As the site of the gene is narrowed down, so pre-natal and carrier testing becomes more likely. Mitochondria are very small structures that are present within every cell in the body. They are vitally important for the chemical processes that generate the energy required to keep the cell alive and functioning normally. However, mitochondria are unique in that they also have a small amount of their own DNA which is responsible for producing some of the mitochondrial proteins. Another unique feature is that this mitochondrial DNA is always inherited from the mother, not the father.
Ptosis is the first feature, followed by progressive limitation of the range of eye movements.
Diplopia is uncommon. Particularly common, but rarely causing symptoms, is a pigmentary retinopathy. At the back of the eye, over the outer edges of the retina, dark spots can be seen. Rarely, this can cause impairment of night vision or more troublesome visual problems. Mild facial, neck and limb weakness may be apparent, and other common associated symptoms include mild dysphagia, deafness and short stature.