Understanding the nomenclature of mitochondrial DNA mutations through examples of two specific disease entities: Mitochondrial encephalopathy with lactic acidosis and stroke-like episodes and Leber hereditary optic neuropathy.

Mitochondrial diseases are genetic disorders that can arise either from maternally inherited mitochondrial DNA (mtDNA) or from mutations in nuclear DNA. This article is the second in a series of papers reviewing mitochondrial genetics and several of the disorders associated with mitochondrial gene variants. With a prevalence of 1:∼4,300 persons, mitochondrial disorders are diagnostic entities with which nurse practitioners should be familiar. In describing genetic mutations, numbering nucleotides (nuclear or mtDNA) is critical for communicating exactly where a variation has occurred in a stretch of nucleotides. This article discusses the nomenclature associated with mtDNA mutations, using the examples of mutations causing mitochondrial encephalopathy with lactic acidosis and stroke-like episodes and Leber hereditary optic neuropathy. Pathophysiology, symptoms, and treatment options for these disease entities are discussed.