Kearns-Sayre syndrome associated with de Toni-Debré-Fanconi syndrome due to cytochrome-c-oxidase (COX) deficiency.

We report a 43-year-old female with complete Kearns-Sayre syndrome, focal deficiency of cytochrome-c-oxidase (COX) and extensive deletion of the mtDNA in muscle fibers, which showed progressive insufficiency of the renal tubule: first hyperphosphaturia and hyperaminoaciduria and, later, also glucosuria (de Toni-Debré-Fanconi syndrome), a syndrome to date rarely diagnosed in association with complete Kearns-Sayre syndrome. In our opinion, this case, in view of the relationships between retinal and kidney disorders, suggests a search for de Toni-Debré-Fanconi syndrome in all patients with Kearns-Sayre syndrome also by quantitative and chromatographic methods for the assessment of aminoacids, phosphates and sugars in the urine.