Mitochondrial Cytopathy
Certain diseases are caused by mutations in mitochondrial DNA. These diseases are transmitted through the mother and have variable expression because of the phenomenon of heteroplasmy, whereby different cells in the body can have varying proportions of mitochondria that have normal DNA and mutant DNA. In general, the higher the proportion of mutant mitochondrial DNA, the higher the likelihood of abnormal tissue function. Examples of mitochondrial cytopathies include Kearns -Sayre syndrome and Pearson Syndrome.