Dominant traits are rare in mitochondrial disorders but include important nosological entities such as alterations of organellar biogenesis and abnormalities in the structural integrity of the mitochondrial genome, determined by mutations in genes involved in its maintenance and propagation. Both haplo-insufficiency and 'gain-of-function' mechanisms underlie the pathogenesis of these disorders. Impairment in energy supply, abnormal mitochondrial trafficking, increased toxic damage by oxygen radicals, and mitochondrially driven apoptosis have been documented in different dominant syndromes. In addition, maternally inherited mutations of mitochondrial DNA can sometimes simulate dominant traits, mainly because of reduced penetrance and complex interaction with genetic and environmental factors.
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