Anyway, mitochondrial diseases tend to affect the brain because the mitochondria generate the energy for the cell, and the brain consumes a great deal of energy for its weight. An interesting thing about mitochondrial diseases, though, is that the effects vary tremendously from one person to another. The reason for this is because only some of the mitochondria in any given cell are affected; cells with too many defective mitochondria will commit suicide (apoptosis) or die from lack of energy (necrosis). Whenever a cell divides, the mitochondria are distributed between the daughter cells, and the resultant balance in sick and healthy mitochondria in each cell is random. A sick cell might produce two equally sick daughter cells, or one healthy cell and one terminally sick cell that then dies, or something in-between. So these random factors very early in embryonic development can lead to very different overall results in terms of what organs and systems are affected.