R’s mom, BB (her chosen grandma name), has mitochondrial myopathy, which is a neuromuscular disease caused by damage to the mitochondria, the energy-producing structures in cells that serve as power plants for our bodies. There are many types of mitochondrial myopathies. Some of the more common forms include Kearns-Sayre syndrome, myoclonic epilepsy with ragged-red fibers, and the MELAS syndrome of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes. Since mitochondrial myopathies are sometimes passed down genetically, R and I have been concerned about what this could mean for our little Button.
We went to an appointment with the specialist that has been working with BB to learn more about her illness and how it affects her, but also to find out what the ramifications could be for our baby. The good news is that BB has been cleared for the known genetic syndromes, the bulk of which are extremely serious. Since BB doesn’t have any of these, there is no reason to believe that anyone in R’s family does.
More good news is that we found out that the majority of mitochondrial disorders (75-80%) are autosomal recessive, so that means that both parents have to carry a copy of the defective gene. If that is the case, it would be pretty rare that anyone except BB and her four siblings could have the defect. Of BB and her siblings, each would have a 25% chance of having the defect. Even if one of the other four besides BB did, there may not be enough saturation of the genetic material to cause any symptoms. Happily BB’s offspring, as well as her siblings’ offspring, would only have a 1% chance of having the defective gene. So, it’s not 100%, but the odds are strong that there is nothing for anyone outside of BB to worry about, and as she says, we already know what her symptoms are.
In the event that it does turn out to be maternally transferred (20-25% chance), then anyone in the maternal line could have the defect. Again, not everyone would necessarily have any symptoms.
We can’t get any firm answers until BB’s gene sequencing is complete, which might be by the end of the year. At that time, we expect to know which of the above is the case, and what the specific defect is.
Overall, we came away with some good odds. As BB says, there’s no need to worry ’til we have something to worry about!