Newborn screening research sponsored by the NIH: From diagnostic paradigms to precision therapeutics.

Newborn screening (NBS) is a successful public health initiative that effectively identifies pre-symptomatic neonates so that treatment can be initiated before the onset of irreversible morbidity and mortality. Legislation passed in 2008 has supported a system of state screening programs, educational resources, and an evidence-based review process to add conditions to a recommended universal newborn screening panel (RUSP). The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), NIH, has promoted NBS research to advance legislative goals by supporting research that will uncover fundamental mechanisms of disease, develop treatments for NBS disorders, and promote pilot studies to test implementation of new conditions. NICHD's partnerships with other federal agencies have contributed to activities that support nominations of new conditions to the RUSP. The NIH's Newborn Sequencing In Genomic Medicine and Public Health (NSIGHT) initiative funded research projects that considered how genomic sequencing could be integrated into NBS and its ethical ramifications. Recently, the workshop, "Gene Targeted Therapies: Early Diagnosis and Equitable Delivery," has explored the possibility of expanding NBS to include genetic diagnosis and precision, gene-based therapies. Although hurdles remain to realize such a vision, broad engagement of multiple stakeholders is essential to advance genomic medicine within NBS.

Emerging Concepts in Precision Medicine and Cardiovascular Diseases in Racial and Ethnic Minority Populations.

Cardiovascular diseases remain the leading cause of mortality and a major contributor to preventable deaths worldwide. The dominant modifiable risk factors and the social and environmental determinants that increase cardiovascular risk are known, and collectively, are as important in racial and ethnic minority populations as they are in majority populations. Their prevention and treatment remain the foundation for cardiovascular health promotion and disease prevention. Genetic and epigenetic factors are increasingly recognized as important contributors to cardiovascular risk and provide an opportunity for advancing precision cardiovascular medicine. In this review, we explore emerging concepts at the interface of precision medicine and cardiovascular disease in racial and ethnic minority populations. Important among these are the lack of racial and ethnic diversity in genomics studies and biorepositories; the resulting misclassification of benign variants as pathogenic in minorities; and the importance of ensuring ancestry-matched controls in variant interpretation. We address the relevance of epigenetics, pharmacogenomics, genetic testing and counseling, and their social and cultural implications. We also examine the potential impact of precision medicine on racial and ethnic disparities. The National Institutes of Health's All of Us Research Program and the National Heart, Lung, and Blood Institute's Trans-Omics for Precision Medicine Initiative are presented as examples of research programs at the forefront of precision medicine and diversity to explore research implications in minorities. We conclude with an overview of implementation research challenges in precision medicine and the ethical implications in minority populations. Successful implementation of precision medicine in cardiovascular disease in minority populations will benefit from strategies that directly address diversity and inclusion in genomics research and go beyond race and ethnicity to explore ancestry-matched controls, as well as geographic, cultural, social, and environmental determinants of health.

Participant-Partners in Genetic Research: An Exome Study with Families of Children with Unexplained Medical Conditions.

BACKGROUND: Unlike aggregate research on groups of participants with a particular disorder, genomic research on discrete families' rare conditions could result in data of use to families, their healthcare, as well as generating knowledge on the human genome. OBJECTIVE: In a study of families seeking to rule in/out genetic causes for their children's medical conditions via exome sequencing, we solicited their views on the importance of genomic information. Our aim was to learn the interests of parents in seeking genomic research data and to gauge their responsiveness and engagement with the research team. METHODS: At enrollment, we offered participants options in the consent form for receiving potentially clinically relevant research results. We also offered an option of being a "partner" versus a "traditional" participant; partners could be re-contacted for research and study activities. We invited adult partners to complete a pre-exome survey, attend annual family forums, and participate in other inter-family interaction opportunities. RESULTS: Of the 385 adults enrolled, 79% opted for "partnership" with the research team. Nearly all (99.2%) participants opted to receive research results pertaining to their children's primary conditions. A majority indicated the desire to receive additional clinically relevant outside the scope of their children's conditions (92.7%) and an interest in non-clinically relevant genetic information (82.7%). CONCLUSIONS: Most participants chose partnership, including its rights and potential burdens; however, active engagement in study activities remained the exception. Not surprisingly, the overwhelming majority of participants-both partners and traditional-expected to receive all genetic information resulting from the research study.

Genome-wide association study identifies three novel loci in Fuchs endothelial corneal dystrophy.

The structure of the cornea is vital to its transparency, and dystrophies that disrupt corneal organization are highly heritable. To understand the genetic aetiology of Fuchs endothelial corneal dystrophy (FECD), the most prevalent corneal disorder requiring transplantation, we conducted a genome-wide association study (GWAS) on 1,404 FECD cases and 2,564 controls of European ancestry, followed by replication and meta-analysis, for a total of 2,075 cases and 3,342 controls. We identify three novel loci meeting genome-wide significance (P<5 × 10-8): KANK4 rs79742895, LAMC1 rs3768617 and LINC00970/ATP1B1 rs1200114. We also observe an overwhelming effect of the established TCF4 locus. Interestingly, we detect differential sex-specific association at LAMC1, with greater risk in women, and TCF4, with greater risk in men. Combining GWAS results with biological evidence we expand the knowledge of common FECD loci from one to four, and provide a deeper understanding of the underlying pathogenic basis of FECD.

Informed decision-making about prenatal cfDNA screening: An assessment of written materials.

OBJECTIVES: The introduction of prenatal cfDNA screening for fetal aneuploidy and other genetic conditions has exacerbated concerns about informed decision-making in clinical prenatal testing. To assess the information provided to patients to facilitate decisions about cfDNA screening, we collected written patient education and consent documents created by laboratories and clinics. METHODS: Informed consent documents (IC) were coded by two independent coders. Each IC was assessed for readability, attention to elements of informed consent, and completeness of information about the test and the screened conditions. RESULTS: We found variance between IC produced by commercial laboratories versus those provided by local clinics or health care systems, and considerable variance among materials from all sources. "Commercial" IC were longer and written at a more difficult reading level than "non-commercial" IC, and were less likely to state explicitly that cfDNA only screens for certain conditions. About one-third of IC were combined with laboratory order forms. Though most IC recommended confirmatory testing for positive results, only about half clearly stated that results could be incorrect-including mentions of false positives or false negatives. About one-third of IC explicitly stated that cfDNA screening was optional. While nearly all IC from any source listed the conditions screened by the test, only about half of the IC included any phenotypic descriptions of these conditions. Few IC mentioned psychosocial considerations, and only one IC mentioned the availability of support groups for families of children with genetic conditions. CONCLUSIONS: Based on our findings, we recommend that written and well-informed consent be sought before performing cfDNA screening, and we offer minimal and recommended standards for patient education and consent materials.

OBJECTIFS: L'introduction du dépistage prénatal cfDNA aneuploïdie fœtale et d'autres maladies génétiques a exacerbé des préoccupations au sujet de prise de décisions éclairée dans les cliniques de dépistage prénatal. Afin d'évaluer les informations fournies aux patients pour faciliter les décisions sur le dépistage de la cfDNA, nous avons recueilli patient education et consentement écrits émanant des laboratoires et des cliniques. MÉTHODES: Les documents de consentement éclairé (IC) ont été codées par deux programmeurs indépendants. Chaque IC a été évaluée pour la lisibilité, attention aux éléments du consentement éclairé et l'exhaustivité des informations sur le test et les conditions de dépistage. RÉSULTATS: Nous avons trouvé la variance entre IC produite par les laboratoires commerciaux par rapport à ceux fournis par les cliniques locales ou des systèmes de soins de santé et écart considérable entre les matériaux de toutes les sources. IC "Commercial" étaient plus longs et écrite à un niveau de lecture plus difficile que IC « non commerciales ¼ et étaient moins susceptible d'État explicitement ce cfDNA seulement des écrans pour certaines conditions. Environ un tiers d'IC ont été combinées avec les bons de commande de laboratoire. Si IC plus recommandés pour les résultats positifs des tests de confirmation, seulement environ la moitié a clairement indiqué que les résultats pourraient être incorrectes ­ y compris les mentions de faux positifs ou faux négatifs. Environ un tiers des IC a explicitement déclaré que cfDNA dépistage était facultative. Tandis que presque tous les IC de n'importe quelle source répertorié les conditions examinées par le test, seulement environ la moitié du ci inclus toute description phénotypique de ces conditions. IC peu mentionné les facteurs psychosociaux et seul IC mentionné l'existence de groupes de soutien pour les familles des enfants atteints de maladies génétiques. CONCLUSIONS: D'après nos résultats, nous recommandons que le consentement écrit et bien informé peut rechercher avant d'effectuer le dépistage des cfDNA, et nous offrons des normes minimales et recommandées pour l'éducation du patient et consentement des matériaux. Une de nos neuf recommandations est que quelle que soit la question de savoir si une signature est requise, les documents de consentement éclairé devraient inclure une instruction simple consentement ne pas associée à des accords juridiques ou financières. Figurant en bonne place devrait être aussi le nom et les coordonnées d'un fournisseur local de clinique qui est disponible pour d'autres questions.

Noninvasive Prenatal Genetic Testing: Current and Emerging Ethical, Legal, and Social Issues.

Noninvasive prenatal genetic testing (NIPT) for chromosomal aneuploidy involving the analysis of cell-free fetal DNA became commercially available in 2011. The low false-positive rate of NIPT, which reduces unnecessary prenatal invasive diagnostic procedures, has led to broad clinician and patient adoption. We discuss the ethical, legal, and social issues raised by rapid and global dissemination of NIPT. The number of women using NIPT is anticipated to expand, and the number of conditions being tested for will continue to increase as well, raising concerns about the routinization of testing and negative impacts on informed decision making. Ensuring that accurate and balanced information is available to all pregnant women and that access to NIPT is equitable will require policy guidance from regulators, professional societies, and payers. Empirical evidence about stakeholders' perspectives and experiences will continue to be essential in guiding policy development so that advances in NIPT can be used effectively and appropriately to improve prenatal care.

Perceptions of Personalized Medicine in an Academic Health System: Educational Findings.

OBJECTIVE: Prior reports demonstrate that personalized medicine implementation in clinical care is lacking. Given the program focus at Duke University on personalized medicine, we assessed health care providers' perspectives on their preparation and educational needs to effectively integrate personalized medicine tools and applications into their clinical practices. METHODS: Data from 78 health care providers who participated in a larger study of personalized and precision medicine at Duke University were analyzed using Qualtrics (descriptive statistics). Individuals age 18 years and older were recruited for the larger study through broad email contacts across the university and health system. All participants completed an online 35-question survey that was developed, pilot-tested, and administered by a team of interdisciplinary researchers and clinicians at the Center for Applied Genomics and Precision Medicine. RESULTS: Overall, providers reported being ill-equipped to implement personalized medicine in clinical practice. Many respondents identified educational resources as critical for strengthening personalized medicine implementation in both research and clinical practice. Responses did not differ significantly between specialists and primary providers or by years since completion of the medical degree. CONCLUSIONS: Survey findings support prior calls for provider and patient education in personalized medicine. Respondents identified focus areas in training, education, and research for improving personalized medicine uptake. Given respondents' emphasis on educational needs, now may be an ideal time to address these needs in clinical training and public education programs.

Global perspectives on clinical adoption of NIPT.

OBJECTIVE: The goals of this study were to assess global trends in clinical implementation of noninvasive prenatal testing (NIPT), as commercial tests are marketed increasingly worldwide, and to identify potential challenges for current or future use. METHODS: We surveyed clinicians from 46 countries about the availability of NIPT, their experiences with using NIPT, and their views on clinical, ethical, and legal issues affecting implementation in their countries. RESULTS: Forty-nine respondents from 28 countries completed the survey. The majority reported that NIPT is available in their country (n = 43) and that they offer NIPT in their current practice (n = 38). Eighteen respondents from 14 countries reported that there are plans to introduce NIPT into routine prenatal care in their country. Test prices varied widely, ranging from $350 to $2900, and several respondents observed that high test prices limited or restricted widespread use of NIPT. Responses varied both across and within countries regarding who is offered NIPT and what the overall screening protocol should be. CONCLUSION: This study provides a snapshot of current use and experiences with NIPT globally. It also highlights differences in service provision that exists both across and within countries, emphasizing the need for developing national and international implementation guidelines for NIPT.

Perspectives on genetic and genomic technologies in an academic medical center: the duke experience.

UNLABELLED: In this age of personalized medicine, genetic and genomic testing is expected to become instrumental in health care delivery, but little is known about its actual implementation in clinical practice. METHODS: We surveyed Duke faculty and healthcare providers to examine the extent of genetic and genomic testing adoption. We assessed providers' use of genetic and genomic testing options and indications in clinical practice, providers' awareness of pharmacogenetic applications, and providers' opinions on returning research-generated genetic test results to participants. Most clinician respondents currently use family history routinely in their clinical practice, but only 18 percent of clinicians use pharmacogenetics. Only two respondents correctly identified the number of drug package inserts with pharmacogenetic indications. We also found strong support for the return of genetic research results to participants. Our results demonstrate that while Duke healthcare providers are enthusiastic about genomic technologies, use of genomic tools outside of research has been limited. Respondents favor return of research-based genetic results to participants, but clinicians lack knowledge about pharmacogenetic applications. We identified challenges faced by this institution when implementing genetic and genomic testing into patient care that should inform a policy and education agenda to improve provider support and clinician-researcher partnerships.

Non-invasive prenatal testing: a review of international implementation and challenges.

Noninvasive prenatal genetic testing (NIPT) is an advance in the detection of fetal chromosomal aneuploidies that analyzes cell-free fetal DNA in the blood of a pregnant woman. Since its introduction to clinical practice in Hong Kong in 2011, NIPT has quickly spread across the globe. While many professional societies currently recommend that NIPT be used as a screening method, not a diagnostic test, its high sensitivity (true positive rate) and specificity (true negative rate) make it an attractive alternative to the serum screens and invasive tests currently in use. Professional societies also recommend that NIPT be accompanied by genetic counseling so that families can make informed reproductive choices. If NIPT becomes more widely adopted, States will have to implement regulation and oversight to ensure it fits into existing legal frameworks, with particular attention to returning fetal sex information in areas where sex-based abortions are prevalent. Although there are additional challenges for NIPT uptake in the developing world, including the lack of health care professionals and infrastructure, the use of NIPT in low-resource settings could potentially reduce the need for skilled clinicians who perform invasive testing. Future advances in NIPT technology promise to expand the range of conditions that can be detected, including single gene disorders. With these advances come questions of how to handle incidental findings and variants of unknown significance. Moving forward, it is essential that all stakeholders have a voice in crafting policies to ensure the ethical and equitable use of NIPT across the world.

Mitochondrial polymorphism A10398G and Haplogroup I are associated with Fuchs' endothelial corneal dystrophy.

PURPOSE: We investigated whether mitochondrial DNA (mtDNA) variants affect the susceptibility of Fuchs endothelial corneal dystrophy (FECD). METHODS: Ten mtDNA variants defining European haplogroups were genotyped in a discovery dataset consisting of 530 cases and 498 controls of European descent from the Duke FECD cohort. Association tests for mtDNA markers and haplogroups were performed using logistic regression models with adjustment of age and sex. Subset analyses included controlling for additional effects of either the TCF4 SNP rs613872 or cigarette smoking. Our replication dataset was derived from the genome-wide association study (GWAS) of the FECD Genetics Consortium, where genotypes for three of 10 mtDNA markers were available. Replication analyses were performed to compare non-Duke cases to all GWAS controls (GWAS1, N = 3200), and to non-Duke controls (GWAS2, N = 3043). RESULTS: The variant A10398G was significantly associated with FECD (odds ratio [OR] = 0.72; 95% confidence interval [CI] = [0.53, 0.98]; P = 0.034), and remains significant after adjusting for smoking status (min P = 0.012). This variant was replicated in GWAS1 (P = 0.019) and GWAS2 (P = 0.036). Haplogroup I was significantly associated with FECD (OR = 0.46; 95% CI = [0.22, 0.97]; P = 0.041) and remains significant after adjusting for the effect of smoking (min P = 0.008) or rs613872 (P = 0.034). CONCLUSIONS: The 10398G allele and Haplogroup I appear to confer significant protective effects for FECD. The effect of A10398G and Haplogroup I to FECD is likely independent of the known TCF4 variant. More data are needed to decipher the interaction between smoking and mtDNA haplogroups.

Noninvasive prenatal testing goes global.

Noninvasive prenatal genetic testing is becoming available worldwide--particularly in low- and middle-income countries--but practical and ethical challenges must be overcome.

Preliminary perspectives on DNA collection in anti-human trafficking efforts.

Forensic DNA methodologies have potential applications in the investigation of human trafficking cases. DNA and relationship testing may be useful for confirmation of biological relationship claims in immigration, identification of trafficked individuals who are missing persons, and family reunification of displaced individuals after mass disasters and conflicts. As these applications rely on the collection of DNA from non-criminals and potentially vulnerable individuals, questions arise as to how to address the ethical challenges of collection, security, and privacy of collected samples and DNA profiles. We administered a survey targeted to victims' advocates to gain preliminary understanding of perspectives regarding human trafficking definitions, DNA and sex workers, and perceived trust of authorities potentially involved in DNA collection. We asked respondents to consider the use of DNA for investigating adoption fraud, sex trafficking, and post-conflict child soldier cases. We found some key differences in perspectives on defining what qualifies as "trafficking." When we varied terminology between "sex worker" and "sex trafficking victim" we detected differences in perception on which authorities can be trusted. Respondents were supportive of the hypothetical models proposed to collect DNA. Most were favorable of DNA specimens being controlled by an authority outside of law enforcement. Participants voiced concerns focused on privacy, misuse of DNA samples and data, unintentional harms, data security, and infrastructure. These preliminary data indicate that while there is perceived value in programs to use DNA for investigating cases of human trafficking, these programs may need to consider levels of trust in authorities as their logistics are developed and implemented.

Genetic screen of African Americans with Fuchs endothelial corneal dystrophy.

PURPOSE: Fuchs endothelial corneal dystrophy (FECD) is a genetically heterogeneous disorder that has been primarily studied in patients of European or Asian ancestry. Given the sparse literature on African Americans with FECD, we sought to characterize the genetic variation in three known FECD candidate genes in African American patients with FECD. METHODS: Over an 8-year period, we enrolled 47 African American probands with FECD. All participants were clinically examined with slit-lamp biomicroscopy, and when corneal tissue specimens were available, histopathologic confirmation of the clinical diagnosis was obtained. The coding regions of known FECD susceptibility genes collagen, type VIII, alpha 2 (COL8A2); solute carrier family 4, sodium borate transporter, member 11 (SLC4A11); and zinc finger E-box binding homeobox 1 (ZEB1 [also known as TCF8]) were Sanger sequenced in the 47 probands using DNA isolated from blood samples. RESULTS: Twenty-two coding variants were detected across the COL8A2, SLC4A11, and ZEB1 genes; six were nonsynonymous variants. Three novel coding variants were detected: a synonymous variant each in COL8A2 and SLC4A11 and one nonsynonymous variant in ZEB1 (p.P559S), which is predicted to be benign and tolerated, thus making its physiologic consequence uncertain. CONCLUSIONS: Variation in the COL8A2, SLC4A11, and ZEB1 genes is present in only a small fraction of our African American cases and as such does not appear to significantly contribute to the genetic risk of FECD in African Americans. This observation is on par with findings from previous sequencing studies involving European or Asian ancestry patients with FECD.

Cystic Fibrosis Patents: A Case Study of Successful Licensing.

From 2006-2010, Duke University's Center for Public Genomics prepared eight case studies examining the effects of gene patent licensing practices on clinical access to genetic testing for ten clinical conditions. One of these case studies focused on the successful licensing practices employed by the University of Michigan and the Hospital for Sick Children in Toronto for patents covering the CFTR gene and its ΔF508 mutation that causes a majority of cystic fibrosis cases. Since the licensing of these patents has not impeded clinical access to genetic testing, we sought to understand how this successful licensing model was developed and whether it might be applicable to other gene patents. We interviewed four key players who either were involved in the initial discussions regarding the structure of licensing or who have recently managed the licenses and collected related documents. Important features of the licensing planning process included thoughtful consideration of potential uses of the patent; anticipation of future scientific discoveries and technological advances; engagement of relevant stakeholders, including the Cystic Fibrosis Foundation; and using separate licenses for in-house diagnostics versus kit manufacture. These features led to the development of a licensing model that has not only allowed the patent holders to avoid the controversy that has plagued other gene patents, but has also allowed research, development of new therapeutics, and wide-spread dissemination of genetic testing for cystic fibrosis. Although this licensing model may not be applicable to all gene patents, it serves as a model in which gene patent licensing can successfully enable innovation, investment in therapeutics research, and protect intellectual property while respecting the needs of patients, scientists, and public health.

Replication of TCF4 through association and linkage studies in late-onset Fuchs endothelial corneal dystrophy.

Fuchs endothelial corneal dystrophy (FECD) is a common, late-onset disorder of the corneal endothelium. Although progress has been made in understanding the genetic basis of FECD by studying large families in which the phenotype is transmitted in an autosomal dominant fashion, a recently reported genome-wide association study identified common alleles at a locus on chromosome 18 near TCF4 which confer susceptibility to FECD. Here, we report the findings of our independent validation study for TCF4 using the largest FECD dataset to date (450 FECD cases and 340 normal controls). Logistic regression with sex as a covariate was performed for three genetic models: dominant (DOM), additive (ADD), and recessive (REC). We found significant association with rs613872, the target marker reported by Baratz et al.(2010), for all three genetic models (DOM: P = 9.33×10(-35); ADD: P = 7.48×10(-30); REC: P = 5.27×10(-6)). To strengthen the association study, we also conducted a genome-wide linkage scan on 64 multiplex families, composed primarily of affected sibling pairs (ASPs), using both parametric and non-parametric two-point and multipoint analyses. The most significant linkage region localizes to chromosome 18 from 69.94cM to 85.29cM, with a peak multipoint HLOD = 2.5 at rs1145315 (75.58cM) under the DOM model, mapping 1.5 Mb proximal to rs613872. In summary, our study presents evidence to support the role of the intronic TCF4 single nucleotide polymorphism rs613872 in late-onset FECD through both association and linkage studies.

Polymorphic variants in tenascin-C (TNC) are associated with atherosclerosis and coronary artery disease.

Tenascin-C (TNC) is an extracellular matrix protein implicated in biological processes important for atherosclerotic plaque development and progression, including smooth muscle cell migration and proliferation. Previously, we observed differential expression of TNC in atherosclerotic aortas compared with healthy aortas. The goal of this study was to investigate whether common genetic variation within TNC is associated with risk of atherosclerosis and coronary artery disease (CAD) in three independent datasets. We genotyped 35 single nucleotide polymorphisms (SNPs), including 21 haplotype tagging SNPs, in two of these datasets: human aorta tissue samples (n = 205) and the CATHGEN cardiovascular study (n = 1,325). Eleven of these 35 SNPs were then genotyped in a third dataset, the GENECARD family study of early-onset CAD (n = 879 families). Three SNPs representing a block of linkage disequilibrium, rs3789875, rs12347433, and rs4552883, were significantly associated with atherosclerosis in multiple datasets and demonstrated consistent, but suggestive, genetic effects in all analyses. In combined analysis rs3789875 and rs12347433 were statistically significant after Bonferroni correction for 35 comparisons, p = 2 × 10(-6) and 5 × 10(-6), respectively. The SNP rs12347433 is a synonymous coding SNP and may be biologically relevant to the mechanism by which tenascin-C influences the pathophysiology of CAD and atherosclerosis. This is the first report of genetic association between polymorphisms in TNC and atherosclerosis or CAD.

Missense mutations in TCF8 cause late-onset Fuchs corneal dystrophy and interact with FCD4 on chromosome 9p.

Fuchs corneal dystrophy (FCD) is a degenerative genetic disorder of the corneal endothelium that represents one of the most common causes of corneal transplantation in the United States. Despite its high prevalence (4% over the age of 40), the underlying genetic basis of FCD is largely unknown. Here we report missense mutations in TCF8, a transcription factor whose haploinsufficiency causes posterior polymorphous corneal dystrophy (PPCD), in a cohort of late-onset FCD patients. In contrast to PPCD-causing mutations, all of which are null, FCD-associated mutations encode rare missense changes suggested to cause loss of function by an in vivo complementation assay. Importantly, segregation of a recurring p.Q840P mutation in a large, multigenerational FCD pedigree showed this allele to be sufficient but not necessary for pathogenesis. Execution of a genome-wide scan conditioned for the presence of the 840P allele identified an additional late-onset FCD locus on chromosome 9p, whereas haplotype analysis indicated that the presence of the TCF8 allele and the disease haplotype on 9p leads to a severe FCD manifestation with poor prognosis. Our data suggest that PPCD and FCD are allelic variants of the same disease continuum and that genetic interaction between genes that cause corneal dystrophies can modulate the expressivity of the phenotype.