Gomori trichrome stain showing several ragged red fibers (arrowhead). (b) Cytochrome c oxidase stain showing Type-1 lightly stained and Type II fibers, darker fibers, and a few fibers with abnormal collections of mitochondria (arrowhead). Note cytochrome c oxidase negative fibers as usually seen in mitochondrial encephalopathy, lactic acidosis and stroke-like episodes<unk> . (c) Succinate dehydrogenase staining showing a few ragged blue fibers and intense staining in the mitochondria of the blood vessels (arrow). (d) Electron microscopy showing abnormal collection of mitochondria with paracrystalline inclusions (arrowhead), osmiophilic inclusions (large arrowhead) and mitochondrial vacuoles (small arrowhead).<unk>  is mostly caused by mutations in the genes in mitochondrial DNA, but it can also be caused by mutations in the nuclear DNA. NADH dehydrogenase Some of the genes (MT-ND1, MT-ND5) affected in<unk>  encode proteins that are part of NADH dehydrogenase (also called complex I) in mitochondria, that helps convert oxygen and simple sugars to energy. Transfer RNAs Other genes (MT-TH, MT-TL1, and MT-TV) encode mitochondrial specific transfer RNAs (tRNAs). Mutations in MT-TL1 cause more than 80 percent of all cases of<unk> . They impair the ability of mitochondria to make proteins, use oxygen, and produce energy. Researchers have not determined how changes in mitochondrial DNA lead to the specific signs and symptoms of<unk> . They continue to investigate the effects of mitochondrial gene mutations in different tissues, particularly in the brain. Inheritance This condition is inherited in a mitochondrial pattern, which is also known as maternal inheritance and heteroplasmy. This pattern of inheritance applies to genes contained in 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, but fathers do not pass mitochondrial traits to their children. In most cases, people with<unk>  inherit an altered mitochondrial gene from their mother. Less commonly, the disorder results from a new mutation in a mitochondrial gene and occurs in people with no family history of<unk> .
MELAS syndrome
Bannayan–Riley–Ruvalcaba syndrome
Pashayan syndrome
Fitzsimmons–Guilbert syndrome
Teunissen–Cremers syndrome
Fryns-Aftimos syndrome
Abruzzo–Erickson syndrome
Berk–Tabatznik syndrome