It is a clinically heterogeneous group of mitochondrial disorders characterized by a reduction in the number of mtDNA copies in the affected tissues without mutations or rearrangements in the mtDNA. The syndrome is phenotypically heterogeneous and can affect a specific organ or combination of organs. The main presentations described are:
- Hepatocerebral: liver dysfunction, psychomotor retardation
- Myopathic: hypotonia, muscle weakness, bulbar weakness
- Encephalomyopathic: hypotonia, muscle weakness, psychomotor retardation
- Neuro-gastrointestinal: gastrointestinal dysmotility, peripheral neuropathy
Additional phenotypes include:
- Fatal infantile lactic acidosis with methylmalonic aciduria
- Spastic ataxia: early-onset ataxia-spastic neuropathy syndrome
- Alpers syndrome
