KSS is a progressive multi-system disease that often begins with CPEO. Degeneration of the retina usually causes difficulty seeing in dark environments. Incoordination (ataxia) and abnormalities of cardiac electrical conduction are common.
Patients with KSS may also have other problems, such as deafness, dementia, kidney dysfunction, and muscle weakness. Endocrine abnormalities including delayed growth, short stature, diabetes, and deficiency of parathyroid hormone may also occur.
KSS is usually caused by a single large deletion (segmental loss) of mtDNA). These deletions, of which there are over 150 species, typically arise spontaneously. Rarely, the mutation is transmitted by the mother.
As with all mitochondrial diseases, there is no cure for KSS. Treatments are based on the types of symptoms and organs involved, and may include: CoQ10, insulin for diabetes, cardiac drugs, and a cardiac pacemaker, which may be life-saving. Surgical intervention for drooping eyelids may be considered but should be performed by specialists in ophthalmic surgical centers.
The prognosis varies depending on severity. Death is common in the third or fourth decade and may be due to organ system failures.