Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Kearns-Sayre Syndrome ?
    ### Response:
    Kearns-Sayre syndrome (KSS) is a rare neuromuscular disorder with onset usually before the age of 20 years. It is the result of abnormalities in the DNA of mitochondria - small rod-like structures found in every cell of the body that produce the energy that drives cellular functions.
    