C16: The Twins Misdirection

            The most common way to prove that a personality trait or medical outcome is or is not genetic is to look at the experience of identical twins. Basically, so the argument goes, if identical twins both display the same characteristic or medical outcome, then it is genetic. If they don't, then it is not genetic. This is because it is understood that identical twins have identical DNA. If both twins suffer the same medical outcome significantly more than would be expected for the general population, then it is assumed that that outcome is due to DNA in whole or in part, rather than other factors, such as, the environment, viruses, toxins, diet, etc.
That makes perfect sense. And because of this assumption, many outcomes have been considered genetic. Researchers use data on identical twins to determine how genetic an outcome is.
            But I disagree. The twins data doesn't necessarily point only to genetics.
            Identical Twin Rethink:
            It is my theory that in most cases the reason that identical twins share the same outcome, such as autism, is that, as fetuses, they shared the same placenta. There are many complications that put fetuses at risk when they share the same placenta, and it is these complications that result in the outcomes, not genetics. These complications may lead to interruption or limits to the flow of blood and oxygen to each fetus. It is this complication of blood flow and oxygen supply that results in these outcomes. There could also be complications with nutrient supply. It is important to consider that about 75% of all identical twins share the same placenta. Also, identical twins share the same amniotic sac in about 1% of cases.
            Because of my theory here, I believe that many outcomes that are now considered as genetic, should now be reconsidered as possibly also due to complications of pregnancy. There may be no genetic link to these outcomes whatsoever.
            Fraternal Twin Rethink:            
            Fraternal twins are never considered to share the same placenta. There have been rare cases, but that was for "test tube" babies, and it has been considered that somehow the procedures used in the fertilization process resulted in this anomaly. Fraternal twins never share the same amniotic sac. In other words their birth experience is identical to that of single births.
            Considering this, we should be able to expect that the incidence of any outcome, such as autism, for fraternal twins should be about the same as that of other single sibling births in a family. Even if there is a genetic factor in the outcome, the incidence should still be the same for fraternal twins as it is for single births in the same family. If the incidence of fraternal twins is higher than that for single births in the same family, then it should be considered that the cause is a complication before or during birth, not genetics. From that, you could expect that the incidence for identical twins for the same outcome should be higher, as there is the added significant risk inherent in identical twin births. This is always the case.
            Repeat, for any particular outcome, if the incidence for fraternal twins is higher than for single births, then the cause should be considered as a complication of birth, not genetics, and if the incidence for identical twins is higher than for fraternal and single births, then it should be concluded that the cause may be a complication of birth, not just genetics.
             In summation, it is my belief that all studies that concluded that particular outcome were due to genetics as determined by twin studies, need to be rethought. These may be a misdirection, and lead to fruitless research. They may be due to complications before or during birth. It is important that the medical profession consider this "Twins Misdirection" and if it is valid, then sponsor studies that try to link particular outcomes, with particular complications before or during birth. This is will be a total new focus. It is my belief that currently several millions of dollars are being wasted on trying to pin down genetic causes, which may never succeed.
            But genetics may still be involved. I'm trying to consider how we parse out from the data what is due to complications of birth, and what may still be due to genetics. Perhaps the best we can do is that if it runs in families, it's probably genetic, if it doesn't, then it's not genetic. Or find  an outcome that we believe has no genetic impact, and then consider their data as only due to complications of pregnancy. Having this data, subtract data this from other twins studies, to net out the true genetic relationship to their outcome.

Barry Stanley