ABSTRACT
The clinical presentation and course of patients with mitochondrial syndromes are extremely diverse. These diseases may manifest at any age from birth until late adulthood with acute manifestation or as a chronic progressive disease. Virtually any organ may be impaired, but the organs with the highest energetic demands are most frequently involved, including brain, muscle, heart and liver. Some mitochondrial disorders affect a single organ (e.g., the eye in Leber hereditary optic neuropathy), but many involve multiple organ systems. Many patients display an assemblage of clinical features that can be ascribed to a discrete clinical syndrome, such as the Kearns-Sayre syndrome (KSS), chronic progressive external ophthalmoplegia (CPEO), neurogenic weakness with ataxia and retinitis pigmentosa (NARP), myoclonic epilepsy with ragged-red fibers (MERRF), or mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS). On the other hand, many other mitochondrial disorders do not clearly fit into one particular and recognizable syndrome category, and the spectrum of disease phenotypes can be broadly overlapping among several syndromes. All possible inheritance patterns can be found (maternal, X linked, autosomal recessive, autosomal dominant, and de novo occurrence) due to the dual involvement of the mitochondrial and nuclear genomes.
