The emerging importance of genetics in epidemiologic research II. Issues in study design and gene mapping

Skeletal Class II Malocclusion: From Clinical Treatment Strategies to the Roadmap in Identifying the Genetic Bases of Development in Humans with the Support of the Collaborative Cross Mouse Population

Depending on how severe it is, malocclusion, which may involve misaligned teeth, jaws, or a combination of the two, can hurt a person's overall facial aesthetics. The maxillary molar develops before the mandibular molar in class II malocclusion, which affects 15% of the population in the United States. With a retrusive mandible, patients typically have a convex profile. The goal of this study is to classify the skeletal and dental variability present in class II malocclusion, to reduce heterogeneity, present the current clinical treatment strategies, to summarize the previously published findings of genetic analysis, discuss these findings and their constraints, and finally, propose a comprehensive roadmap to facilitate investigations aimed at determining the genetic bases of malocclusion development using a variety of genomic approaches. To further comprehend the hereditary components involved in the onset and progression of class II malocclusion, a novel animal model for class II malocclusion should be developed while considering the variety of the human population. To overcome the constraints of the previous studies, here, we propose to conduct novel research on humans with the support of mouse models to produce contentious findings. We believe that carrying out a genome-wide association study (GWAS) on a large human cohort to search for significant genes and their modifiers; an epigenetics-wide association study (EWAS); RNA-seq analysis; integrating GWAS and the expression of quantitative trait loci (eQTL); and the testing of microRNAs, small RNAs, and long noncoding RNAs in tissues related to the skeletal class II malocclusion (SCIIMO) phenotype, such as mandibular bone, gum, and jaw in humans and the collaborative cross (CC) mouse model, will identify novel genes and genetic factors affecting this phenotype. We anticipate discovering novel genetic elements to advance our knowledge of how this malocclusion phenotype develops and open the venue for the early identification of patients carrying the susceptible genetic factors so that we can offer early prevention treatment strategies.

Heteropaternal twinning: Unique case of opposite-sex twins with different fathers

A presumably rare, but naturally occurring twinning event is heteropaternal (HP) twinning. HP twinning results from superfecundation, a reproductive process in which offspring share their mothers, but not their fathers. The resulting twins share an average of 25% of their segregating genes, the same proportion as half-siblings. A recently identified case of HP opposite-sex twins was confirmed by DNA analyses available for the twins and for multiple family members. Thus, an exceptional feature of the current report is the inclusion of data for the twins' brothers, sisters, half-siblings, nieces, nephews and cousins, as well as several parent-child pairs. HP twins often go unnoticed so are typically classified as dizygotic (DZ) twins whose genetic overlap is 50%, on average, but varies across traits. As a unique category of non-identical twins, HP twinning is important to acknowledge as it may affect twins' physical resemblance, behavioral similarity, personal identity, family relations and health concerns. While including HP pairs in twin research has been shown to have minimal impact on heritability estimates, it could conceivably affect the outcomes of small-scale studies. Given a lack of consistent and known prevalence, case studies provide valuable knowledge regarding the occurrence of HP twinning. Its implications for forensic science and for twin research are considerable.

Fifty Years of Research in ARDS. The Epidemiology of Acute Respiratory Distress Syndrome. A 50th Birthday Review

Since its first description 50 years ago, no other intensive care syndrome has been as extensively studied as acute respiratory distress syndrome (ARDS). Despite this extensive body of research, many basic epidemiologic questions remain unsolved. The lack of gold standard tests jeopardizes accurate diagnosis and translational research. Wide variation in the population incidence has been reported, making even simple estimates of the burden of disease problematic. Despite these limitations, there has been an increase in the understanding of pathophysiology and important risk factors both for the development of ARDS and for important patient-centered outcomes like mortality. In this Critical Care Perspective, we discuss the historical context of ARDS description and attempts at its definition. We highlight the epidemiologic challenges of studying ARDS, as well as other intensive care syndromes, and propose solutions to address them. We update the current knowledge of ARDS trends in incidence and mortality, risk factors, and recently described endotypes.

GenePANDA-a novel network-based gene prioritizing tool for complex diseases

Here we describe GenePANDA, a novel network-based tool for prioritizing candidate disease genes. GenePANDA assesses whether a gene is likely a candidate disease gene based on its relative distance to known disease genes in a functional association network. A unique feature of GenePANDA is the introduction of adjusted network distance derived by normalizing the raw network distance between two genes with their respective mean raw network distance to all other genes in the network. The use of adjusted network distance significantly improves GenePANDA’s performance on prioritizing complex disease genes. GenePANDA achieves superior performance over five previously published algorithms for prioritizing disease genes. Finally, GenePANDA can assist in prioritizing functionally important SNPs identified by GWAS.

Epidemiology of multiple sclerosis

Multiple sclerosis (MS) is the most common disease of the central nervous system that causes permanent disability in young adults. Based on strong circumstantial evidence, MS is considered to be putative autoimmune disorder, but much remains to be understood about the etiology and clinical onset of the disease. It seems unlikely that MS results from a single causative event, but rather is the result of genetic and environmental factors and the interactions thereof. This article discusses the epidemiology of MS.

Health-and disease-related biomarkers in aging research

This article focuses on a synthesis of knowledge about healthy aging research in human beings and then synthesized nurse-led research in gerontology and geriatrics that use biomarkers. Healthy aging research has attracted considerable attention in the biomedical and basic sciences within the context of four major areas: (a) genetic variations as an expression of successful or unsuccessful aging; (b) caloric restriction as an intervention to slow the progression of aging; (c) immunological aging; (d) neurobiology of the aging brain. A systematic review of the literature was performed to identify nurse-led geriatric-related biomarker research. Nurse researchers who have chosen to integrate biomarkers as part of their research studies have been working in six focal areas, which are reviewed: health promotion within risk populations, cancer, vascular disease, Alzheimer's disease, caregiving, and complementary therapies. The article provides a discussion of contributions to date, identifying existing gaps and future research opportunities.

Heritability of depressive symptoms: a case study using a multilevel approach

We present a case study using a multilevel modeling approach to determine whether depressive symptoms are affected by genetic factors. Existing studies examining this question have focused on twins. The present study built on the literature by conducting a preliminary study of the heritability of depressive symptoms within extended families. At the same time, this study assessed the need for adjustment of a heritability measure in a family study using a multigenerational sample. The sample consisted of 230 community-dwelling extended families that included 431 adult offspring, comprising full siblings, half siblings and cousins that participated in the University of Southern California Longitudinal Study of Generations. All participants filled out the Center for Epidemiologic Studies Depression (CES-D) scale. The multilevel analysis allowed us to model the natural hierarchy of the extended family. Results indicate that the proportion of the phenotypic variance for CES-D that occurs due to genetic differences is not significantly larger than zero among these participants [h(2) = 8.6%, 95% confidence interval (CI) = 0-57%, p = 0.71]. Our findings suggest that future studies examining depressive symptoms in this sample can focus on non-genetic explanatory factors without the necessity to control for genetic variation. However, our study may be limited by measurement of prevalent depressive symptoms, which may not generalize to lifetime depressive symptoms.

Acute respiratory distress syndrome 40 years later: time to revisit its definition

OBJECTIVE

Acute respiratory distress syndrome is a common disorder associated with significant mortality and morbidity. The aim of this article is to critically evaluate the definition of acute respiratory distress syndrome and examine the impact the definition has on clinical practice and research.

DATA SOURCES

Articles from a MEDLINE search (1950 to August 2007) using the Medical Subject Heading respiratory distress syndrome, adult, diagnosis, limited to the English language and human subjects, their relevant bibliographies, and personal collections, were reviewed.

DATA SYNTHESIS

The definition of acute respiratory distress syndrome is important to researchers, clinicians, and administrators alike. It has evolved significantly over the last 40 years, culminating in the American-European Consensus Conference definition, which was published in 1994. Although the American-European Consensus Conference definition is widely used, it has some important limitations that may impact on the conduct of clinical research, on resource allocation, and ultimately on the bedside management of such patients. These limitations stem partially from the fact that as defined, acute respiratory distress syndrome is a heterogeneous entity and also involve the reliability and validity of the criteria used in the definition. This article critically evaluates the American-European Consensus Conference definition and its limitations. Importantly, it highlights how these limitations may contribute to clinical trials that have failed to detect a potential true treatment effect. Finally, recommendations are made that could be considered in future definition modifications with an emphasis on the significance of accurately identifying the target population in future trials and subsequently in clinical care.

CONCLUSION

How acute respiratory distress syndrome is defined has a significant impact on the results of randomized, controlled trials and epidemiologic studies. Changes to the current American-European Consensus Conference definition are likely to have an important role in advancing the understanding and management of acute respiratory distress syndrome.

Study designs to enhance identification of genetic factors in healthy aging

The sequencing of the human genome and the growing understanding of its function are providing powerful new research tools for identifying genetic variants that are associated with complex diseases and traits. Somewhat less emphasis has been given to genes related to healthy aging, although the approaches for studying health-related traits are analogous to those used for disease-related studies. A critical step prior to the design of such studies is to define a healthy aging phenotype, which should be standardized to permit comparisons across studies and should involve more than simple longevity. Phenotypes of particular value for genetic research are those with high heritability and close relationships to gene products or pathways, preferably with minimal or at least measurable environmental influences. Appropriate study designs to identify genotype-phenotype associations include family-based linkage studies, candidate gene association analyses, and genome-wide association studies. Advances in genotyping and sequencing technologies, and the generation of the human haplotype map database, now permit the cost-effective investigation of the very large sample sizes needed for genome-wide association studies in unrelated individuals. Challenges in interpretation and translation of such studies include assessing the potential for bias and confounding, as well as determining the clinical validity and utility of findings proposed for wider application. Many such studies are currently supported or being planned across the National Institutes of Health (NIH), and lend themselves to the kind of coordinated clinical research envisioned in programs such as the NIH Roadmap.

Definition of phenotype

Definition of the phenotype is crucial in designing any genetic study, especially an association study, intended to detect the disease predisposing genes. In this chapter, we review the different types of phenotypes such as discrete or continuous and discuss the issues impacting on the phenotype definition related to study design, specifically, the impact of diagnostic error (misclassification) in case-control studies and measurement error in continuous traits. We show that the power of a study depends heavily on the phenotype measured and that misclassification or measurement error can dramatically reduce the power. We also suggest some possible responses to these challenges.

Epidemiology and Outcomes of Acute Lung Injury

Acute lung injury (ALI) and its presentation with more severe hypoxemia, the ARDS, is a challenging entity for clinical investigation because, like many critical illness syndromes, it lacks an accepted diagnostic test and relies on a constellation of clinical findings for diagnosis. Despite these barriers, there have been important advances in the clinical and population epidemiology of ALI. This article will review recent studies of the incidence, diagnosis, etiologic and prognostic factors, relevant disease subsets, mortality, and long-term outcomes of ALI. A detailed understanding of the epidemiology and outcomes of ALI is essential for future research on mechanisms of both the acute presentation and long-term sequelae, for designing studies to identify genetic risk factors for developing ALI, and to develop strategies to treat or prevent the morbidity encountered by survivors.

Genetic epidemiology of acute respiratory distress syndrome: implications for future prevention and treatment

The genetic susceptibility to the development of and variable outcomes in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) has become a topic of great interest in the pulmonary and critical care community. Published studies of variable genetic susceptibility to ALI/ARDS already have identified some important candidate genes and potential gene-environment interactions. This article reviews these recent studies, features of the current approach, and implications for future prevention and treatment in ALI. The challenges and potential contributions of genetic epidemiology to the future prevention and treatment in ALI are discussed.

Dissecting complex disease: the quest for the Philosopher's Stone?

Is the search for the causes of complex disease akin to the alchemist's vain quest for the Philosopher's Stone? Complex chronic diseases have tremendous public health impact in the industrialized world. Much effort has been expended on research into their causes, with the aim of predicting who will be affected or preventing effects before they arise, but progress has been halting at best. In this paper, we discuss possible reasons including the use of models and methods that fit point-source and Mendelian diseases but may not be as appropriate for complex diseases, reliance on causal criteria that may not be as relevant as they are for communicable diseases, and the biology of complex disease itself. Finally, we ask whether most complex diseases are even good candidates for the kind of prediction and prevention that we have come to expect based on experience with infectious and Mendelian disease.

Dissection of heterogeneous phenotypes for quantitative trait mapping

We discuss analyses of Genetic Analysis Workshop 14 data from the Collaborative Study on the Genetics of Alcoholism (COGA) as well as from a simulated complex disease, Kofendrerd personality disorder (KPD), with both genetic and phenotypic heterogeneity. Both data sets included numerous related phenotypes in addition to disease definitions. All analyses either chose from the given selection of phenotypes or defined new ones, including traits that may not have been related to alcoholism or KPD. Some contributors evaluated the genetic components of the trait. Many investigated genome-wide linkage and/or association, using microsatellites and/or single-nucleotide polymorphism (SNP) chip data. Here we will focus on methodological issues that the investigators faced. Their results depended on phenotype selection, whether continuous or discrete, the covariates included, and ethnicity of the study population. For SNP chip data, members of our group detected no difference in results for Affymetrix or Illumina chips, although higher marker density for association studies appeared to be advantageous. Overall, there were some observations that different chromosomal segments, i.e., physical locations on the p-arm, q-arm, or middle segment, might lead to possible differences in type I error rates. This finding and others highlight the importance of empirical determination of P-values to determine significance.

Genetic epidemiology of acute lung injury: choosing the right candidate genes is the first step

In an innovative scientific review in this issue, Grigoryev and colleagues report a method for choosing candidate genes for acute lung injury (ALI) based on gene expression data derived from multiple animal models of mechanical ventilation and shear stress. The authors conclude there are five key biologic processes that warrant further investigation: inflammatory and immune responses, cell proliferation, chemotaxis, and blood coagulation. This review represents an important first step toward studying the genetic epidemiology of ventilator-induced lung injury and ALI. The application of these findings to future human studies of the genetic influence on ALI risks and outcomes is discussed here.

Transmission disequilibrium test (TDT) for case–control studies

Genetic association, case-control studies are becoming a major instrument in the attempt to identify disease susceptibility markers of complex diseases. However, a major drawback of population-based studies of genetic association is the confounding effect of the population subdivision. We developed a statistic named T-value that estimates the differential transmission of marker alleles from heterozygous parents to the affected offspring, based on population data. Our method does not assume Hardy-Weinberg equilibrium and it can be used in very different population structures. A great advantage of this approach is that the genetic structure of the population can be assessed with a few unlinked loci and using classical population genetics theory (i.e. Wright's F-statistics). Four general models, assuming either one population with random mating, or one population without random mating, or several populations with random mating within them, or several populations without random mating within them, were developed to determine the behavior of the T-value under different mating conditions. Although a complete knowledge of the population structure is ideal to choose the best model, the simulations show that for a total inbreeding of 0.30 or less the last three models gave very similar estimates of the T-value. The model that assumed that total departure of Hardy-Weinberg proportions is due to population subdivision was the most robust under different scenarios of population structure. In sum, this study describes a novel procedure that can be used to identify the transmission of disease susceptibility markers in population-based studies.

"Are we there yet?": Deciding when one has demonstrated specific genetic causation in complex diseases and quantitative traits

Although mathematical relationships can be proven by deductive logic, biological relationships can only be inferred from empirical observations. This is a distinct disadvantage for those of us who strive to identify the genes involved in complex diseases and quantitative traits. If causation cannot be proven, however, what does constitute sufficient evidence for causation? The philosopher Karl Popper said, "Our belief in a hypothesis can have no stronger basis than our repeated unsuccessful critical attempts to refute it." We believe that to establish causation, as scientists, we must make a serious attempt to refute our own hypotheses and to eliminate all known sources of bias before association becomes causation. In addition, we suggest that investigators must provide sufficient data and evidence of their unsuccessful efforts to find any confounding biases. In this editorial, we discuss what "causation" means in the context of complex diseases and quantitative traits, and we suggest guidelines for steps that may be taken to address possible confounders of association before polymorphisms may be called "causative."

Epidemiology of acute lung injury

OBJECTIVE

To review the epidemiology of acute lung injury (ALI) with particular emphasis on its effect on public health.

DATA SOURCES

Published studies on the definitions, incidence, and outcomes of ALI.

DATA SUMMARY

ALI is a syndrome of acute hypoxemic respiratory failure that is not primarily cardiac in origin. The diagnostic criteria for the syndrome have not been well studied for their reliability or validity. The lack of a gold standard for the diagnosis of ALI is a challenge to clinical investigation. Recent data on the incidence of ALI (20-50 cases/105 person-years) indicate that it is more common than previous estimates for the incidence of acute respiratory distress syndrome (3-8 cases/105 person-years). There is conflicting evidence as to whether the mortality rate in the broader patient population with ALI is different from the mortality rate in acute respiratory distress syndrome. Mortality attributable to and associated with ALI in the United States is comparable to HIV infection, breast cancer, and asthma. Morbidity from impaired cognitive function, functional status, and psychiatric complications has been reported in survivors of ALI.

CONCLUSIONS

Recent studies of the epidemiology of ALI have reported higher incidence rates for this syndrome than previously described. The mortality and morbidity rates associated with ALI are considerable, with significant impact on public health.

A review of genetic polymorphisms and prostate cancer risk

In this study, we review a variety of genetic polymorphisms that may have an etiologic role in prostate cancer. We include associations identified in molecular epidemiology studies and the consistency of findings reported to date. Suggestions for further research are also offered. For the purposes of this review, we identified relevant articles through a MEDLINE search for the period of January 1987 through March 2001. The searches were limited to articles published in English. Medical subject headings were used to scan titles, abstracts, and subject headings in the databases using the keywords "prostate neoplasms," "genetics," and "polymorphisms."

Role of genetics in osteoporosis

Osteoporosis is a disease characterized by fragile bones and high susceptibility to low-trauma fractures. It is a serious health problem, especially in elderly women. Bone mineral density (BMD) has been employed most commonly as the index for defining and studying osteoporosis. BMD has high genetic determination, with heritability ranging from 50 to 90%. Various gene-mapping approaches have been applied to identify specific genes underlying osteoporosis, largely using BMD as the study phenotype. We review here the genetic determination of osteoporosis as defined by BMD and discuss a fundamental issue we encounter in genetic research in osteoporosis: the choice of phenotype(s) to study. We briefly summarize and discuss advantages and disadvantages of various approaches used in genetic studies of osteoporosis. Finally, we review and discuss the current status for mapping and identification of genes for osteoporosis. We focus on linkage studies in humans and quantitative trait loci mapping in mice to supplement the already extensive reviews of association studies made by many investigators for candidate genes.

Genomics and large scale phenotypic databases

Progress in the development of molecular genetic tools and in sequencing the human genome will accelerate the understanding of complex genetic diseases. However, phenotypic clinical data needs to be obtained and recorded to a similar degree of precision in order to match the wealth of molecular genetic data. To achieve this goal, large scale phenotypic databases of complex genetic diseases are under construction. LURIC (the LUwigshafen Risk and Cardiovascular Health Study) is such a project, aiming to identify new genetic and environmental risk factors or markers for cardiovascular disease in order to better understand the pathophysiology of complex genetic disease. It should also allow the determination of the prognostic role of new markers by studying functional genomics, (the association between a gene variant and phenotype), and pharmacogenomics (the influence of genetic variation on the response to therapeutic agents).

Update on the genetics of the idiopathic inflammatory myopathies

A number of lines of investigation suggest that, as is likely the case for other autoimmune diseases, the idiopathic inflammatory myopathies (IIM) develop as a result of specific environmental exposures in genetically susceptible individuals. Current data imply that multiple genes are involved in the etiology of these complex disorders. Targeted gene studies and whole genome approaches have begun to identify several genetic risk factors for autoimmune diseases, but the rarity and heterogeneity of the IIM have limited our knowledge of their associated genes. Current findings suggest that human leukocyte antigen (HLA) genes on chromosome 6, particularly HLA DRB1*0301 and the linked allele DQA1*0501, have the strongest associations with all clinical forms of IIM in white patients. Different HLA alleles, however, may confer risk or protection for myositis in distinct ethnic, serologic, and environmental exposure groups. Non-HLA genetic risk factors, which have been documented for other autoimmune diseases, are now being identified for the IIM. These include polymorphic genes encoding immunoglobulin heavy chains (defined by serologic markers known as Gm allotypes), cytokines and their receptors, and certain proteins that accumulate in the myocyte vacuoles of inclusion body myositis patients. Selected allelic polymorphisms of interleukin-1 receptor antagonist variable number tandem repeats and genes for tumor necrosis factor alpha and interleukin-1 alpha also have recently been associated with IIM. The pathogenic bases for the differences among the many clinically, pathologically and immunologically defined syndromes known as the IIM will be elucidated through a better understanding of the multiple genes that define risks for their development, as well as through investigations of gene-gene and gene-environment interactions.

Short-term storage of blood samples and DNA isolation in serum separator tubes for application in epidemiological studies and clinical research

PURPOSE

To investigate the use of a simple DNA isolation technique for application in epidemiologic studies. To analyze systematically the potential impact of lag time between blood drawing and DNA isolation and the condition of storage of blood samples on the quantity and quality of isolated DNA in large-scale epidemiologic studies.

METHODS

A modified single tube DNA isolation technique was used. DNA was isolated from samples collected from six participants and processed in triplicate: a) without delay after blood drawing; b) after blood cells were stored at 4 degrees C for 7 days; c) after blood cells were stored at -70 degrees C for 7 days; and d) after storage for 7 days at -70 degrees C with addition of lysis/digestion buffer. Polymerase chain reaction (PCR) and Southern blot analysis were performed to analyze the quality of the isolated DNA.

RESULTS

The average amount of DNA isolated ranged from 27.0 to 71.1 microg/4.5 ml whole blood. Storage at 4 degrees C yielded, on the average, 20% less DNA than the samples processed without delay or after storage at -70 degrees C, although this difference was not statistically significant. All four conditions studied allowed isolation of highly pure DNA suitable for genetic analyses by Southern blot analysis and polymerase chain reaction.

CONCLUSIONS

This pilot study suggests that storage for 7 days and at different temperatures allows isolation of high quality DNA. Using the described technique, storage of up to 7 days permits processing of large numbers of samples (50-70) in a single day, allowing for a reliable and cost-efficient way of processing in various settings. Further studies are needed to investigate the influence of long-term storage of biological specimens on DNA isolation and quality.

Pro12Ala mutation in the peroxisome proliferator-activated receptor gamma2 (PPARgamma2) and severe obesity: a case-control study

OBJECTIVE

To explore the association of the Pro12Ala mutation in the peroxisome proliferator-activated receptor gamma2 with severe obesity and the features of the metabolic syndrome in a population-based sample of Caucasians.

PARTICIPANTS AND METHODS

The study is based on a case-control design: 95 non-diabetic severely obese (body mass index, BMI > 35 kg/m2) cases and 280 normal weight (BMI < 25 kg/m2), age- and sex-matched controls selected from the same population were studied. Height, weight, waist circumference, as well as blood pressure were measured according to a standard protocol. BMI at age 25 y was calculated on the basis of current height and reported weight at age 25 y Biochemical measurements included fasting glucose, triglycerides, high-density lipoprotein cholesterol and insulin. DNA analysis was conducted by PCR and gel electrophoresis.

RESULTS

Age and gender distribution were similar in obese and normal weight participants. The percentage of people with the Pro12Ala mutation was not significantly different in obese or normal weight participants (20% and 15%, respectively; P = 0.32). Conversely, in obese participants with obesity starting in early adulthood (ie with BMI at age 25 above 26.9kg/m2 which represents the median of the whole obese group), the Pro12Ala mutation was observed significantly more frequently than in the normal weight controls (29% vs 15%; chi square = 4.5, P < 0.05; odds ratio 2.4; 95% CI 1.03-5.36). No association of the Pro12Ala variant with any of the component of the metabolic syndrome measured in the study was observed in either obese, juvenile obese or normal weight participants.

CONCLUSIONS

Results of this study indicate that the Pro12Ala mutation does not play a major role as a determinant of severe obesity and/or features of the metabolic syndrome in the general population. However, this mutation may be of greater importance as a contributor to early onset obesity.

Search for schizophrenia susceptibility genes

Identification of a gene or genes that contribute to the development of schizophrenia, a complex psychiatric disorder, may be possible through genetic linkage analysis. Although to date no single causative gene has been identified, several chromosomal loci have shown positive linkage results and are under investigation as tentative schizophrenia susceptibility loci. Despite such obstacles as locus heterogeneity among sample populations, epistatic inheritance models, and failure to obtain statistical significance in studies, patterns have emerged that focus research efforts on chromosomes 13, 8, 22, and 6 and 10. Initial heterogeneity analyses suggests that identifiable subgroups of the families may not contribute equally to these linkage findings. Findings on several additional chromosomes await further replication. Future progress in the search for schizophrenia susceptibility genes will require collaboration among researchers from both academia and industry.