ATRX encodes a novel member of the SNF2 family of proteins: mutations point to a common mechanism underlying the ATR-X syndrome

It was shown recently that mutations of the ATRX gene give rise to a severe, X-linked form of syndromal mental retardation associated with alpha thalassaemia (ATR-X syndrome). In this study, we have characterised the full-length cDNA and predicted structure of the ATRX protein. Comparative analysis shows that it is an entirely new member of the SNF2 subgroup of a superfamily of proteins with similar ATPase and helicase domains. ATRX probably acts as a regulator of gene expression. Definition of its genomic structure enabled us to identify four novel splicing defects by screening 52 affected individuals. Correlation between these and previously identified mutations with variations in the ATR-X phenotype provides insights into the pathophysiology of this disease and the normal role of the ATRX protein in vivo.      

Force enhancement by PEG during ramp stretches of skeletal muscle

We have investigated the effects of a stronger actomyosin bond on force (Ps) during rapid stretch of active permeabilized rabbit psoas muscle fibers as a function of temperature from 5 to 30 degrees C. The strength of the actomyosin bond is enhanced by addition of polyethylene glycol (PEG), especially in pre-powerstroke states [Chinn et al. (2000) Biophys J 49: 437-451]. We have hypothesized that such states produce much of the force when activated muscles are stretched [Getz et al. (1998) Biophys J 75: 2971-2983]. Addition of PEG to activated fibers produced a small increase in isometric tension, Po (50-90 kN/m2), which was approximately independent of temperature. In contrast PEG produced a dramatic increase in Ps at low temperatures (200-300 kN/m2), but a modest increase at higher temperatures (70-90 kN/m2). We also measured Ps and Po in solutions containing the phosphate analog aluminum fluoride (AlF4) with and without PEG. In the absence of PEG, AlF4 reduced Po much more than Ps. Addition of PEG did not enhance Po, but enhanced Ps significantly. The contrasting effects of PEG on Ps and Po, and the effect of temperature can be explained by a model in which stretch force is produced by pre-powerstroke cross-bridges whose maximum distension is increased by PEG, and isometric force is produced by strongly bound cross-bridges whose bond strength is also enhanced by PEG, but to a lesser extent.     

HIV testing within at-risk populations in the United States and the reasons for seeking or avoiding HIV testing

OBJECTIVES: We determined proportions of high-risk persons tested for HIV, the reasons for testing and not testing, and attitudes and perceptions regarding HIV testing, information that is critical for planning prevention programs. METHODS: Cross-sectional interview study of persons at high risk for HIV infection (men who have sex with men [MSM]; injection drug users [IDUs]; and heterosexual persons recruited from gay bars, street outreach, and sexually transmitted disease clinics) among six states participating in the HIV Testing Survey (HITS) in 1995 to 1996 (HITS-I) and 1998 to 1999 (HITS-II). RESULTS: Overall testing rates were lower in the HITS-I (1226/1599 [77%]) than in the HITS-II (1375/1711 [80%]) (p =.01). Persons <25 years old tested less frequently than those >or=25 years old (HITS-I: 71% vs. 78%, respectively, p=.007; HITS-II: 63% vs. 85%, respectively, p<.001). The main reasons for testing and not testing were the same in both surveys, but the proportions of reasons for not testing differed (e.g., "unlikely exposed to HIV" [HITS-I (17%) vs. HITS-II (30%), p<.0001], "afraid of finding out HIV-positive" [HITS-I (27%) vs. HITS-II (18%), p<.0001]). Attitudes regarding HIV testing differed among tested and untested respondents, especially among MSM. CONCLUSIONS: HIV testing rates were higher in the HITS-II, but testing rates decreased among the youngest respondents. Denial of HIV risk factors and fear of being HIV-positive were the principal reasons for not being tested. Availability of new HIV therapies may have contributed to decreased fear of finding out that one is HIV infected as a reason to avoid testing. The increased proportion of persons at risk who did not test because they believed they were unlikely to have been exposed highlights the need for prevention efforts to address risk perceptions.     

Peanut lectin binding sites in transitional cell carcinoma of the urinary bladder

Peanut lectin (PNA) binds to D Gal B (1-3) D Gal NAc which is the purported antigenic determinant of the so-called T blood group antigen (TAg). We used PNA in an indirect immunofluorescent technique to study TAg in transitional cell carcinomas of the bladder (TCC). All 14 control tissues failed to express TAg, whereas all controls (100%) expressed TAg on the cell membrane after prior treatment with neuraminidase. Sixty-nine percent of Stage O TCC expressed TAg, whereas 100% of cases expressed TAg after treatment with neuraminidase. Staining patterns noted were: granular intracytoplasmic, intracytoplasmic globular, and membrane. There was no correlation between TAg positivity or negativity and subsequent muscle wall invasion in the Stage O TCC group. Fifty percent of Stage B or greater TCC expressed TAg, whereas 27 of 30 (90%) cases expressed TAg after neuraminidase treatment. TAg-staining patterns noted in Stage B tumors were: membrane, granular intracytoplasmic, intracytoplasmic globular, and glycocalyx. Only 47% of Grade III TCC expressed TAg compared with 72% of low-grade TCC. The authors conclude that the expression of TAg reflects the neoplastic transformation of bladder epithelium. The data also suggest that in TCC, TAg positivity is most likely due to incomplete synthesis of MN blood group glycoprotein, as evidenced by loss of a terminal sialic acid, and that there is also evidence of cytostructural "relocalization" of TAg.     

Effect of age and breast density on screening mammograms with false-positive findings

OBJECTIVE: The objective of this study was to examine the effect of breast density and age on screening mammograms with false-positive findings. MATERIALS AND METHODS: The study sample was taken from the Washington State Mammography Tumor Registry, which links data from participating radiologists with the Puget Sound Cancer Surveillance System and the Washington State Cancer Registry. Participants (n = 73,247) were women 35 years old and older who underwent screening mammography for which an assessment and a four-category density rating were coded. A total of 46,340 mammograms were sampled to avoid interpreter bias. In this study of false-positive mammograms, only women with no diagnosis of breast cancer within 12 months of the index mammogram were included. Logistic regression was used to estimate the odds ratios of a false-positive mammogram being associated with each category of breast density or age, adjusting for the other factor as a covariate. RESULTS: After controlling for breast density, we found that the risk of a false-positive mammogram was not affected by age (p = 27). However, the trend of increasing risk of a false-positive mammogram with increasing breast density was highly significant (p < .001). Women with extremely dense breast tissue were almost two times more likely to have a false-positive mammogram than were women with fatty breast tissue. This effect persisted after controlling for age. CONCLUSION: Breast density, not age, is an important factor when predicting risk of a false-positive mammogram. Breast density should be considered when educating individual women on the risks and benefits of screening mammography.