KSS is the result of deletions in mitochondrial DNA (mtDNA) that cause a particular constellation of medical signs and symptoms. mtDNA is transmitted exclusively from the mother's ovum. Mitochondrial DNA is composed of 37 genes found in the single circular chromosome measuring 16,569 base pairs in length. Among these, 13 genes encode proteins of the electron transport chain (abbreviated "ETC"), 22 encode transfer RNA (tRNA), and two encode the large and small subunits that form ribosomal RNA (rRNA). The 13 proteins involved in the ETC of the mitochondrion are necessary for oxidative phosphorylation. Mutations in these proteins results in impaired energy production by mitochondria. This cellular energy deficit manifests most readily in tissues that rely heavily upon aerobic metabolism such as the brain, skeletal and cardiac muscles, sensory organs, and kidneys. This is one factor involved in the presentation of mitochondrial diseases.