NUCLEAR-DNA ORIGIN OF CYTOCHROME-C-OXIDASE DEFICIENCY IN LEIGHS SYNDROME - GENETIC-EVIDENCE BASED ON PATIENTS-DERIVED RHO-DEGREES TRANSFORMANTS

Defects of the respiratory chain carrying out oxidative phosphorylatio n (OXPHOS) are the biochemical hallmark of human mitochondrial disorde rs. Faulty OXPHOS can be due to mutations in either nuclear or mitocho ndrial genes, that are involved in the synthesis of individual respira tory subunits or in their post-translational control. The most common mitochondrial disorder of infancy and childhood is Leigh's syndrome, a severe encephalopathy, often associated with a defect of cytochrome c oxidase (COX). In order to demonstrate which genome is primarily invo lved in COX-deficient (COX((-)))-Leigh's syndrome we generated two lin es of transmitochondrial cybrids. The first was obtained by fusing nuc lear DNA-less cytoplasts derived from normal fibroblasts, with mitocho ndrial DNA-less (rho(o)) transformant fibroblasts derived from a patie nt with COX((-))-Leigh's syndrome. The second cybrid line was obtained by fusing rho(o) cells derived from 143B.TK- human osteosarcoma cells , with cytoplasts derived from the same patient. The first cybrid line showed a specific and severe COX((-)) phenotype, while in the second all the respiratory chain complexes, including COX, were normal. These results indicate that the COX defect in our patient is due to a mutat ion of a nuclear gene. The use of cybrids obtained from 'customized', patient-derived rho(o) cells can have wide applications in the identif ication of respiratory chain defects originated by nuclear DNA-encoded mutations, and in the study of nuclear DNA-mitochondrial DNA interact ions.