Twin and Family Risk from Environment and Epigenetics (FREE) Studies Reveal Strong
Environmental and Weaker Genetic Cues That Explain High Heritability of Eosinophilic
Esophagitis
A dissertation submitted to the Graduate School of the University of Cincinnati
in partial fulfillment of the requirements for the degree of
Doctor of Philosophy
in the Division of Epidemiology and Biostatistics
of the Department of Environmental Health
of the College of Medicine
2014
by
Eileen Steinle Alexander M.S.
B.S.N. University of Cincinnati College of Nursing, June 1980
M.S. University of Cincinnati College of Arts and Sciences Department of Biology, June 1993
with thanks to
Committee Co-Chairs: Paul A Succop, Ph.D. and Lisa J. Martin, Ph.D.
Members: Margaret H. Collins, M.D., Vincent A. Mukkada, M.D., Erin N. Haynes, D.Sc.
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Abstract
Background: Eosinophilic esophagitis (EoE) is a chronic antigen-driven allergic inflammatory disease, likely involving the interplay of genetic and environmental factors, yet their respective contributions to heritability are unknown. This work was developed to meet the needs of families affected by eosinophilic esophagitis, who asked, “Will my next child have EoE?”
Objectives: 1) recruit two study groups: a nuclear family group and twin registry and their first degree relations, collect data and samples, create database, design, analyze and fund family-based studies, 2) quantify risk associated with genes and environment on familial clustering of EoE, and
3) explore and direct new lines of EoE and family-based research, including epigenetic mechanisms and environmental factors, for EoE and related immunologic conditions. The long- term objective is to mitigate risk for families with underlying genetic susceptibility by reducing exposure effects.
Methods: Family history was obtained from a hospital-based cohort of 914 EoE probands,
(n=2192 first-degree “Nuclear-Family” relatives) and the new international registry of monozygotic and dizygotic twins/triplets (n=63 EoE “Twins” probands). Frequencies, recurrence risk ratios (RRRs), heritability and twin concordance were estimated. Environmental exposures were preliminarily examined. DNA collected from twins was analyzed using the Illumina
450Human Methylation array.
Results: Analysis of the Nuclear-Family–based cohort revealed the rate of EoE, in first-degree relatives of a proband, was 1.8% (unadjusted), 2.3% (sex-adjusted), RRRs ranged from 10-64, depending on family relationship, and were higher in brothers (64.0; p=0.04), fathers (42.9; p=0.004) and males (50.7; p<0.001) compared to sisters, mothers and females, respectively. EoE risk for other siblings was 2.4%. In the Nuclear-Families, combined gene and common
2 environment heritability (hgc ) was 72.0±2.7% (p<0.001). In the Twins, genetic heritability was
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14.5±4.0% (p<0.001); common family environment contributed 81.0±4% (p<0.001) to phenotypic variance. Proband-wise concordance in MZ co-twins was 57.9±9.5% compared to
36.4±9.3% in DZ (p=0.11). Greater differences in birth-weight were associated with disease discordance in twin pairs (p=0.01;n=35). Birth season was significantly different in concordant and discordant twin pairs (p=0.03;n=63); specifically, birth in Fall was associated with EoE discordance (p=0.02;n=63). Food allergies (p<0.001;n=97) and penicillin allergies (p=0.17; n=66) were associated with EoE. Breastfeeding (p=0.15;n=59) may reduce risk for EoE.
Epigenetic methylation screen of effect size ≥5% difference between affected and unaffected monozygotic twins revealed 349 sites of interest, including candidate and novel genes.
Conclusions: EoE recurrence risk ratios are increased 10 to 64-fold compared to population prevalence. EoE in relatives is 1.8-2.4%, depending upon relationship and sex. Nuclear-Family heritability appeared to be high (72.0%). However, Twins cohort analysis revealed a powerful role for common environment (81.0%) compared with additive genetic heritability (14.5%). The risk of having a second child with EoE is 2.4%. Common family environment (81.0%) and additive genetic heritability (14.5%) explain familial clustering. Early environmental modification may lessen EoE risks. Importantly, epigenetic methylation associated with EoE suggests novel mechanisms and genes. Familial clustering is largely attributable to common environmental exposures, suggesting that identifying modifiable common family environmental factors, in genetically susceptible individuals and families, particularly in early life, may mitigate risk.
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Copyright Information
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Acknowledgements:
Ever since I nervously gave my first injection at Children’s, I’ve wanted to practice here, in my hometown. Thanks to all who helped my work to become my dream, and my dreams help children.
I thank Dr. Marc Rothenberg and Sean Jameson and the families of the Cincinnati Center for
Eosinophilic Disorders and the Twins with EoE Registry for making me aware of their need for family-based inheritance and risk information to share with families and clinicians. Parents have been so very generous with their time, and sharing their information, in hopes of helping other
EoE families.
Thanks to Dr. Chuck DeBrosse for the serendipitous errant email that sent me down the genomic road.
Special thanks to my committee members, Dr. Paul A. Succop, Dr. Lisa J. Martin, Dr. Margaret
H. Collins, Dr. Vincent A. Mukkada and Dr. Erin N. Haynes for their time and thoughtful guidance. Special thanks to Dr. Succop, who has been an excellent teacher.
I am indebted to Dr. Lisa Martin, who has gone well beyond the duty of mentorship to educate, train and inspire me to be an independent scientist. She must surely have the patience of Job.
Note to Dr. Margaret Collins: everybody says you’re awesome!
Thanks for ongoing support from our Genetics Study Group: Dr. Xue Zhang, Dr. Lili Ding, Hua
He, Valentina Pilipenko, Dr. Brad Kurowski, Dr. Tesfaye Mersha, and, especially, Dr. Leah
Kottyan, who often saves me from re-inventing the wheel.
Importantly, thanks for support from the faculty of the Division of Biostatistics and Epidemiology at Cincinnati Children’s Hospital Medical Center: especially, Drs. Jessica Woo, Heidi Sucharew,
Rick Ittenbach, Jane Khoury, Jareen Meinzen-Derr, Bin Huang and Maurizio Macaluso. I’m
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deeply indebted to each of you for the collegial environment, excellent coursework and good natured help with my frequent questions. Thanks to Shannon Hatfield for helping me through the administrative hurdles, even when I panicked. I breathe a sigh of relief when I hit the “10” in “S”
(S comes after R and R stands for research) of the new William Cooper Proctor Research
Pavilion.
This work would not have come to fruition without Alexa Greenler, Tommie Grotjan, Heather
Foote, Mike Eby, and Emily Stucke of the Cincinnati Center for Eosinophilic Disorders. Thank you!
Many thanks for support from Dr. Shuk-mei Ho, Dr. Grace LeMasters and Dr. Dan Woo for great advice and essential financial support from the Center for Environmental Genetics and the
Molecular Epidemiology in Environmental Health National Institutes of Health T32 Fellowship.
Thank you to the members of my Qualifying Exam Committee, Drs. Lisa Martin, M.B. Rao and
Melinda Butsch-Kovasic, who gave generously of their time and expertise so that I might pass that milestone on the path to a new career.
Dean Margaret Hanson of the Graduate School of the University of Cincinnati provided amazing opportunities that increased my understanding of professional development, mentorship and polish.
My gratitude extends to Dr. Karen Conneely, who graciously invited me to study methylation analysis with her at Emory University. Thanks to Dr. Hemant Tiwari, and the Section on
Statistical Genetics at the University of Alabama, Birmingham for their support. Fresh perspectives are so helpful.
Thanks to my new colleagues in Health Services Administration at Xavier University, especially
Dr. Eddie Hooker, for their faith and Ignatian philosophy, cura personalis. Thanks to Drs. Hooker
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and Browne for their mentorship and encouragement to teach. Thanks to Dr. Sr. Nancy
Linenkugel for modeling leadership, and for those informative and cheery “Chair-y” emails.
Fond thanks to my longtime colleagues at Deaconess Hospital and the University of Cincinnati:
Sandy Oppelt, Carolyn Fiutem, Marcia Endres, Susan Bennett and the GRRL Genius Club.
Thanks to Nancy Wilson, boss, teacher and risk manager extraordinaire, Dr. Jim Sammarco and
Dr. Tim Ramsey (Organic Chem TA who is now at Novartis, Cambridge MA) for writing winning letters of recommendation way back in 2008. Thanks to Ann Marie Kreft for sparking thoughts of geoclustering Type 1 Diabetes.
With help from Drs. Mark Snyder and Jim Sammarco, who tuned me up and gave me the energy needed to compete and achieve my dreams, I can be of service to our community. Thank you.
Thanks to my pseudo lil’ bro, Dr. Glenn Rinsky, for commiserating and cheering on the path to academic scholarship. Apparently, you won :)
Dear friends, Dr. Lakshmi Sammarco, Shirin Zandvakili and Carol Schwetschenau Wood, Esq., have stayed with me, even when I’ve ignored them or complained too much. We’ll have fun again!
Love to my siblings, the Steinle sisters: Carole, Mary Ann, Nancy, Elizabeth, Joyce and Jo ann, who’ve looked after me my whole life, and our mother, Alberta Helen Schloemer Steinle.
Most importantly, my family, Richard Marshall Alexander, our daughters, Katherine Alyssa,
Jennifer Marshall (Jamie), Sara Lauren and my canine supporters, Sophie, Nana, Dakota
Sioux, Heidi, Brisco and Jodie have been there every step of the way, in vivo or spirit. Jodie teaches all of us the joy and charm of living with some genetic imperfection. They fed me, tolerated my whining, forgave my impatience when I was tired and taught me so much about love and commitment. They each deserve an honorary degree. Jodie would probably eat it.
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Special thanks for financial support from:
Campaign Urging Research for Eosinophilic Diseases (CURED);
Food Allergy Research and Education (FARE);
Buckeye Foundation;
2014 University of Cincinnati Research Council Graduate Student Fellowship;
2014 Frank C. Woodside, Dinsmore & Shohl Fellowship/Cincinnati Children’s Hospital Div.
Biostatistics and Epidemiology;
National Institute of General Medical Sciences (NIGMS) 2013 Bursary Award R25GM093044;
NIH 1R25GM093044-01 UAB Section on Statistical Genetics 2013;
NIH 8 UL1-TR000077-04 Center for Clinical and Translational Science and Training, CCTST,
CTSA, NCATS 2012 Just in Time; CCTST REDCap UL1-RR026314-01 NCRR/NIH;
NIEHS P30-ES006096 Center for Environmental Genetics 2011 New Investigator Scholar and
2012 Principal Investigator Mentee/Mentor;
NIH T32-ES10957 2011-2013 Molecular Epidemiology in Children’s Environmental Health
Predoctoral Fellowship in, “the key areas of statistical genetics, epidemiology and molecular genetics.”
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Table of contents
Abstract ...... ii
Copyright Information ...... iv
Acknowledgements ...... v
Table of Tables and Figures ...... ix
Chapter 1: Introduction, Specific Aims and Significance ...... 1
Chapter 2: Published Abstract: Sex of Affected Parent is Associated with Familial Risk of EoE .... 5
Chapter 3: Aims 1 and 2: Research Manuscript accepted July 3, 2014 ...... 13
Twin and Family Studies Reveal Strong Environmental and Weaker Genetic Cues
Explaining Heritability of Eosinophilic Esophagitis ...... 13
Introduction ...... 19
Methods ...... 21
Results ...... 26
Discussion ...... 30
Tables ...... 35
Figures ...... 42
Online Supplement ...... 48
Chapter 4: Biases, Limitations and Challenges, unabridged ...... 44
Chapter 5: Future Directions ...... 46
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Chapter 6: Conclusions ...... 55
References ...... 60
Appendices:
A: Pilot: Sex and Related Conditions Are Associated With Eosinophilic Esophagitis ...... 70
B: Project Management Documents ...... 82
B1: Nuclear Family Study Design and Project Management Plan ...... 82
B2: Twin Study Design and Project Management Plan ...... 86
B3: Analysis Plan, abridged ...... 91
B4: Aim 1: Recruitment, Data and Sample Collection, REDCap data collection forms...... 101
C: Related Grants and Published Abstracts, Manuscripts ...... 117
C1: Center for Environmental Genetics (CEG) 2012 PI Mentee/Mentor ...... 117
C1a: Published Abstracts ...... 137
C1ai: Twin Shared Environment Increases The Risk of Eosinophilic Esophagitis in Families ...... 137
C1aii: Histology Scoring System (HSS) is Superior to Peak Eosinophil Count (PEC) to Identify
Treated vs Untreated Eosinophilic Esophagitis (EoE) Patients ...... 141
C2a: Letters of Support and Award ...... 142
C3: Letter of Acceptance, J. Allergy & Clinical Immunology ...... 155
D: Comparative Heritability Estimation ...... 156
D1: Mplus Twin SEM Model ...... 162
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E: Preliminary Environmental Exposure Associations Determine Domains ...... 163
F: Manuscript in Preparation: Methylation Differences in Discordant Monozygotic Twins.... 173
G: UC Reliance review ...... 206
H: CCHMC Human Subjects Documentation ...... 207
References, Appendices ...... 223
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Table of Tables and Figures:
Table 2.1 ...... 9
Figure 2.1...... 10
Table 3.1 ...... 30
Table 3.2 ...... 31
Table 3.3 ...... 32
Table 3.4 ...... 33
Figure 3.1...... 39
Figure 3.2...... 40
Figure 3.3...... 41
Figure 3.4...... 42
Figure 5.1...... 55
Figure 5.2...... 56
Figure A1 ...... 79
Figure A2 ...... 80
Figure A3 ...... 81
Figure B4.1 ...... 114
Figure B4.2 ...... 115
Figure B4.3 ...... 116
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Table D1 ...... 158
Table E1 ...... 166
Table E2 ...... 168
Table E3 ...... 170
Table E1 ...... 166
Table E2 ...... 168
Table E3 ...... 170
Table F1 ...... 184
Table F2 ...... 185
Table F3 ...... 194
Table F4 ...... 197
Figure F5 ...... 198
Figure F1 ...... 199
Figure F2 ...... 200
Figure F3 ...... 201
Figure F4 ...... 202
Table F5 ...... 203
Table F6 ...... 204
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Chapter 1: Introduction, Specific Aims and Significance
INTRODUCTION
Eosinophilic esophagitis (EoE) is a debilitating, chronic food and swallowed antigen driven allergic inflammatory disease. Although the prevalence of EoE has increased in both adult(1) and pediatric populations,(2) treatment options are very limited.(3)Further, ~70% of those affected by EoE are male,(2,
4, 5) suggesting sex-specific genomic and epigenomic mechanisms. This project is motivated by parents of children treated at the Cincinnati Center for Eosinophilic Disorders (CCED) who asked, “Will my next child will have EoE?”
EoE is due in part to an underlying genetic susceptiblity, given strong family clustering,(6, 7) high sibling recurrence risk(6) and single nucleotide variants associated with EoE.(8-10) However, associated odds ratios are small, and both persistent and transient dysregulation of gene expression in esophageal epithelium(11, 12) suggests the interaction of genes with environment. Further, our new Twins Registry estimates the concordance rate of EoE in MZ twins at 58%, much lower than expected, and dizygotic
(DZ), or fraternal, twins’ concordance at 36%, much higher than expected. Taken together, these results suggest that environmental factors also contribute to EoE risk in genetically susceptible individuals an families. The additive genetic heritability and relative contributions of genes and environmental factors to
EoE have not been quantified.
Indeed, recent environmental survey data have identified early life and environmental factors associated with increased risk,(13-18) including antibiotic exposure in the first year of life.(19) One such mechanism of action for environmental factors is epigenetic variability.(20, 21) Epigenetic modification such as cytosine methylation of CpG sites can result in altered gene expression that may lead to the development of EoE. However, no studies have addressed whether epigenetic changes are associated with
EoE. 1
Although EoE likely involves genes, epigenetics, and environmental factors, their relative contributions and underlying mechanisms are unknown. Our long term goal is to reduce the rate, and therefore, the risk, of EoE. As a first step, we seek to understand the enrichment of EoE and related conditions in families with an EoE proband. Twin studies are designed to disentangle and quantify the effects of shared genes from common household environment.(22-24) A study of allergic disease in twins calculated total serum
IgE heritability at 61%.(24) Further, a twin study of peanut allergy(25) calculated high heritability of
81.6% by path analysis, with concordance reduced by 89.4% in DZ twins, consistent with a predominantly genetic mode of inheritance. In contrast to peanut allergy, I propose that EoE has a complex non-Mendelian mode of inheritance, mediated by both an underlying genetic susceptibility and exposure to environmental factors.
Study Objectives: I will recruit and develop a new Twins Registry cohort. Using this unique resource, I will provide novel evidence that EoE has a complex mode of inheritance, using both nuclear family and twin designs to differentiate and quantify the effects of shared genes from common household environment.(22, 23) I will show that early life factors are associated with increased risk for developing
EoE. Screening methylation chip array studies of discordant twins will identify epigenetic modifications that may contribute to the underlying etiology of EoE for future confirmatory studies. Although the prevalence of EoE has increased,(1, 2, 4, 26) prevention and management are very limited.(3)
Identification of these mechanisms and exposures will give clinicians and genetically susceptible families tools to mitigate their risk of EoE. The central purpose of this study is to quantify the contributions of genetic and environmental factors to EoE.
Hypotheses: EoE has a complex mode of inheritance, with familial enrichment from both genetic and shared common familial environmental effects. Twin models differentiate additive genetic heritability separately from common family environment. Further, environmental factors potentiate risk and result in 2
sustained methylation differences between discordant twins. Thus the EoE-related methylome signature in genetically identical pairs will differ between affected and unaffected individuals. To test these hypotheses, a cross-sectional study of CCED nuclear families and a twin study design using our newly developed international EoE Twins registry will address the following specific aims:
Specific Aims:
Specific Aim 1: Develop a CCED Nuclear Family group and Twins with EoE Registry: develop a nuclear family group at CCED; recruit an international registry of twins, one of whom has EoE for family-based studies.
Specific Aim 2: Quantify the separate contributions of genes and environmental factors on the frequency and variability of EoE: compare the frequency of EoE in nuclear families and twins to expected rates.
Specific Aim 3: Explore and direct new lines of EoE and family-based research, including epigenetic mechanisms and environmental factors, for EoE and related immunologic conditions
Significance/relevance to environmental health: EoE phenotypic variation is an unquantified complex interaction of genes and environment. Defining risk by sex and family relationship is a crucial first step to understanding EoE. Importantly, parents ask clinicians if their next child will have EoE. In addition to heritable genetic components, our preliminary data suggest a strong environmental component in the pathogenesis of EoE. We will open a new area of preventive research, focused on modifiable environmental factors and the unique methylation pattern in individuals with EoE using family-based quantitative designs, new epigenetic assays and computationally intense tools.
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Dissertation Objectives: It didn’t have to be this difficult. Adult graduate students are consumers of professional education in an increasingly free market. Evidence-based leadership and education tools are well-supported in the literature. Briefly, andragogy, vis-a-vis pedagogy, is a problem solving approach to adult learning. According to Knowles, adults are internally motivated and self-directed, bring life experiences and knowledge, are goal-oriented, relevancy-oriented, practical, and like to be respected
(http://www.qotfc.edu.au/resource/?page=65375 http://www.medscape.com/viewarticle/547417_2). Therefore, the central purposes of this dissertation are
1) the partial fulfillment of University requirements for the degree of Doctor of Philosophy to provide
“documentation of this research,” as required in the Graduate School Handbook, 2) acquisition of technical and professional skills needed to support a career as an independent scientist and educator in
2014, including grantsmanship and publication, with supporting documentation in the appendices.
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Chapter 2: Sex of Parent is Associated with Familial Risk of EoE
INTRODUCTION
Eosinophilic esophagitis (EoE) is a debilitating, chronic food and swallowed antigen driven allergic inflammatory disease. Although the prevalence of EoE has increased in both adult(1) and pediatric populations,(2) treatment options are very limited.(3, 27) Further, ~70% of those affected by EoE are male,(2, 4, 5) suggesting sex-specific genomic and epigenomic mechanisms. EoE prevalence is 5.5 per
10,000(1, 4, 26, 28, 29) EoE patients have co-occurring atopy, asthma and other gastrointestinal disorders.(30, 31) Older pediatric patients present with food impaction and dysphagia.(30) Asthma, eczema, allergic rhinitis, urticaria and food allergies share inflammatory features that may result in a progressive “atopic march.” (32-36) This is important because, as an epidemiology student naive to the study of immunologically mediated disorders, it is necessary to explore biological plausibility prior to study design to 1) identify possible confounders, 2) consider inclusion criteria that maximizes either sensitivity, specificity, or both, and 3) consider proximal and distal causes of disease for future study designs, as described in Aim 3. For example, do genes and environmental nodes that turn on the “atopic march” precede nodes that determine respiratory versus gastrointestinal diseases, and finally, what are the specific susceptibilities and exposures that determine risk of EoE?
The natural history and variability of related conditions in EoE families (Figure 2.1) is not well characterized. I sought to identify co-morbid conditions that define the EoE phenotype and quantify the risk of developing EoE and related conditions in first degree relatives of affected individuals, stratified by sex. Recurrence risk of both EoE and related gastrointestinal and allergic conditions has not been reported. Related conditions are described in Appendix A.
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METHODS
Subject Identification and Eligibility
A retrospective, cross sectional study was conducted for the period August 2008 to July 2010 to identify proband patients with documented family history. Probands confirmed by histology (15eos/400xhpf).
Previsit parent questionnaire with physician confirmation was conducted for family relations and their comorbid conditions, i.e., allergic rhinitis, asthma, eczema, food allergies, urticaria, EoE, other eosinophilic gastrointestinal disorders (EGID), food impaction, esophageal dilation. Affected or nonaffected status was recorded for gastrointestinal (GI) and allergic conditions. GI conditions included
EoE, non-esophageal eosinophilic GI disease (EGID), food impaction and esophageal dilation.
Eosinophilic gastritis, eosinophilic enteritis and eosinophilic colitis were combined to the category
“EGID” by the CCED physician. Confirmed data are recorded in EPIC. Only first degree relations were included, i.e., parents and siblings for our pediatric proband population, who do not yet have children of their own. Sex was available for proband patients and inferred for relations: mother, father, sister, brother.
Exclusion criteria: Proband patients for whom confirmed family history was not available in EPIC.
Statistical Analysis
Pedigrees were constructed to identify related pairs, using PEDSYS and SOLAR software, from a database with first degree relation information for 29%. Data were analyzed with Chi-square and Fisher’s
Exact at p≤0.05. Stratified analysis of co-morbid conditions was by sex and relation. Data were analyzed using SAS 9.2. Recurrence risk ratios (RRR) were calculated as (number affected/total)/prevalence.
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RESULTS
Proband patients (n=1059) with EoE were identified at Cincinnati Children’s from our research database;
306 had family history in the medical record. This sample had 1.77 siblings per family compared to the
Ohio mean of 1.87 and the US mean of 1.86. Pedigrees were constructed for 306 families of proband patients. First degree relatives affected with EoE included 3.3% of fathers, 0.4% of mothers, 3.4% of brothers, 2.4% of sisters and 2.9% of siblings overall (Table 2.1). All are significantly increased compared to population prevalence. Related conditions are reported in Appendix A.
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DISCUSSION
EoE is a Substantial Disease Burden in Families
Overall, siblings have ~3% risk of EoE. All first degree relatives of EoE probands have a significantly increased frequency of EoE compared to population prevalence. Fathers have the highest rates of EoE and food impaction compared to mothers and other first degree relations. Parents and siblings show distinctly different patterns of comorbid conditions. Siblings report more asthma, eczema and EGID. Half of all first degree relatives of EoE probands have allergic rhinitis, regardless of sex or age. Parents report more food impaction and dilation than siblings.
Further, ~70% of those affected by EoE are male,(2, 4, 5) suggesting sex-specific genomic and epigenomic mechanisms. Reduced rates of EoE in mothers further suggests sex-specific mechanisms, including a possible protective effect from estrogen. Differences, by sex of the parent but not by sex of siblings, need to be confirmed, as this implies specific and testable mechanisms of complex inheritance, such as hormonal mediation and imprinting Studies of sex-based inheritance patterns and family-based quantification of shared environment are warranted.
In summary, clinicians should be aware of a modestly increased risk (~3%) of EoE in siblings of an EoE proband. Symptomatic family members of EoE patients should be evaluated with a high index of suspicion for EoE. Co-morbid variability and relatively rare disorders are associated with complex mechanisms of inheritance.
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Table 2.1. Frequency of EoE by sex and relation for first degree relations.
U n Af aff Percen fecte ec te Relations d d t p value Parents 8 430 1.83% Fathers 7 203 3.33% 0.03 ns Mothers 1 227 0.44% Siblings 7 229 2.97% Brothers 4 109 3.54% ns Sisters 3 120 2.44% All 15 659 2.23% Males 11 312 3.41% ns (0.06) Females 4 347 1.14%
Fathers report significantly more EoE than mothers (p = 0.03). The average risk for siblings is ~3%. ns = not significant at p ≤ 0.05. Percent is affected/total x 100.
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Figure 2.1. Co-morbid variability in pedigree of EoE research family.
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Chapter 3: Twin and Family Studies Reveal Strong Environmental and Weaker Genetic Cues Explaining Heritability of Eosinophilic Esophagitis
Research Manuscript accepted by the Journal of Allergy and Clinical Immunology July 3, 2014, letter Appendix C.
Author: Eileen S. Alexander, MS,a,b,c
Co-authors: Lisa J. Martin, PhD,a,b Margaret H. Collins, MD,a,b Leah Kottyan, PhD,b Heidi Sucharew,
PhD,b Hua He, MS,b Vincent A. Mukkada, MD,a,b Paul A. Succop, PhD,a J. Pablo Abonia, MD,a,b Heather
Foote,b Michael D. Eby, BS,b Tommie M. Grotjan, BS,b Alexandria J. Greenler, BS,b Evan S. Dellon,
MD, MPH,d Jeffrey G. Demain, MD,e Glenn T. Furuta, MD,f Larry E. Gurian, MD, AGAF,g John B.
Harley, MD, PhD,a,b,h Russell J. Hopp, DO,i Ajay Kaul, MD,a,b Kari C. Nadeau, MD, PhD,j,k Richard J.
Noel, MD, PhD,l,m, Philip E. Putnam, MD,a,b Karl F. von Tiehl, MD,n Marc E. Rothenberg, MD, PhDa,b
Affiliations: aUniversity of Cincinnati College of Medicine, Departments of Environmental Health, Pediatrics,
Pathology and Laboratory Medicine, Cincinnati, OH bCincinnati Children's Hospital Medical Center, Divisions of Biostatistics and Epidemiology; Human
Genetics; Pathology; Rheumatology, Center for Autoimmune Genomics and Etiology; Gastroenterology,
Hepatology and Nutrition; Allergy and Immunology, Cincinnati Center for Eosinophilic Disorders,
Cincinnati, OH cXavier University, Health Services Administration, Cincinnati, OH dUniversity of North Carolina School of Medicine, Division of Gastroenterology and Hepatology, Center for Esophageal Diseases and Swallowing, Chapel Hill, NC eDirector, Allergy, Asthma and Immunology Center of Alaska, Anchorage, AK fChildren's Hospital Colorado, Digestive Health Institute, Gastrointestinal Eosinophilic Diseases Program,
University of Colorado School of Medicine, Aurora, CO
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gFerrell Duncan Clinic and CoxHealth, Springfield, MO hU.S. Department of Veterans Affairs Medical Center, Cincinnati, OH iDepartment of Pediatrics, Division of Allergy and Immunology, Creighton University, Omaha, NE jStanford Medical School, Stanford, CA kStanford Medical Center and Lucille Packard Children's Hospital, Division of Allergy and Immunology,
Stanford, CA lChildren's Hospital of Wisconsin, Milwaukee, WI mMedical College of Wisconsin, Milwaukee, WI nBowTie Allergy Specialists, Huntington Memorial Hospital, Pasadena, CA
Correspondence: Marc E. Rothenberg, MD, PhD, Cincinnati Children's Hospital Medical Center,
Division of Allergy and Immunology, MLC 7028, 3333 Burnet Avenue, Cincinnati, OH 45229.
E-mail: [email protected]
Supported in part by the: Frank C. Woodside, Dinsmore & Shohl Fellowship through Cincinnati
Children’s Hospital Division of Biostatistics and Epidemiology; National Institutes of Health grants T32-
ES10957 Molecular Epidemiology in Children’s Environmental Health Fellowship 2011-2013; NIEHS
P30-ES006096 Center for Environmental Genetics New Investigator Scholar and PI Mentee/Mentor; NIH
8 UL1-TR000077-04 Center for Clinical and Translational Science and Training, CTSA, NCATS Just in
Time; CCTST REDCap UL1-RR026314-01 NCRR/NIH; 1R25GM093044-01 UAB Section on Statistical
Genetics; NIH-1K24DK100303 (GTF); University of Cincinnati Research Council; Campaign Urging
Research for Eosinophilic Diseases (CURED); Food Allergy Research and Education; Buckeye
Foundation. This work was completed in partial fulfillment of the Doctor of Philosophy degree in
Epidemiology in the Department of Environmental Health, Division of Epidemiology and Biostatistics,
University of Cincinnati College of Medicine.
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Abstract
Background: Eosinophilic esophagitis (EoE) is a chronic antigen-driven allergic inflammatory disease, likely involving the interplay of genetic and environmental factors, yet their respective contributions to heritability are unknown.
Objective: To quantify risk associated with genes and environment on familial clustering of EoE.
Methods: Family history was obtained from a hospital-based cohort of 914 EoE probands, (n=2192 first- degree “Nuclear-Family” relatives) and the new international registry of monozygotic and dizygotic twins/triplets (n=63 EoE “Twins” probands). Frequencies, recurrence risk ratios (RRRs), heritability and twin concordance were estimated. Environmental exposures were preliminarily examined.
Results: Analysis of the Nuclear-Family–based cohort revealed that the rate of EoE, in first-degree relatives of a proband, was 1.8% (unadjusted) and 2.3% (sex-adjusted). RRRs ranged from 10-64, depending on the family relationship, and were higher in brothers (64.0; p=0.04), fathers (42.9; p=0.004) and males (50.7; p<0.001) compared to sisters, mothers and females, respectively. Risk of EoE for other
2 siblings was 2.4%. In the Nuclear-Families, combined gene and common environment heritability (hgc ) was 72.0±2.7% (p<0.001). In the Twins cohort, genetic heritability was 14.5±4.0% (p<0.001), and common family environment contributed 81.0±4% (p<0.001) to phenotypic variance. Proband-wise concordance in MZ co-twins was 57.9±9.5% compared to 36.4±9.3% in DZ (p=0.11). Greater birth- weight difference between twins (p=0.01), breastfeeding (p=0.15) and Fall birth season (p=0.02) were associated with twin discordance in disease status.
Conclusions: EoE recurrence risk ratios are increased 10-64-fold compared with the general population.
EoE in relatives is 1.8-2.4%, depending upon relationship and sex. Nuclear-Family heritability appeared to be high (72.0%). However, Twins cohort analysis revealed a powerful role for common environment
(81.0%) compared with additive genetic heritability (14.5%).
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Clinical Implications: The risk of having a second child with EoE is 2.4%. Common family environment
(81.0%) and additive genetic heritability (14.5%) explain familial clustering. Early environmental modification may lessen EoE risks.
Capsule Summary: Familial clustering is largely attributable to common environmental exposures, suggesting that identifying modifiable common family environmental factors, in genetically susceptible individuals and families, particularly in early life, may mitigate risk.
Key Words: eosinophilia; medical genetics; twins; immune system diseases; heritability; gene- environment interaction; drug hypersensitivity; gastrointestinal diseases; skin diseases
Abbreviations: Eosinophilic esophagitis (EoE), recurrence risk ratio (RRR), narrow-sense additive
2 2 genetic heritability (hag ), combined additive genetic and common environment heritability (hgc ),
Cincinnati Center for Eosinophilic Disorders (CCED), Cincinnati Children’s Hospital Medical Center
(CCHMC), monozygotic (MZ), dizygotic (DZ), eosinophilic gastrointestinal disease (EGID), esophagogastroduodenoscopy (EGD), gastroesophageal reflux disease (GERD), variance components model (VCM)
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INTRODUCTION
Eosinophilic esophagitis (EoE) is a debilitating, chronic allergic inflammatory disease of the esophagus triggered by food and ingested antigen sensitization followed by T helper type 2 (Th2) cell adaptive immune responses. Although EoE prevalence has increased in both adult(1, 4, 26, 28) and pediatric(2, 37) populations, strategies for prevention, management and risk mitigation are limited.(3) Research on underlying biologic processes has resulted in new opportunities for treatment, yet risk factors for EoE remain unclear.
One mechanism for high EoE risk is genetic variation. Indeed, Blanchard, et al., estimated an 80-fold increase in sibling recurrence risk, compared to population prevalence, suggesting a strong genetic component.(6) The importance of genetic variants is supported by both candidate gene and genome-wide association studies.(8) Genetic variants in CAPN14, TSLP, TSLPR, CCL26, and FLG have been associated with EoE.(9, 10, 38) However, these variants explain only a small portion of EoE cases, leaving a large portion of the variation unexplained.
There is also substantial evidence that environmental factors influence EoE risk. First and foremost, EoE is an allergic condition responsive to allergen exposure via respiratory, gastrointestinal or cutaneous routes.(17, 39-41) For example, EoE is induced in murine models via respiratory exposure of Aspergillus fumigatus antigens,(17) and molds, including Aspergillus and Penicillium, are associated with eosinophilic asthma.(42) Recently, early environmental exposures, such as antibiotic exposure in the first year of life,(19) have been implicated. Indeed, birth season, climate, seasonality(13, 14, 18, 43, 44) and
Helicobacter pylori exposure(16, 45) modify disease susceptibility. Further, epigenetic regulation(46, 47) may play a role in altered expression(11, 12, 48) associated with EoE. Despite these intriguing findings, the relative roles of genetic and environmental factors in EoE risk are unclear.
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The purpose of this study was to estimate the contributions of genes and environment to EoE risk in susceptible families. To accomplish this objective, we used a cohort of nuclear families at the Cincinnati
Center for Eosinophilic Disorders (CCED) at Cincinnati Children’s Hospital Medical Center (CCHMC) and established a new cohort with histologically confirmed EoE in at least one twin/triplet. We estimated
EoE risk as 1.8% in first-degree relatives of probands and 2.4% in siblings of probands. Combined
2 additive genetic and common environment heritability (hgc ) in nuclear families was 72.0±2.7%
(p<0.001). Twin analysis allowed separation of effects of shared genes from common household environment.(49, 50) The majority of phenotypic variance was accounted for by common family
2 environment (81.0%), whereas additive genetic heritability (hag ) accounted for 14.5±4.0%.
Environmental factors of interest include food allergies (p<0.001), twin birth-weight difference (p=0.01),
Fall birth season (p=0.02), penicillin allergy in each twin (p=0.17) and breastfeeding (p=0.15). Therefore, actionable environmental alterations may mitigate risk in susceptible families.
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METHODS
To quantify EoE risk due to genes and environment in familial clustering, a retrospective cross-sectional study was conducted using the Nuclear-Family cohort derived from the CCED database and the newly created EoE Twins Registry. The study was performed with CCHMC IRB approval and review by the
University of Cincinnati IRB. Participants or their parent/guardians provided written consent. Children over the age of eleven years provided written assent.
The CCED database was used for the period of August 1, 2008 to April 30, 2013 to identify patients and collect basic demographics, clinical testing and family history. Probands were identified by their CCED physician. Additional history of related medical conditions for first-degree relatives was obtained by parent-report or self-report, using pre-visit questionnaire with subsequent physician confirmation, available in CCHMC’s electronic medical record. Family medical conditions included EoE and other eosinophilic gastrointestinal (GI) diseases (EGID), including eosinophilic gastritis, eosinophilic enteritis and eosinophilic colitis. CCED probands missing physician-confirmed family history were excluded.
Among the 1366 CCED patients seen during this time period, 914 (69%) were included.
Established in 2008, the EoE Twins Registry is an international twin/triplet cohort for EoE and related eosinophilic conditions and was created for this CCHMC study. Recruitment is from physicians specializing in allergy and gastroenterology, centers specializing in EoE, patient and parent EoE interest foundations and twin social networking groups. Initial screening of potential participants was by self/parent report of EoE and EGID. EoE Twins are from the continental United States (n=57), Alaska
(n=2) and Australia (n=4). Information for Twins ˂18 years of age was provided by parent report.
Inclusion and Exclusion Criteria
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Eligible participants/parents were asked for reported diagnosis (EoE, other GI conditions, or unaffected).
For all participants that reported EoE, esophagogastroduodenoscopy (EGD) pathology report at diagnosis was reviewed. Pathology slides were requested for all participants with esophageal eosinophils and reviewed by a single pathologist at the CCED (MHC) for the area (0.3 mm2) of greatest intraepithelial eosinophil density. Peak counts were generated (100% of Nuclear-Family; 96% of Twins) to confirm ≥15 eosinophils per high-power field (hpf) at 400X magnification. Slides were requested from an endoscopy performed while the participant was receiving therapy with proton pump inhibitors (PPI) but had not received therapy specifically for EoE, such as steroids and/or diet elimination, as recommended in the
EoE consensus guidelines.(3) PPI administration prior to a positive endoscopy was confirmed in 52% of
Nuclear-Family probands for whom data were available (55%). Affected Twins diagnostic dates ranged from 2001-2012, with 93% diagnosed prior to publication of the current guidelines recommending PPI screening prior to diagnostic endoscopy. Participants with known causes of peripheral blood eosinophilia were excluded. Individuals with reported EoE without confirmatory pathology reports were excluded.
Registry data included demographics (race, ethnicity, sex, age), birth information (gestational age, use of fertility treatments, birth order, birth-weight, birth-length), medical history and family medical history for each family member. Twins were requested to provide a saliva sample for DNA collection; OrageneTM kit
(DNA Genotek, Kanata, Ontario, Canada) was used according to manufacturer’s instructions, with sponges added for children unable to expectorate, typically ≤5 years of age, and prepITTM L2P manual
DNA purification protocol.
Zygosity
Three tools determined zygosity of same-sex twins as monozygotic (MZ) or dizygotic (DZ): 1) genotyping, 2) pea pod questionnaire(51) and 3) parent report. To genetically determine zygosity, we estimated the proportion of identity-by-descent (IBD) sharing between each pair of genotyped individuals and compared it to the proportion expected based on genealogical information.(52) The percentage of 18
identical markers was determined from 94544 high-quality, polymorphic markers, among 196524 variants genotyped by Immunochip(53) (Illumina, San Diego, CA). MZ pairs have identical markers at more than
99% of loci with observed IBD sharing of 0.99-1.0. Analysis was limited to same-sex pairs (n=48) with paired DNA samples available (n=40). For same-sex pairs without paired DNA samples, pea pod questionnaire determined zygosity. Pea pod questionnaire is a validated survey designed to determine how alike twins are based on who can tell them apart34, with 96% accuracy relative to genotyping.(54)
Genetic zygosity results were used as the determinant when available.
Data Management
Study data were collected and managed using REDCap electronic data capture tools hosted at
CCHMC.(55)
Environmental Screening
Because EoE often has an early onset, we focused on perinatal exposures, such as prenatal vitamins, gestational age, breastfeeding and birth-weight, length and order. Birth seasons included winter (northern hemisphere, December 1-March 20), spring (March 21-May 31), summer (June 1-September 20) and autumn (September 21-November 30). Participants from Australia were coded for southern hemisphere birth seasons. Environmental data included food and medication allergies. Data for parent/self-reported factors were obtained from the EGID database for Nuclear-Families and by telephone interview for Twins and their nuclear families. Penicillin, amoxicillin and cephalosporins were grouped together for analysis.
Statistical Analysis
Demographic data and EoE risk estimates were analyzed using JMP Genomics 6.0 (SAS Institute, Cary,
NC). Reported p-values are two-tailed with significance at p≤0.05, unless otherwise specified; exact values at p≥0.001 or p<0.001, were confirmed by permutation test for zero cells.
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Demographic characteristics were described using mean ± standard deviation (SD) for normally distributed continuous traits, median and interquartile range for non-normally distributed continuous traits and frequency for discrete traits. Comparability of subgroups was tested using non-parametric Wilcoxon rank sum, parametric t-tests or Chi-square, as appropriate.
Recurrence Risk Ratios and Concordance Estimates
Recurrence risk ratios (RRR) were calculated as (number affected/total)/prevalence, with the point estimate for prevalence set at 5.5 per 10,000.(4, 26, 28) Given the male preponderance of EoE, sex- adjusted frequencies and RRR were calculated; prevalence was set at 8.1 for males and 2.8 for females, on the basis of the 74% male proband frequency in the Nuclear-Family cohort. RRR estimates were