Differences in animal housing facilities and diet may affect study outcomes-a plea for inclusion of such information in publications.

No journal would accept a manuscript about microbiology or tissue culture without information on the medium or growth conditions used. However, manuscripts about transgenic animals infrequently mention the animal housing facilities and almost never mention the diet used. Since the publication volume of manuscripts dealing with transgenics increases dramatically and as discussed below there is emerging evidence that the housing facilities and the diet may have an effect on the phenotypes observed we urge inclusion of this information in manuscripts dealing with transgenics. It is not infrequent for researchers in different laboratories and sometimes even within a single laboratory to observe different phenotypes on the same transgenic animals. Here, we attempt to address the issue of the life span of the same knockout mice being significantly different from one study to the next. To exemplify this phenomenon, we compiled data for Atm deficient mice used as animal model for the cancer-prone disorder ataxia telangiectasia (AT). Previous studies showed that Atm −/− mice die of thymic lymphomas between ages of 2 and 5 months [1–3]. In our study, at 5 months, 94% of Atm −/− mice were alive and 50% still lived after 12.5 months (unpublished data). During our ongoing study other investigators also reported that survival of Atm deficient mice is much longer than in earlier studies. For example, 50% mice were alive at 7 [4–6] or 10 months of age [7] and 40% Atm −/− mice still lived after 18 months [4]. Different animal backgrounds may often account for mixed study outcome. However, survival studies on Atm deficient mice have failed to show any differences between inbred and mixed backgrounds. Median survival of 129SvEv background mice varied from 2.5 to 7.5 months [6,8–10] and the median survival of 129SvEv:C57BL/6J mice was 4–10 months [4,5,7,10] (Table 1). Thus, there seem to be other factors affecting tumor onset and mouse survival. As far back as the 1960s researchers observed that improved environmental conditions during the 1960s as compared to the 1940s and 1950s increased the lifespan of inbred mice [11,12]. Reduced levels of pathogens and improved diets were considered important factors contributing to prolonged lifespan.