Paediatrics (RCH) - Theses
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Item4.7 Tesla magnetic resonance imaging and spectroscopy of infants with neonatal encephalopathy(University of Melbourne, 2007)
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ItemNo Preview AvailableEarly lifecourse body composition and adolescent cardiovascular function and structure: A community-based longitudinal cohort study( 2021)http://hdl.handle.net/11343/321883 Background: Understanding if the timing, duration and severity of childhood body composition, from lean to obese, is associated differentially with adolescent cardiovascular phenotype will enable a better understanding of the timing and nature of adiposity-associated cardiovascular risk. Aims: To examine how adolescent cardiovascular function and structure are associated with (1a) individual or (1b) combined measures of adolescent body composition; (2) body mass index (BMI) trajectories between birth and 14 years; and (3) BMI, fat mass index (FMI), lean mass index (LMI) and waist-to-height ratio (WHtR) trajectories between 4 and 14 years. Methods: Design: Participants from the PEAS Kids Growth Study, a longitudinal community-based cohort in Melbourne, Australia, were measured on 16 occasions from birth (n=493) to 14-17 years (n=196 with cardiovascular data). Measures: Body composition: BMI/waist z-score, WHtR, FMI, LMI. Cardiovascular phenotypes: Systolic/diastolic blood pressure (S/DBP), augmentation index (AIx), pulse wave velocity (PWV), retinal arteriole-to-venule ratio (AVR), carotid intima media thickness (cIMT). Analysis: Aim 1-3: Adjusted linear regression models assessed associations between adolescent body composition/childhood trajectory and cardiovascular phenotype. Aims 2-3: Latent class analysis identified participants with similar childhood body composition trajectories. Results: 196 PEAS adolescents (75% of invited, 46% male) completed a direct assessment of cardiovascular phenotype. Aim 1: Each SD increase in adolescent BMI z-score was associated with higher SBP (2.5mmHg, CI: 0.9 to 4.0) and AIx (2.9%, CI 1.2 to 4.6). Higher waist z-score, FMI and LMI were also associated with higher SBP and AIx; but not DBP, PWV, AVR, or cIMT. Moderate variance was explained by each adjusted model (highest for BMI z score with SBP, R2=0.24). Aim 2: Three BMI trajectories were identified: low normal, high normal, and consistently overweight between birth and 14 years. Consistently overweight children had higher AIx (7.8%, CI 2.6 to 13.0, R2=0.13) but no other differences in cardiovascular phenotype compared the reference group. Aim 3: Three trajectory groups of BMI, WHtR, FMI and LMI (low, medium, and high) were identified between 4-14 years. Children following the high FMI trajectory had higher SBP (5.6mmHg, CI 1.1 to 10.1, R2=0.22) and DBP (3.9mmHg, CI 0.7 to 7.2, R2=0.08), compared to the reference group. Those in high BMI and WHtR trajectories had higher AIx and SBP (WHtR trajectory only); but vascular structure was similar for all, regardless of body composition trajectory. In contrast, LMI trajectories were not associated with any measure of function or structure. Discussion: Associations were evident between adolescent and 10-year trajectories of BMI, FMI, and WHtR with cardiovascular function. Interestingly, associations between LMI and cardiovascular function were only evident cross-sectionally in adolescence. Nonetheless, despite high BMI, FMI and WHtR for over a decade, and poorer cardiovascular function, following a high trajectory during childhood was not associated with worse vascular structure in mid-adolescence in this cohort. This may be due to the small number of very obese adolescents in this sample. Future studies measuring body composition and cardiovascular phenotype throughout childhood and into adulthood are necessary to understand how to minimise adiposity-associated lifecourse cardiovascular risk.
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ItemInter-arm blood pressure differences at rest and exercise: significance in children and potential mechanisms( 2021)High blood pressure (BP) is one of the leading risk factors for cardiovascular disease and is a key contributor to arterial stiffening, end organ damage, and cognitive decline. Importantly, high BP often begins in childhood, and if left untreated may track into adulthood. However, if diagnosed and treated, reducing high BP lowers the risk of disease. Clinical guidelines for best practice with regards to BP measurement have been established for both adults and children. Although not routinely followed in many settings, a common recommendation for both adult and paediatric populations is to measure BP in both arms. The measurement of bilateral BP holds clinical importance as an inter-arm blood pressure difference (IAD) of greater than or equal to 10 mmHg (IAD+) is associated with cardiovascular disease and premature morbidity and mortality in adults. Additionally, both the magnitude and prevalence of IAD+ has been shown to increase with exercise. While IAD has been investigated in adults, no studies exist on IAD in children despite the recommendation to measure bilateral BP in clinical guidelines. Further, the mechanisms which cause this difference remain unknown. Therefore, the primary purpose of this thesis was to examine IAD in children and adolescents under resting conditions, exercise conditions, and explore a potential mechanism which may result in IAD. Four investigations were performed that 1) quantified the magnitude of IAD and the frequency of IAD+, as well as determined inter-arm BP classification differences, under resting conditions in children and adolescents; 2) generated normative data for exercise BP response in children and adolescents undergoing treadmill exercise stress tests to enable objective assessment of exercise BP classification; 3) quantified the magnitude of IAD and frequency of IAD+ and inter-arm classification differences under exercise conditions in children and adolescents; 4) used a one-dimensional computational model to investigate inter-arm difference in arterial stiffness as a potential mechanism underlying IAD. The frequency of IAD+ in children and adolescents was similar to that of adults under both resting an exercise conditions. The average magnitude of IAD was 5 mmHg under resting conditions and 7 mmHg under exercise conditions.The inter-arm classification difference was ~20% under resting conditions. Normative data generated from treadmill exercise tests was used to determine that ~10% of children and adolescents have an exercising inter-arm classification difference. Lastly, the modelling study supported the hypothesis that inter-arm differences in regional arterial stiffness may contribute to IAD. Data presented in this thesis supports the recommendation to measure BP in both arms and provides a strong rationale for conducting this measurement in apparently healthy children. Measuring BP in both arms under both resting and exercise conditions may be important for detecting high BP in children and adolescents. Lastly, it was shown that mechanistic investigations with regards to IAD can be performed using 1D models and may be useful where in-vivo studies are not physiologically possible.
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ItemExome sequencing in infants with congenital deafness, a model for genomic newborn screening( 2021)Background Genomic technology is emerging as a powerful diagnostic tool to provide precision management and personalised care. It also has potential to be used at a population level to provide predictive and tailored health information, including as part of newborn screening (NBS). NBS traditionally detects serious and treatable childhood conditions, including congenital hearing impairment. As the majority of childhood hearing impairment has an underlying genetic cause, genomics is the ideal technology to investigate this condition. Aims and Methods The aims of this research were to: a) characterise the genetic causes of congenital hearing impairment in the population; b) understand the impact genomic testing has on the pathway of care following this diagnosis; and c) examine the factors that may influence the uptake and success of a genomic NBS tool. The methods used to investigate these aims were: 1. Offering diagnostic genomic testing to a cohort of infants with hearing impairment and observing the effect of this investigation on their healthcare journey; 2. Determining the cost-effectiveness of this genomic testing pathway when compared with the standard of care; 3. Offering parents additional analysis of non-deafness genes and investigating what factors influence their choices around seeking predictive health information for their infant; 4. Undertaking a systematic literature review to understand the current status of the field of genomics as a potential tool for NBS. Results Genomic sequencing was performed on 106 infants diagnosed with congenital deafness through newborn screening. Fifty-nine infants (56%) had a genetic cause for their hearing impairment. The majority (n=38, 36%) had a diagnosis that indicated their hearing impairment was isolated, such that they did not need to undertake surveillance for other health conditions. Those who received a syndrome diagnosis (n=21, 20%) were able to access accurate prognostic information, support and tailored healthcare. Streamlining the care of this cohort according to their underlying diagnosis was cost-effective when compared to standard of care, where most infants do not have a cause for their hearing impairment identified. Genomic testing also had non-health related benefits for families, i.e., personal utility. Parents made varying choices regarding receiving predictive information from the testing. Seventy-two parents (68%) accepted the offer of additional information. These findings are consistent with those identified in our systematic review of the literature – that “one size does not fit all”. Conclusion Offering genomic sequencing to a cohort of infants with congenital hearing impairment served as an ideal model to investigate genomic NBS. It re-enforced the diagnostic power of the test for congenital hearing impairment, translating into a cost-effectiveness analysis and an application for a Medicare item number. More broadly, this research identified the key elements required for genomic NBS to be acceptable and successful at a population level. Areas for future work are to refine the scope of testing with a strategy for gene list composition, and to identify the optimum timing and consent process. Getting these elements right will enhance newborn screening by increasing its scope and sensitivity, not just for congenital hearing impairment, but for improving the health of many children and their families.
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ItemModelling development of the human adaptive immune system in vitro( 2021)The human adaptive immune system provides a specialized function in the defense of the body against invading pathogens. Abnormal development of the adaptive immune system is thought to cause autoimmune disorders. Its development requires spatiotemporal coordination of multiple embryonic activities, including hematopoiesis, development of lymphoid organs, and hematopoietic colonization. Here, we focus on T cell and thymus development and use pluripotent stem cells (PSCs) to create multiple cell types that are known to contribute to thymus ontogeny. We demonstrate new methods for generating human hematopoietic cells, endothelial cells and thymic epithelial cells from PSCs in vitro, supported by three results chapters. Chapter 3 describes the generation of macrophages from PSCs and comprises a submitted manuscript in the journal format. The manuscript describes a novel streamlined protocol that enables the differentiation of macrophages from different PSC lines and shows that these PSC-derived macrophages can be infected with Mycobacterium abscessus. This submitted manuscript also includes a proof-of-principle demonstrating that this platform can be used to assess antibiotic sensitivities. Chapter 4 describes the derivation and characterization of thymic epithelial cells from PSCs and primary human thymus. This work comprises a manuscript which has been peer-reviewd and published in the journal Frontiers in Immunology; the published version is included in Chapter 4. The manuscript shows the identification of a new CD90 (THY1) + thymic epithelial cell population expressing genes associated with both epithelial and mesenchymal cell profiles, highlighting the ambiguous cell identity of thymic epithelial cells. Chapter 5 describes the derivation of arterial-like endothelial cells expressing DLL4, a ligand that is important for inducing hematopoietic stem cells to commit to the T cell lineage. Additional experiments explored the effects of different concentrations of SCF and IL7 on the production of CD4+CD8+ T cell progenitors, assessed by expression of RAG1:GFP, CD7 and IL7R, and CD4 and CD8. These experiments suggest opposing functions of SCF and IL7 in lymphoid cell production. This chapter also describes a pilot coculture experiment aimed at assembling an artificial thymus using the above materials. This thesis examined multiple lineages that are known to be important during the ontogeny of the human adaptive immune system, with a particular emphasis on events related to thymus development. This work lays a foundation for future studies aimed at understanding and manipulating the generation of human immune cells. This thesis also includes three scientific blog articles in the Appendix, written and published for the International Society for Stem Cell Research for scientific communication and public engagement.
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ItemEarly life oral exposures as risk factors for food allergy and the impact of infant feeding guidelines( 2021)Food allergy is a severe immune reaction affecting around 10% of infants. The recent rise in food allergy is a growing public health concern. Susceptibility to food allergy is affected by environmental exposures that affect infant gut immunity, including oral food and microbial exposures. Changes in infant feeding guidelines recommending introduction of allergenic foods in the first year were the first public health measure introduced specifically to prevent food allergy. I aimed to evaluate their impact on timing of allergenic food introduction and prevalence of food allergy, as well as investigating oral microbial exposure as a potential food allergy risk factor. The effect of 2016 updates to infant feeding guidelines on food allergy was evaluated using two large population-based cross-sectional studies (n=5,300 and n=1,933) that recruited 12-month-old infants in Melbourne, Australia 10-years apart (2007-2011 and 2018-2019) to study allergenic food introduction and peanut allergy. Microbial exposure was investigated in relation to food allergy using data from a cohort study (n=1,072) based in south-east Australia which measured pacifier cleaning methods in the first year of life. Data were analyzed using multivariable logistic regression models and direct standardization. Regression models were adjusted for known food allergy risk factors, depending on the exposure. An overview of systematic reviews searched systematic reviews in four databases to examine age of complementary feeding in relation to other health outcomes. These studies are the first report that peanut introduction by 12 months of age (inclusive) in the population increased (88% in 2018-2019 vs 28% in 2007-2011) following the implementation of 2016 infant feeding guidelines. Despite this massive shift, peanut allergy prevalence did not decrease as much as expected (3.1% to 2.6%). However, the increase in peanut introduction seems to have halted the rise of peanut allergy in one-year-old infants. The systematic review found 27 reviews on age of complementary or allergenic food introduction on multiple outcomes. There was no evidence of a detrimental effect on other health outcomes of the recommended introduction of solids and allergenic foods starting around 6 months of age, though solids introduced earlier than 4 months could increase the risk of overweight. Furthermore, sanitization of infant pacifier with antiseptics at 6 months of age increased the risk of food allergy at age one, possibly an effect of the chemicals on oral or gut microbiome. An increase in early introduction following 2016 guideline changes has halted the overall rise in peanut allergy. Nevertheless, peanut allergy is still high in Melbourne, thus additional prevention strategies are required. Reassuringly, other health outcomes are not risked by the recommended age of allergenic food introduction. The findings on cleaning pacifiers with antiseptics suggests that suggests microbial exposure can protect against food allergy. This warrants further interventional studies to determine if microbial exposures could prevent food allergy. Moreover, early life risk factors, prior to food introduction, need to be explored further.
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ItemEffect of a high-level mobility skills training programme on sustained physical activity participation among ambulant children with cerebral palsy( 2021)Abstract: Objective: Sustained participation in physical activity is important for everyone. This thesis (i) systematically reviewed the evidence for the ability of physical activity interventions to enhance attendance and involvement in physical activity (study 1); (ii) assessed the effect of a community-based high-level mobility skills programme (HLMP) on participation in physical activity among ambulant children with cerebral palsy (study 2); and (iii) explored the children and their parents’ experiences of being active (study 3). Methods: Study 1 consisted of a systematic literature review. Seven databases were searched using PRISMA guidelines (2001-2020). Study 2 used a single-subject research design (SSRD) to evaluate quantitative outcomes after implementation of the HLMP. Ambulant children with cerebral palsy (aged 7–18 years) were invited to participate in a 12-week community-based HLMP that provided task-specific training of running skills. Each study participant set personal participation attendance, involvement, and physical competency goals and completed activity diaries for 56–58 weeks. Outcomes were collected during a baseline phase (4–6 weeks), an intervention phase (12 weeks), and during a nine-month follow-up phase that included a COVID lockdown. In study 3, semi-structured interviews were conducted at baseline, post-intervention, and at the end of follow-up with child-parent pairs. An interpretive description approach was used and guided coding and development of themes. Results: The systematic review included 11 randomised controlled trials and two cohort studies, all of which included only short-term follow-up. Two studies reported short-term gains in attendance in the 4–14 weeks following the physical activity intervention and one study reported an improvement in involvement during a follow-up period of one month. Eight ambulant children with cerebral palsy (aged 11–16 years, seven male) were recruited for study 2. Seven of the eight participants attended a median 23 of 24 HLMP sessions over 12 weeks, attained their involvement goal in at least two study phases and achieved at least one physical goal during the HLMP (11/15 goals), with continued attainment over the next 9 months (9/16 goals achieved). The frequency of attendance varied, with participant’s diaries indicating 0–17 sessions of being active per week during all study phases. Diversity of physical activities (variety and range of formal and informal physical activities) remained stable at 1–4 different activities per week (range 0–7). On testing, physical capacity increased post-intervention in the seven children who attended the HLMP and skill competency increased in six participants at the 6-month follow-up. Children and their parents valued being active now and into adulthood, reporting improved motivation, confidence, and physical well-being following the HLMP. Core themes were developed: ‘just doing it’, ‘getting the mix right’ (right people, right place, right time), ‘balancing the continua’ and ‘navigating the systems’. Co-designing, connecting and collaborating were seen as important to promote sustained participation for life. Conclusion: Children with cerebral palsy can achieve participation and physical goals, be highly involved in their chosen physical activities, and improve their physical competency. The community-based, task-specific goal-directed HLMP was able to keep some, but not all, children “on track” to achieve sustained participation in physical activity. Each child’s journey was complex and dynamic.
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ItemAtrioventricular valve function during single ventricle palliation( 2021)Single ventricle anomalies encompass a spectrum of the most severe congenital heart disease. Staged surgical palliation culminates in the Fontan circulation, wherein the functional single ventricle pumps blood to the systemic circulation and returning blood flows passively through the pulmonary circulation, without the support of a subpulmonic ventricle. Surgical modifications and advancements in non-operative management have led to a significant decline in early mortality following the Fontan operation. As such, the population of patients living with a Fontan circulation is expected to double over the next 20 years, including a growing proportion of patients surviving well into adulthood. Due to inherent anatomical and physiological limitations, the Fontan circulation is characterised by elevated systemic venous pressure and reduced cardiac output. Atrioventricular valve (AVV) regurgitation impairs pulmonary venous return leading to increased post-capillary venous pressures and further increasing systemic venous pressure. Furthermore, AVV regurgitation increases the volume load on the single ventricle which can lead to ventricular dilatation and impaired function. Studies have demonstrated that AVV regurgitation and AVV surgery are associated with worse clinical outcomes during the initial stages of single ventricle palliation, but little is known about the cumulative impact of AVV regurgitation and AVV surgery over the lifetime of patients undergoing single ventricle palliation. The aim of this thesis was to (i) determine the cumulative incidence of, and risk factors for, moderate or greater AVV regurgitation during the lifetime of patients undergoing Fontan palliation, (ii) determine the impact of moderate or greater AVV regurgitation on clinical outcomes in patients with a Fontan circulation, and (iii) determine the impact of AVV surgery on long-term AVV competency and clinical outcomes in patients undergoing single ventricle palliation. The studies contained within this thesis were conducted with data primarily from the Australia and New Zealand Fontan Registry, which is the largest database of Fontan survivors in the world. In this thesis I have demonstrated that: (i) there is a high rate of moderate or greater AVV regurgitation during the lifetime of patients with a Fontan circulation, (ii) risk factors for moderate or greater AVV regurgitation and AVV surgery include right ventricular (RV) dominance, atrioventricular septal defect (AVSD), mitral atresia, right atrial isomerism, aortic atresia, and prior AVV repair, (iii) moderate or greater AVV regurgitation in patients with a Fontan circulation is associated with an over two-fold increased risk of death or transplantation, but only in patients with RV dominance, (iv) in patients with AVSD and a Fontan circulation, the high rate of moderate or greater AVV regurgitation is primarily due to the anatomy of the common AVV, and is not impacted by ventricular dominance, (v) AVV surgery itself is not a risk factor for death or transplantation in patients with a Fontan circulation, but rather it is the patient’s characteristics necessitating AVV surgery that are associated with an increased risk of death or transplantation, (vi) patients with tricuspid valve repair failure are at high risk of death or transplantation, but successful tricuspid valve repair improves transplantation-free survival rates in patients with moderate or greater AVV regurgitation, (vii) patients with functional AVV regurgitation and impaired ventricular systolic function are at increased risk of death or transplantation after AVV repair, (viii) AVV closure is a safe and effective surgical technique for management of AVV regurgitation in patients with a Fontan circulation and two AVVs, where the diminutive valve is regurgitant. This thesis has revealed the enormous burden of AVV regurgitation and AVV surgery in patients with a Fontan circulation. In doing so, it has drawn attention to AVV regurgitation as one of the most important issues in the management of patients undergoing single ventricle palliation. Ultimately, by improving our understanding of the incidence and natural history of AVV regurgitation, this thesis will improve the long-term outcomes of many patients living with a single ventricle circulation.
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ItemAutism spectrum disorder in children with neurofibromatosis type 1: A cross-sectional study of the autistic phenotype and sex- and age-differences in autistic symptoms( 2021)Background: Neurofibromatosis type 1 (NF1) is a monogenic syndrome associated with complex and impairing clinical and neurodevelopmental sequelae. Social difficulties are commonly reported and there is accumulating evidence for an elevated prevalence of autism spectrum disorder (ASD) in children with NF1. While the genetic specificity of NF1 offers a promising model for clarifying the causal pathways to ASD, the autistic symptom profile in children with NF1 remains poorly understood. Aims: This thesis aimed to critically evaluate ASD phenomenology in NF1, and to elucidate the autistic phenotype and the factors that might influence the expression of core autistic symptoms in children with NF1. Methods: We conducted a systematic review and meta-analysis to examine the existing evidence for social dysfunction and ASD in NF1. A cohort of children with NF1 that scored within the clinical range on the Social Responsiveness Scale, Second Edition (SRS-2) was assessed with the Autism Diagnostic Interview - Revised (ADI-R) and the Autism Diagnostic Observation Schedule, Second Edition (ADOS-2). Participants also underwent evaluation of their intellectual function and data pertaining to emotional and behavioural functioning were gathered via parent rating scales. Results: Meta-analytic data indicated a significantly increased incidence of social dysfunction (g = 0.79) and autistic symptomatology (g = 0.91) in NF1. In the NF1 cohort (N = 68; 3-16 years), a substantial proportion of children met algorithmic cut-offs on the ADI-R (63%) and ADOS-2 (34%). Social communication deficits were analogous to those observed in idiopathic ASD, but we detected a distinct profile of restricted and repetitive behaviours (RRBs) characterised by ‘insistence on sameness’ behaviours such as circumscribed interests and difficulties with minor changes. Males displayed greater social communication deficits relative to females, and age-related gains in social communication skills were evident in males but not females. Generally weak associations were found between autistic symptoms and child characteristics not specific to ASD (e.g., language delay, anxiety). However, sex differences in early language development and verbal intellect contributed to the observed sex disparities in social communication skills. Conclusions: Our novel findings identify a unique autistic phenotype in children with NF1 and establish the relative independence of autistic symptoms from common NF1-related neurodevelopmental comorbidities. This work also provides new insights into the modulating effects of sex and age on the severity of autistic symptoms and underscores the importance of taking non-specific child characteristics into account when interpreting scores from autism measures in this population. Current findings may be used to facilitate earlier and more accurate recognition of ASD in children with NF1 and represent a significant step towards the identification of precise genotype-phenotype relationships in NF1.