Kearns-Sayre syndrome (KSS) is a multisystem genetic disorder caused by defects of mitochondrial DNA. KSS is one of the more frequent forms of mitochondrial respiratory chain deficiency. Most if not all cases have been sporadic. Clinical manifestations are highly variable, multisystem defects that involve abnormality of the central nervous system (CNS), skeletal muscle, heart, and kidney or a combination thereof. Cardiac conduction defects are one of the three main symptoms in KSS.