Biomedical subjects

R J Mitchell

Publications and source records attributed to R J Mitchell.

At least 19 recordsLinked to original sources

PubMed2006

Effects of elevated atmospheric carbon dioxide on biomass and carbon accumulation in a model regenerating longleaf pine community.

Plant species vary in response to atmospheric CO2 concentration due to differences in physiology, morphology, phenology, and symbiotic relationships. These differences make it very difficult to predict how plant communities will respond to elevated CO2. Such information is critical to furthering our understanding of community and ecosystem responses to global climate change. To determine how a simple plant community might respond to elevated CO2, a model regenerating longleaf pine community composed of five species was exposed to two CO2 regimes (ambient, 365 micromol mol(-1) and elevated, 720 micromol mol(-1)) for 3 yr. Total above- and belowground biomass was 70 and 49% greater, respectively, in CO2-enriched plots. Carbon (C) content followed a response pattern similar to biomass, resulting in a significant increase of 13.8 Mg C ha(-1) under elevated CO2. Responses of individual species, however, varied. Longleaf pine (Pinus palustris Mill.) was primarily responsible for the positive response to CO2 enrichment. Wiregrass (Aristida stricta Michx.), rattlebox (Crotalaria rotundifolia Walt. Ex Gmel.), and butterfly weed (Asclepias tuberosa L.) exhibited negative above- and belowground biomass responses to elevated CO2, while sand post oak (Quercus margaretta Ashe) did not differ significantly between CO2 treatments. As with pine, C content followed patterns similar to biomass. Elevated CO2 resulted in alterations in community structure. Longleaf pine comprised 88% of total biomass in CO2-enriched plots, but only 76% in ambient plots. In contrast, wiregrass, rattlebox, and butterfly weed comprised 19% in ambient CO2 plots, but only 8% under high CO2. Therefore, while longleaf pine may perform well in a high CO2 world, other members of this community may not compete as well, which could alter community function. Effects of elevated CO2 on plant communities are complex, dynamic, and difficult to predict, clearly demonstrating the need for more research in this important area of global change science.

Atmosphere↗

PubMed2006

Adjustments in hydraulic architecture of Pinus palustris maintain similar stomatal conductance in xeric and mesic habitats.

We investigated relationships between whole-tree hydraulic architecture and stomatal conductance in Pinus palustris Mill. (longleaf pine) across habitats that differed in soil properties and habitat structure. Trees occupying a xeric habitat (characterized by sandy, well-drained soils, higher nitrogen availability and lower overstory tree density) were shorter in stature and had lower sapwood-to-leaf area ratio (A(S):A(L)) than trees in a mesic habitat. The soil-leaf water potential gradient (psiS - psiL) and leaf-specific hydraulic conductance (kL) were similar between sites, as was tissue-specific hydraulic conductivity (Ks) of roots. Leaf and canopy stomatal conductance (gs and Gs, respectively) were also similar between sites, and they tended to be somewhat higher at the xeric site during morning hours when vapour pressure deficit (D) was low. A hydraulic model incorporating tree height, A(S):A(L) and psiS-psiL accurately described the observed variation in individual tree G(Sref) (G(S) at D = 1 kPa) across sites and indicated that tree height was an important determinant of G(Sref) across sites. This, combined with a 42% higher root-to-leaf area ratio (A(R):A(L)) at the xeric site, suggests that xeric site trees are hydraulically well equipped to realize equal--and sometimes higher potential for conductance compared with trees on mesic sites. However, a slightly more sensitive stomatal closure response to increasing D observed in xeric site trees suggests that this potential for higher conductance may only be reached when D is low and when the capacity of the hydraulic system to supply water to foliage is not greatly challenged.

Adaptation, Physiological↗

PubMed2005

Prevalence of family history of colorectal cancer in the general population.

BACKGROUND: Robust estimates of the prevalence of a family history of colorectal cancer in the general population are essential to inform planning of provision for colonoscopic surveillance and for clinical genetics services. However, there is a paucity of high-quality data. METHODS: Computerized record linkage was used to assess systematically the family history of 160 cancer-free community subjects and thereby provide prevalence data that are independent of participant recall. The data set comprised 2664 first- and second-degree relatives of study subjects, with 148 068 years at risk. RESULTS: Of people in the 30-70 years age range, 9.4 (95 per cent confidence interval (c.i.) 5.8 to 14.9) per cent had a first-degree relative affected by colorectal cancer, and 28.8 (95 per cent c.i. 22.3 to 36.2) per cent had an affected first- or second-degree relative. Between 0 and 3.1 per cent of study subjects merited colonic surveillance, depending on the stringency of the guidelines used. CONCLUSION: An appreciable proportion of the general population has a relative affected by colorectal cancer, sufficient to merit screening under certain criteria. In the absence of good-quality evidence supporting colonoscopic surveillance in groups at moderate risk, these data directly inform the planning of services for people with a family history of colorectal cancer. However, the clinical risk and financial implications of screening should be taken into account.

Adult↗

PubMed2005

FMR1 alleles in Tasmania: a screening study of the special educational needs population.

The distribution of fragile X mental retardation-1 (FMR1) allele categories, classified by the number of CGG repeats, in the population of Tasmania was investigated in 1253 males with special educational needs (SEN). The frequencies of these FMR1 categories were compared with those seen in controls as represented by 578 consecutive male births. The initial screening was based on polymerase chain reaction analysis of dried blood spots. Inconclusive results were verified by Southern analysis of a venous blood sample. The frequencies of common FMR1 alleles in both samples, and of grey zone alleles in the controls, were similar to those in other Caucasian populations. Consistent with earlier reports, we found some (although insignificant) increase of grey zone alleles in SEN subjects compared with controls. The frequencies of predisposing flanking haplotypes among grey zone males FMR1 alleles were similar to those seen in other Caucasian SEN samples. Contrary to expectation, given the normal frequency of grey zone alleles, no premutation (PM) or full mutation (FM) allele was detected in either sample, with only 15 fragile X families diagnosed through routine clinical admissions registered in Tasmania up to 2002. An explanation of this discrepancy could be that the C19th founders of Tasmania carried few PM or FM alleles. The eight to ten generations since white settlement of Tasmania has been insufficient time for susceptible grey zone alleles to evolve into the larger expansions.

Adolescent↗

PubMed2004

Hierarchical Bayes model for random haplotype and family effects in the transmission of fragile-X.

A model for the transmission of the CGG repeat sequence associated with the fragile-X dynamic mutation in the FMR1 gene is developed. The model incorporates both haplotype and family effects on the expansion rate of the sequence. The resulting random effects model is fitted to new data, using computer-intensive Markov chain Monte Carlo methods. The results demonstrate both the FRAXAC1-DXS458 haplotype and family effects on the transmission of CGG repeats from mother to offspring.

Australia↗

PubMed2004

The influence of floral display size on selfing rates in Mimulus ringens.

Pollinators often visit several flowers in sequence on plants with large floral displays. This foraging pattern is expected to influence the rate of self-fertilization in self-compatible taxa. To quantify the effects of daily floral display on pollinator movements and selfing, we experimentally manipulated flower number in four replicate (cloned) arrays of Mimulus ringens (Scrophulariaceae), each consisting of genets with unique combinations of homozygous marker genotypes. Four display classes (two, four, eight and 16 flowers) were present in each array. Pollinator visitation rate per flower and seed set per fruit were unaffected by display. However, flower number strongly influenced the frequency of within-plant pollinator movements, which increased from 13.8% of probes on two-flower displays to 77.6% of probes on 16-flower displays. The proportion of within-plant movements was significantly correlated with selfing (r = 0.993). The increase from 22.9% selfing on two-flower displays to 37.3% selfing on 16-flower displays reflects changes in the extent of geitonogamous self-pollination. We estimate that approximately half of all selfing on 16-flower displays resulted from geitonogamy. Selfing also varied dramatically among fruits within display classes. Nested ANOVA indicates that differences among flowers on two-flower ramets accounted for 45.4% of the variation in selfing, differences among genets accounted for 16.1% of the variation, and statistical and sampling error accounted for 38.5% of the variation. Differences among flowers within ramets may reflect the order of sequential floral probes on a display.

Crosses, Genetic↗

PubMed2004

Accuracy of reporting of family history of colorectal cancer.

BACKGROUND AND AIMS: Family history is used extensively to estimate the risk of colorectal cancer but there is considerable potential for recall bias and inaccuracy. Hence we systematically assessed the accuracy of family history reported at interview compared with actual cancer experience in relatives. METHODS: Using face to face interviews, we recorded family history from 199 colorectal cancer cases and 133 community controls, totalling 5637 first and second degree relatives (FDRs/SDRs). We linked computerised cancer registry data to interview information to determine the accuracy of family history reporting. RESULTS: Cases substantially underreported colorectal cancer arising both in FDRs (sensitivity 0.566 (95% confidence interval (CI) 0.433, 0.690); specificity 0.990 (95% CI 0.983, 0.994)) and SDRs (sensitivity 0.271 (95% CI 0.166, 0.410); specificity 0.996 (95% CI 0.992, 0.998)). There was no observable difference in accuracy of reporting family history between case and control interviewees. Control subjects similarly underreported colorectal cancer in FDRs (sensitivity 0.529 (95% CI 0.310, 0.738); specificity 0.995 (95% CI 0.989, 0.998)) and SDRs (sensitivity 0.333 (95% CI 0.192, 0.512); specificity 0.995 (95% CI 0.991, 0.995)). To determine practical implications of inaccurate family history, we applied family history criteria before and after record linkage. Only two of five families reported at interview to meet surveillance criteria did so after validation, whereas only two of six families that actually merited surveillance were identified by interview. CONCLUSIONS: This study has quantified the inaccuracy of interview in identifying people at risk of colorectal cancer due to a family history. Colorectal cancer was substantially underreported and so family history information should be interpreted with caution. These findings have considerable relevance to identifying patients who merit surveillance colonoscopy and to epidemiological studies.

Aged↗

PubMed2003

An Escherichia coli biosensor capable of detecting both genotoxic and oxidative damage.

A two-plasmid dual reporter Escherichia coli biosensor was developed using the genes for bacterial bioluminescence and a mutant of the green fluorescent protein, GFPuv4. To achieve this, the two plasmids, which were derivatives of pBR322 and pACYC184, had compatible origins of replication and different antibiotic selection markers: ampicillin and tetracycline. The parent strains DK1 and ACRG43, each carrying a single plasmid with one of the fusion genes (strain DK1 harboring a fusion of the katG promoter to the lux operon while in ACRG43, the recA promoter was fused with the GFP gene), were responsive to oxidative and DNA damage, respectively, resulting in higher bioluminescence or fluorescence under the relevant toxic conditions. The responses of the dual sensor strain, DUAL22, to various toxicants, e.g., mitomycin C, N-methyl-N-nitro--nitrosoguanidine, hydrogen peroxide and cadmium chloride, were characterized and compared with the responses of the parent strains to the same chemicals. Finally, several chemical mixtures that cause various stress responses were tested to demonstrate the ability of this biosensor to detect specific stress responses within a multiple toxicity environment.

Artificial Gene Fusion↗

PubMed2003

Unintentional fatal injuries arising from unpaid work at home.

OBJECTIVE: Unpaid work in and around the home is a common and potentially high risk activity, yet there is limited information about the circumstances surrounding resulting injuries. This study aimed to describe circumstances surrounding fatal injuries resulting from home duties activities, in order to identify and prioritise areas for prevention. DESIGN AND SETTING: Coroners' reports on all unintentional deaths in Australia from 1989-92 inclusive were inspected to identify deaths of interest. Rates were calculated using population data and incorporating measures of time engaged in particular home duties activities. RESULTS: There were 296 home duties deaths over the four year period. Most (83%) deaths were of males, and males had 10 times the risk of fatal injury compared with females. The most common activities resulting in fatal injuries were home repairs, gardening, and car care. The highest risk activities (deaths per million persons per year per hour of activity) were home repairs (49), car care (20), home improvements (18), and gardening (16). Being hit by inadequately braced vehicles during car maintenance, falls from inadequately braced ladders, contact with fire and flames while cooking, and contact with electricity during maintenance were the most common injury scenarios. CONCLUSIONS: Fatal injury of persons engaged in unpaid domestic work activities is a significant cause of death. Use of activity specific denominator data allows appropriate assessment of the degree of risk associated with each activity. The recurrence of similar circumstances surrounding many independent fatal incidents indicates areas where preventative interventions might be usefully targeted.

Accidental Falls↗

PubMed2002

Mismatch repair genes hMLH1 and hMSH2 and colorectal cancer: a HuGE review.

Evidence to support a role for the mismatch repair genes human mutL homolog 1 (hMLH1) and human mutS homolog 2 (hMSH2) in the etiology of colorectal cancer has come from linkage analysis, segregation studies, and molecular biologic analysis. More recently, carriers of potentially pathogenic mutations in the hMLH1/hMSH2 genes have consistently been shown to be at a greatly increased risk of developing colorectal cancer compared with the general population. When considered together, the available evidence shows a strong, consistent, and biologically plausible association between mismatch repair gene mutations and colorectal cancer. The penetrance of mutations in hMLH1/hMSH2 is incomplete and is significantly higher in males (approximately 80%) than in females (approximately 40%). To date, evidence for gene-gene or gene-environment interactions is limited, although preliminary studies have revealed a number of avenues that merit exploration. Population screening for mutation carriers is not currently a feasible option, and mutation analysis remains restricted to either relatives of mutation carriers or colorectal cancer cases selected on the basis of phenotype.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Alleles and haplotypes of tumor necrosis factor (TNF) alpha and beta genes in three ethnic populations of Sulawesi Indonesia.

Polymorphic variation in two cytokine genes, tumor necrosis factor (TNF) -alpha and -beta, was examined in three ethnic groups, the Bugis, the Makassans, and the Torajans, who inhabit Sulawesi, a large island in the Indonesian archipelago, and formerly a Dutch colony. TNF-alpha and -beta are key molecules in immune responses to infection, and both have been implicated in the pathogenesis and clinical manifestations of parasitic diseases. Several polymorphic variants with the potential to affect cytokine levels in autoimmune diseases and parasitic and bacterial infection have been reported. Two loci in the promoter region of TNF-alpha and two sites in the first intron of TNF-beta were scored in a maximum of 150 Bugis, 168 Makassans, and 58 Torajans. Genotypes at the two TNF-alpha loci are not in Hardy-Weinberg equilibrium because of a deficit of heterozygotes (p < 0.05). However, genotypes at the TNF-beta loci exhibit Hardy-Weinberg equilibrium. A comparison of allelic and genotypic frequencies at all TNF loci across the ethnic groups reveals that the differences are significant for TNFalpha(308) (p < 0.01) and for TNFbeta(NcoI) (p < 0.05). Overall, the distribution of the alleles differs from that seen in the few Asian populations for which data are available (p < 0.05). Construction of 4-locus haplotypes showed that, in addition to the five previously reported, four novel haplotypes were present in Sulawesi. These novel haplotypes were in low frequency, and two were seen only in Bugis (haplotypes F and J) and one (haplotype K) only in Makassans. The other, haplotype D, was present in Makassans and Torajans. Preliminary sampling of other ethnic groups suggests that three of these haplotypes (D, F, and J) may be restricted to Asian or Asian-derived populations. The frequency of the common TNF haplotypes differed between Dutch and Sulawesi populations, and these data also indicated that haplotype E, which has a relatively high frequency in the Dutch (25%), may be a useful marker of Dutch/European admixture in Indonesian populations, in which it is either rare (1%) or absent. The results suggest that unique allelic combinations with potential to influence cytokine secretion are present in Sulawesi, possibly as a consequence of parasite-driven selection, and argue for more extensive investigation of haplotype distribution in parasite-endemic areas.

Alleles↗

PubMed2001

Farm-related fatalities involving children in Australia, 1989-92.

OBJECTIVE: To describe the types of and circumstances surrounding unintentional farm-related fatal injuries involving children aged less than 15 years in Australia. METHODS: Information concerning 115 deaths were obtained from inspection of coronial files for the period 1989-92. RESULTS: Children less than 15 years made up 20% of all unintentional farm-related fatalities in Australia, with children less than 5 years representing 63% of all child fatalities. The majority of children were fatally injured while bystanders to farm work and equipment used on the farm (including dams), with drowning the most common mechanism of the fatal incident for children aged both 5 years or less and 5-9 years. Vehicle accidents were common for children aged 10-14 years. CONCLUSIONS: Children are exposed to various hazards in the farming environment and as such are at risk of being injured. IMPLICATIONS: This study has highlighted a number of particular hazards for children on farms, with drowning, transport and tractor-related injuries of particular concern. A national strategy for child safety on farms has been developed by Farmsafe Australia aimed at providing a nationally co-ordinated plan for improving child safety on farms.

Adolescent↗

PubMed2001

Agricultural work-related fatalities in Australia, 1989-1992.

Farm-related fatalities in Australia were studied as part of a larger study of all work-related traumatic fatalities from 1989-1992. Information concerning 373 unintentional work-related fatalities was obtained from inspection of coronial files and described. The fatality rate per 100,000 workers was four times higher for agricultural industry workers (20.6) compared to the all-industry rate during the same time frame (5.5). Males comprised 95% of all agricultural work-related deaths. Agents such as farm vehicles, mobile farm machinery (mainly tractors), and farm structures (mainly dams) were among the most common involved in the fatal incident. Being hit by moving objects, vehicle accidents, and rollovers of mobile machinery (mainly tractors) were among the most common mechanisms of fatal injury on farms. Transport for work purposes, working with animals, working with crops, and maintenance were the most common activities being undertaken. The information obtained from this study is being used to develop health and safety risk profiles for agricultural industries, and these profiles are being used in turn to develop guidance material for farmers, on-farm checklists, and other tools to help farmers manage their occupational health and safety risk.

Adolescent↗

PubMed2001

Non-work-related farm fatalities in Australia, 1989-1992.

This study aims to examine farm fatalities, between 1989-1992 in Australia, of individuals not working at the time of the incident. Non-work-related farm fatalities in Australia were studied as part of a larger study of all work-related traumatic fatalities from 1989-1992. Information on 214 unintentional non-work-related farm fatalities was obtained from inspection of coronial files. The information was examined according to type of bystander (bystander to work or bystander to farm equipment) and other farm deaths. Agents such as dams, tractors, utilities, and cars were among the most common causes of death for bystanders involved in fatal incidents. Fire and smoke, creeks or rivers, and cars were the most common agents for other farm deaths. Drowning, vehicle accidents, and being hit by moving objects were among the most common mechanisms of fatal injury for non-work-related farm deaths. The information gained from this study has been used to develop the Child Safety on Farms Strategy for Farmsafe Australia and Farmsafe Australia's Farm Machinery Safety Strategy.

Accidents↗

PubMed2000

Y-chromosomal diversity in Europe is clinal and influenced primarily by geography, rather than by language.

Clinal patterns of autosomal genetic diversity within Europe have been interpreted in previous studies in terms of a Neolithic demic diffusion model for the spread of agriculture; in contrast, studies using mtDNA have traced many founding lineages to the Paleolithic and have not shown strongly clinal variation. We have used 11 human Y-chromosomal biallelic polymorphisms, defining 10 haplogroups, to analyze a sample of 3,616 Y chromosomes belonging to 47 European and circum-European populations. Patterns of geographic differentiation are highly nonrandom, and, when they are assessed using spatial autocorrelation analysis, they show significant clines for five of six haplogroups analyzed. Clines for two haplogroups, representing 45% of the chromosomes, are continentwide and consistent with the demic diffusion hypothesis. Clines for three other haplogroups each have different foci and are more regionally restricted and are likely to reflect distinct population movements, including one from north of the Black Sea. Principal-components analysis suggests that populations are related primarily on the basis of geography, rather than on the basis of linguistic affinity. This is confirmed in Mantel tests, which show a strong and highly significant partial correlation between genetics and geography but a low, nonsignificant partial correlation between genetics and language. Genetic-barrier analysis also indicates the primacy of geography in the shaping of patterns of variation. These patterns retain a strong signal of expansion from the Near East but also suggest that the demographic history of Europe has been complex and influenced by other major population movements, as well as by linguistic and geographic heterogeneities and the effects of drift.

Africa, Northern↗

PubMed2000

A polymorphic L1 retroposon insertion in the centromere of the human Y chromosome.

We have identified a novel polymorphic L1 retroposon insertion, designated LY1, in the centromeric alphoid array of the human Y chromosome. The element belongs to the transpositionally active Ta subset and its presence is compatible with normal centromere function. It was found at highest frequency in China, where it accounts for 23% of the Han sample, and was present at low frequencies in the surrounding areas, but was not found at all outside Asia. Chromosomes carrying LY1 show considerable microsatellite diversity, suggesting an ancient origin for the lineage at approximately 10 000 years ago (with wide confidence limits), but only limited subsequent migration.

Base Sequence↗

PubMed2000

Evaluation of an 8 hour versus a 12 hour shift roster on employees at a power station.

Several studies exist that have conducted research into the effects of different shiftwork patterns on the individual, especially regarding 8 and 12 h rosters. The findings of these studies have been largely supportive of longer shifts, however, the effects on work performance are not as clear cut. This study aimed to examine the changeover from an 8 h roster to a 12 h roster in a power station via monitoring on-shift performance, general health and well-being, sleep and mood behaviour, as well as absence and accident data. Results suggest that the domestic and social life of workers was markedly improved under the 12 h roster. Improvements in physical health, sleeping behaviour and mood state of employees were also documented. On-shift performance measures showed an increase in error rates at the end of a 12 h shift. Ways of reducing the risk of error towards the end of a 12 h shift should be explored. The results of this study suggest that 12 h shifts are a valid alternative to 8 h shifts in this particular workplace, although tasks that require error-free activities should not be performed towards the end of a 12 h shift.

Health Status↗

PubMed2000

A biosensor for the detection of gas toxicity using a recombinant bioluminescent bacterium.

A whole-cell biosensor was developed for the detection of gas toxicity using a recombinant bioluminescent Escherichia coli harboring a lac::luxCDABE fusion. Immobilization of the cells within LB agar has been done to maintain the activity of the microorganisms and to detect the toxicity of chemicals through the direct contact with gas. Benzene, known as a representative volatile organic compound, was chosen as a sample toxic gas to evaluate the performance of this biosensor based on the bioluminescent response. This biosensor showed a dose-dependent response, and was found to be reproducible. The immobilizing matrices of this biosensor were stored at 4 degrees C and were maintained for at least a month without any noticeable change in its activity. The optimal temperature for sensing was 37 degrees C. A small size of this sensor kit has been successfully fabricated, and found to be applicable as a disposable and portable biosensor to monitor the atmospheric environment of a workplace in which high concentrations of toxic gases could be discharged.

Benzene↗