Paediatrics (RCH) - Theses
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ItemThe epidemiology and risk factors of anaphylaxis and food-induced anaphylaxis worldwide( 2019)Anaphylaxis is a severe allergic reaction that is rapid in onset and may cause death. There are increasing reports from individual countries and regions on anaphylaxis prevalence or incidence; however, there has been no systematic summary of the worldwide evidence among the paediatric population. An increasing rate of hospital admissions for food-induced anaphylaxis was observed in Australia from 1993 to 2012, especially among young children. Although rising rates of anaphylaxis have also been reported in other western countries, little is known about the time trends in Asian regions. Time trends of adrenaline auto-injectors (AAI) prescription is a good supplement surrogate for the time trends of anaphylaxis risk in the community. Some studies reported time trends of AAI prescription internationally, such as USA, UK and Canada; however, there is little information on the time trends of AAI prescription or dispensing in Australia in recent years. Previous international studies have reported that ethnicity is associated with the risk of anaphylaxis. Food allergy was found to be more common in children born in Australia with Asian parents than children born in Australia with Caucasian parents. However, it is not known whether ethnicity is also a risk factor for the development of anaphylaxis and food-induced anaphylaxis in Australia. Food allergy is an important cause of anaphylaxis. People with food allergy have a high risk of anaphylaxis, but not all of them will have an anaphylactic reaction. It is hence crucial to know the risk factors of having anaphylactic reactions in the food allergic population. Few studies have examined risk factors for food-induced anaphylaxis in food-allergic children. The characteristics of children with food allergy who are more likely to experience anaphylaxis are unknown. Therefore, this thesis aims to describe the worldwide incidence and prevalence of anaphylaxis and identify risk factors for anaphylaxis and food-induced anaphylaxis in both the general population and the food-allergic population. Firstly, I conducted a systematic review to describe the incidence and prevalence of anaphylaxis in children worldwide. I found a high heterogeneity between studies which limited the interpretation of an overall combined incidence and prevalence. I found increasing time trends of all-cause anaphylaxis and food-induced anaphylaxis in children from included studies and studies in developing areas were underrepresented. By using hospital admission data for anaphylaxis from the Hospital Authority of Hong Kong, I reported increasing time trends of both all-cause anaphylaxis and food-induced anaphylaxis in the paediatric population in Hong Kong between 2001 and 2015. By analysing AAI dispensing data from the Australian Pharmaceutical Benefits Scheme (PBS) database, I found an increasing incidence rate of patients with AAI in Australia from 2005 to 2014. Different trends were reported by sex, age and state. I found a shift towards more AAI prescriptions being provided by general practitioners (GPs) rather than specialists in most regions in Australia. By using the data from the School Entrant Health Questionnaire in Victoria, Australia, I investigated the risk factors of anaphylaxis in the general population. I found an association between Asian ethnicity and anaphylaxis risk in children living in Australia and identified the high-risk group (Australian-born children with Asian-born mothers) for anaphylaxis. Lastly, I used data from the HealthNuts study to explore the frequency and risk factors of anaphylaxis in food allergic children from a community setting. I found a high frequency of experiencing anaphylactic reactions (11.5%) in the preceding 12 months in children with food allergy. In summary, the results presented in this thesis have provided further knowledge on the epidemiology of anaphylaxis and food-induced anaphylaxis in the general population and identified important predictors of anaphylaxis in the general population and the food allergic population. The identification of these essential predictors has important implications for the management of anaphylaxis and will improve our understanding of the development of anaphylaxis.
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ItemIntragenic DNA methylation and neurodevelopmental outcomes in children with fragile X-related disorders( 2019)The type and severity of clinical involvement in children with fragile X syndrome (FXS) and disorders related to premutations (PM) of the fragile X mental retardation 1 gene (FMR1), herein collectively denoted as fragile X-related disorders (FXDs), is highly variable. Multiple molecular factors contribute to the heterogeneity of neurodevelopmental outcomes. Increased intragenic DNA methylation (DNAm) in blood of the fragile X-related epigenetic element 2 (FREE2) region, located at the FMR1 exon 1/intron 1 boundary, was associated with lower intellectual functioning in a cohort of female children and adults with FXS and with neuro-cognitive and psychiatric phenotypes in women with PM. Nevertheless, FREE2 DNAm has not yet been investigated in exclusively paediatric male and female FXDs cohorts. The overarching aim of this thesis was to explore FREE2 DNAm and neurodevelopmental outcomes of Australian male and female children with FXDs. Matrix assisted laser desorption/ionization time-of-flight mass spectrometry and methylation specific-quantitative melt analysis were used to analyse FREE2 DNAm in venous blood, buccal epithelial cells (BEC) and retrieved newborn blood spots (NBS). In addition, FMR1 mRNA levels in blood were assessed using real-time polymerase chain reaction (PCR) relative standard curve method. The evaluation of the neurodevelopmental outcomes concentrated on direct clinical assessment of intellectual functioning and autism spectrum disorder (ASD) symptom severity. Intelligence Quotient (IQ) scores were corrected for floor effect using the Whitaker and Gordon (WG) extrapolation method. The findings highlighted the variability of the clinical presentation of children with PM. Results also showed that compared to sex-matched paediatric controls, children with FXS had significantly higher levels of FREE2 DNAm levels in blood and BEC and, within the FXS group, higher FREE2 DNAm levels in blood correlated with lower FMR1 mRNA levels. In children with FXS, the application of the WG method effectively addressed the floor effect inherent in standardised intelligence scales, unmasked inter-individual variability in IQ scores and uncovered significant associations between intragenic DNAm and neurodevelopmental outcomes. Strength and statistical significance of these epigenotype-phenotype relationships varied based on sex, position of the differentially methylated sites, tissue analysed, assay used and neurodevelopmental domain investigated. The most significant finding was in males with FXS, for whom higher levels of BEC FREE2 DNAm were associated with lower WG-corrected Full Scale IQ (cFSIQ) and Performance IQ (cPIQ) scores. Finally, findings showed that the best-performing FREE2 biomarker had sensitivity, specificity, negative and positive predictive values of 100% for detection of full mutation alleles in NBS of males and females with FXS. Additionally, this study revealed that for males with FXS, FREE2 DNAm in NBS was significantly associated with lower cFSIQ and cPIQ scores obtained in childhood and adolescence. This is the first study in any monogenic neurodevelopmental disorder associated with intellectual disability, showing that a perinatal epigenetic biomarker is significantly associated with paediatric neuropsychological outcomes. In conclusion, the results of this thesis contribute to the characterisation of the neurodevelopmental outcomes in children with FXDs, provide evidence that FREE2 DNAm is a sensitive epigenetic biomarker significantly associated with the variability of intellectual functioning in male children with FXS, and may have implications for the development of new methylation specific tests for earlier diagnosis with potential prognostic applications.