CPEO/KSS Project Fund

Chronic Progressive External Ophthalmoplegia

Chronic progressive external ophthalmoplegia (CPEO) is a condition characterized mainly by a loss of the muscle functions involved in eye and eyelid movement. Signs and symptoms tend to begin in early adulthood and most commonly include weakness or paralysis of the muscles that move the eye (ophthalmoplegia) and drooping of the eyelids (ptosis). Some affected individuals also have general weakness of the skeletal muscles (myopathy), which may be especially noticeable during exercise. Muscle weakness may also cause difficulty swallowing (dysphagia). CPEO can be caused by mutations in any of several genes, which may be located in mitochondrial DNA or nuclear DNA. It has different inheritance patterns depending on the gene involved in the affected individual.

CPEO can occur as part of other underlying conditions, such as ataxia neuropathy spectrum and Kearns-Sayre syndrome. These conditions may not only involve CPEO, but various additional features that are not shared by most individuals with CPEO.


The signs and symptoms of chronic progressive external ophthalmoplegia (CPEO) typically begin in young adults between the ages of 18 and 40.The most common symptoms in affected individuals include drooping eyelids (ptosis) and weakness or paralysis of the eye muscles (ophthalmoplegia). The condition may be unilateral (affecting one eye) or bilateral (affecting both eyes). Some affected individuals also have weakness of the skeletal muscles (myopathy), specifically of the arms, legs, and/or neck. This may be especially noticeable during exercise. Muscle weakness may also cause difficulty swallowing (dysphagia).

Sometimes, CPEO may be associated with other signs and symptoms. In these cases, the condition is referred to as “progressive external ophthalmoplegia plus” (PEO+). Additional signs and symptoms can include hearing loss caused by nerve damage in the inner ear (sensorineural hearing loss), weakness and loss of sensation in the limbs due to nerve damage (neuropathy), impaired muscle coordination (ataxia), a pattern of movement abnormalities known as parkinsonism, or depression.

More information at the NIH >>

Kearns-Sayre Syndrome

KSS is a slowly progressive multi-system mitochondrial disease that often begins with drooping of the eyelids (ptosis). Other eye muscles eventually become involved,  resulting  in  paralysis  of  eye  movement.  Degeneration  of  the retina usually causes difficulty seeing in dimly lit environments.

KSS is characterized by three main features:

  • typical onset before age 20 although may occur in infancy or adulthood
  • paralysis of  specific  eye  muscles  (called  chronic  progressive  external ophthalmoplegia CPEO)
  • degeneration of the retina causing abnormal accumulation of pigmented (colored) material (pigmentary retinopathy).

In addition, one or more of the following conditions is present:

  • block of electrical signals in the heart (cardiac conduction defects)
  • abnormally high levels of protein in the fluid that surrounds and protects the brain and spinal cord (Elevated cerebrospinal fluid protein)
  • problems with coordination and balance that cause unsteadiness while walking (ataxia)

Patients with KSS may also have such problems as deafness, dementia, kidney dysfunction,  and  muscle  weakness.  Endocrine  abnormalities  including decreased or slow growth, short stature, or diabetes may also be evident.

KSS is a rare disorder. One online eMedicine article found only 226 cases worldwide  in the literature  by 1992 (Kearns-Sayre  Syndrome  by  Ewa Posner, MD). It is  usually  caused  by a single  large  deletion  (loss)  of genetic  material within the DNA of the mitochondria (mtDNA), rather than in the DNA of the cell nucleus. These deletions, of which there are over 150 species, typically arise spontaneously. Less frequently, 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: Coenzyme  Q10, 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  undertaken  by  specialists  in  ophthalmic  surgical centers.

KSS is slowly progressive and prognosis varies depending on severity and the number of systems or organs involved which widely varies from patient to patient.

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