Mitochondrial disorders

Last updated: Monday, 20, December, 2010
CausesAppropriate Tests

An increasing number of genetic mitochondrial disorders are being identified.

Although some show autosomal recessive inheritance, most are due to point mutations or deletions of mitochondrial DNA, so show maternal inheritance.

Many cases are sporadic.

The diagnosis is made 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 genetics of leucocytes 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.

Consult pathologist. Many of these disorders are uncommon; some of the more important ones are noted:

Leber hereditary optic neuroretinitis

MELAS 

Mitochondrial myopathy, encephalopathy, lactic acidosis, stroke-like episodes.

MERRF 

Myoclonic epilepsy, ragged red fibres.

CPEO 

Chronic progressive external ophthalmoplegia.

Leigh syndrome 

Subacute necrotising encephalomyelopathy.

NARP 

Neurogenic muscle weakness, ataxia, retinitis pigmentosa.