Current clinical criteria for Lynch syndrome are not sensitive enough to identify MSH6 mutation carriers.

BACKGROUND: Reported prevalence, penetrance and expression of deleterious mutations in the mismatch repair (MMR) genes, MLH1, MSH2, MSH6 and PMS2, may reflect differences in the clinical criteria used to select families for DNA testing. The authors have previously reported that clinical criteria are not sensitive enough to identify MMR mutation carriers among incident colorectal cancer cases. OBJECTIVE: To describe the sensitivity of the criteria when applied to families with a demonstrated MMR mutation. METHODS: Families with an aggregation of colorectal cancers were examined for deleterious MMR mutations according to the Mallorca guidelines. All families with a detected MMR mutation as of November 2009 were reclassified according to the Amsterdam and Bethesda criteria. RESULTS: Sixty-nine different DNA variants were identified in a total of 129 families. The original Amsterdam clinical criteria were met by 38%, 12%, 78% and 25% of families with mutations in MSH2, MSH6, MLH1 and PMS2, respectively. Corresponding numbers for the revised Amsterdam criteria were 62%, 48%, 87% and 38%. Similarly, each of the four clinical Bethesda criteria had low sensitivity for identifying MSH6 or PMS2 mutations. CONCLUSION: Amsterdam criteria and each of the Bethesda criteria were inadequate for identifying MSH6 mutation-carrying kindreds. MSH6 mutations may be more common than currently assumed, and the penetrance/expression of MSH6 mutations, as derived from families meeting current clinical criteria, may be misleading. To increase detection rate of MMR mutation carriers, all cancers in the Lynch syndrome tumour spectrum should be subjected to immunohistochemical analysis and/or analysis for microsatellite instability.

Identification of Friend murine retrovirus-infected immune cells and studies of the effects of sex and steroid hormones in the early phase of infection.

Male mice are more susceptible than female mice to the murine retrovirus FIS-2. We previously reported that sex-related factors influence early virus replication via mechanisms involving a glucocorticoid response element (GRE) in the long terminal repeat (LTR) enhancer region. In the present study, we investigated further the influence of sex and steroid hormones on early murine retrovirus dissemination and immune functions. In male mice we found a correlation between an early expansion of the CD8+ cell subset and rapid infection of lymphocytes, including CD8+ cells. Virus load in blood declined faster in females than in males, and the postpeak declines coincided with more rapidly generation of antibodies against virus-positive cells. Moreover, female-derived T-cells responded better to in vitro mitogen stimuli than male-derived T-cells. Physiological concentrations of progesterone and dexamethasone induced a dose-dependent inhibition of T-cell proliferation. Administration of progestin in vivo did not modify early FIS-2 production in female mice. Male castrated mice, who were notably less involved in aggressive behaviour and fighting compared to male control mice, had a significant delay of virus dissemination. We suggest that testosterone-dependent aggression, with successive enhanced stress hormone levels, may influence both FIS-2 replication and immune responses during infection.

Early dissemination rates of Friend murine leukaemia virus variants correlate with late pathogenesis.

FIS-2, a less oncogenic, immunosuppressive variant of the Friend murine leukaemia virus (F-MuLV), was used to explore whether the differences in biological features were related to early virus dissemination rates or sites of replication. We found that erythroblasts were the primary target cells for both F-MuLV and FIS-2, while B- and T-cells were infected later in the infection. Although FIS-2 replicated to similar titres as F-MuLV, we observed a delay in peak viraemia titre and in the number of virus-positive cells in bone marrow and spleen. Studies including the chimeric viruses RE3 (FIS-2LTR with a F-MuLV background) and RE4 (F-MuLV LTR with a FIS-2 background) indicated that the delay in dissemination was due to mutations in FIS-2 LTR. The kinetics for early virus replication correlated with previously reported mean latency time for virus-induced erythroleukaemia in mice inoculated as newborns and with the onset of immunosuppression in adult mice. In addition, F-MuLV-induced late immunosuppression coincided with signs of erythroleukaemia and persistent viraemia. FIS-2 induced a more moderate late immunosuppression without persistent viraemia or signs of erythroleukaemia. Overall, our findings indicated that early viral replication is a prognostic factor in murine retrovirus-induced pathogenesis.

A glucocorticoid response element in the LTR U3 region of Friend murine leukaemia virus variant FIS-2 enhances virus production in vitro and is a major determinant for sex differences in susceptibility to FIS-2 infection in vivo.

The nucleotide sequence of the Friend murine leukaemia virus variant FIS-2 LTR has high identity with the closely related Friend murine leukaemia virus (F-MuLV) LTR, except for the deletion of one direct repeat, a few point mutations and the generation of a glucocorticoid response element (GRE) in the U3 region. The GRE can mediate gene induction by glucocorticoids, mineral corticoids, progesterone and androgens, and it has been shown that incorporation of a GRE(s) within the LTR can increase the transcriptional activity of retroviral enhancers. We have previously reported an increased early virus replication in male mice compared with female mice when infected with a virus containing the FIS-2 LTR and have proposed that the GRE might contribute to this sex difference. In the present study, we introduced a single point mutation in the GRE and performed comparative studies in NIH 3T3 cells and in young adult male and female NMRI mice. We found that significantly more virus was produced from NIH 3T3 cells infected with wt FIS-2 than from cells infected with the FIS-2 GRE mutant and that this difference was further augmented by glucocorticoids. The glucocorticoid antagonist RU486 inhibited virus production in a dose-dependent manner. The wt FIS-2 disseminated significantly faster than the FIS-2 GRE mutant in both male and female mice. There was no significant difference in the dissemination rate between male and female mice infected with the FIS-2 GRE mutant. Hence, the GRE in the FIS-2 LTR is one determinant of the significant sex difference in susceptibility to FIS-2 infection.

Gender-related differences in susceptibility, early virus dissemination and immunosuppression in mice infected with Friend murine leukaemia virus variant FIS-2.

An emerging amount of data indicates a correlation between gender-related factors and regulation of virus infection and supports what is known in clinical circles, that these topics are of great importance in many infectious diseases. In the present study we found that young adult NMRI male mice are more susceptible to infection by a variant of Friend murine leukaemia virus, FIS-2, than are female mice. We observed that the level of virus in serum, bone marrow and spleen was initially higher in male mice. Male mice were also more susceptible to FIS-2-induced immunosuppression. These results indicate a more efficient virus replication and dissemination in male mice. Studies with recombinant viruses between FIS-2 and the prototype Friend murine leukaemia virus revealed that FIS-2 LTR is one major factor contributing to the observed gender differences. A possible sex hormone influence on FIS-2 transcription due to the presence of a glucocorticoid response element in FIS-2 LTR is discussed.