Short Communication: RNASEL Alleles and Susceptibility to Infection by Human Retroviruses and Hepatitis Viruses

R estriction factors comprise an important layer of host defenses against viral infections. RNASEL is a part of the interferon-mediated immune response to some viruses, blocking infections through cleavage of viral and cellular single-stranded RNA. ^{1 –4} The RNASEL gene variant R462Q has been suggested to increase the susceptibility for prostate cancer (PrCa) ^{5 –7} although it can be found in only 13% of PrCa patients. ⁸ Hypothetically, R462Q could increase the risk of infection by some viral agents, such as the xenotropic murine leukemia virus-related gammaretrovirus (XMRV). ⁹ The discovery of XMRV and its involvement in PrCa ¹⁰ and chronic fatigue syndrome (CFS) ¹¹ has generated enormous controversy with reports of conflicting results by different investigators. ^{12 –17} Information about the role of RNASEL variants in the susceptibility to other viral infections or putative viral-related conditions is scarce.

Plasma and peripheral blood mononuclear cells (PBMCs) were collected from 410 individuals, classified as follows: 71 with HIV-1 infection, 18 with HTLV-1 infection, 27 with chronic hepatitis C, 15 with chronic hepatitis B, 67 with PrCa, 107 with CFS, and 105 healthy blood donors. All individuals chronically infected with human retroviruses or hepatitis viruses were on regular follow-up at Hospital Carlos III, a reference infectious diseases clinic located in Madrid. Samples from patients with PrCa were obtained at one urology clinic in Madrid. Specimens belonging to patients with CFS were obtained from the National DNA Repository located in Salamanca, although a subset was collected at Hospital Carlos III. Finally, samples from healthy blood donors were provided by blood banks located in Madrid.

DNA was isolated from PBMCs. All patients were genotyped for RNASEL R462Q variants (rs486907) using Taqman probes. A 7000 real-time PCR system (Applied Biosystems, Foster City, CA) was used for amplification. XMRV gag and env sequences were tested using sensitive nested-PCR protocols. Finally, XMRV antibodies were examined using a prototype ARCHITECT XMRV p15 and gp70 research assay (Abbott Diagnostics, Abbott Park, IL).

The majority of individuals with CFS were female (86.1%) with a mean age of 46 years. The most common symptoms of CFS patients were recurrent headache (82%), nonrestorative sleep (98%), chronic pain (79%), muscle weakness (93%), and extreme exhaustion lasting more than 24 h after physical exercise (98%). All patients with PrCa were white with a mean age of 63.7 years. The mean prostate serum antigen titer was 12.5 (1.8–199) ng/ml at the time of diagnosis. The tumor stage was T1 in 84.6%, T2 in 9.6%, T3 in 3.8%, and T4 in 1.9%.

The allelic frequency at the R462Q in the whole study population was 139 (33.7%), 204 (49.9%), and 67 (16.3%) for RR, RQ, and QQ, respectively. There were no significant differences comparing blood donors (27%, 54%, and 19%, respectively), HIV-1 infection (37%, 44%, and 20%, respectively), chronic hepatitis C (33%, 52%, and 15%, respectively), PrCa (25%, 60%, and 15%, respectively), and CFS patients (35%, 51%, and 14%, respectively). However, patients infected with HTLV-1 or hepatitis B virus (HBV) showed a significantly lower rate of RQ and QQ variants than the rest (p=0.01). The rate of the RR variant in HTLV-1 and HBV carriers was 67% and 61%, respectively (Table 1).

A total of 14 (3.6%) individuals were reactive for XMRV antibodies, although only one of them was positive for XMRV gag sequences. A trend toward a higher rate of XMRV seroreactivity was found in individuals with the RR genotype compared to the rest (6.1% vs. 2.3%, respectively; p=0.083). The single patient positive for XMRV gag sequences had PrCa and harbored RR at the RNASEL gene. It is noteworthy that Casey et al. ¹⁶ estimated that individuals with the common missense mutation R462Q in homozygosis had a more than 2-fold increased risk of PrCa. We found an overall low rate of the QQ variant in all different study groups. These results are consistent with data reported by others ^{18 –20} who failed to show a significant association between codon 462 variants and the risk of PrCa in whites. Likewise, other studies have failed to show any linkage between PrCa, XMRV, and R462Q polymorphisms at the RNASEL gene. ^12,14,21

Despite the limited size of the population examined with HTLV-1 infection or chronic hepatitis B, nearly two-thirds of these patients harbored codon 462 RR homozygosis. In contrast, it was found in only around a third of the rest of individuals tested in our study. Further studies testing a larger number of patients with these conditions will clarify whether RNASEL variants may influence the susceptibility to HTLV-1 infection and/or chronic hepatitis B.

In summary, we did not find any evidence of an association between RNASEL polymorphisms and the risk of infection with human retroviruses, hepatitis viruses, and/or conditions potentially linked to XMRV infection, such as CSF or PrCa. Thus, the evidence for any influence of R462Q variants on human viral diseases is limited if there is any at all.