What is Kearns-Sayre syndrome (KSS)?

Kearns-Sayre syndrome (KSS) is a rare neuromuscular disorder with onset usually before the age of 20. It is the result of abnormalities in the DNA of the mitochondria, small rod-like structures found in every cell of the body. The mitochondria produce the energy that drives cellular functions. Mitochondrial diseases co-relate with specific DNA mutations that can cause problems with many other organs and tissues in the body. KSS is characterized by progressive limitation of eye movements until there is complete immobility, accompanied by eyelid droop. It is also associated with abnormal accumulation of pigmented material on the membrane lining the eyes. Additional symptoms may include mild skeletal muscle weakness, heart block (a cardiac conduction defect), short stature, hearing loss, an inability to coordinate voluntary movements (ataxia), impaired cognitive function, and diabetes. Seizures are infrequent. Several endocrine disorders can also be associated with KSS.

This answer is based on source information from the National Institute of Neurological Disorders and Stroke.