When I see people in my office with VHL or other genetic disorders, and we go through tests and scans and plans for the next evaluation, at the end I always ask if there are any questions. Lately everyone has the same question: What's going to happen now that the human genome has been sequenced? So I thought that today I could give you some of my impressions of how the sequencing of the human genome will make a difference for medicine.

There are some gaps in the sequence, and some proofreadings and checks to do, but the consortium has announced that for all practical purposes the genome has been sequenced at least to some level. Although this is not a magical breakthrough, it's a major breakthrough, and it has happened very quickly since the researchers first decided that instead of simply finding genes one by one, there should be a concerted effort to sequence it all. It is hoped that this will move things forward faster. I'd like to give you some idea of the work remaining, and how I hope this will affect clinical care in the coming years.

Figure 1: Structure of a gene.

The gene for VHL is on the short arm of chromosome 3. We can't see that gene under the microscope, it's too small. So let's look at a chromosome (see Figure 1), and dissect what's really in it, so that you have some understanding of what the scientists have been doing and where it is leading us.

To understand how this is all done, imagine these coils being unraveled into strings, and the molecules spelling out words. The molecules comprise a code of letters, not just eight or ten letters long, but thousands or tens of thousands of letters long. In spite of the very long length of the "word", each of those base pairs are made up of only four different letters: AGCT, which stand for adenine, guanine, cytosine, and thymine, the four bases on DNA. When you sequence a gene you learn the exact sequence of these letters. Obviously it took very sophisticated science to sequence the entire genome. But when you're done, now what do you do with it? Does it automatically tell us everything about how the genome functions? Very definitely not.

The next step is called "Annotating the Genome." This important job is to take this very long and complicated sequence, which is about three billion letters long, and start to make sense out of it. Here's one example, a very simplistic example of what the scientists have to do. Try reading the sentence:

T heca thidun dert hec hair.

(Yes, it's in English). If we know where to start and stop each word, we can make better sense of it:

The cat hid under the chair.

All we had to do is move the spaces. But in this example, it was relatively easy. We know what a cat is, and a chair, but what if we didn't know? What if we moved the spaces and got a sentence like this one?

The snurb hid under the fump.

It may look like a sentence, but we still don't know what a "snurb" is, or a "fump".

The new buzzword for this annotation process is proteomics. We're going to move from genomics to the protein that the genome encodes.

The gene in the cell unravels, and the DNA code makes a messenger RNA code, and in most cases this makes a protein. If all goes well, we get a normal healthy protein. So we talk about the VHL protein, and the other proteins that interact with the VHL protein. If the process does not go well and the genetic material is altered, then we get an altered protein, and it may not work. Our job now is to understand what alterations occur in the proteins so that we understand what is really causing the disease and why things are not working as they should.

This is a diagram (see Figure 2) of the VHL protein and how it acts with hypoxia inducible factor (HIF). If the VHL protein isn't working right it affects some other proteins and the cell begins to think it isn't getting enough oxygen. So it starts to make some new blood vessels to bring more oxygen, and vascular tumors begin to form. The VHL protein interacts with a number of other proteins and enzymes, each of which also has to be normal for this process to work.

Figure 2: pVHL attracts and degrades HIF-1 molecules thus regulating the levels of HIF-1 in the cell. Nature 399 (1999) 203-4.

If we know all this, if we know what the VHL protein is, why do we need the entire human genome? We have learned a great deal about the VHL gene from the researchers who have presented for the past two days of meetings in Rochester. But we know only 5-10% of human genes, and there are estimated to be somewhere between 30,000 and 100,000 human genes. Among those other 90-95% of genes that we don't yet understand, I can almost guarantee you that there are some other genes that will impact the function of the VHL protein. As we understand more about those influences on VHL, we are going to learn more and more about this disorder. We heard about one just yesterday from Dr. Maxwell (see inset). As we learn more about what the rest of the genome is doing, it will make a tremendous difference for VHL.

To make this more clear, and to help you understand why better understanding can lead to better treatment, I want to provide a classic example for which Goldstein and Brown won a Nobel prize some years ago in medicine. It has become a classic example, and it's another disorder that we've all heard of: arteriosclerosis, or hardening of the arteries. We've all heard that elevated cholesterol levels is one of the factors that can predispose us to hardening of the arteries. These investigators found that there was a LDL receptor that has to be formed appropriately in the cell, similar to the little notch that HIF-1 fits into in Figure 2, but shaped more like a little pit (see Figure 3). This LDL receptor protein has to find its way to the cell membrane, it has to enter the little pit. If this process worked well, the receptor would bring cholesterol into the cell as a particle called LDL cholesterol, and process it.

However, if the LDL receptor wasn't working well and didn't bring the cholesterol into the cell, the cell got confused and said "We don't have enough cholesterol, we'd better make some more!" (Does that sound familiar? It's like "We don't have enough oxygen, we'd better build some blood vessels.") So it's the same kind of problem as in VHL -- there are some abnormal signals going on because of a lack of the appropriate feedback.

Figure 3: LDL receptor as presented by Goldstein and Brown, Nature.

So one could say that if we were going to treat this disorder, maybe we'd better find a way to get that protein back into the cell, or get it into the cell so that it gets into the pit, or make sure that the process works right. Yes, that would have been one approach. But if that were the only approach, we'd still be looking for those answers, and we still wouldn't have any treatments for this disorder. But instead the investigators widened the scope of their inquiry. They tried to find out what else was going on -- what other proteins are active in this process? And they found some of these other proteins, such as the enzyme HMG CoA Reductase. Next, researchers found some medications, some of the statin drugs, that turn off that confused enzyme that was making more cholesterol that was clogging up the arteries. These medications essentially tell that enzyme to stop making cholesterol . This has proven to effectively lower many people's cholesterol into a range where they are no longer at risk for arteriosclerosis.

So the more you understand, the broader you widen the circle of understanding of all these proteins and how they interact, it gives us more and more treatment options. I do believe that the same kind of thing will happen with VHL and other genetic disorders. The more we know, the better chance we have that somewhere along the pathway, along the chain of events that occurs during this process in the cell, we will find something that will be effective. Maybe it won't be effective for each complication, but we will chip away at the problem and will find medications that will be effective for some of the challenges in VHL.

Another thing that is important to remember is that a particular gene can function a little bit differently in different cells. So a gene that works one way in a brain cell might have a different role in a pancreas cell. You can readily see how this relates to VHL. When that gene is not working right in the brain, we get a hemangioblastoma which is not a malignant tumor, and when it's not working right in the kidney we know that it can cause a malignant tumor. We also know that malignant tumors generally are made up not just one abnormality. There are many different genetic changes that contribute to the development of the cancer. For someone in the general population it takes even more events to accumulate before that person gets a malignancy. If we understand more about how all the genes work, we might be able to find out why the same VHL gene in the brain does not cause malignancy, and take that factor and somehow use it to treat the kidneys and keep the kidney tumors benign and non-cancerous. Wouldn't that be a wonderful breakthrough?

Here's another example. We really don't understand why a small VHL hemangioblastoma may sometimes sit quietly in the cerebellum for years, but then one day it begins to grow. It becomes a bigger lesion, perhaps with a cyst. If we can begin to understand through the Human Genome Project what proteins are being expressed and what genes are being turned on, and why these tumors are suddenly being "activated", maybe we could find a marker, something that might be identified through a blood test, that would indicate when a tumor is going to start to act up. Perhaps then we would know when to treat it before it grows. Or maybe if we could find such a marker, we might be able to devise a medication that would halt that next step and keep the tumor quiet and prevent it from growing.

I am hopeful that in the next decade these advances will move the whole field of genetics forward. Our understanding of genes, of the proteins they make, and how they interact, will be like a snowball. It starts very small, but as you roll it along the ground, it gets bigger and bigger, faster and faster.

Similarly, our accumulated knowledge about the VHL protein and its associated proteins and enzymes will eventually lead to some major breakthroughs in the new millennium for treatment of VHL disease.

1. Based on her talk at the VHL Symposium, 21 July 2000

Dozens of New Genes in Tumor Blood Vessels

In the August issue of the journal Science, Scientists at Genome Molecular Oncology in Framingham, Massachusetts, in conjunction with researchers at Johns Hopkins University in Baltimore have identified dozens of new genes involved in angiogenesis, the building of blood vessels. "This gives us a whole bunch more of potential targets for cancer therapy," Brad St. Croix of Johns Hopkins told Reuters, "but it is going to take several years to figure out which of these are going to be useful." This underscores Dr. Michels’ point above that in broadening our knowledge of genes and how they interact we will discover many new possibilities for impacting tumor growth.

Reported August 18, 2000, by Reuters and CNN.

As printed in the VHL Family Forum 8:3, September 2000. For permission to reprint, please contact VHL Family Alliance, editor@vhl.org. Further information is available from the VHL Family Alliance, info@vhl.org.