An increasing number of genetic mitochondrial disorders are being identified.
Some disorders are caused by mutations in mitochondrial DNA (mtDNA) and they show maternal inheritance. Other disorders caused by defects of the nuclear DNA may have an autosomal recessive or autosomal dominant inheritance.
A significant proportion of cases are sporadic.
Disorders with mtDNA mutations can be diagnosed by demonstrating the mitochondrial DNA abnormality, possibly requiring examination of more than one tissue.
Muscle biopsy and/or Liver biopsy with histology, together with chemical assay of respiratory chain enzymes. Molecular genetic analysis of leukocytes is less reliable.
At times, there are structurally abnormal mitochondria (including ragged red fibres in skeletal muscle).
Many diseases are associated with Lactic acidosis, which may be best detected in CSF.
Additional information about genetic tests may be available in Catalogue of Genetic Tests and Laboratories.
Consult pathologist. Many of these disorders are uncommon; some of the more important ones are noted: