Development of an early life risk stratification tool to facilitate primary prevention of the metabolic syndrome by infant nutritional intervention
The metabolic syndrome is of enormous global importance due to its high prevalence and consequent health and socioeconomic burden. Whilst much of the pathogenesis of the metabolic syndrome centres around adult lifestyle influences, there is also a significant contribution from early life influences, consistent with the Developmental Origins of Health and Disease paradigm. The early life period of developmental plasticity affords an opportunity to implement interventions which may modify an
... idual's risk of adult metabolic disease. Identifying those at increased disease risk is paramount in selecting candidates who are most likely to benefit from early life primary prevention. Such identification requires a novel approach as traditional risk factors are not apparent in early life. Abnormal fetal growth, given its association with metabolic disease, may identify those at risk. Genetic risk assessments may also be undertaken based upon those variants known to be associated with adult metabolic phenotypes; however, the relationship between these variants and early life pathophysiology requires assessment. Aim This thesis aims to develop a method for the early life identification of individuals at high risk of adult metabolic syndrome and to assess the role of early life nutrition upon metabolic outcomes. Methods and Findings This study employed the unique resource to epidemiological research that is the Western Australian Pregnancy Cohort (Raine) Study, whose detailed longitudinal data concerning fetal growth trajectories, early life nutrition, family sociodemographic factors, adolescent and young adult metabolic phenotypes, and genomic variants allow the assessment of Abstract v relationships between these contributors to the developmental origins of the metabolic syndrome. Phase 1 required the assessment of the cohort and its representativeness of its source population in order to determine the external validity of the findings of this work. There was no evidence of significant perinatal selection bias within the Raine Study, although it is of note that the further analyses of this thesis were limited to a homogeneously Caucasian subset and caution is required in the extrapolation of the results to other ethnic groups. Phase 2 involved the assessment of the relationship between adequacy of fetal growth and adult metabolic disease risk factors. Novel methodology for the customised assessment of fetal biometric parameters was developed. Overall, no measure of fetal growth was found to be useful as a screening test to stratify individual risk of subsequent metabolic disease risk. Phase 3 assessed the capacity of genomic markers to predict later disease risk. A proof of principle study was performed using variants from within the leptin candidate pathway, demonstrating significant associations of LEP and LEPR variants with both altered fetal growth and adult metabolic parameters suggesting the feasibility of this approach. Expansion of this methodology showed the importance of assessing both maternal and fetal genomic variants in order to determine their influence upon early life physiology, whereby the majority of variants associated with adult metabolic disease phenotypes also had demonstrable associations with altered fetal growth. A unique genetic association between fetal macrosomia and adult hyperglycaemia was found, leading to the proposal of a novel genetic hypothesis linking these two outcomes. In Phase 4, genetic risk scores were derived, describing an individual's complement of genomic variants known to influence metabolic outcomes and also fetal growth. These risk scores were Abstract vi strongly correlated with relevant phenotypes in the Raine Study participants and were able to stratify individuals by their disease risk. Phase 5 assessed the interactions between genetic risk score and early life nutrition in relation to adult metabolic outcomes. This demonstrated a significant benefit of exclusive breastfeeding, with those at high genetic risk showing the greatest reductions in adult disease risk when exclusive breastfeeding was maintained for longer periods. Conclusion This thesis describes the capacity of a genetic risk score to identify, during early life, individuals at high risk of adverse adult metabolic phenotypes. An interaction with infant nutrition suggests exclusive breastfeeding in those at high genetic risk of adult metabolic syndrome has the capacity to substantially mitigate this risk. The concept of early life primary prevention of adult disease appears to have substantial clinical merit and requires further refinement. vii CONTENTS Thesis declaration i Abstract iv Aim iv Methods and Findings iv Contents vii REFERENCES 318 xiii ACKNOWLEDGEMENTS This thesis is the result of over six years of effort and would not have been completed without the significant contributions of several people. I would like to take this chance to acknowledge those individuals and their contributions. Firstly, I wish to acknowledge the ongoing commitment of the participants of the Raine Study and their families who continue to engage with this study after nearly three decades of research. I also wish to acknowledge the support of the Faculty of Medicine, Dentistry, and Health Sciences at The University of Western Australia and the Athelstan and Amy Saw Scholarship, the Royal Australian and New Zealand College of Obstetricians and Gynaecologists and the Jean Murray Jones Memorial Scholarship, and the Women and Infants Research Foundation for their generous financial support of my candidature. Prior to starting this project, I had no formal experience in scientific research. My supervisors have guided me through the process of formulating a research question, developing an experiment to test the hypothesis, evaluating and presenting its results, and assessing the findings in the relevant scientific context. Professor Stephen Lye and Assistant Professor Laurent Briollais provided particular support in experimental design and statistical methodology and I am very grateful for their assistance. Professor John Newnham provided expert assistance with the interpretation and presentation of results and greatly contributed to my development as a scientific writer and presenter. Associate Professor Craig Pennell provided guidance in all aspects of this work. With their mentorship, patience, and wisdom, my supervisors have helped me transform from clinician to clinical academic, and I will remain indebted to them for this support.