Mitochondrial DNA (mtDNA or mDNA) is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate (ATP). Mitochondrial DNA can be regarded as the smallest chromosome. Human mitochondrial DNA was the first significant part of the human genome to be sequenced. In most species, including humans, mtDNA is inherited solely from the mother. Thus mtDNA is a powerful tool for tracking ancestry through females (matrilineage) and has been used in this role to track the ancestry of many species back hundreds of generations.
Mitochondrial DNA was discovered in the 1960s by Margit M. K. Nass and Sylvan Nass by electron microscopy as DNase-sensitive thread inside mitochondria(1), and by Ellen Haslbrunner, Hans Tuppy and Gottfried Schatz by biochemical assays on highly purified mitochondrial fractions(2).
Mutations in the mitochondria, organelles that produce a cell’s energy and carry their own DNA, can cause a range of symptoms, including heart failure, dementia, and blindness. The severity and onset of symptoms can vary, but they tend to affect tissue with high energy demands, such as heart, muscle, and brain. There is no way to treat the condition because mitochondrial DNA (mtDNA) in embryos primarily comes from the oocyte, or egg cell.
Several groups of researchers have been working to find ways to prevent the condition using modified IVF techniques. IVF is a technique to allow women who carry the mutations a chance to conceive children with healthy mitochondria. With the help of this modified in vitro fertilization (IVF) techniques, researchers are a step closer to finding a way to prevent mitochondrial diseases that can cause a range of potentially fatal disorders.
These techniques were previously shown to work in monkeys, but now scientists report that they have successfully transferred DNA from one human egg cell containing mutant mitochondria to another without those mutations, thus producing embryos that can develop for several days and give rise to embryonic stem cells.
The article says that the current technique is not very efficient and not ready yet to try in patients.
The study(3) published in Nature suggested the feasibility of mtDNA replacement in human oocytes. The study has used spindle transfer technique (ST; also called spindle–chromosomal complex transfer) and concluded that all embryonic stem cell lines derived from ST zygotes had normal euploid karyotypes and contained exclusively donor mtDNA. Although some ST oocytes displayed abnormal fertilization, the authors say, the mtDNA can be efficiently replaced in human oocytes.
Note: ethical questions raised needs to be answered because any female children born after the technique would pass the donated mtDNA to their children. A prominent ethics group in the United Kingdom said that the technique is justified as a way to prevent an otherwise untreatable disease.
Since the success rate is worryingly low, says Mary Herbert, a reproductive biologist at Newcastle University in the United Kingdom who also works on techniques to prevent mitochondrial disease, further research and scrutiny is warrented.
LETS HOPE THE BETTER FUTURE
1. NASS MM, NASS S (December 1963).“INTRAMITOCHONDRIAL FIBERS WITH DNA CHARACTERISTICS : I. Fixation and Electron Staining Reactions”. The Journal of Cell Biology 19 (3): 593–611.PMC 2106331. PMID 14086138.
2. Ellen Haslbrunner, Hans Tuppy and Gottfried Schatz (1964 at the Institut for Biochemistry at the Medical Faculty of theUniversity of Vienna in Vienna, Austria): “Deoxyribonucleic Acid Associated with Yeast Mitochondria” (PDF) Biochem. Biophys. Res. Commun. 15, 127 – 132.
- “Oxidized Mitochondrial DNA” – a missing link between apoptosis and inflammasome activation (tginnovations.wordpress.com)
- 2 Moms, 1 Dad, Lotsa Issues (foxnews.com)
- Genetic Diseases May Be Fixed Pre-Conception in Eggs, Study Says (bloomberg.com)
- Researchers Moving Toward Controversial Germ-Line Gene Therapy (biotech.about.com)
- New technique replaces diseased DNA, but would give kids two mothers (vitals.nbcnews.com)
- Could Genetic Diseases Be Cured in the Womb? (livescience.com)
- Oregon scientists make embryos with 2 women, 1 man (kansascity.com)
- sex-specific genetic mechanism for the control of mitochondrial DNA levels (tginnovations.wordpress.com)