Onset: Before age 20 Symptoms: This disorder is defined by PEO
and pigmentary retinopathy, a “salt-and-pepper” pigmentation in
the retina that can affect vision, but often leaves it intact.
Other common symptoms include conduction block (in the heart)
and ataxia. Less typical symptoms are mental retardation or
deterioration, delayed sexual maturation and short stature.
Symptoms: Leigh syndrome causes brain abnormalities that can
result in ataxia, seizures, impaired vision and hearing,
developmental delays and altered control over breathing. It also
causes muscle weakness, with prominent effects on swallowing,
speech and eye movements. Symptoms: This disorder typically
causes muscle weakness and/or liver failure, and more rarely,
brain abnormalities. “Floppiness,” feeding difficulties and
developmental delays are common symptoms; PEO and seizures are
less common. Onset: Childhood to early adulthood Symptoms: MELAS
causes recurrent strokelike episodes in the brain, migraine-type
headaches, vomiting and seizures