My son, Oliver, is one year old and is under investigation to determine what mitochondrial disorder he has, if he does indeed have a mitochondrial disorder. A couple of months ago he had a muscle biopsy. The surgeon removed two grams of tissue from his right thigh for testing. When the results were in we were told two things. One, that his muscle fibers were not bundling properly. A muscle is made of two types of fibers, conveniently labeled type one and type two. If you were to look at a cross section of a muscle sample you should see the two fibers equally distributed, so at a 50% mix. Oliver’s fibers are bundling at 60%/40%. This is somewhat mild. The second thing we were told was that everything else was at normal levels, but they wanted to do one last test. Why? I asked (later, of course, through a series of phone messages between myself and the R.N.) should we do one more test if everything was mostly normal? I finally got a response back from the geneticists R.N. explaining that while the mitochondrial activity levels were normal, he had more mitochondria than they would expect to find.
Mitochondria, hmmm, I remember making a cell cookie for a middle school biology project once, and I recall that we used some type of candy, jelly beans I think, to represent the mitochondria, but that’s about all that I remember. This post is to rediscover mitochondria and why they’re so important.
What are mitochondria? Google provided me with this succinct description: mitochondrion – A spherical or ovoid organelle found in the cytoplasm of eukaryotic cells, contains genetic material separate from that of the host; it is responsible for the conversion of food to usable energy in the form of ATP.
Mitochondria are the body’s powerhouses, the batteries if you will. Interestingly, mitochondria have their own DNA separate from that of the individual they reside inside of. Mitochondria were once a parasitic bacteria that has degraded over time until now its an integral part of our bodies and is passed on from mother to child in the egg. Even more fascinating, mitochondrial DNA can trace the maternal geneology back fifty thousand years and has been used to prove theories, such as we are descended from Neanderthals, false.
Mitochondria contain 2 types of genetic material:
• mitochondrial DNA, which can only be passed on from the mother
• nuclear DNA, which is passed on from both parents
Autosomal recessive inheritance
The nuclear DNA in mitochondria is inherited from both parents (half from
each parent). Mitochondrial disease can be passed on only if BOTH the mother and
father are “carriers”. This means that they carry the mutated gene, but not the
disease – so they don’t have any symptoms. This is called autosomal recessive
When both parents are carriers, there is:
• a 25% chance of having a child with the disease
• a 50% chance of having a child who is a carrier like the parents
(has the mutation, but not the disease)
• a 25% chance of having a child that is not a carrier and does not have
While I read many articles, Mitochondrial DNA and Human History from the Human Genome website (http://genome.wellcome.ac.uk/doc_WTD020876.html) was the simplest to digest.
But back to my original questions, what are mitochondria and how can I better understand mitochondrial disorders? Mitochondria reproduce faster than other human cells because they do not have a system check to identify mutated DNA. Because they don’t check, they reproduce faster, twenty times faster than other cells. One mutated mitochondria reproduces twenty times in X amount of time, and is why some mitochondrial issues do not manifest until adolescents or adulthood. It takes that many years for the original few defective mitochondria to reproduce to the level that they can impact their host.
What does this mean for Oliver? I have no idea, but it is a fascinating subject. If they’d told me in middle school biology that mitochondria are actually the remnants of an ancient parasitic bacteria that we now use to power our bodies I may have gone into genetics. Why do they keep all the cool stuff a secret?