Paediatrics (RCH) - Theses
Permanent URI for this collection
Search Results
1 - 3 of 3
-
ItemVariation of the Microbiome in Paediatric Crohn’s Disease( 2019)Introduction: Crohn’s Disease (CD) is a chronic, relapsing condition of the human gastrointestinal system with several significant extraintestinal manifestations. It can affect any age group; 10% of patients being diagnosed prior to their 18th birthday. Pediatric CD is known to have a more severe and difficult to manage phenotype. A rising incidence has been observed in recent years although the disease phenotype has remained largely unchanged. There is a growing body of literature describing dysbiosis in patients with CD. Despite extensive research, the role and behaviour of the gut microbiome in pediatric CD is not well understood. Aims: We aimed to characterize the microbiome in patients with CD longitudinally and compare it with non-IBD patients. We also sought to explore if there were any microbiome differences between ASCA positive and ASCA negative patients. Methods: We analysed the microbiome of 345 biopsies from 204 patients, including 88 CD first diagnosis (CDFD) patients, 38 patients in relapse (CDRL), 12 patients in remission (CDRM), and 66 controls. Species identification was conducted using oligotyping in combination with ARB/SILVA taxonomic annotation. Comparison was also made between ASCA status, microbial diversity and clinical characteristics. Results: We observed 45 bacteria to be statistically different between CDFD samples and controls, with Fusobacterium being the most implicated species in CDFD patients. We also identified gender specific differences in CD. Five species showed a strong association with patients with CD in relapse and 10 species in patients with CD in remission. Three taxa showed a positive co-occurrence across the two groups. Hespellia porcina (closest taxonomic neighbor to Clostridium oroticum) had the strongest association with samples from patients with CD in relapse. Interestingly, Fusobacterium was not part of the CD relapse associated taxa group. Faecalibacterium prausnitzii was equally present in CDFD and in control samples. ASCA was highly specific but poorly sensitive for the diagnosis of CD. In patients with CD, ASCA positivity was more likely to be present in patients older than 10 years, and associated with increased likelihood of ileocolonic disease distribution and long-term risk of surgery. Microbial alpha and beta diversity were similar in patients with CD with or without ASCA, but significantly less when compared to non-IBD controls. 14 bacterial species were statistically associated with ASCA positive patients with CD and 14 species with ASCA negative patients (p< 0.05). By using a false discovery rate corrected P value, two species remained statistically associated with both the groups. Ruminococcus torques and bacterium Yersinia enterocolitica were statistically associated with CD ASCA positive patients (p = 0.0178). Enterobacter cloacae and Faecalibacterium prausnitzii were statistically associated with CD ASCA negative patients (p = 0.0178 and 0.0342, respectively). Conclusions: This is the first study to investigate gut mucosal microbiome in a pediatric CD cohort with longitudinal sampling. Significant differences in microbiome were observed between treatment naïve patients with CD, patients with CD in relapse, patients with CD in remission and non-IBD patients. We also identified differences in the gut microbiome between patients with CD depending on presence of ASCA.
-
ItemCombined genetic and epigenetic analysis to identify early life determinants of complex phenotype( 2019)There is now considerable evidence indicating that risk of many complex diseases in adulthood may be influenced by exposure to environmental exposures in utero. A growing number of studies suggest epigenetic markers, including DNA methylation, are involved in this process. Understanding how DNA methylation is impacted by pregnancy exposures, and related to later health, may both contribute to unravelling the aetiology of complex disease risk in later life and provide a potential early-life biomarker for risk prediction. However, current evidence is limited. There has been a predominance of small, poorly powered studies, failure to consider the effects of genetic variation, and limited replication of previous findings. In addition, previous studies investigating the relationship between DNA methylation and offspring health have been primarily cross-sectional. For these reasons, I investigated the associations between pregnancy exposures (in particular, maternal smoking, nutrition and metabolic health, psychosocial stress, and adverse pregnancy conditions), birth outcomes, and offspring blood DNA methylation of the insulin-like growth factor 2 (IGF2) and H19, hypoxia-inducible factor 3A (HIF3A), leptin (LEP) genes. I also considered how genetic variation impacted on these associations. I then investigated the longitudinal relationship between early life methylation and anthropometry, as well as the association between early life methylation and later childhood measures of weight, adiposity, and cardiovascular health. To do this, the large, population-based longitudinal Barwon Infant Study pre-birth cohort (n=1,074) was used, with clinical and questionnaire measures from 28 weeks pregnancy, birth, 12 months post-birth and 4 years post-birth time points. DNA methylation of candidate regions was measured using the Sequenom EpiTyper mass-spectrometry platform in cord (birth) and peripheral (12-month) blood. Infant genetic variation in and near the candidate genes was considered. Infant adiposity was assessed as sum of triceps and subscapular skinfold thicknesses in infancy, and with DEXA scanning at 4 years of age. We found evidence that exposure to maternal psychosocial stress, gestational diabetes, and pre-eclampsia was associated with differences in offspring methylation at the candidate regions, as was infant sex. Genetic variation showed strong effects on DNA methylation levels, with some evidence for the associations of pre-eclampsia and infant adiposity with LEP methylation differing by infant genotype. Early life methylation of HIF3A and LEP showed modest associations with four-year blood pressure and BMI, respectively. While these associations persisted with adjustment for potential confounding factors, they explained relatively little variance in the four-year phenotypes compared to traditional predictors, such as weight. These findings suggest that offspring DNA methylation of these candidate genes involved in regulation of growth and metabolism are sensitive to several environmental exposures and genetic factors. While there is modest evidence for methylation in infant blood associating with later phenotypes, methylation of these genes appears unlikely to have useful predictive utility in isolation. This study is the first to perform early life longitudinal analysis to investigate the association between anthropometry and methylation in infancy. It is also the first to report evidence of earlier methylation associating with later cardiovascular phenotypes. However, as gene expression data was not available, the functional consequences of the altered methylation observed in blood is unclear. Further work is required to replicate these findings in independent cohorts, to determine the nature of expression of these genes in blood, and to investigate if the relationship between early life methylation and later health persists into adulthood.
-
ItemEnvironmental and genetic risk factors for food allergy in children with Asian ancestry( 2019)Epidemiological and genetic studies on food allergy to date have focused primarily on the Caucasian population. This is despite emerging evidence that food allergy appears to be rising in Asian countries, alongside the increasing Westernisation and urbanisation in these countries. Even less is known about Asian migrants living in Western countries. A population-based study on food allergy found the risk of food allergy to be three times higher in infants of East Asian ancestry than infants of Caucasian ancestry. It is thought that infants growing up in Australia are exposed to environmental agents that have a differential effect on the immune system depending on their genetic background. However, the influence of specific genetic and environmental risk factors is currently unknown. It is also unclear if the increased risk of food allergy translates to higher risk of other allergic diseases later in childhood. The main objective of this thesis is to identify specific environmental and genetic factors on the risk of food allergy in the Asian population living in Australia. This thesis aims to quantify the prevalence of, and identify risk factors for food allergy and allergic comorbidities in the Asian population. An additional aim is to identify genetic variants that increase the risk of food allergy in the East Asian population and compare this to the Caucasian population living in Australia. This thesis primarily used data and samples from the longitudinal HealthNuts study where 5,276 1-year-old infants attending council run vaccination sessions across Melbourne were recruited. Skin prick tests to a range of food were carried out on infants and those with a wheal size less than 1 mm underwent an oral food challenge. The 1-year-old infants were followed up again at age 6 years and data collected at this follow-up visit were also used for analyses in this thesis. Additionally, data collected from a Growing Up in Singapore Towards Healthy Outcomes (GUSTO) birth cohort was also used to compare the risk factors and prevalence of allergic diseases between East Asians living in Melbourne and East Asians living in Singapore. This thesis reports that Australian-born children with East Asian parents have a higher burden of allergic rhinitis, eczema and aeroallergen sensitisation but not asthma, in the first six years of life compared to children of Caucasian ancestry. Moreover, children with IgE-mediated food allergy and eczema in infancy were 3 times more likely to have asthma and 2 times more likely to have allergic rhinitis at age 6 years, irrespective of ancestry. Additionally, East Asian children living in Melbourne have a higher risk of food allergy compared to East Asian children living in Singapore. Despite delayed introduction of allergens into the diet compared to the Asian population in Melbourne, Asian children in Singapore had less food allergy. While eczema rates were lower in Singapore than in Melbourne, early onset eczema was associated with an increased risk of food allergy in both Singapore and Melbourne. In terms of genetic risk factors, a systematic review conducted as part of this thesis identified several genes of interest known to be involved in immune regulation, cell function and epidermal barrier function. However, studies were of varied quality and the reproducibility of findings for the same SNPs were minimal. Some of the highly re-producible genes identified from the literature include HLA, FLG and IL13. Additionally, there was also a paucity of studies carried out in the Asian population that were able to elucidate underlying mechanisms for the differential food allergy risks observed in the population. This highlighted the need for genetic studies focused in this population. This thesis found that HLA rs7192 minor allele was associated with increased risk of peanut allergy in the Caucasian population but not East Asian population. Among sensitised children with two East Asian born parents, those with the minor allele for rs231735, rs231804 or rs11571291 (all CTLA4) have a reduced risk of egg allergy. The findings of this thesis identify Asian children living in Australia as a high risk allergic group not just in infancy but throughout early childhood. As a multifactorial disease, both environmental and genetic factors are known to contribute to the pathogenesis of food allergy. Therefore, it may be that the increased risk of food allergy observed in genetically predisposed East Asian children living in Melbourne unmasked upon exposure to environmental risk factors.