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Spring 1999

Gene Hunter
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One of the diseases unique to Finland is a children's brain disorder called neuronal ceroid lipofuscinosis, or NCL. To get the disease, a child must inherit a mutated gene from each parent. Though it strikes only about 50 families a year, NCL is especially cruel. Children with the disease appear normal at birth, but by the age of 1 they begin to go blind. Eventually, they lose their brain function and die a slow, brutal death. Because no one knew what caused the disorder, there was no way to prenatally diagnose children with NCL.

In 1988, Peltonen was contacted by a neurologist who had been treating these children. "She came to me and said, 'Something must be done; this is such a terrible disease. We have to solve the basis of this. We have nothing to offer parents. It's very frustrating to them.' "Peltonen approached the parents of the affected children, and each agreed to participate in a project to find the genetic cause of the disease. After collecting blood samples from the healthy parents and their sick children, Peltonen set out to scour their DNA for genetic markers - landmarks she could use to narrow the location of the gene. Meanwhile, she also searched their genealogical histories to try to find the origin of the disease.

At the time, the human genome was not well-known, so hunting for genes was an agonizingly slow process. As Palotie explains: "This was very primitive compared to today's technology. You would run these markers around the genome, then narrow the region where the defective gene was. If some of these markers are always similar in affected individuals, by having 400 markers from all places of your genome, you usually hit with a few of them. Then you try to pull out more of these markers for areas that are similar between these patients. Then you get the statistical confidence that this is the place, but you're still far away. In the end you have to combine various mapping techniques."

It took Peltonen and another scientist seven years to find the gene. In January 1995, they traced the mutation to a site on Chromosome 1. When Peltonen learned what the gene actually did, she was amazed: Its function is to make a protein that removes fatty acids, or lipids, from the cells. If this process is disrupted - as it is in babies with NCL - the brain cells die. This finding, it turns out, was significant not just for NCL, but for understanding the molecular process behind other brain disorders. "This is so fascinating," says Peltonen, "because we'd have never thought that something involved in the lipid metabolism would be so dramatic for brain cells. This has now become obvious in many other diseases. So in many ways it opened a new concept of how crucial this lipid modification of the protein is for brain cells.

"I think this is a beautiful story," she adds, "how a globally uninteresting disease in a small corner of the world opened a new field of research. I think it's an educational story. You can't always bet which project produces the most valuable biological information."

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