Original photo by Jani Mahkonen/Photomosaic ® by Robert Silvers
On Westwood Boulevard in Los Angeles, just off the University of California campus, the street is jammed at lunchtime. The tones of all humanity flow past, faces from Santa Monica, Singapore, and Senegal, a stroboscopic stream of light and dark. Notwithstanding such contrasts in appearance, comparisons of our DNA show that human populations are continuous, one blending into the next, like the spectrum of our skin coloring. We all carry the same genes for skin color, but our genes responded differently to changes in solar intensity as bands of Homo sapiens migrated away from the unrelenting sun of the equator.
Still, it seems to be human nature to assign types to our fellow humans and then make judgments based on those types. Take this tall woman coming along the sidewalk and entering an Italian restaurant. Blond, but not California blond. In her early fifties, wearing a stylish suit and elegant shoes—a European. Physically she belongs to what one observer has called “the fair-skinned, fair-haired, gray-to-blue-eyed, long-limbed, relatively narrow-faced individuals that constitute a substantial portion of the population of Sweden, Denmark, Iceland, Norway, western Finland.” That is, the Nordic type.
Leena Peltonen is one of the world’s leading medical geneticists. In 1998 she was recruited from Helsinki University to become the founding chairwoman of the Department of Human Genetics at UCLA’s medical school. Trained as both a physician and a molecular biologist, she has discovered the genetic sources for many rare diseases, such as Marfan syndrome, a connective-tissue disorder. She has also found hereditary links to more prevalent conditions, such as multiple sclerosis, schizophrenia, osteoarthritis, and migraine.
The raw material for her investigations is DNA collected from people in Finland. Research by Peltonen and by her compatriots Juha Kere, Jukka Salonen, Albert de la Chapelle, and Jaakko Tuomilehto have made Finland into a sort of DNA laboratory for mankind. Now its scientists are detecting the heritable imprints of heart disease, diabetes, and asthma. The country’s contributions to medicine and genetics are far out of proportion to its size and population of 5 million.
As research subjects the Finns are an agreeable lot. When asked to participate in studies, Peltonen noted, three out of four will say yes. Access to clinical records is much easier in Finland than in the United States because the health care system is streamlined, centralized, and computerized. Foreign collaborators may tap into the resource as well. The U.S. National Institutes of Health has helped fund a dozen biomedical projects in Finland in the last decade.
But even more important for a geneticist, “the genealogies are already built,” said Peltonen, referring to the family pedigrees through which diseases can be tracked. “The setting of a limited number of ancestors and hundreds of years of isolation make Finns good study subjects.”
The genetic homogeneity, or sameness, of the Finns makes them easier to study than Californians, say, who hail from all over. To illustrate, Peltonen drew two pairs of human chromosomes, which were shaped something like swallowtail butterflies. Symbolizing two Finnish people, the four chromosomes were similar—banded horizontally with the same light-and-dark patterns. “These guys are the boring Finns,” she said with a trace of irony.
She drew another set of chromosomes representing a pair of Californians, and the banding patterns were quite dissimilar. The variance shows up better at the group level. Think of the human genome as a very large deck of cards, each card bearing a gene variant. The number of cards in the Finnish deck is fewer than the number of cards in the California deck because the Finns have fewer gene variants, or alleles, to play with. When scientists look for variants that cause diseases, they’re easier to spot in the Finnish deck because so many cards are similar.
The uniformity of Finns, created by several centuries of isolation and intermarriage, results in a large set of hereditary disorders. So far researchers have identified 39 such genetic diseases, many of them fatal, that crop up in the unlucky children of unwary carriers. Peltonen, who began her career as a pediatrician, said: “Genetic diseases transform the family. You know the children won’t get better.” Since switching her focus to research, Peltonen and her associates have identified 18 of the 39 endemic conditions.
Although far less common than cardiovascular ailments and much less of a drain on the health-care system, the hereditary disorders identified so far are so well known to Finns that they are part of the lore of the nation. The Finnish Disease Heritage has its own Web site.
“In school, children are taught that Finnish genes are slightly different,” Peltonen explained. “The textbooks and public press contain significant information about them. The search for the special selection of genes—actually they are alleles—is considered as a cause for pride.”
Clearly the Finns were an exceptional bunch, wedged at the top of the world between Sweden and Russia and speaking an odd tongue that is unrelated to other languages of Scandinavia. Does all of this make Finns a race?
“How do you genetically define race?” Peltonen answered, shaking her head. Race is used in biology for birds and animals—the term is tantamount to subspecies—but her studies had no use for it. Patterns of human variation can be linked to geography, and geographic ancestry can be linked to health risks. As a genetic explorer Peltonen has followed the movement of populations in history, knowing that genes had diversified during the moves, but in Finland as elsewhere only a tiny fraction of the alleles and health risks are distinctive. “Race may fade away once we understand all the variants,” she said. “But for diagnostic purposes it will be useful to know where your roots are. That’s the value of the Finnish Disease Heritage. The story of these genes helps us visualize how Finland was settled.”
By convention the Finns are white or Caucasian. Peltonen was probably the palest person on Westwood Boulevard. Nevertheless, in the 19th century she would have been classed with the Mongol race because anthropologists of that day lumped Finns with the Laplanders, or Sami, as they call themselves—the nomadic, faintly Asiatic people who roam the Scandinavian Arctic. That’s how arbitrary “race” can be.
Enlarge 118k Maps by Don Foley
A Family Affair Congenital nephrosis is a deadly kidney disease that crops up in Finland. To become ill, the patients (black) in the above group had to inherit a gene variant from both parents. When geneticists traced their pedigrees back nine generations, they found that the parents of the patients were related through three individuals. | Clusters of Vulnerability The red dots show where grandparents of patients with congenital nephrosis lived. Many were in areas of Finland that were only sparsely settled after 1550, which made intermarriage among relatives more likely. |
about the series This is the second of three articles exploring the relationship between race, genes, and medicine in three far-flung populations. Although race is a socially powerful concept, most geneticists think it has no foundation in biology. Modern DNA studies show that the world’s population is too homogeneous to divide into races. But while dismantling the barriers of race, scientists have uncovered patterns of genetic mutation and adaptation in human populations. As archaic bands of Homo sapiens left Africa and spread over the world’s continents, their DNA evolved. Geography has left faint marks on everyone’s DNA. Although the differences are small, they show up in the diseases that different groups get and how these groups respond to drugs. To measure these differences is not to resurrect race by another name but to emphasize the role of history in shaping medical legacies. Researchers seeking genetic explanations for health have to explore the events written in the record of DNA. In the first article (http://www.discover.com/issues/mar-05/features/human-study-thyself/) about African Americans, geneticist Georgia Dunston points out that Africa contains the richest DNA diversity because it is the site of humanity’s oldest genes. Africans and their recent descendants in America may harbor clues to fighting diseases that other populations don’t possess. The second and third articles follow gene hunters into more isolated and homogeneous gatherings of people—the Finns at the top of the European continent and the Native Americans in Arizona and New Mexico. In the future, doctors will examine the genetic portraits of individuals, not populations. The path to understanding how individuals fit into genetically similar populations would run straighter if not for the old stigmas of race. Two of the three groups in Discover’s series, being minorities, are wary of genetic studies that may stereotype them further. In the past, science was not an innocent bystander when people were separated into races. |
