Christopher R. Croasdale

A multicenter study to map genes for Fuchs endothelial corneal dystrophy: Baseline characteristics and heritability

Purpose: To describe the methods for family and case–control recruitment for a multicenter genetic and associated heritability analyses of Fuchs endothelial corneal dystrophy (FECD). Methods: Twenty-nine enrolling sites with 62 trained investigators and coordinators gathered individual and family information, graded the phenotype, and collected blood and/or saliva for genetic analysis on all individuals with and without FECD. The degree of FECD was assessed in a 0 to 6 semiquantitative scale using standardized clinical methods with pathological verification of FECD on at least 1 member of each family. Central corneal thickness was measured by ultrasonic pachymetry. Results: Three hundred twenty-two families with 330 affected sibling pairs with FECD were enrolled and included a total of 650 sibling pairs of all disease grades. Using the entire 7-step FECD grading scale or a dichotomous definition of severe disease, heritability was assessed in families via sib–sib correlations. Both binary indicators of severe disease and semiquantitative measures of disease severity were significantly heritable, with heritability estimates of 30% for severe disease, 37% to 39% for FECD score, and 47% for central corneal thickness. Conclusions: Genetic risk factors have a strong role in the severity of the FECD phenotype and corneal thickness. Genotyping this cohort with high-density genetic markers followed by appropriate statistical analyses should lead to novel loci for disease susceptibility.

Differing Roles for TCF4 and COL8A2 in Central Corneal Thickness and Fuchs Endothelial Corneal Dystrophy

Fuchs endothelial corneal dystrophy (FECD) is the most common late-onset, vision-threatening corneal dystrophy in the United States, affecting about 4% of the population. Advanced FECD involves a thickening of the cornea from stromal edema and changes in Descemet membrane. To understand the relationship between FECD and central corneal thickness (CCT), we characterized common genetic variation in COL8A2 and TCF4, genes previously implicated in CCT and/or FECD. Other genes previously associated with FECD (PITX2, ZEB1, SLC4A11), and genes only known to affect CCT (COL5A1, FOXO1, AVGR8, ZNF469) were also interrogated. FECD probands, relatives and controls were recruited from 32 clinical sites; a total of 532 cases and 204 controls were genotyped and tested for association of FECD case/control status, a 7-step FECD severity scale and CCT, adjusting for age and sex. Association of FECD grade with TCF4 was highly significant (OR  = 6.01 at rs613872; p = 4.8×10−25), and remained significant when adjusted for changes in CCT (OR  = 4.84; p = 2.2×10−16). Association of CCT with TCF4 was also significant (p = 6.1×10−7), but was abolished with adjustment for FECD grade (p = 0.92). After adjusting for FECD grade, markers in other genes examined were modestly associated (p ∼ 0.001) with FECD and/or CCT. Thus, common variants in TCF4 appear to influence FECD directly, and CCT secondarily via FECD. Additionally, changes in corneal thickness due to the effect of other loci may modify disease severity, age-at-onset, or other biomechanical characteristics.

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.

Eye bank tissue utilization between endothelial keratoplasty and penetrating keratoplasty.

Purpose: To determine rates of tissue use for corneal transplants via endothelial keratoplasty (EK) relative to penetrating keratoplasty (PK). Methods: Retrospective chart review of all cornea tissues (n = 3669) distributed from the Lions Eye Bank of Wisconsin for EK or PK from August 1, 2004 through July 31, 2009 (60 months). Rates of tissue use for EK relative to PK were determined both on a yearly basis and for the overall study period. Replacement frequency and time to subsequent surgery were established for each group. Donor tissue and recipient characteristics were compared between groups. Results: Donor characteristics did not differ between the 2 groups; 11.9% of EK tissues failed and were replaced during the study period compared with 5.1% of PK tissues (P < 0.0001). Additional tissue for the same eye came at a mean of 174 days after an EK surgery compared with 558 days after a PK (P < 0.0001). Surgeons requesting tissue for EK increased each year, whereas the number of repeat tissue requests decreased over time. Conclusions: Additional tissues were required for recipients of EK more than twice as often as for recipients of PK, and replacement of EK grafts occurred at a mean of more than 1 year before replacement of PK grafts. This pattern of tissue utilization during the first 5 years of distribution for EK did not negatively affect the Lions Eye Bank of Wisconsin from meeting the surgeon demand for tissue in its service area. Eye banks may wish to monitor tissue utilization as part of their quality assurance program.

Whole Exome Sequencing and Segregation Analysis Confirms That a Mutation in COL17A1 Is the Cause of Epithelial Recurrent Erosion Dystrophy in a Large Dominant Pedigree Previously Mapped to Chromosome 10q23-q24

Purpose To report identification of a COL17A1 mutation in a family with a corneal dystrophy previously mapped to chromosome 10q23-q24. Methods Whole-exome sequencing was performed on DNA samples from five affected family members and two unrelated, unaffected individuals. Identified variants were filtered for those that were: located in the linked interval on chromosome 10q23-q24; novel or rare (minor allele frequency ≤0.01); heterozygous; present in all affected individuals and not in controls; and present in genes that encode proteins expressed in human corneal epithelial cells (reads per kilobase per million ≥1). Sanger sequencing of identified variants (SNVs) was performed in additional family members. In silico analysis was used to predict the functional impact of non-synonymous variants. Results Three SNVs located in two genes were identified that met the filtering criteria: one rare synonymous c.3156C>T variant in the collagen, type XVII, alpha I (COL17A1) gene; and two rare variants, one synonymous and one missense, in the dynamin binding protein (DNMBP) gene. Sanger sequencing of additional family members determined that only the COL17A1 variant segregates with the affected phenotype. In silico analysis predicts that the missense variant in DNMBP would be tolerated. Conclusions The corneal dystrophy mapped to chromosome 10q23-q24 is associated with the c.3156C>T variant in COL17A1. As this variant has recently been identified in five other families with early onset recurrent corneal erosions, and has been shown in vitro to introduce a cryptic splice donor site, this dystrophy is likely caused by aberrant splicing of COL17A1 and should be classified as epithelial recurrent erosion dystrophy.

Keratolimbal Allograft: Recommendations for Tissue Procurement and Preparation by Eye Banks

PURPOSE To facilitate increased use of keratolimbal allograft transplantation (KLAL) for severe ocular surface disease (OSD) by informing clinicians and eye banks of differences in tissue requirements and preparation for the procedure and to describe the surgical technique of KLAL transplantation. METHODS The protocol of the Minnesota Lions Eye Bank is described for procuring and preparing tissue for KLAL transplantation. The surgical technique is described in detail. RESULTS Over the last several years, we have modified our eye-banking procedures as well as our surgical technique to improve the success of KLAL transplantation. CONCLUSION KLAL transplantation for patients with severe ocular-surface disease is an important management option. Success is influenced by the ability to obtain appropriate tissue; this requires clinicians and eye banks to expand current procurement guidelines.

Conjunctival Limbal Autograft

A conjunctival limbal autograft (CLAU) is indicated for patients needing epithelial stem cell (SC) transplantation for management of corneal surface disease due to unilateral limbal stem cell deficiency (Table 16.1). Prior chemical or thermal injuries are the most common causes of limbal SC deficiency. Other etiologies include iatrogenic limbal SC deficiency and extensive limbal or conjunctival neoplasias, such as conjunctival intraepithelial neoplasia, squamous cell carcinoma, and sebaceous cell carcinoma. Although these groups account for the majority of cases of unilateral limbal SC deficiency, it is important to recognize that additional cases can occur as a result of any condition where the common underlying pathology is chronic, usually severe, ocular surface inflammation.