Mitochondrial tRNALeu(UUR) mutation in a patient with steroid-resistant nephrotic syndrome and focal segmental glomerulosclerosis

Background. The heterogeneity of mitochondrial cytopathies is characteristic for this group of disorders, which preferentially affect the muscle and nerve system. The A3243G transition in the tRNA (Leu)(UUR) gene has been associated with slowly progressive forms of focal segmental glomerulosclerosis (FSGS). Here we present a patient who developed a severe nephrotic syndrome during her first pregnancy, which persisted after delivery. and proved resistant to immunosuppressive therapy. A sister of our patient had developed diabetes mellitus. We analysed the DNA for the presence of the mitochondrial DNA (mtDNA) A3243G transition. Methods. DNA was isolated from peripheral blood leukocytes and urine sediments. Polymerase chain reaction was performed to amplify the mtDNA. Restriction enzyme analysis was used to detect the presence of the A3243G transition. Quantitative analysis of the A3243G mutation was done using the pyrosequencing technique. Results. Quantitative analysis revealed a proportion Of Mutated mtDNA of 30% in the leukocytes and 68% in the urine sediments of the proband. On further analysis, we also found the transition in the mother, the diabetic sister and the daughter of the proband. Conclusion. MtDNA abnormalities can cause a steroid-resistant nephrotic syndrome, histologically characterized by FSGS. Physicians should be especially mindful of mitochondrial abnormalities when hearing loss, diabetes mellitus or neuromuscular disorders are present in the patient or family members.