Segregation analysis suggests that keratoconus is a complex non-mendelian disease

Misclassification of Eyes With Progressive Keratoconus Using the KISA% Index

PURPOSE

To determine the misclassification rate of the keratoconus percentage (KISA%) index efficacy in eyes with progressive keratoconus.

METHODS

This was a retrospective case-control study of consecutive patients with confirmed progressive keratoconus and a contemporaneous normal control group with 1.00 diopters or greater regular astigmatism. Scheimpflug imaging (Pentacam HR) was obtained for all patients. KISA% index and inferior-superior (IS) values were obtained from the Pentacam topometric/keratoconus staging map. Receiver operating characteristic curves were generated to determine the area under the receiver operating characteristic curve (AUROC), sensitivity, and specificity values.

RESULTS

There were 160 eyes from 160 patients evaluated, including 80 eyes from 80 patients with progressive keratoconus and 80 eyes from 80 control patients. There were 20 eyes (25%) with progressive keratoconus misclassified by the KISA% index, with 16 eyes (20%) of the progressive keratoconus cohort classified as normal (ie, KISA% < 60). There were 4 eyes (5%) with progressive keratoconus that would classify as having "normal topography" using the published criteria for very asymmetric ectasia with normal topography of KISA% less than 60 and IS value less than 1.45. All controls had a KISA% index value of less than 15. The optimal cut-off value to distinguish cohorts was 15.31 (AUROC = 0.972, 93.75% sensitivity). KISA% index values of 60 and 100 achieved low sensitivity (80% and 73.75%, respectively).

CONCLUSIONS

The KISA% index misclassified a significant proportion of eyes with progressive keratoconus as normal. Although highly specific for clinical keratoconus, the KISA% index lacks sensitivity, does not effectively discriminate between normal and abnormal topography, and thus should not be used in large data analysis or artificial intelligence-based modeling. [J Refract Surg. 2024;40(9):e614-e624.].

Whole-exome sequencing screening for candidate genes and variants associated with primary sporadic keratoconus in Chinese patients

The pathogenesis of keratoconus (KC) is complex, and genetic factors play an important role. The purpose of this study was to screen and analyse candidate genes and variants in Chinese patients with primary sporadic KC. Whole-exome sequencing (WES) was performed to identify candidate genes and variants in 105 unrelated Chinese patients with primary sporadic KC. Through a series of screening processes, 54 candidate variants in 26 KC candidate genes were identified in 53 KC patients (53/105, 50.5%). These 54 candidate variants included 10 previously identified variants in 9 KC candidate genes and 44 novel variants in 20 KC candidate genes. The previously identified variants occurred in 25.7% (27/105) of patients. Of these, 4 variants (COL6A5, c.5014T > G; CAST, c.1814G > A; ZNF469, c.946G > A; and MPDZ, c.3836A > G) were identified for the first time in Chinese KC patients. The novel variants occurred in 33.3% (35/105) of patients. Of the 26 screened KC candidate genes, 11 KC candidate genes (CAT, COL12A1, FLG, HKDC1, HSPG2, PLOD1, ITGA2, TFAP2B, USH2A, WNT10A, and COL6A5) were found to be potentially pathogenic in Chinese KC patients for the first time. Gene Ontology (GO) biological process (BP) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed on the 26 KC candidate genes using the Database for Annotation, Visualization, and Integrated Discovery (DAVID). The results showed that the KC candidate genes were significantly enriched in biological processes such as collagen fibril organization and extracellular matrix (ECM) organization and in ECM-receptor interaction and protein digestion and absorption pathways. The results further expand the spectrum of KC candidate variants and provide a basis for further KC gene studies.

AvaGen Genetic Testing versus Ocular Screening Assessments Including the Keratoconus Severity Score (KSS) and Randleman Ectasia Risk Score System (ERSS) in Refractive Surgery Candidates

Purpose

To determine whether the AvaGen (AG) Genetic Eye Test provided additional information for screening for the presence of keratoconus (KC) and assessing KC risk in refractive surgery candidates, as compared to the Keratoconus Severity Score (KSS) and Randleman Ectasia Risk Score System (ERSS).

Methods

This retrospective study analyzed patients seeking refractive surgery at an eye clinic in the United States between January 2022 and July 2023. The inclusion criteria encompassed those with a family history of KC, positive KC indices, or both. Corneal evaluations and demographic information were recorded and analyzed. KSS and ERSS criteria were utilized to evaluate postoperative KC and ectasia risk, respectively. Patients were categorized on how the AG genetic test compared to KSS and ERSS criteria. Clinicians assessed topographic indices, criteria scoring, and AG testing to deliver a definitive surgical recommendation.

Results

Among the 19 patients evaluated for ectasia risk, AG testing showed lower KC risk than ocular screening in three patients (15.8%), equal risk in three patients (15.8%), and higher risk in 13 patients (68.4%). The mean AG scores were 45.7 ± 7.0, 49.0 ± 3.46, and 61 ± 13.0 for these respective categories. The most frequently identified KC risk genes were ADAMTS18, COL2A1, and COL4A1. The AG test modified the physician's recommendation for refractive surgery in nine cases (47.4%).

Conclusion

Despite the promising application of AG testing for assessing KC risk, further research and development are needed to enhance its applicability for screening refractive surgery candidates, in addition to standard ocular screening approaches.

Animal Models for the Study of Keratoconus

Keratoconus (KC) is characterized by localized, central thinning and cone-like protrusion of the cornea. Its precise etiology remains undetermined, although both genetic and environmental factors are known to contribute to disease susceptibility. Due to KC's complex nature, there is currently no ideal animal model to represent both the corneal phenotype and underlying pathophysiology. Attempts to establish a KC model have involved mice, rats, and rabbits, with some additional novel animals suggested. Genetic animal models have only been attempted in mice. Similarly, spontaneously occurring animal models for KC have only been discovered in mice. Models generated using chemical or environmental treatments have been attempted in mice, rats, and rabbits. Among several methods used to induce KC in animals, ultraviolet radiation exposure and treatment with collagenase are some of the most prevalent. There is a clear need for an experimental model animal to elucidate the underlying mechanisms behind the development and progression of keratoconus. An appropriate animal model could also aid in the development of treatments to slow or arrest the disorder.

Clinical and genetic analysis VSX1 variants among families with keratoconus in northwest China

Purpose: To screen VSX1 gene sequence variations and describe the clinical features of families with keratoconus (KC) from northwest China.

Methods: We screened VSX1 sequence variations and clinical data of 37 families including 37 probands with diagnosed KC from Ningxia Eye Hospital (China). VSX1 was screened by targeted next-generation sequencing (NGS) and verified by Sanger sequencing. In silico analysis including Mutation Taster, MutationAssessor, PROVEAN, MetaLR, FATHMM, M-CAP, FATHMM-XF_coding and DANN was performed to identify the pathogenicity of the sequence variations as well as the conserved amino acid variations of VSX1 was implemented by Clustal X. All subjects were assessed in Pentacam Scheimpflug tomography and corneal biomechanical Corvis ST examinations.

Results: Five VSX1 gene variants, were identified in six (16.2%) unrelated families with KC. In silico analysis predicted deleterious effects of the three missense variants (p.G342E, p.G160V, and p.L17V) in the encoded protein. Another previously reported synonymous variation (p.R27R) in the first exon and one heterozygous change in the first intron (c.425-73C&gt;T) were identified in three KC families. Clinical examination of the asymptomatic first-degree parents from these six families who shared the gene with the proband had suspected KC changes in topographic and biomechanical markers. These variants co-segregated with the disease phenotype in all affected individuals but not in unaffected family members or healthy controls, though with variable expressivity.

Conclusion: The variant p.G342E of VSX1 is implicated in the pathogenesis of KC, which expands the range of the spectrum of VSX1 mutations with an autosomal dominant inheritance pattern and variable expression in the clinical phenotype. Genetic screening combined with clinical phenotype may help in the genetic counseling of patients with KC and identification of individuals with subclinical KC.

Heritability of Corneal Parameters in Nuclear Families With Keratoconus

Purpose

This study aimed to investigate the heritability of corneal parameters obtained by Pentacam in nuclear families with keratoconus (KC).

Methods

A total of 82 patients with KC and their biological parents (n = 164) were recruited in the current study. All subjects underwent corneal tomography with Pentacam. Family units were analyzed to calculate the heritability of corneal parameters by linear mixed effects model using the R statistical software.

Results

The pachymetry at apex, pupil, and thinnest point were all significantly heritable at 43.26%, 42.63%, and 43.09%, respectively. The heritability of flat meridian keratometry, steep meridian keratometry, and mean keratometry in the anterior surface were 10.36%, 9.05%, and 10.21%, respectively, and that of flat meridian keratometry, steep meridian keratometry, and mean keratometry in the posterior surface were 8.44%, 9.67%, and 9.06%, respectively. The posterior radius of curvature had higher heritability in comparison with anterior radius of curvature (19.16% vs. 14.37%). Moreover, among combined topometric indices, the heritability of index of vertical asymmetry was the highest (19.49%), and that of central keratoconus index was the lowest (6.64%).

Conclusions

The present study demonstrated a substantial heritability of corneal parameters in nuclear families with KC. The pachymetric indices are heritable and may be suitable as KC endophenotypes, suggesting a necessity to discover the genes associated with corneal thickness in KC.

Translational Relevance

The pachymetric indices are heritable and may be suitable as KC endophenotypes, indicating that the pachymetric indices might be a corneal characteristic to predict the occurrence of KC.

A Hospital-Based Study on the Prevalence of Keratoconus in First-Degree Relatives of Patients with Keratoconus in Central China

Purpose

The present study investigated the prevalence of keratoconus (KC) among first-degree relatives of KC patients in Central China.

Methods

From July 2018 to March 2022, 661 first-degree relatives of 384 KC patients were included in the present study. Corneal tomography, uncorrected distance visual acuity, manifest refraction with corrected distance visual acuity, intraocular pressure, slit-lamp microscopy, and fundus examination were performed. The diagnosis of KC was based on the Belin/Ambrosio enhanced ectasia total deviation value (BAD-D value) on the Pentacam® system (Oculus GmbH). BAD-D value <1.6 was diagnosed as healthy, 1.6≤ BAD-D value <2.6 was diagnosed as suspected KC, and BAD-D value ≥2.6 was diagnosed as KC.

Results

The present study included 337 (50.98%) female and 324 (49.02%) male subjects. The prevalence of KC and suspected KC in first-degree relatives was 8.77% (n = 58) and 29.05% (n = 192), respectively. The prevalence of KC was 9.70% among parents and 7.23% among siblings.

Conclusions

The higher prevalence of KC among first-degree relatives of patients with KC suggests that first-degree relatives of KC are at high risk of developing KC.

Keratoconus: An updated review

Keratoconus is a bilateral and asymmetric disease which results in progressive thinning and steeping of the cornea leading to irregular astigmatism and decreased visual acuity. Traditionally, the condition has been described as a noninflammatory disease; however, more recently it has been associated with ocular inflammation. Keratoconus normally develops in the second and third decades of life and progresses until the fourth decade. The condition affects all ethnicities and both sexes. The prevalence and incidence rates of keratoconus have been estimated to be between 0.2 and 4,790 per 100,000 persons and 1.5 and 25 cases per 100,000 persons/year, respectively, with highest rates typically occurring in 20- to 30-year-olds and Middle Eastern and Asian ethnicities. Progressive stromal thinning, rupture of the anterior limiting membrane, and subsequent ectasia of the central/paracentral cornea are the most commonly observed histopathological findings. A family history of keratoconus, eye rubbing, eczema, asthma, and allergy are risk factors for developing keratoconus. Detecting keratoconus in its earliest stages remains a challenge. Corneal topography is the primary diagnostic tool for keratoconus detection. In incipient cases, however, the use of a single parameter to diagnose keratoconus is insufficient, and in addition to corneal topography, corneal pachymetry and higher order aberration data are now commonly used. Keratoconus severity and progression may be classified based on morphological features and disease evolution, ocular signs, and index-based systems. Keratoconus treatment varies depending on disease severity and progression. Mild cases are typically treated with spectacles, moderate cases with contact lenses, while severe cases that cannot be managed with scleral contact lenses may require corneal surgery. Mild to moderate cases of progressive keratoconus may also be treated surgically, most commonly with corneal cross-linking. This article provides an updated review on the definition, epidemiology, histopathology, aetiology and pathogenesis, clinical features, detection, classification, and management and treatment strategies for keratoconus.

Keratoconus concordance in monozygotic twins before and after combined CXL/PRK (Athens Protocol) using Scheimflung and OCT tomography

PUPOSE

To describe the concordance of keratoconus expression in two pairs of monozygotic twins before and after a combined CXL/PRK procedure.

SETTING

Private Ambulatory Eye Surgery Unit.

DESIGN

Retrospective Interventional Twin Study.

METHODS

Two pairs of male monozygotic twins with keratoconus (KCN) were studied retrospectively. Improvement of flattest (k1) and steepest (k2) keratometry, Index of Height Decentration (IHD), corneal thickness at thinnest point and corneal epithelial thickness measured by AS-OCT and Scheimpflug tomography was compared between respective eyes of monozygotic twin siblings 1 to 5 years after the application of combined corneal cross linking (CXL) and topography guided photorefractive keratectomy (PRK) of part of the refractive error (the Athens Protocol).

RESULTS

Significant improvement was noted in all the keratometric indices of all 8 eyes after the combined CXL/PRK procedure.The difference in k1, k2, IHD corneal thickness at thinnest point and corneal epithelial thickness percentage improvement between the right eyes of each pair of twins was statistically significant 1 and 5 years post-operatively (P < .05). Statistically significant discordance in the aforementioned parameters percentage improvement was likewise observed between the left eyes of each pair of twins (P < .05).

CONCLUSIONS

Although a genetic predisposition in KCN is well documented, the discordance in keratometric indices improvement after a CXL/PRK procedure between respective eyes of monozygotic twins suggests that environmental influences may contribute to the disease expression as well. Variable degree of synergy in a combined CXL/PRK procedure may also explain the aforementioned discordant improvement.

Evaluating the association between single nucleotide polymorphisms in the stonin 2 (STON2) gene and keratoconus in a Han Chinese population

Background

A recent genome-wide association study (GWAS) identified a significant association between the single nucleotide polymorphism (SNP) rs2371597 in the stonin 2 gene (STON2) and keratoconus (KCTN) susceptibility. The current study further explored the association between STON2 and KCTN susceptibility in an independent Han Chinese population.

Methods

Three SNPs (rs2371597, rs8004137, and rs8008602) located in the STON2 gene were examined in 164 Han Chinese patients with KCTN and 239 age- and gender-matched healthy subjects. The TaqMan SNP genotyping assays were performed, and the LDlink, RegulomeDB, and PLINK package were applied for data analyses. The gene expression levels of STON2 were investigated in various murine organ tissues using quantitative real-time polymerase chain reaction (qRT-PCR).

Results

The SNP rs2371597 was significantly associated with KCTN risk in this Han Chinese population. The frequency of the C allele in KCTN patients was significantly higher than that in healthy subjects [34.8% vs. 26.6%; odds ratio (OR) =1.47; 95% confidence interval (CI): 1.08 to 2.02; P=0.01409]. The genotype distribution of the SNP rs2371597 was also significantly different between KCTN patients and controls. The other two genotyped SNPs allele and genotypic frequencies were not remarkably different between the KCTN group and the control group. However, the haplotype CAT formed by the three SNPs was substantially associated with the risk of KCTN (P=0.04101). Also, gene expression pattern analysis showed a relatively higher expression of STON2 in the cornea in comparison to other tissues.

Conclusions

The current study demonstrated that SNPs in the STON2 gene were associated with an increased risk of developing KCTN in this Han Chinese population, suggesting that the STON2 gene may play an important role in the etiology of KCTN.

Omics analyses in keratoconus: from transcriptomics to proteomics

Purpose of Review

To summarize the recent advances in transcriptomics and proteomics studies of keratoconus using advanced genome-wide gene and protein expression profiling techniques.

Recent Findings

Second-generation sequencing including RNA sequencing has been widely used to characterize the genome-wide gene expression in corneal tissues or cells affected by keratoconus. Due to different sample types, sequencing platforms, and analysis pipeline, different lists of genes have been identified to be differentially expressed in KC-affected samples. Gene ontology and pathway/network analyses have indicated the involvement of genes related with extracellular matrix, WNT-signaling, TGFβ pathway, and NRF2-regulated network. High throughput proteomics studies using mass spectrometry have uncovered many KC-related protein molecules in pathways related with cytoskeleton, cell matrix, TGFβ signaling, and extracellular matrix remodeling, consistent with gene expression profiling.

Summary

Both transcriptomics and proteomics studies using genome-wide gene/protein expression profiling techniques have identified significant genes/proteins that may contribute to the pathogenesis of keratoconus. These molecules may be involved in functional categories related with extracellular matrix and TGFβ signaling. It is necessary to perform comprehensive gene/protein expression studies using larger sample size, same type of samples, up-to-date platform and bioinformatics tools.

Resequencing of candidate genes for Keratoconus reveals a role for Ehlers-Danlos Syndrome genes

The involvement of genetic factors in the pathogenesis of KC has long been recognized but the identification of variants affecting the underlying protein functions has been challenging. In this study, we selected 34 candidate genes for KC based on previous whole-exome sequencing (WES) and the literature, and resequenced them in 745 KC patients and 810 ethnically matched controls from Belgium, France and Italy. Data analysis was performed using the single variant association test as well as gene-based mutation burden and variance components tests. In our study, we detected enrichment of genetic variation across multiple gene-based tests for the genes COL2A1, COL5A1, TNXB, and ZNF469. The top hit in the single variant association test was obtained for a common variant in the COL12A1 gene. These associations were consistently found across independent subpopulations. Interestingly, COL5A1, TNXB, ZNF469 and COL12A1 are all known Ehlers-Danlos Syndrome (EDS) genes. Though the co-occurrence of KC and EDS has been reported previously, this study is the first to demonstrate a consistent role of genetic variants in EDS genes in the etiology of KC. In conclusion, our data show a shared genetic etiology between KC and EDS, and clearly confirm the currently disputed role of ZNF469 in disease susceptibility for KC.

Pathogenic alleles in microtubule, secretory granule and extracellular matrix-related genes in familial keratoconus

Keratoconus is a common corneal defect with a complex genetic basis. By whole exome sequencing of affected members from 11 multiplex families of European ancestry, we identified 23 rare, heterozygous, potentially pathogenic variants in 8 genes. These include nonsynonymous single amino acid substitutions in HSPG2, EML6 and CENPF in two families each, and in NBEAL2, LRP1B, PIK3CG and MRGPRD in three families each; ITGAX had nonsynonymous single amino acid substitutions in two families and an indel with a base substitution producing a nonsense allele in the third family. Only HSPG2, EML6 and CENPF have been associated with ocular phenotypes previously. With the exception of MRGPRD and ITGAX, we detected the transcript and encoded protein of the remaining genes in the cornea and corneal cell cultures. Cultured stromal cells showed cytoplasmic punctate staining of NBEAL2, staining of the fibrillar cytoskeletal network by EML6, while CENPF localized to the basal body of primary cilia. We inhibited the expression of HSPG2, EML6, NBEAL2 and CENPF in stromal cell cultures and assayed for the expression of COL1A1 as a readout of corneal matrix production. An upregulation in COL1A1 after siRNA inhibition indicated their functional link to stromal cell biology. For ITGAX, encoding a leukocyte integrin, we assayed its level in the sera of 3 affected families compared with 10 unrelated controls to detect an increase in all affecteds. Our study identified genes that regulate the cytoskeleton, protein trafficking and secretion, barrier tissue function and response to injury and inflammation, as being relevant to keratoconus.

Genetics vs chronic corneal mechanical trauma in the etiology of keratoconus

Both genetic and environmental factors have been considered to play a role in the etiology keratoconus. Eye rubbing, and more recently eye compression due to sleeping position, have been identified to be highly related to the condition, and are present in a high percentage of patients. Today, the predominant model is that these factors can provide the "second hit" necessary to generate the condition in a genetically susceptible individual. In addition, the extremely high prevalence in Arab populations, where endogamy could play a role, the high concordance rate in monozygotic twins, and the presence of family history of the condition between 5 and 23% of cases, support a genetic influence. Segregation analysis studies suggest that keratoconus is a complex non-Mendelian disease. Results from linkage analysis, next generation sequencing studies and genome-wide association studies also have suggested that genetic factors are involved in the condition. Recently, it has been proposed that mechanical trauma (i.e. eye rubbing or eye compression at night), is a sine quanon condition for the onset of keratoconus, and quite possibly its only cause. There are various arguments for and against this hypothesis. Indeed, it is possible, as initially suggested around 55 years ago, that the term "keratoconus" include diverse phenotypically similar conditions, which are actually of different etiology.

Genetic and Environmental Risk Factors for Keratoconus

Keratoconus, a progressive corneal ectasia, is a complex disease with both genetic and environmental risk factors. The exact etiology is not known and is likely variable between individuals. Conditions such as hay fever and allergy are associated with increased risk, while diabetes may be protective. Behaviors such as eye rubbing are also implicated, but direct causality has not been proven. Genetics plays a major role in risk for some individuals, with many large pedigrees showing autosomal inheritance patterns. Several genes have been implicated using linkage and follow-up sequencing in these families. Genome-wide association studies for keratoconus and for quantitative traits such as central corneal thickness have identified several genetic loci that contribute to a cumulative risk for keratoconus, even in people without a family history of the disease. Identification of risk genes for keratoconus is improving our understanding of the biology of this complex disease.

Interplay between hereditary and environmental factors to establish an in vitro disease model of keratoconus

Keratoconus (KC) is a bilateral corneal dystrophy and a multifactorial, multigenic disorder with an etiology involving a strong environmental component and complex inheritance patterns. The underlying pathophysiology of KC is poorly understood because of potential crosstalk between genetic-epigenetic variants possibly triggered by the environmental factors. Here, we decode the etiopathological basis of KC using genomic, transcriptomic, proteomic and metabolic approaches. The lack of relevant models that accurately imitate this condition has been particularly limiting in terms of the effective management of KC. Tissue-engineered in vitro models of KC could address this need and generate valuable insights into its etiopathology for the establishment of disease models to accelerate drug discovery.

Estimation of Trait-Model Parameters in a MOD Score Linkage Analysis

Background/Aims

Theoretically, the trait-model parameters (disease allele frequency and penetrance function) can be estimated without bias in a MOD score linkage analysis. We aimed to practically evaluate the MOD score approach regarding its ability to provide unbiased trait-model parameters for various pedigree-type and trait-model scenarios. We further investigated the ability of the MOD score approach to detect imprinting using affected sib pairs (ASPs) and affected half-sib pairs (AHSPs) when all parental genotypes are missing.

Methods

Simulated pedigree data were analyzed using the GENEHUNTER-MODSCORE software package. Parameter estimation performance in terms of bias and variability was evaluated with regard to trait-model type and pedigree complexity.

Results

Generally, parameters were estimated with lower bias and variability with increasing pedigree complexity, especially for recessive and overdominant models. However, dominant and additive models could hardly be distinguished even when using 3-generation pedigrees. Imprinting could clearly be detected for mixtures of mainly ASPs and only few AHSPs with the common parent of the imprinted sex, even though no parental genotypes were available.

Conclusion

Our results provide guidance to researchers regarding the possibility to estimate trait-model parameters by a MOD score analysis, including the degree of imprinting, with certain types of pedigrees.

Molecular and Histopathological Changes Associated with Keratoconus

Keratoconus (KC) is a corneal thinning disorder that leads to loss of visual acuity through ectasia, opacity, and irregular astigmatism. It is one of the leading indicators for corneal transplantation in the Western countries. KC usually starts at puberty and progresses until the third or fourth decade; however its progression differs among patients. In the keratoconic cornea, all layers except the endothelium have been shown to have histopathological structural changes. Despite numerous studies in the last several decades, the mechanisms of KC development and progression remain unclear. Both genetic and environmental factors may contribute to the pathogenesis of KC. Many previous articles have reviewed the genetic aspects of KC, but in this review we summarize the histopathological features of different layers of cornea and discuss the differentially expressed proteins in the KC-affected cornea. This summary will help emphasize the major molecular defects in KC and identify additional research areas related to KC, potentially opening up possibilities for novel methods of KC prevention and therapeutic intervention.

Genomic strategies to understand causes of keratoconus

Keratoconus (KTCN) is a degenerative disorder of the eye characterized by the conical shape and thinning of the cornea. The abnormal structure of KTCN-affected cornea results in loss of visual acuity. While many studies examine how environmental factors influence disease development, finding the genetic triggers has been a major emphasis of KTCN research. This paper focuses on genomic strategies that were implemented for finding candidate genes, including linkage and association studies, and presents different approaches of mutation screening. The advantages and limitations of particular tools are discussed based on literature and personal experience. Since etiology underlying KTCN is complex, numerous findings indicating heterogeneity of genetic factors involved KTCN etiology are presented.

Evidence against ZNF469 being causative for keratoconus in Polish patients

PURPOSE

Keratoconus (KTCN) is a degenerative disorder characterized by stromal thinning and protrusion of the cornea, resulting in severe impairment of visual function. A recent study proposed that rare heterozygous mutations in ZNF469 determine KTCN aetiology.

METHODS

To investigate the contribution of ZNF469 to KTCN, we Sanger sequenced ZNF469 in 42 unrelated Polish patients with KTCN and 49 Polish individuals with high myopia (HM) and compared the results with whole-exome sequencing (WES) data performed in 268 Polish individuals without ocular abnormalities.

RESULTS

The average number of ZNF469 non-synonymous variants was 16.31 and 16.0 for individuals with KTCN and HM, respectively (p = 0.3724). All identified variants were previously reported. Alternative allele frequency (AAF) was determined based on the WES results. Among missense variants, only one (rs528085780) has AAF ≤ 0.001 and was identified in one patient with sporadic KTCN. However, the resulting Arg1864Lys substitution was not predicted to be deleterious.

CONCLUSION

In summary, we have not found a significant enrichment of sequence variants in ZNF469 in Polish patients with KTCN. High prevalence of ZNF469 variants identified in our KTCN group is typical for a common genetic variation observed in general population. Our findings indicate that variation in ZNF469 is not responsible for KTCN and other genetic variants are involved in the development and progression of this disease in Polish patients.

Contemporary Treatment Paradigms in Keratoconus

The past 20 years have witnessed an explosion in our knowledge of keratoconus, accompanied by a radical transformation of management options. A 2-hit hypothesis proposes an underlying genetic predisposition coupled with external environmental factors, including eye rubbing and atopy. The variable prevalence and natural history have been better defined including significant cone progression in middle age. Therefore, current management must include early diagnosis, regular monitoring, and treatment of environmental cofactors. Spectacles and contact lenses remain fundamental to the optical management of keratoconus. Intrastromal corneal ring segments have been increasingly used, providing improvement in the corneal shape, corrected visual acuity, and contact lens wear. However, like contact lenses, intrastromal corneal ring segments do not treat the underlying disease process. Therefore, current approaches must also consider treatments to minimize keratoconus progression. Fortunately, there is increasing evidence that corneal collagen crosslinking will halt or slow progression in most cases. Until relatively recently, penetrating keratoplasty was the preferred intervention for advanced keratoconus, with long-term success in the region of 90%; however, the greatest risk of failure remains endothelial allograft rejection. Deep anterior lamellar keratoplasty has emerged in the new millennium as a preferred approach to conserve the host endothelium and avoid rejection. Nonetheless, the overall superiority of deep anterior lamellar keratoplasty compared with penetrating keratoplasty, in terms of optical and survival benefits, is still debated. This perspective provides an overview of our current knowledge of keratoconus and current management options. A step-ladder approach to managing keratoconus is outlined to provide the practitioner with a contemporary management paradigm.

Presence of Fleischer ring and prominent corneal nerves in keratoconus relatives and normal controls

AIM

To examine the occurrence of commonly known clinical signs of keratoconus (KC), i.e. Fleischer ring, prominent corneal nerves and thinning, among unaffected family members of KC patients and healthy control individuals.

METHODS

Data of both eyes of 117 relatives of KC patients having no manifest disease based on videokeratography indices (KC relatives), and 142 controls were used for Pearson correlation and t-test statistics. Correlation of Fleischer ring, prominent corneal nerves and central pachymetry data were tested with each other and with videokeratography indices (KSI, KISA, 3 and 6 mm Fourier asymmetry, and I-S).

RESULTS

A moderate correlation was found between Fleischer ring and all examined topographical indices. Most important correlation was present with 6 mm Fourier asymmetry, and corneal pachymetry (r=0.272, P<0.001; r=-0.234, P=0.027, respectively). Similar correlations were found with prominent corneal nerves (r=0.234, P<0.001 for 6 mm Fourier asymmetry and r=-0.235, P=0.0265 for pachymetry). KC family members who exhibited Fleischer ring or prominent nerves had thinner and more asymmetric corneas than those without Fleischer ring or prominent corneal nerves (P<0.05 for pachymetry and topographic indices with t-test and Mann-Whitney rank sum test). Though rarely, Fleischer ring and prominent corneal nerves occurred among normal controls, indicating the existence of forme fruste cases in the normal population. Control subjects, who had corneal Fleischer ring or prominent nerves had corneas more similar to KC than other controls (t-test: increased KSI and KISA, P=0.048 and 0.012, respectively).

CONCLUSION

In KC family members and healthy individuals, Fleischer ring and prominent corneal nerves are associated with features of KC and may suggest a possibility of forme fruste KC. Searching for the possible presence of Fleischer ring or prominent nerves on the cornea may help in the decision whether or not to diagnose subclinical KC in a borderline case.

Keratoconus: an inflammatory disorder?

Keratoconus has been classically defined as a progressive, non-inflammatory condition, which produces a thinning and steepening of the cornea. Its pathophysiological mechanisms have been investigated for a long time. Both genetic and environmental factors have been associated with the disease. Recent studies have shown a significant role of proteolytic enzymes, cytokines, and free radicals; therefore, although keratoconus does not meet all the classic criteria for an inflammatory disease, the lack of inflammation has been questioned. The majority of studies in the tears of patients with keratoconus have found increased levels of interleukin-6 (IL-6), tumor necrosis factor-α(TNF-α), and matrix metalloproteinase (MMP)-9. Eye rubbing, a proven risk factor for keratoconus, has been also shown recently to increase the tear levels of MMP-13, IL-6, and TNF-α. In the tear fluid of patients with ocular rosacea, IL-1α and MMP-9 have been reported to be significantly elevated, and cases of inferior corneal thinning, resembling keratoconus, have been reported. We performed a literature review of published biochemical changes in keratoconus that would support that this could be, at least in part, an inflammatory condition.

Genetics of keratoconus: where do we stand?

Keratoconus is a progressive thinning and anterior protrusion of the cornea that results in steepening and distortion of the cornea, altered refractive powers, and reduced vision. Keratoconus has a complex multifactorial etiology, with environmental, behavioral, and multiple genetic components contributing to the disease pathophysiology. Using genome-wide and candidate gene approaches several genomic loci and genes have been identified that highlight the complex molecular etiology of this disease. The review focuses on current knowledge of these genetic risk factors associated with keratoconus.