Will studies of our genes change medicine and improve our lives?

In yesterday’s column, a reader asked whether she should be tested for genes linked to Alzheimer’s disease. Today, I thought I’d give you my view on the larger question: Will studies of our genes change the practice of medicine and improve our lives?

My answer: During my career, progress in human genetics has been greater than virtually anyone imagined. However, human genetics also has turned out to be much more complicated than people imagined. As a result, we have not moved as rapidly as we had hoped in changing medical practice.

I graduated from medical school in the late 1960s. We knew what human genes were made of — DNA — and we were beginning to understand how genes work. We had even identified a handful of genes that were linked to specific diseases. We assumed that disease resulted from an abnormality in the structure of a gene.

If I had asked any biologist on the day I graduated, “Will we ever know how many genes we have, and the exact structure of each gene?” I’ll bet the answer would have been: “Not in my lifetime, or my children’s lifetime.”

They would have been wrong. Today we do know those answers. Indeed, some diseases are caused by an abnormality in the structure of genes. In fact, sometimes it is very simple: one particular change at one particular spot in just one particular gene leads to a specific disease. Sickle cell anemia is an example.

Unfortunately, with most diseases it’s far from that simple. The first complexity: Most diseases are influenced by the structure of multiple genes, not just one. Examples are diabetes and high blood pressure.

The second complexity: Many diseases are explained not by an abnormal gene structure, but by whether genes are properly turned on or off. Most cancers fall into this category.

What do I mean by that? Every cell in our body has the same set of genes. Yet, a cell in our eye that sees light is different from a cell in our stomach that makes acid. Why? Because different genes are turned on in each type of cell.

Similarly, if a gene with a normal structure is not properly turned on or off, a cell can malfunction — it can become diseased. Whether a gene is turned on properly is proving to be a more important cause of disease than we once imagined.

The third complexity: We have 10 times as many bacterial cells living on and inside our body as there are cells in our body. And the genes of those bacterial cells — not just the genes in our own cells — affect our health, perhaps profoundly. Bacterial genes may play an important role in obesity, heart disease, even autism spectrum disorders.

So, am I discouraged about whether progress in human genetics will improve our lives? To the contrary, I’m more convinced than ever that it will. We are already seeing earlier and more accurate diagnosis and prognosis and improved treatments.

And just as 40 years ago very few would have imagined what has been achieved by 2014, very few today can imagine what will be achieved in the next 40 years.