Kearns-Sayre syndrome

Kearns-Sayre syndrome is caused by defects in mitochondria, which are structures within cells that us oxygen to convert the energy from food into a form that can be used by cells. This process is called oxidative phosphorylation. Although most DNA is packaged in chromosomes within the nucleus (nuclear DNA), mitochondria also have a small amount of their own DNA called mitochondrial DNA (mtDNA). This type of DNA contains many genes essential for normal mitochondrial function. People with Kearns-Sayre syndrome have a single, large deletion of mtDNA which results in the loss of genes important for mitochondrial formation and oxydative phosphorylation. While researchers have not determined how these deletions cause the features of Kearns-Sayre syndrome, they may be related to a lack of cellular energy The underlying cause of the deletion in affected individuals remains unknown.^[1] 

Most cases of Kearns-Sayre syndrome are not inherited; they arise from mutations in the body's cells that occur after conception. This alteration, called a somatic mutation, is present only in certain cells. Rarely, this condition is inherited in a mitochondrial pattern. This pattern of inheritance, also known as maternal inheritance, refers to genetic alterations involving mitochondrial DNA. Because egg cells, but not sperm cells, contribute mitochondria to the developing embryo, only females pass mitochondrial conditions to their children. Mitochondrial disorders can appear in every generation of a family and can affect both males and females. Males that are affected do not pass mitochondrial traits to their children.^[1]

The children of males with Kearns-Sayre syndrome are not at risk.^[2]