The row between Icelandic company deCODE Genetics and its opponents has been rekindled by an analysis of European DNA sequences.

Based in Reykjavik, deCODE has claimed that Icelanders are relatively genetically homogeneous, and that analysis of the population's sequence data and medical history should therefore aid the hunt for disease-related genes. To those ends, the Icelandic parliament granted deCODE exclusive access to the medical records of the country's inhabitants. Opponents such as lobby group Mannvernd object to the commercial use of Iceland's medical records.

The claims for Iceland's homogeneity made by deCODE are based on results published over the past few years. Researchers at the company and at the University of Oxford, UK, compared the sequences of mitochondrial DNA samples from about 400 Icelanders with those from other nationalities stored in various sequence databases (A. Helgason et al. Am. J. Hum. Genet. 66, 999–1016; 2000).

Einar Árnason, a geneticist at the University of Iceland in Reykjavik and a member of Mannvernd's board, now says that deCODE's researchers were misled by extensive errors in some of the databases they used in their analysis. He also questions a few of the assumptions behind the technique the company used to compare the sequences.

Árnason re-analysed available data, but avoided using databases. He compared mitochondrial DNA sequences generated by his research group and by deCODE, and compared them with data in research papers on 26 different European populations. His results suggest that several characteristics of the mitochondrial DNA sequences vary as much in Iceland as they do in the rest of Europe (E. Árnason Ann. Hum. Genet. 67, 5–16; 2003).

Scientists at deCODE do not dispute Árnason's sequence data, but say that he has misinterpreted them. The firm's chief executive, Kári Stefánsson, says that the database errors have only a “limited” effect on Iceland's position in the hierarchy of European genetic homogeneity. The company adds that Iceland's extensive genealogical data will aid the hunt for disease genes, whatever the genetic variation within the country's population proves to be.