The title is misleading; the most frequent treatments are unproven and not tailored well to the numerous disorders lumped under the term ‘mitochondrial disease.’ A nice review on what’s up-to-date with ‘mito’ disorders is in a recent NEJM (NEJM 2012; 366; 1132-41).
The first part of the review details the structure and function of the mitochondria including those pesky pathways for the production of ATP: glucose –>pyruvate through glycolysis. In turn, pyruvate –>lactate –>acetyl coenzyme A (CoA). Acetyl CoA generates NADH & flavin via tricarboxylic acid cycle. Fatty acids and glutamine can also serve as substrates. NADH & FADH2 fuel oxidative phosphorylation through five coupled mitochondria protein complexes. Coenzyme Q10 helps transport electrons across the complexes.
Primary and secondary mitochodrial disorders.
- 1000 genes encoding mitochondrial proteins have been identified in humans
- 228 mutations of protein-encoding nuclear DNA (nDNA) and 13 mitoDNA (mtDNA) have been linked to human disorders
- Secondary mito disorders include mito dysfunction due to viral infections and ‘off-target’ drug effects. Specific drugs include valproic acid, statins, halothane, doxorubicin, and aspirin
- Mito dysfunction is seen in a number of other diseases including Alzheimer’s, Parkinson’s, cancers, cardiac disease, diabetes, and obesity
Diagnosis: Biopsy specimens from patients can be studied to assess cellular and mitochondrial physiology in comparison to healthy samples. This review does not discuss molecular testing for mutations; however, an extensive list of genes associated with mitochondrial disorders (mtDNA & nDNA) is listed in Figure 2; a supplementary online appendix to the article explains these mutations in more depth.
Four potential treatments –all with a goal of increasing ATP production:
- genetic therapy
- small molecule treatment
- metabolic manipulation
Previous Cochrane review (2006) has not found evidence to support the use of any therapeutic interventions. More recent trials have shown limited positive effects on clinical or biochemical end points but have not led to a New Drug Application with the FDA. A few specific disorders that have treatments include the following:
- Idebenone (a CoQ10 variant) for Friedreich’s ataxia & Leber’s hereditary optic neuropathy
- Ketogenic diet for improving seizures in children with electron-transport defects
- Cyclosporin A for secondary mito dysfunction in Ulrich’s congenital muscular dystrophy & Bethlem’s myopathy
- Overview of current trials: http://www.clinicaltrials.gov/ct2/results?term-mitochondrial+disease
As one of my colleagues (LS) has said, making a diagnosis of a mitochondrial disorder is like getting the license plate of the bus that ran you over. Until treatments improve, this is pretty much the case.
- -Mitochondrion 2011; 11: 679-85. Why are there no proven therapies for genetic mitochondrial diseases?
- -J Pediatr 2011; 158: 802. Developing liver toxicity with VPA is a contraindication to OLTx (even in the absence of documented mitochondrial dz). Rx with carnitine and d/c VPA. 82% of 17 children died w/in 1 yr of OLTx. POLG1 mutations are associated with Alpers syndrome.
- -Pediatrics 2007; 120: 1326. Diagnosis and complications of mitochondrial disease.
- -Pediatrics 2007; 119: 722. long-term outcome of mito dz –variable.
- -NEJM 2003; 348: 2656. Review