Identical genes don’t always behave identically in different people—even people with completely identical DNA. Take Adam and Neil Pearson, for example. Born as monozygotic, or identical, twins, these brothers are thought to carry indistinguishable genomes, including a genetic change that causes neurofibromatosis type 1. But Adam has a face that is bloated and disfigured—so badly that a drunken nightclub patron once tried to rip it off, thinking it was a mask. Neil, on the other hand, could pass for Tom Cruise from a certain angle but suffers from memory loss and occasional seizures. Identical genes, completely different expression. So all of those physical signs I walked you through in chapter 1? They are common expressions and generally indicative of certain genetic conditions, but those traits certainly don’t encompass the spectrum of all expressions of those genetic conditions. All of which prompts us to ask, why the difference in expression? Because our genes do not respond to our lives in a binary fashion. As we will come to learn, and contrary to Mendel’s findings, even if our inherited genes seem set in stone, the way they express themselves can be anything but. Whereas our inheritance may have been initially understood through a black-and-white Mendelian lens, today we’re starting to understand the power of seeing things in full and genetically expressive color. Which is why now, as physicians, we have a new challenge. Patients look to us to have the answers in clean, discrete categories: benign or malignant, treatable or terminal. The hard part of explaining genetics to patients is that everything we thought we knew is not always static or binary. Figuring out the best way to explain that to patients has become much more critical, since they need the best information possible to help them make some of the most important decisions of their lives. Because your behavior can and does dictate your genetic destiny.
A new perspective on how we can view the debate between “nature” and “nurture”. Our nature might set things in stone for us, but our daily environment from the time we are born can impact our lives in deep ways. Our behaviour and the choices we make can also affect our genes.
