There are numerous mitochondrial disorders that affect the neurological and muscular systems in a variety of ways:
- Kearns-Sayre syndrome
- Leigh syndrome
- mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS)
- myoclonus epilepsy with ragged red fibers (MERRF)
- mitochondrial deletion syndromes, e.g. POLG-related disorders
- trichopoliodystrophy (also known as Menkes disease)
As spermatozoa are deficient of mitochondria, these diseases are only inherited from the mother. The genes are located in mitochondrial DNA (mtDNA) of which there is a degree of heterogeneity within the one individual: not all mitochondria share the same genetic material. The percentage of affected mitochondria will dictate the degree to which the disease is clinically manifested .
The findings are variable ranging from specific findings (uncommon) to non-specific abnormalities (most common) as well as normal appearing studies . Findings are discussed separately for each condition listed above but as a general rule of thumb bilateral deep grey matter involvement and peripheral white matter delayed myelination in young adults or children should suggest the diagnosis. This is especially the case if associated with an elevated lactate level on MRS.