About Kearns-Sayre Syndrome (KSS)
The New York Center for Rare Diseases supports the mission and guidelines of the Genetic and Rare Diseases Information Center (GARD). The following information is provided by the NIH.
Summary
Kearns-Sayre syndrome (KSS) is a neuromuscular disorder defined by the triad of features: onset of symtpoms before age 20 years; pigmentary retinopathy (a "salt-and-pepper" pigmentation in the retina that can affect vision, but often leaves it intact); and progressive external ophthalmoplegia (PEO). In addition, affected individuals have at least one of the following: cardiac conduction block, cerebrospinal fluid protein concentration greater than 100 mg/dL, or cerebellar ataxia. Kearns-Sayre syndrome is a mitochondrial DNA (mtDNA) deletion syndrome. It results from 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. This and other mitochondrial diseases correlate with specific DNA genetic changes that cause problems with many of the organs and tissues in the body, resulting in multisystem effects.
Causes
What Causes This Disease?
Genetic Mutations: Kearns-Sayre syndrome is caused by genetic mutations, also known as pathogenic variants. Genetic mutations can be hereditary, when parents pass them down to their children, or they may occur randomly when cells are dividing. Genetic mutations may also result from contracted viruses, environmental factors, such as UV radiation from sunlight exposure, or a combination of any of these.
If you suspect you may have this disease, you may want to start collecting your family health history. Information such as other family members who have had similar symptoms, when their/your symptoms first appeared, or exposures to any potential disease-causing environmental factors should be discussed with your medical team.
Known Genetic Mutations: Kearns-Sayre syndrome is caused by genetic mutations in the following known gene(s):
RRM2B
Given these known genetic mutation(s), you may want to ask your health care team if genetic testing is right for you. Genetic tests are laboratory tests that use samples of blood, saliva, or other tissues to help identify changes in genes, chromosomes, or proteins. Genetic testing can help confirm or rule out a suspected genetic disease, or can provide other useful information to your health care team.
Disruption in Metabolism: Kearns-Sayre syndrome is caused by a disruption in a person's metabolism. Metabolism is the series of chemical reactions in our body that turns the food we eat into energy and removes toxins. Hormones and specific proteins, called enzymes, help make the right chemical reactions happen in the right order. However, genetic changes can prevent hormones or enzymes from working properly, which can lead to a disruption in metabolism such as energy not being created for the body or toxins not being removed from the body.
Impaired Mitochondrial Function: Kearns-Sayre syndrome is caused by an impairment, or issue, in mitochondrial function. Mitochondria make the energy needed for cells to work properly. When mitochondria are unable to produce enough energy for a cell, the cell can become damaged or can die. Depending on the location and number of damaged cells, different organs and body systems can be affected.
Can This Disease Be Passed Down From Parent to Child?
Yes. It is possible for a biological parent to pass down genetic mutations that cause or increase the chances of getting this disease to their child. This is known as inheritance. Knowing whether other family members have previously had this disease, also known as family health history, can be very important information for your medical team. This tool from the Surgeon General can help you collect your family health history.
There are multiple ways, or patterns, a disease can be inherited depending on the gene(s) involved. Based on GARD's current data, this disease can be inherited in the following pattern(s):
Mitochondrial Inheritance: Mitochondrial inheritance means the genetic mutation is located in a specific type of DNA, called mtDNA. mtDNA is found within the cell's mitochondria. Mitochondria are tiny structures that produce energy for the body. Genetic mutations within mtDNA can prevent the mitochondria from working properly.
During human conception, egg cells, or the cells that come from the female parent, provide mitochondria. If a female parent is affected by a mitochondrial genetic mutation, there is a 100% chance their child inherits the mutated gene. However, the child may or may not be affected by the disease. A male parent cannot pass mitochondrial genetic mutations to their children.
Autosomal Recessive: Autosomal means the gene involved is located on one of the numbered chromosomes. Recessive means that a child must inherit two copies of the mutated gene, one from each biological parent, to be affected by the disease. A carrier is a person who only has one copy of the genetic mutation. A carrier usually doesn't show any symptoms of the disease.
If both biological parents are carriers, there is a 25% chance their child inherits both copies of the mutated gene and is affected by the disease. Additionally, there is a 50% chance their child inherits only one copy of the mutated gene and is a carrier.