Michael White says we need to follow up our success in reading our own genetic code by decoding a different one:
There are thousands of mutations that occur in the breast cancer-linked genes BRCA1 and BRCA2. Some of these cause breast or ovarian cancer, while others are harmless. When we design a genetic test for predisposition to breast cancer, we have to know which ones to test for. The same is true of almost any gene that plays a role in disease — you’ll find many mutations in that gene in the general population, only some of which cause health problems. So how do we know which mutations to worry about?
We start by using the genetic code. The genetic code, cracked by scientists in the 1960s, makes it surprisingly easy to “read” our DNA and understand how a particular mutation affects a gene. As genetic testing takes on a bigger role in predicting, diagnosing, and treating disease, we rely on this code to help us make sense of the data. Unfortunately, the genetic code applies to less than two percent of our DNA. In an effort to read the rest, researchers are trying to crack a new genetic code — and this next one is turning out to be much more difficult to solve than the first. In fact, scientists may have to give up the idea that we can use a “code” to “read” the rest of our DNA.
When scientists were working out the original genetic code in the 1950s and ’60s, all sorts of complicated schemes were proposed to explain how information is stored in our genes. The problem they were trying to solve was how a gene, made of DNA, codes the information to make a particular protein — an enzyme, a pump, a piece of cellular scaffolding, or some other critical component of the cell’s working machinery. They were looking for a code that would translate the four-letter DNA alphabet of genes into the 20-letter amino acid alphabet of proteins.
Thanks to its simplicity, the genetic code is a powerful tool in our hunt for mutations that cause disease. Unfortunately, it has also led to the genetic equivalent of a drunk looking for his lost keys under the lamppost. Researchers have put much of their effort into looking for disease mutations in those parts of our genomes that we can read with the genetic code — that is, parts that consist of canonical genes that code for proteins. But these genes make up less than two percent of our DNA; much more of our genetic function is outside of genes in the relatively uncharted “non-coding” portions. We have no idea how many disease-causing mutations are in that non-coding portion — for some types of mutations, it could be as high as 90 percent.