1 Improvement of the nutritional management of glycogen storage disease type I Kaustuv Bhattacharya Presented for the degree of MD (res) at University College London 2 “The roots below the earth claim no rewards for making the branches fruitful” Sir Rabrindranath Tagore Stray Birds (1917) Acknowledgements Whilst this thesis is my own work, it is the product of several helpful discussions with many people around the world. It was conducted under the supervision of Philip Lee who, since completion of the data collection, faced bigger personal challenges than he could have imagined. I hope that this work is a fitting conclusion to one strategic direction, of some of his research, which I hope he can be proud of. I am very grateful for his help. Peter Clayton has been a source of inspiration throughout my “metabolic” career and his guidance throughout this process has been very gratefully received. I appreciate the tolerance of my other colleagues at Queen Square and Great Ormond Street Hospital that have accommodated in different ways. The dietetic experience of Maggie Lilburn has been invaluable to this work. Simon Eaton has helped tremendously with performing the assays in chapter 5. I would also like to thank, David Morley, Amy Cole, Martin Christian, and Bridget Wilcken for their constructive thoughts. None of this work would have been possible without the Murphy family’s generous support. I thank the Dromintee Trust for keeping me in worthwhile employment. I would like to thank the patients who volunteered and gave me so much of their time. The Association for Glycogen Storage Disease (UK), Glycologic Ltd and Vitaflo Ltd have also sponsored these trials and hopefully facilitated a better experience for patients. Thank you. My wife Geraldine and children Aarun and Mya have had to accommodate this work at times when it would have been very inconvenient for them. Thank you for your patience. 3 Contents Summary of thesis……………………………………………………………….. 8 Chapter 1 – Introduction 1.1 Carbohydrates - properties and metabolism ………………………………... 9 Glucose 9 Starch 10 Release of glucose from dietary starch 11 Absorption of glucose 12 Humoral response to glucose 14 1.2 Hepatic glycogen storage diseases…………………………………………….. 19 Glycogen 19 Metabolism of glucose and glycogen 19 Glycogen storage disease – Historical aspects 21 Glycogen storage disease type I 23 Glycogen storage disease type III 25 Glycogen storage disease type VI 26 Glycogen storage disease type IX 27 Historical treatment of glycogen storage disease type I 29 Complications of GSD I related to diet 29 1.3 Carbohydrates – Dietary treatment in GSD and in healthy individuals…...32 Specific Dietary Treatment of GSD 32 The role of the physical properties of a starch on metabolic control 34 Studies in the general population – GIycemic Index and Insulin 35 1.4 Outline and Aim of thesis………………………………………………………... 38 4 Chapter 2 - Patients and methods 2.1 Background to methods used…………………………………………………... 39 Cornstarch loads 39 Glucose & lactate 41 13 Stable isotopes - natural enrichment of CO2 in the breath 43 Hydrogen breath test 46 Dietary assessment 47 2.2 Patients………………………………………………………………………………. 51 Chapter 3 – Dietary analysis of glycogen storage disease Introduction………………………………………………………………………………55 3.1 Dietary case histories……………………………………………………………... 56 3.2 A cross sectional survey of the diets of children and adults with hepatic glycogen storage disease…………………………………………………………….. 63 Method 63 Results 64 3.3 Discussion………………………………………………………………………….. 74 Total Energy and Carbohydrate 74 Intake of Fat 79 Micronutrient intake 83 Social impact of the diet 85 Appraisal of methods 86 3.4 Conclusion....................................................................................................... 90 5 Chapter 4 - Short –term biochemical response to heat modified waxy maize starch 4.1 Introduction…………………………………………………………………………. 91 4.2 Pilot Study…………………………………………………………………………… 91 Method 91 Results 92 4.3 Short-term biochemical outcome of the use of WMHM20 in adults and children with GSD I and III……………………………………………………………. 94 Introduction 94 Methods 94 Results 96 4.4 Short-term Biochemical outcome of the use of Vitastarch in adults with GSD I……………………………………………………………………………………… 102 Introduction 103 Methods 103 Results 104 4.5 Discussion………………………………………………………………………….. 110 4.6 Conclusion………………………………………………………………………….. 117 Chapter 5 – Gastrointestinal processing of uncooked cornstarch & heat modified waxy maize starch – breath tests 5.1 Introduction………………………………………………………………………… 118 5.2 Short-term study of the utilisation and fermentation of 2g/kg of uncooked cornstarch compared to WMHM20 in children and adults with GSD I and III.. 119 Introduction 119 Method 119 Results 122 6 5.3 Short-term study of the fermentation 50g of uncooked cornstarch compared to Vitastarch adults with GSD I…………………………………………. 126 Introduction 126 Method 127 Results 128 5.4 Discussion…………………………………………………………………………. 130 5.5 Conclusion…………………………………………………………………………. 139 Chapter 6 – Longterm use of Vitastarch in GSD 6.1 Introduction..................................................................................................... 141 Methods 141 Results 146 6.2 Discussion…………………………………………………………………………. 158 6.3 Conclusion…………………………………………………………………………. 162 7 – Discussion And Further Studies 7.1 Summary of studies performed…………………………………………………. 163 7.2 Limitations of studies…………………………………………………………….. 165 7.3 Further Studies…………………………………………………………………….. 166 Dietary Therapy 166 Efficacy of Vitastarch 172 Mechanism of action 174 7.4 Conclusion 176 References 177 Appendix 1 (Dietary control data for chapter 3) 189 Appendix 2 (Symptom monitoring data – chapter 6) 19 Appendix 3 (Product evaluation questionnaire chapter 6) 7 Summary Patients with hepatic glycogen storage diseases are at risk of hypoglycaemia after short fasts. They require an intensive dietary treatment regimen, including feeds as often as 2 hourly and overnight continuous glucose feeds. The use of uncooked corn- starch helps children and adults to have longer fasting intervals and some to discontinue overnight pump feeds of glucose polymer via a gastric feeding tube. Unfortunately, some adults still remain dependent on nocturnal pump feeds and, for some, frequent doses of starch are still required during the daytime. Some have symptoms of flatulence, abdominal bloating and diarrhoea which may be caused by starch mal-digestion. This thesis studies the short- and longer-term effects of the introduction of a novel, physically-modified corn-starch into the dietary regimen of patients with two of the more severe forms of hepatic glycogen storage disease. Based on the findings of this thesis, updated dietary recommendations can be made to patients with hepatic glycogenoses and their families. 8 CHAPTER 1 - INTRODUCTION 1.1 Carbohydrates – properties and metabolism Glucose The metabolism of glucose is a fundamental requirement for many energy requiring processes in living organisms. Plants fixate energy from the sun by photosynthesis to create simple sugars such as glucose, polymers of which form the most exported form of energy. 2 At physiological pH, the straight-chain form of glucose forms covalent bonds between the aldehyde group of carbon 1 and carbon 5 forming a glucopyranose ring (figure 1.1). The orientation of the hydrogen and hydroxyl group around carbon 1 determines whether D-glucose is an alpha or beta orientation. This stereochemistry of glucose gives it wide ranging properties, such that it can be stored in several different forms. 6 6 5 5 4 1 4 1 3 2 3 2 Figure 1.1 – Structure of straight chain glucose (Fisher projection - 1.1a), α- glucopyranose (1.1b) and β-glucopyranose (1.1c) In animals, under aerobic conditions, the breakdown of each molecule of glucose culminates in the formation of 38 adenosine triphosphate molecules – this process is a fast and efficient means of releasing energy, allowing organisms to respond rapidly to changes in energy requirements.3 Plants store glucose as glucose polymer in various forms of starch, providing a reservoir of energy to be used according to fluctuating demands. 9 Starch Starch is a form of plant glucose polymer. It comprises linear chains of glucose molecules linked by α-1-4-glycosidic bonds, as well as alternative branched chains created by α-1-6 glycosidic bonds (figure 1.2). Amylose is almost exclusively linear 1,4 bonds whereas amylopectin comprises of both linear chains and branched 1,6 glycosidic bonds. 6 5 4 1 3 2 6 6 5 5 4 1 4 1 2 3 3 2 Figure 1.2 – Glucose polymerisation by the formation of linear α1-4 glycosidic bonds and branched α1-6 glycosidic bonds. Different species of plants have specific proportions of amylopectin and amylose as stored starch, resulting in species specific starch types. The significant effect stereochemistry has on glucose polymeric properties is typified by the structure of cellulose comprising glucose β-1-4-glycosidic bonds. In the β-orientation, the glycosidic bond is further strengthened by hydrogen bonds between adjacent 10 hydroxyl groups.2 Like amylose, cellulose is straight chained, but it is tough and fibrous and forms part of cellular architecture. It is also very resistant to digestion. Starch is organised as granules comprising both amylose and amylopectin chains. Amylopectin chains are often organised to form a crystalline structure with amylose chains filling intermediate space. Variation in granular organisation, determined by relative amounts and molecular interactions of amylose and amylopectin,