Kearns-Sayre syndrome presenting as renal tubular acidosis. Renal tubular acidosis and tetany were the 1st manifestations of Kearns-Sayre syndrome in a 5-year-old child. Subsequently, he developed progressive external ophthalmoplegia, ptosis, retinopathy, heart block, and endocrinopathy. There was a 7.5-kb deletion of mitochondrial DNA documented in muscle, kidney, skin fibroblasts, and leukocytes, providing evidence for a multisystem mitochondrial cytopathy. 