Paediatrics (RCH) - Theses

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    Whole-genome expression profiling of cord blood mononuclear cells from monozygotic twin pairs
    Andronikos, Roberta Helen ( 2010)
    Substantial variation in gene expression levels exists between individuals, within specific tissues or cell types. With gene expression being the primary mechanism through which genetic information is translated into phenotype, the extent, nature and sources of this variation constitutes an important aspect of human biology. Variation in gene expression levels reflects a complex interplay of genetic and environmental factors. Certain environmental factors and exposures can modify gene expression through epigenetic modifications of DNA and chromatin, thus regulating transcription in a manner largely independent of genetic variation. The sensitivity of epigenetic mechanisms to these factors offers a means through which the environment can modulate expression of the genotype, with effects upon gene expression and ultimately, the phenotype. Studies of variation in gene expression in monozygotic (genetically identical) twins support a substantial environmental contribution to variation in gene expression levels. It is known that the epigenetic and gene expression profiles of monozygotic twins diverge throughout life. Mounting evidence suggests that the period of pre-natal development represents a particularly sensitive one for the occurrence of environmentally induced changes to epigenetic status and gene activity. The current study forms part of a larger research program investigating epigenetic variation in twins and its association with birth weight, maternal nutrition and foetal genotype. The Peri-/Post-natal Epigenetic Twins Study (PETS) builds upon the ‘developmental origins of adult disease’ hypothesis, based on the association between low birth weight and increased risk of cardiovascular and metabolic disease in later life, and focuses on epigenetic changes occurring in utero as the basis of the ‘foetal programming’ phenomenon. The current study is based on the hypothesis that divergence of epigenetic and gene expression profiles occurs from conception in monozygotic twins, in response to differing environments as experienced in utero. This study investigates the gene expression profiles of the cord blood mononuclear cells (CBMCs) of twelve newborn monozygotic twin pairs, including six pairs with birth weight discordance at greater than 15%. Genome-wide expression profiling was performed using the Illumina® Human-6 v2 BeadChip system. Gene expression discordance within twin pairs was assessed using three measures. Of these, the measure of Euclidean distance was considered to be the most systematic and useful. Expression discordance was found to vary substantially across pairs in our sample, with expression discordance being generally lower within twin pairs than between unrelated individuals. A significant correlation was identified between expression discordance and chorionicity, with greater expression discordance in dichorionic pairs compared to monochorionic pairs. The measure of Euclidean distance was also applied to publicly available datasets from genome-wide expression profiling of comparable tissues from adult twin pairs, revealing higher levels of expression discordance within the adult pairs relative to the newborn pairs. All genes surveyed by the microarray analysis were ranked according to the degree of within-pair variation shown across twin pairs. This ranked gene list was subjected to gene ontology analysis to identify gene ontology (GO) terms for which the corresponding ranks were higher than expected. Of the 27 GO terms ranked significantly higher than expected, one third related to immune response or response to other external signals. This data supports our hypothesis that divergence of gene expression profiles occurs from conception in monozygotic twins, and is reflected in differential expression phenotypes detectable at birth. Taken together, these results highlight the role of environment in determining gene expression profiles, and the contribution of environmentally induced changes in gene expression to expression discordance within monozygotic twin pairs. The increased variation observed within dichorionic twin pairs, coupled with the prominence of genes involved in immune/external signal response amongst those showing increased variation across pairs, implies that this variation may arise in response to subtly differing environments experienced by co-twins in utero. Birth weight is a phenotype of particular interest in the Peri-/Post-natal Epigenetic Twins Study (PETS), due to the association of low birth weight with an elevated risk of cardiovascular and metabolic disease in later life. In this study, linear modelling identified 342 genes whose expression levels showed a significant association with birth weight in dichorionic twin pairs. Gene ontology analysis of these genes revealed significant over-representation of GO terms relating to protein dephosphorylation, a process intrinsic to many forms of signal transduction. These data imply a link between the environmental modulation of gene activity via signal response/transduction and the phenotype of birth weight. Due to the myriad number of signal transduction pathways and physiological processes regulated by protein phosphorylation and dephosphorylation, it is not possible to pinpoint with certainty those that may be linked to birth weight or implicated in the association between low birth weight and elevated disease risk from our data. However, these results do provide a basis for further investigation of the specific environmental factors involved in the determination of gene expression variants associated with birth weight. It is to be hoped that future analyses will assist in the identification of the mechanisms underlying the correlation between low birth weight and an elevated risk of cardiovascular and metabolic disease in later life.
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    A prospective study of the psychological impact, understanding and disclosure of gene test results for hypertrophic cardiomyopathy and long QT syndrome.
    MACCIOCCA, IVAN ( 2010)
    Hypertrophic cardiomyopathy (HCM) and Long QT syndrome (LQTS) are inherited cardiovascular conditions for which genetic testing has become more common in clinical practice. The most concerning feature of these conditions is sudden death which can be prevented if those at risk are identified. Research into the clinical and molecular aspects of these conditions has advanced rapidly but research on the psychosocial implications of genetic testing for these conditions has lagged behind. The present study aimed to add to the limited body of research about the impact of genetic testing for HCM and LQTS to guide genetic health professionals working with families who are considering genetic testing. A multi-centre prospective questionnaire-based study was conducted to examine the impact of diagnostic and predictive testing for HCM and LQTS. Understanding of test results, risk perception, motivations for and concerns about testing and psychological impact of result disclosure were examined as well as disclosure of gene test result to relatives. Participants were recruited from four Australian and one British site. Questionnaires were completed before testing and at two weeks and three months post-disclosure. Data from participants who underwent diagnostic testing (n=46, 15-76 years old, 40 (80%) tested positive) were analysed separately to those who had predictive testing (n=77, 14-67 years old, 29 (38%) tested positive). A high proportion of participants from both the diagnostic and predictive gene testing groups were pleased they had testing, recalled their result accurately and in the diagnostic group, understood the implications of their result for their own health and their relatives. In those who had predictive testing, perceptions of the likelihood of developing disease, level of worry, and the number of concerns about LQTS and HCM reported were consistent with gene test result. More than 90% of participants in both groups disclosed their gene test results to first‐degree relatives. Concerns about sudden death were evident in participants from both the diagnostic and predictive group, confirming anecdotal reports from clinical practice. Concerns about the possibility of at-risk relatives inheriting either LQTS or HCM and the unpredictable natural history of both conditions were also common concerns. For the predictive testing group, multivariable linear regression analysis adjusting for baseline psychological scores and potential confounders, and accounting for family clusters demonstrated a higher mean anxiety (p=0.005) and distress (p=0.003) score in gene positive compared to gene negative participants at 2 weeks, but these differences were less apparent at 3 months. There was no difference in depression scores at any time point in those who underwent predictive testing. The same analysis was performed in the diagnostic testing group and there were no statistically significant differences in adjusted mean anxiety, distress and depression scores when comparing participants with gene positive and gene negative results at any time point. Overall, high proportions of participants who underwent diagnostic and predictive testing were pleased to have undergone testing, understood the implications of their result and disclosed their result to relatives. There was no evidence for significant negative psychological sequelae three months after receipt of test result in participants who had either diagnostic or predictive testing. Implications for practice are presented.
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    Childhood pneumonia and hypoxaemia in an urban diarrhoeal hospital, Dhaka, Bangladesh
    Chisti, Mohammod Jobayer ( 2010)
    The aim of this prospective cohort study was to evaluate clinical and socio-demographic predictors of pneumonia, deaths from pneumonia, and hypoxaemia in children. All under-five children who were admitted to the special care ward of ICDDR,B during September 2007-December 2007 were enrolled. Children sleeping in a bare bed and those having parents/caregivers with poor knowledge were at risk of pneumonia. Children with severe malnutrition, hypoxaemia, or severe sepsis were at higher risk of death. Chest wall-indrawing was the best predictor of hypoxaemia.