The rise and fall of XMRV

Due to the relatively recent emergence of the human T-lymphotropic and the human immunodeficiency viruses, enthusiasm for the identification of novel viruses, especially retroviruses, with pathogenic potential in humans, remains high. Novel technologies are now available with the ability to search for unknown viruses, such as gene arrays and new generation sequencing of tissue and other samples. In 2006, chip technology identified a novel retrovirus in human prostate cancer (PCa) tissue samples. Due to close homology to a mouse retrovirus, the virus was named xenotropic murine leukaemia virus-related virus (XMRV). Ever since the initial disease association with PCa, XMRV has stirred a lot of attention and concern worldwide for the medical community, public health officials and in particular global transfusion services. Public response, in this new era of electronic communication and advocacy was rapid, wide and unprecedented. In this review, we outline the course of biomedical research efforts that were put forward internationally in the process of determining the risk to the human population, the response of the blood banking community and review the current state of knowledge of xenotropic murine retroviruses. Although XMRV is no longer regarded as an infection of humans, a lesson was learnt in modern virology that holds deeper implications for biomedical research, particularly stem cell generation and transplantation practices.

Chronic fatigue syndrome: 3 cases and a discussion of the natural history of attention-deficit/hyperactivity disorder

Fatigue is commonly reported in the primary care setting; however, its cause is often unclear. This article presents 3 cases involving patients with chronic fatigue syndrome who responded poorly to treatment. After clinical evaluation, all patients were found to meet criteria for attention-deficit/hyperactivity disorder (ADHD) and underwent a standard regimen of a psychostimulant medication. After treatment with psychostimulants, the 3 patients reported improved symptoms of fatigue and pain, and cognitive and core ADHD symptoms. These cases suggest that ADHD and chronic fatigue syndrome (and possibly fibromyalgia) share a common underlying mechanism. This article presents a model suggesting that over time, ADHD (predominantly inattentive type) develops into a syndrome of chronic fatigue and pain. These cases indicate that fatigue may be an important presenting symptom of adult ADHD. These cases also suggest the need for additional research to determine the prevalence of ADHD in patients who present with fatigue, and, in those meeting criteria for ADHD, the responsiveness of fatigue to psychostimulant treatment.

The tale of xenotropic murine leukemia virus-related virus

In 2006, a new retrovirus was isolated from prostate cancer patient tissue. Named xenotropic murine leukemia virus-related virus (XMRV), this was potentially the third class of retrovirus to be pathogenic in humans. XMRV made a more dramatic impact on the wider scientific community, and indeed the media, in 2009 when it was reported to be present in a remarkably high proportion of patients with chronic fatigue syndrome as well as a significant, albeit smaller, proportion of healthy controls. The apparent strong link to disease and the fear of a previously unknown retrovirus circulating in the general population lead to a surge in XMRV research. Subsequent studies failed to find an association of XMRV with disease and, in most cases, failed to find the virus in human samples. In 2011, the case against XMRV and human disease strengthened, ending with several decisive publications revealing the origin of the virus and demonstrating contamination of samples. In this review, we outline the passage of research on XMRV and its potential association with disease from its isolation to the present day, where we find ourselves at the end of a turbulent story.

Evidence and controversies on the role of XMRV in prostate cancer and chronic fatigue syndrome

The recent discovery of xenotropic murine leukaemia virus-related virus (XMRV) in prostate cancer tissues and in the blood of individuals suffering from chronic fatigue syndrome has attracted considerable interest. However, the relevance and significance of XMRV to human disease remain unclear, since the association has not been confirmed in other studies. XMRV is the first gammaretrovirus to be found in humans. XMRV and murine leukaemia viruses share similar structures and genomic organisation. Human restriction factors such as APOBEC3 or tetherin inhibit XMRV replication. Although XMRV induces low rates of transformation in cell culture, it might be able to induce cancer by low-frequency insertional activation of oncogenes or through the generation of highly active transforming viruses. A preference for regulatory regions of transcriptional active genes has been observed after a genomic-wide analysis of XMRV integration sites. Genes related to carcinogenesis and androgen signalling have been identified in the vicinity of integration sites. The XMRV genome contains a glucocorticoid responsive element, and androgens could modulate viral replication in the prostate. Evidence supporting the involvement of XMRV in chronic fatigue syndrome is still very weak, and needs further confirmation and validation. Currently approved anti-retroviral drugs such as zidovudine, tenofovir and raltegravir are efficient inhibitors of XMRV replication in vitro. These drugs might be useful to treat XMRV infection in humans. The identification of XMRV has potentially serious health implications for the implementation of novel techniques including gene therapy or xenotransplantation, while raising concerns on the need for screening donated blood to prevent transmission through transfusion.