Final answer:
High-energy-demand tissues like the eyes and heart are often the first affected by mitochondrial diseases like LHON due to their high energetic requirements. When mitochondria are defective, less energy is available, which impairs these tissue functions. This is why symptoms like muscle weakness and vision loss manifest earlier in such conditions.
Step-by-step explanation:
The reason tissues with high energy demands, such as the eyes and heart, are often the first to exhibit symptoms of mitochondrial diseases like Leber's Hereditary Optic Neuropathy (LHON) is due to the significant energy requirements to maintain their normal functions. Mitochondria are the powerhouses of cells, and they provide necessary energy through cellular respiration. When the mitochondria are defective, they generate less energy, leading to the first failures often seen in energetically demanding tissues.
Since cells in the eyes and heart require a continuous supply of energy to function correctly, any dysfunction in the mitochondrial DNA will disproportionately affect them. For instance, retinal ganglion cells in the eyes are particularly vulnerable due to their high energy consumption for visual processing. Similarly, heart muscle cells constantly require energy to pump blood efficiently throughout the body.
Additional information about the essentiality of mitochondria in energy provision further supports the grave impact of mitochondrial diseases on tissues with a high energetic requirement. Mutations in mitochondrial DNA can lead to symptoms such as muscle weakness, lack of coordination, and vision loss as seen in mitochondrial diseases. Therefore, defects in mitochondria significantly compromise the function of these energetically demanding cells, leading to the early onset of symptoms in associated tissues.