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Biomedical subjects

A M Johnson

Publications and source records attributed to A M Johnson.

At least 109 records · Page 6Linked to original sources
PubMed1998

Nature vs nurture: are leaders born or made? A behavior genetic investigation of leadership style.

With the recent resurgence in popularity of trait theories of leadership, it is timely to consider the genetic determination of the multiple factors comprising the leadership construct. Individual differences in personality traits have been found to be moderately to highly heritable, and so it follows that if there are reliable personality trait differences between leaders and non-leaders, then there may be a heritable component to these individual differences. Despite this connection between leadership and personality traits, however, there are no studies of the genetic basis of leadership using modern behavior genetic methodology. The present study proposes to address the lack of research in this area by examining the heritability of leadership style, as measured by self-report psychometric inventories. The Multifactor Leadership Questionnaire (MLQ), the Leadership Ability Evaluation, and the Adjective Checklist were completed by 247 adult twin pairs (183 monozygotic and 64 same-sex dizygotic). Results indicated that most of the leadership dimensions examined in this study are heritable, as are two higher level factors (resembling transactional and transformational leadership) derived from an obliquely rotated principal components factors analysis of the MLQ. Univariate analyses suggested that 48% of the variance in transactional leadership may be explained by additive heritability, and 59% of the variance in transformational leadership may be explained by non-additive (dominance) heritability. Multivariate analyses indicated that most of the variables studied shared substantial genetic covariance, suggesting a large overlap in the underlying genes responsible for the leadership dimensions.

Adult↗
PubMed1998

Private sexual behavior, public opinion, and public health policy related to sexually transmitted diseases: a US-British comparison.

OBJECTIVES: The purpose of this study was to characterize sexual behavior and opinions about sex in the United States and Britain; implications are discussed for effective public health policy regarding sexually transmitted diseases (STDs) in the United States. METHODS: Large-scale national probability surveys conducted in the 2 countries detailed sexual behavior, opinions, and the prevalence of STDs. RESULTS: In comparison with that of Britain, the US population has greater variability in sexual behavior, less tolerant opinions about sexual behavior, and a higher STD prevalence and lower condom usage among men. CONCLUSIONS: The survey data show compelling evidence from both countries of a strong association between number of sex partners and STD risk. In the United States relative to Britain, there is both greater dispersion in sexual behavior and a greater incidence of unconditional opposition to certain sexual practices. The former implies a need for strong public health policy to address the risks of STDs, but the latter implies strong opposition to that policy. This disjuncture between public health need and feasibility may contribute to the high US rate of STDs.

Adolescent↗
PubMed1998

Is there more than one species in the genus Toxoplasma??

A complete life cycle for the ubiquitous protozoan parasite Toxoplasma was proposed over 25 years ago. Since that time, despite attempts to make the genus polyspecific, there has been only one species, Toxoplasma gondii, consistently recognised in the genus. Recent studies on taxa in genera closely related to Toxoplasma such as Neospora, Hammondia, Frenkelia, Isospora and Sarcocystis, have convincingly showed the need for a reclassification of many of the species in these genera. However, in addition to these genus level studies, over the last 10 years several laboratories have used molecular techniques including isoenzyme electrophoresis, restriction fragment length polymorphism analyses, random amplified polymorphic DNA - polymerase chain reaction, and comparisons of the small subunit ribosomal RNA gene, DNA polymerase alpha intron, and 70 kDa heat shock protein gene nucleotide sequences to investigate the genetic diversity among strains in the species T. gondii. Overall, the results of these analyses confirm that the strains in the genus Toxoplasma comprise a limited number of clonal lineages, directly correlated with their virulence in mice. The aim of this presentation is to review the molecular research in this area in order to raise the hypothesis that there may be more than one species in the genus Toxoplasma, which may contain taxa with distinct and different life cycles.

Animals↗
PubMed1998

Active surveillance of sexual behaviour among homosexual men in London.

The objective of this study was to establish a surveillance programme to monitor high risk sexual behaviour among homosexual and bisexual men socializing and/or using health care services in London. Between November 1996 and January 1997 a brief, self-completed questionnaire was distributed in various commercial venues (bars, clubs, and saunas) and genitourinary medicine (GUM) clinics in inner London. A total of 2482 questionnaires were returned (response rate 75%). A third of men (32%) reported having had unprotected anal intercourse in the previous year and 18% had done so with one or more partners of unknown or different HIV status. High risk sexual behaviour was associated with younger age, having casual partners, and recruitment from GUM clinics. The combination of high levels of both sexual risk behaviour and HIV prevalence demonstrates the need for sustained and innovative health promotion campaigns among homosexual men in London.

Adult↗
PubMed1997

Laguna Negra virus associated with HPS in western Paraguay and Bolivia.

A large outbreak of hantavirus pulmonary syndrome (HPS) recently occurred in the Chaco region of Paraguay. Using PCR approaches, partial virus genome sequences were obtained from 5 human sera, and spleens from 5 Calomys laucha rodents from the outbreak area. Genetic analysis revealed a newly discovered hantavirus, Laguna Negra (LN) virus, to be associated with the HPS outbreak and established a direct genetic link between the virus detected in the HPS cases and in the C. laucha rodents, implicating them as the primary rodent reservoir for LN virus in Paraguay. Virus isolates were obtained from two C. laucha, and represent the first successful isolation of a pathogenic South American hantavirus. Analysis of the prototype LN virus entire S and M and partial L segment nucleotide and deduced amino acid sequences showed that this virus is unique among the Sigmodontinae-borne clade of hantaviruses. Analysis of PCR fragments amplified from a serum sample from a Chilean HPS patient, who had recently traveled extensively in Bolivia (where C. laucha are known to occur), revealed an LN virus variant that was approximately 15% different at the nucleotide level and identical at the deduced amino acid level relative to the Paraguayan LN virus. These data suggest that LN virus may cause HPS in several countries in this geographic region.

Animals↗
PubMed1997

Regional differences in use of antiretroviral agents and primary prophylaxis in 3122 European HIV-infected patients. EuroSIDA Study Group.

Little is known about how widely HIV-related drugs are used outside controlled clinical trials. We therefore assessed factors associated with use of antiretroviral (ARV) therapy and primary prophylactic regimens to prevent HIV-associated opportunistic infections. Baseline data from a prospective study from May to August 1994, on 3122 consecutive HIV infected patients with a CD4 count <500 cells/microl, followed in 37 centers from 16 European countries, were analyzed. Two thousand and twenty patients (65%) were receiving at least 1 ARV drug at the time of the study. ARV therapy was more frequently used among patients from southern and central Europe as compared with patients from northern Europe, especially among patients with CD4 counts >200 cells/microl (73%, 57%, and 42%, respectively, p < 0.0001). Of patients on ARV therapy, 34% received open-label combination therapy. This proportion was higher in central Europe compared with other regions (27%, 50%, and 31% for southern, central, and northern Europe, respectively, p < 0.0001). Primary prophylaxis against Pneumocystis carinii pneumonia (PCP) was used by 85% of patients with a CD4 count <200 cells/microl, without marked regional differences. In patients without esophageal candidiasis or other invasive fungal infections, antifungal drugs were far less frequently used in patients from southern and central Europe compared with patients from northern Europe (10%, 10%, and 25%, respectively, p < 0.0001). Only 5% of patients with a CD4 count <100 cells/microl received rifabutine as primary prophylaxis against nontuberculous mycobacterioses. ARV and antifungal therapies are used differently in different parts of Europe, whereas primary PCP prophylaxis is uniformly administered to most at-risk patients. U.S. recommendations on the use of antimycobacterial prophylaxis have not been implemented in Europe.

AIDS-Related Opportunistic Infections↗
PubMed1997

Comparison of two methods of screening for genital chlamydial infection in women attending in general practice: cross sectional survey.

OBJECTIVES: To estimate the prevalence of Chlamydia trachomatis in asymptomatic women attending general practice: to assess the potential of the ligase chain reaction as a screening tool; and to evaluate selective screening criteria. DESIGN: Cross sectional survey. SETTING: Four general practices in northeast London. SUBJECTS: 890 women aged 18-35 years attending general practice for a cervical smear or a "young well woman" check between October 1994 and January 1996. The women were tested for C trachomatis with confirmed enzyme immunoassay (endocervical specimens) and ligase chain reaction assay on urine specimens. MAIN OUTCOME MEASURES: Prevalence of C trachomatis infection in women aged 18-35 on the basis of each test; sensitivity and specificity of both tests in this population. RESULTS: Prevalence of confirmed infection was 2.6% (95% confidence interval 1.6% to 3.6%) in all women. Prevalence on the basis of enzyme immunoassay was 1.6% (0.8% to 2.7%), with a sensitivity of 60% and a specificity of 100%. Prevalence on the basis of ligase chain reaction was 2.5% (1.5% to 3.9%), with 90% sensitivity and 99.8% specificity. Screening all women aged < or = 25 and all women who had had two or more partners in the past year would have detected 87% (20/23) of infections. CONCLUSION: Ligase chain reaction on urine samples performs at least as well as enzyme immunoassay on cervical specimens in this low prevalence population. It offers potential as a non-invasive screening tool. A simple selective screening strategy might be appropriate and would be able to detect most cases of infection. However, a rigorous economic evaluation of possible screening strategies is needed first.

Adult↗
PubMed1997

Cloning and sequence analysis of the DNA polymerase alpha gene of Leishmania donovani: comparison with the human homologue.

The gene encoding the DNA polymerase alpha catalytic subunit of the kinetoplastid parasite L. donovani has been isolated, sequenced and compared with other eukaryotic homologues. The coding region is 4020 bp in length and specifies an inferred protein sequence of 1339 amino acids (aa). There is a high level of variability between the human and L. donovani gene sequences, but functional substrate-binding residues identified in humans and yeast appear to also be conserved in this parasite. The discovery of a cysteine-rich region located in the midst of the active sites of the enzyme, which appears to be unique to the Kinetoplastids, and aa differences found between some of the conserved regions implicated in catalytic function, may aid in drug design. The putative DNA binding Zn finger at the C-terminus of the protein appears highly species specific and may have potential as a drug target for blocking enzyme catalysis in the parasite.

Amino Acid Sequence↗
PubMed1997

Toxoplasma gondii virulence markers identified by random amplified polymorphic DNA polymerase chain reaction.

Genomic DNAs from 35 Toxoplasma gondii strains were amplified by random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) using 18 arbitrary 10-mer primers. At least four primers were found to generate DNA fragments that discriminate the 35 T. gondii strains into a genotype of virulent strains and a genotype of avirulent strains. Primer B12 was found to generate a virulence-specific fragment and primers B5, C8, and C20 were found to generate avirulence-specific fragments, which in all cases clearly identified either the virulence phenotype or the avirulence phenotype, respectively. In addition, the DNA polymorphic bands detected were analyzed by parsimony and distance analysis. A similar genetic relationship among the T. gondii strains was determined by the two phylogenetic methods, which use completely different assumptions. Consistent with the division of the 35 strains into a genotype of virulent strains and a genotype of avirulent strains, both analyses revealed 2 clonal lineages directly correlated with murine virulence. These results strongly support the hypothesis that the genus Toxoplasma may actually contain two clonal lineages correlated with virulence, which have evolved independently following their initial separation.

Animals↗
PubMed1997

Speculation on possible life cycles for the clonal lineages in the genus toxoplasma.

Recent evidence suggests that the strains currently classified in the genus Toxoplasma, ie. within the species Toxoplasma gondii, may actually comprise at least two clonal lineages correlated with their virulence in mice. Here, Alan Johnson reviews these data in the context of evolution and speciation within the genus, and raises hypotheses on how the virulent lineage may undergo an asexual life cycle in nature, similar to that found for the very closely related coccidian, Neospora camnum. The putative vertical transmission life cycle of this mouse virulent lineage of T. gondii could involve passage to the foetus late in pregnancy, or transmission in milk to the neonate after birth.

Journal Article↗
PubMed1997

A eubacterial gene conferring spectinomycin resistance on Chlamydomonas reinhardtii: integration into the nuclear genome and gene expression.

We have constructed a dominant selectable marker for nuclear transformation of C. reinhardtii, composed of the coding sequence of the eubacterial aadA gene (conferring spectinomycin resistance) fused to the 5' and 3' untranslated regions of the endogenous RbcS2 gene. Spectinomycin-resistant transformants isolated by direct selection (1) contain the chimeric gene(s) stably integrated into the nuclear genome, (2) show cosegregation of the resistance phenotype with the introduced DNA, and (3) synthesize the expected mRNA and protein. Small linearized plasmids appeared to be inserted into the nuclear genome preferentially through their ends, with relatively few large deletions and/or rearrangements. Multiple copy transformants often integrated concatemers of transforming DNA. Our detailed analysis of the complex integration patterns of plasmid DNA in C. reinhardtii nuclear transformants should be useful for improving the technique of insertional mutagenesis. We also found that the spectinomycin-resistance phenotype was unstable in about half of the transformants. When maintained under nonselective conditions, neither the aadA mRNA nor the AadA protein were detected in these subclones. Moreover, since the integrated transforming DNA was not altered or lost expression of the RbcS2::aadA::RbcS2 gene(s) appears to be repressed. Measurements of transcriptional activity, mRNA accumulation, and mRNA stability suggest that expression of this chimeric gene(s) may also be affected by rapid RNA degradation, presumably due to defects in mRNA processing and, or nuclear export. Thus, both gene silencing and transcript instability, rather than biased codon usage, may explain the difficulties encountered in the expression of foreign genes in the nuclear genome of Chlamydomonas.

Animals↗
PubMed1997

Assessing participation bias in a sexual behaviour survey: implications for measuring HIV risk.

OBJECTIVES: To assess the likelihood of participation bias in a large population-based sex survey, and its possible effect on estimates of HIV risk behaviours. DESIGN: Construction of general hypotheses about non-participants through comparisons of willing and unwilling participants. METHODS: British adults aged 16-59 years were surveyed in 1990-1991. Interviews consisted of a face-to-face section combined with a self-completion booklet (n = 18876). Interviewers recorded interviewee embarrassment. Homosexual experience and number of lifetime heterosexual partners (grouped 0, 1, 2 or more) were recorded prior to booklet offer. Logistic regression was performed, with embarrassment and booklet refusal as outcome variables, assessing their association with sexual behaviour after controlling for demographic variables. Assuming that, in sexual behaviour, non-participants are closer to the embarrased and the booklet refusers ('unwilling' participants) than to others, these analyses provide an indication of the nature of participation bias. RESULTS: Higher refusal an embarrassment rates were associated with both reporting no homosexual experience and fewer heterosexual partners. CONCLUSIONS: Under our untestable assumption, these results are consistent with non-participants being generally at lower risk of HIV infection. Methods need to be developed both to reduce participation bias in sex surveys, and to incorporate it in analysis.

Adolescent↗
PubMed1997

Epigenetic silencing of a foreign gene in nuclear transformants of Chlamydomonas.

The unstable expression of introduced genes poses a serious problem for the application of transgenic technology in plants. In transformants of the unicellular green alga Chlamydomonas reinhardtii, expression of a eubacterial aadA gene, conferring spectinomycin resistance, is transcriptionally suppressed by a reversible epigenetic mechanism(s). Variations in the size and frequency of colonies surviving on different concentrations of spectinomycin as well as the levels of transcriptional activity of the introduced transgene(s) suggest the existence of intermediate expression states in genetically identical cells. Gene silencing does not correlate with methylation of the integrated DNA and does not involve large alterations in its chromatin structure, as revealed by digestion with restriction endonucleases and DNase I. Transgene repression is enhanced by lower temperatures, similar to position effect variegation in Drosophila. By analogy to epigenetic phenomena in several eukaryotes, our results suggest a possible role for (hetero)chromatic chromosomal domains in transcriptional inactivation.

Animals↗
PubMed1997

HIV partner notification policy and practice within GUM clinics in England: where are we now?

OBJECTIVES: To evaluate the extent to which larger genitourinary medicine (GUM) clinics in England have established local clinic policies for HIV Partner Notification (PN) and to describe the process of HIV PN within this setting. DESIGN: A cross-sectional survey of HIV PN policies and practices within GUM clinics. SUBJECTS AND SETTING: Senior consultants in 59 GUM clinics in England. MAIN OUTCOME MEASURES: The presence of clinic policies for HIV PN, indicators of HIV PN activity (that is, its initiation, documentation, performance and evaluation) and factors hindering the acceptance of HIV PN into clinical practice. RESULTS: Only 18% (10/57) of respondents stated that their clinics had developed their own local policies for HIV PN. Fifteen percent (9/58) of clinics had audited HIV PN activity, 15% had provided specific HIV PN training for doctors and 47% (27/58) for health advisers. Within GUM clinics, health advisers play a key role in the HIV PN process, being responsible for initiating the discussion of partners, patient follow-up and documenting HIV PN activity in patients' notes. Notifying partners was primarily seen as the responsibility of the newly diagnosed HIV positive patient. Although 77% (43/56) of responding consultants believed that HIV PN had become an accepted part of their clinics' practice, the perceived unacceptability of HIV PN to patients and health care workers were seen as important limiting factors. CONCLUSION: In many GUM clinics, local policies on HIV PN have yet to be established and appropriate training for the health personnel provided. Nevertheless, there appears to be wide-spread acceptance of HIV PN in clinical practice with an acknowledgement of its limiting factors. Further research into the acceptability of HIV PN to health care workers and patients in this setting should be undertaken.

Attitude of Health Personnel↗