John M. Coffin1 and Jonathan P. Stoye2:
1Department of Molecular Microbiology, Tufts University, Boston, MA 02111, USA
2National Institute for Medical Research, Mill Hill, London NW7 1AA, UK
Two characteristics of XMRV are particularly noteworthy. One is the near genetic identity of isolates from different diseases and from individuals in different parts of the United States.
The two most distantly related genomes sequenced to date differ by fewer than 30 out of about 8000 nucleotides.
Thus, all of the XMRV isolates are more similar to each other than are the genomes isolated from any one individual infected with the human immunodeficiency virus.
In this respect, XMRV more closely resembles human T cell lymphotropic viruses (HTLVs) isolated from the same geographic region (11).
As in the case with HTLV, the lack of diversity implies that XMRV recently descended from a common ancestor, and that the number of replication cycles within one infected individual is limited.
Another notable feature of XMRV is that the frequency of infection in nondiseased controls is remarkably high—about 4% in both normal individuals from the same geographic region as infected patients with chronic fatigue syndrome, and in nonmalignant prostates. If these figures are borne out in larger studies, it would mean that perhaps 10 million people in the United Sates and hundreds of millions worldwide are infected with a virus whose pathogenic potential for humans is still unknown.
However, it is clear that closely related viruses cause a variety of major diseases, including cancer, in many other mammals.
Further study may reveal XMRV as a cause of more than one well-known “old” disease, with potentially important implications for diagnosis, prevention, and therapy.Read more>>