Abstract
Oncocytomas are mostly benign tumors characterized by accumulation of defective mitochondria, and in sporadic cases, are associated with disruptive mitochondrial DNA (mtDNA) mutations. However, the role mtDNA mutations have in renal tumors of Birt-Hogg-Dubé (BHD) patients and other renal oncocytomas with an apparent genetic component has not been investigated to date. Here we characterize the mitochondrial genome in different renal tumors and investigate the possibility of employing mtDNA sequencing analyses of biopsy specimens to aid in the differential diagnosis of oncocytomas. The entire mitochondrial genome was sequenced in 25 samples of bilateral and multifocal (BMF) renal oncocytomas, 30 renal tumors from BHD patients and 36 non-oncocytic renal tumors of different histologies as well as in biopsy samples of kidney tumors. mtDNA sequencing in BMF oncocytomas revealed that all tumors carry disruptive mutations, which impair the assembly of the NADH-ubiquinone oxidoreductase. Multiple tumors from a given BMF oncocytoma patient mainly harbor the same somatic mutation and the kidneys of these patients display diffuse oncocytosis. In contrast, renal oncocytomas of patients with BHD syndrome and renal tumors with different histologies do not show disruptive mtDNA mutations. Moreover, we demonstrate that it is feasible to amplify and sequence the entire mtDNA in biopsy specimens, and that these sequences are representative of the tumor DNA. These results show that pathogenic mtDNA mutations affecting complex I of the respiratory chain are strongly correlated with the oncocytoma phenotype in non-BHD-related renal tumors and that mtDNA sequences from biopsies are predictive of the tumor genotype. This work supports a role for mtDNA mutations in respiratory chain complexes as diagnostic markers for renal oncocytomas.