<unk>  is a condition that affects many of the body's systems, particularly the brain and nervous system (encephalo-) and muscles (myopathy). In most cases, the signs and symptoms of this disorder appear in childhood following a period of normal development. Children with<unk>  often have normal early psychomotor development until the onset of symptoms between 2 and 10 years old. Though less common, infantile onset may occur and may present as failure to thrive, growth retardation and progressive deafness. Onset in older children typically presents as recurrent attacks of a migraine-like headache, anorexia, vomiting, and seizures. Children with<unk>  are also frequently found to have short stature. Most people with<unk>  have a buildup of lactic acid in their bodies, a condition called lactic acidosis. Increased acidity in the blood can lead to vomiting, abdominal pain, extreme tiredness (fatigue), muscle weakness, loss of bowel control, and difficulty breathing. Less commonly, people with<unk>  may experience involuntary muscle spasms (myoclonus), impaired muscle coordination (ataxia), hearing loss, heart and kidney problems, diabetes, epilepsy, and hormonal imbalances.
MELAS syndrome
Bannayan–Riley–Ruvalcaba syndrome
Pashayan syndrome
Fitzsimmons–Guilbert syndrome
Teunissen–Cremers syndrome
Fryns-Aftimos syndrome
Abruzzo–Erickson syndrome
Berk–Tabatznik syndrome