A host of rare genetic diseases that are more common in Finland than in other European countries may have arisen because Finnish people descended from a small band of ancestors some 4000 years ago, scientists report in the 15 October Proceedings of the National Academy of Sciences.

Finns tend to suffer from a different set of genetic diseases than do most other Europeans. For instance, Finns rarely develop cystic fibrosis or other inherited disorders that are relatively common among other Europeans, but they are prone to some 30 other genetic disorders, including aspartylglucosaminuria (AGU), a condition that arises from a defective enzyme. AGU afflicts some 150 Finns, but only 30 others in the rest of the world.

This pattern of disease susceptibility suggests that Finns ancestral gene pool was small and was cut off early on from the rest of Europes. But despite such tantalizing signs of a genetic bottleneck, "until now there had been no clear genetic evidence of reduced genetic variability," says lead author Svante Pääbo, a geneticist at the University of Munich in Germany.

Pääbo and his colleagues now have that evidence. Sampling DNA from 54 Finns, Pääbos team found that Finns have much less genetic variation than other Europeans do in three small regions of the Y chromosome, which is found only in males. In addition, Finns have reduced variability in DNA from mitochondria, subcellular energy-producing machines inherited from the mother. Tracking genetic similarities in both the Y chromosome and mitochondrial DNA gives a good thumbnail sketch of "the whole [genetic] picture," Pääbo says.

The findings "more firmly document" a Finnish population bottleneck, says Markku Linnoila, a psychiatrist at the National Institute on Alcohol Abuse and Alcoholism. Pääbo says he will next try to backtrack through time to determine how many original Finns there were.