XMRV INFORMATION / DISCLAIMER
XMRV and disease
XMRV (xenotropic murine leukemia virus-related virus) was first isolated in prostate cancer tissue of men with a specific defect of the anti-viral gene RNase L. In 2009, a Science paper from Lombardi et al. reported detection of XMRV in 67% of patients with Chronic Fatigue Syndrome. Recently, another study by Lo et al., published in the PNAS, reported that 86,5% of CFS patients (32 of 37 samples tested) presented murine leukemia virus (MLV)-related sequences in their PBMC DNA.
Other research studies, however, failed to detect XMRV in samples from CFS patients. More research is needed to confirm the implication of XMRV and/or MLVs in CFS and other diseases. Some studies suggest that the virus could be present in 4 to 14% of the general population.
As the test has only recently been introduced at RED laboratories, we do not have accumulated enough data to support any claim regarding XMRV prevalence and association with disease.
Tests currently offered at RED Laboratories
RED Laboratories has licensed the proprietary XMRV test from WP Biotechnologies, a wholly owned subsidiary of the Whittemore Peterson Institute. We use the co-culture procedure, where the sample to be tested is put in contact with an infection-sensitive cell line. XMRV is allowed to replicate in the cells for several days, resulting in significant amplification of viral titers. The amplified virus can then more easily be detected by PCR or Western Blot. This procedure is more sensitive than direct PCR.
In the future a serology test will be available, which may provide more information regarding the stage of infection and may be able to detect the presence of latent viruses that could not be detected by the co-culture technique.
Samples required for analysis, pricing
To perform the co-culture assay we ask 3 x 8 ml whole blood in Na-heparin tubes, 1 x 2 ml yellow cap tube and 1 x 2 ml whole blood in EDTA tube. Specimens must be received within 48 hours at room temperature.
Cost of this test is 340 €.
Cost of serology testing will be communicated as soon as the test is available.
Interpretation of results
Negative results
Co-culture technique is very sensitive but like any other clinical assay, has a detection limit. The virus is typically present at very low-copy numbers, viral titers may fluctuate and could be below the limit of detection at the time your sample is tested.
Currently little is known regarding the life cycle and tropism of XMRV. The virus may be present in some body tissues but not detectable in the blood. Also, detection by the co-culture assay depends on the capacity of the virus to infect the target cell line. The virus may be present in a non-infectious state, in which case the co-culture procedure will yield a negative result.
Therefore, getting a negative result doesn’t definitely mean that you are not infected.
You may consider re-testing when the serology test will be available, as serology may be able to detect presence of latent, non-infectious viruses.
Positive results
Only physicians can do test interpretation, define treatment option, and answer questions regarding transmissibility and health implications.
RED Laboratories does not make any claims regarding the biological significance, and medical implications, of a positive or negative result. A better understanding of XMRV biology is necessary before we can evaluate with certainty the sensitivity and specificity of XMRV testing procedures.