Progressive nephropathy associated with mitochondrial tRNA gene mutation.

Mitochondrial DNA plays a crucial role in oxidative production of energy. Thus, defects in mitochondrial DNA can affect virtually all organ systems. The point mutation A --> G at position 3243 in the mitochondrial tRNAleu(UUR) gene is the cause of several distinct types of mitochondrial cytopathy and several clinical phenotypes, including encephalomyopathy with lactic acidosis and stroke-like episodes and maternally inherited diabetes and deafness. This mutation has been recently described also in association with kidney disease, mainly focal and segmental glomerulosclerosis. At present, little is known about the prevalence of this mitochondrial nephropathy, its clinical course and the pathogenesis of glomerular damage. We describe 2 unrelated patients, who presented with proteinuria and progressed to end-stage renal failure. Other clinical features were short stature, severe headache, hearing loss, diabetes mellitus and hypertrophic cardiomyopathy. The main histological finding was an increased number of abnormal mitochondria in tubular cells and podocytes. Analysis of mitochondrial DNA from leukocytes and urine sediment revealed heteroplasmy for the A3243G mutation in tRNAleu(UUR) gene in both patients. Recognition of the characteristic clinical and histological features of the mitochondrial A3243G mutation-associated glomerulopathy will enable correct diagnosis and better management of a disease which is likely to be underdiagnosed.