCre), without hematuria or deterioration of kidney function. Initially, a kidney biopsy was performed, which showed only minor glomerular abnormalities. Angiotensin II receptor blocker was prescribed, but her proteinuria increased over the next 5 years. A second biopsy was performed when the patient was 14 years old. Histologic examination of biopsy specimen showed focal segmental glomerular sclerosis and granular swollen epithelial cells in the tubular epithelium. The presence of granular swollen epithelial cells suggested that she was affected by mitochondrial disease. Screening of the m.3243A>G mitochondrial DNA mutation revealed a heteroplasmy level of 49% in the peripheral blood. This was diagnosed as focal segmental glomerular sclerosis due to mitochondrial disease. Mitochondrial disease should be thought as a differential diagnosis, even if the patient has no neurologic abnormality, familial diabetes or maternal inheritance.