A Novel Mutation of FOXC1 (R127L) in an Axenfeld-Rieger Syndrome Family with Glaucoma and Multiple Congenital Heart Diseases

A novel missense mutation of FOXC1 in an Axenfeld-Rieger syndrome patient with a congenital atrial septal defect and sublingual cyst: a case report and literature review

Background

Axenfeld–Rieger syndrome (ARS) is a rare autosomal dominant hereditary disease characterized primarily by maldevelopment of the anterior segment of both eyes, accompanied by developmental glaucoma, and other congenital anomalies. FOXC1 and PITX2 genes play important roles in the development of ARS.

Case presentation

The present report describes a 7-year-old boy with iris dysplasia, displaced pupils, and congenital glaucoma in both eyes. The patient presented with a congenital atrial septal defect and sublingual cyst. The patient’s family has no clinical manifestations. Next generation sequencing identified a pathogenic heterozygous missense variant in FOXC1 gene (NM_001453:c. 246C>A, p. S82R) in the patient. Sanger sequencing confirmed this result, and this mutation was not detected in the other three family members.

Conclusion

To the best of our knowledge, the results of our study reveal a novel mutation in the FOXC1 gene associated with ARS.

Therapeutically Targeting Cancers That Overexpress FOXC1: A Transcriptional Driver of Cell Plasticity, Partial EMT, and Cancer Metastasis

Metastasis accounts for more than 90% of cancer related mortality, thus the most pressing need in the field of oncology today is the ability to accurately predict future onset of metastatic disease, ideally at the time of initial diagnosis. As opposed to current practice, what would be desirable is that prognostic, biomarker-based detection of metastatic propensity and heightened risk of cancer recurrence be performed long before overt metastasis has set in. Without such timely information it will be impossible to formulate a rational therapeutic treatment plan to favorably alter the trajectory of disease progression. In order to help inform rational selection of targeted therapeutics, any recurrence/metastasis risk prediction strategy must occur with the paired identification of novel prognostic biomarkers and their underlying molecular regulatory mechanisms that help drive cancer recurrence/metastasis (i.e. recurrence biomarkers). Traditional clinical factors alone (such as TNM staging criteria) are no longer adequately prognostic for this purpose in the current molecular era. FOXC1 is a pivotal transcription factor that has been functionally implicated to drive cancer metastasis and has been demonstrated to be an independent predictor of heightened metastatic risk, at the time of initial diagnosis. In this review, we present our viewpoints on the master regulatory role that FOXC1 plays in mediating cancer stem cell traits that include cellular plasticity, partial EMT, treatment resistance, cancer invasion and cancer migration during cancer progression and metastasis. We also highlight potential therapeutic strategies to target cancers that are, or have evolved to become, “transcriptionally addicted” to FOXC1. The potential role of FOXC1 expression status in predicting the efficacy of these identified therapeutic approaches merits evaluation in clinical trials.

Mechanistic Insights into Axenfeld-Rieger Syndrome from Zebrafish foxc1 and pitx2 Mutants

Axenfeld-Rieger syndrome (ARS) encompasses a group of developmental disorders that affect the anterior segment of the eye, as well as systemic developmental defects in some patients. Malformation of the ocular anterior segment often leads to secondary glaucoma, while some patients also present with cardiovascular malformations, craniofacial and dental abnormalities and additional periumbilical skin. Genes that encode two transcription factors, FOXC1 and PITX2, account for almost half of known cases, while the genetic lesions in the remaining cases remain unresolved. Given the genetic similarity between zebrafish and humans, as well as robust antisense inhibition and gene editing technologies available for use in these animals, loss of function zebrafish models for ARS have been created and shed light on the mechanism(s) whereby mutations in these two transcription factors cause such a wide array of developmental phenotypes. This review summarizes the published phenotypes in zebrafish foxc1 and pitx2 loss of function models and discusses possible mechanisms that may be used to target pharmaceutical development and therapeutic interventions.

The Drosophila Forkhead/Fox transcription factor Jumeau mediates specific cardiac progenitor cell divisions by regulating expression of the kinesin Nebbish

Forkhead (Fkh/Fox) domain transcription factors (TFs) mediate multiple cardiogenic processes in both mammals and Drosophila. We showed previously that the Drosophila Fox gene jumeau (jumu) controls three categories of cardiac progenitor cell division—asymmetric, symmetric, and cell division at an earlier stage—by regulating Polo kinase activity, and mediates the latter two categories in concert with the TF Myb. Those observations raised the question of whether other jumu-regulated genes also mediate all three categories of cardiac progenitor cell division or a subset thereof. By comparing microarray-based expression profiles of wild-type and jumu loss-of-function mesodermal cells, we identified nebbish (neb), a kinesin-encoding gene activated by jumu. Phenotypic analysis shows that neb is required for only two categories of jumu-regulated cardiac progenitor cell division: symmetric and cell division at an earlier stage. Synergistic genetic interactions between neb, jumu, Myb, and polo and the rescue of jumu mutations by ectopic cardiac mesoderm-specific expression of neb demonstrate that neb is an integral component of a jumu-regulated subnetwork mediating cardiac progenitor cell divisions. Our results emphasize the central role of Fox TFs in cardiogenesis and illustrate how a single TF can utilize different combinations of other regulators and downstream effectors to control distinct developmental processes.

Hematopoietic Stem Cell Transcription Factors in Cardiovascular Pathology

Transcription factors as multifaceted modulators of gene expression that play a central role in cell proliferation, differentiation, lineage commitment, and disease progression. They interact among themselves and create complex spatiotemporal gene regulatory networks that modulate hematopoiesis, cardiogenesis, and conditional differentiation of hematopoietic stem cells into cells of cardiovascular lineage. Additionally, bone marrow-derived stem cells potentially contribute to the cardiovascular cell population and have shown potential as a therapeutic approach to treat cardiovascular diseases. However, the underlying regulatory mechanisms are currently debatable. This review focuses on some key transcription factors and associated epigenetic modifications that modulate the maintenance and differentiation of hematopoietic stem cells and cardiac progenitor cells. In addition to this, we aim to summarize different potential clinical therapeutic approaches in cardiac regeneration therapy and recent discoveries in stem cell-based transplantation.

Axenfeld-Rieger syndrome-associated mutants of the transcription factor FOXC1 abnormally regulate NKX2-5 in model zebrafish embryos

FOXC1 is a member of the forkhead family of transcription factors, and whose function is poorly understood. A variety of FOXC1 mutants have been identified in patients diagnosed with the autosomal dominant disease Axenfeld-Rieger syndrome, which is mainly characterized by abnormal development of the eyes, particularly those who also have accompanying congenital heart defects (CHD). However, the role of FOXC1 in CHD, and how these mutations might impact FOXC1 function, remains elusive. Our previous work provided one clue to possible function, demonstrating that zebrafish foxc1a, an orthologue of human FOXC1 essential for heart development, directly regulates the expression of nkx2.5, encoding a transcriptional regulator of cardiac progenitor cells. Abnormal expression of Nkx2-5 leads to CHD in mice and is also associated with CHD patients. Whether this link extends to the human system, however, requires investigation. In this study, we demonstrate that FOXC1 does regulate human NKX2-5 expression in a dose-dependent manner via direct binding to its proximal promoter. A comparison of FOXC1 mutant function in the rat cardiac cell line H9c2 and zebrafish embryos suggested that the zebrafish embryos might serve as a more representative model system than the H9c2 cells. Finally, we noted that three of the Axenfeld-Rieger syndrome FOXC1 mutations tested increased, whereas a fourth repressed the expression of NKX2-5 These results imply that mutant FOXC1s might play etiological roles in CHD by abnormally regulating NKX2-5 in the patients. And zebrafish embryos can serve as a useful in vivo platform for rapidly evaluating disease-causing roles of mutated genes.

Phenotype expansion of heterozygous FOXC1 pathogenic variants toward involvement of congenital anomalies of the kidneys and urinary tract (CAKUT)

PURPOSE

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of chronic kidney disease in childhood and adolescence. We aim to identify novel monogenic causes of CAKUT.

METHODS

Exome sequencing was performed in 550 CAKUT-affected families.

RESULTS

We discovered seven FOXC1 heterozygous likely pathogenic variants within eight CAKUT families. These variants are either never reported, or present in <5 alleles in the gnomAD database with ~141,456 controls. FOXC1 is a causal gene for Axenfeld-Rieger syndrome type 3 and anterior segment dysgenesis 3. Pathogenic variants in FOXC1 have not been detected in patients with CAKUT yet. Interestingly, mouse models for Foxc1 show severe CAKUT phenotypes with incomplete penetrance and variable expressivity. The FOXC1 variants are enriched in the CAKUT cohort compared with the control. Genotype-phenotype correlations showed that Axenfeld-Rieger syndrome or anterior segment dysgenesis can be caused by both truncating and missense pathogenic variants, and the missense variants are located at the forkhead domain. In contrast, for CAKUT, there is no truncating pathogenic variant, and all variants except one are located outside the forkhead domain.

CONCLUSION

We thereby expanded the phenotype of FOXC1 pathogenic variants toward involvement of CAKUT, which can potentially be explained by allelism.

The diagnosis and phacoemulsification in combination with intraocular lens implantation for an Axenfeld-Rieger syndrome patient with small cornea: a case report

BACKGROUND

Axenfeld-Rieger syndrome (ARS) is a congenital disease with a series of developmental abnormalities, and no case of ARS with cataract and small cornea has been reported in previous studies. In the present report, we aimed to describe the diagnosis and phacoemulsification of an ARS patient with small cornea.

CASE PRESENTATION

A 58-year-old Han Chinese male patient who was referred to Eye Center of the Second Affiliated Hospital of Zhejiang University Medical College was diagnosed with ARS. Systemic and ophthalmic examination and genetic testing were performed. The slit-lamp microscopic examination of anterior segment showed obvious nuclear cataract, iris lesions, and the abnormal cornea of both eyes with small transversal and longitudinal diameters. ARS with bilateral complicated cataract and small cornea was diagnosed. Microincision-phacoemulsification in combination with intraocular lens implantation was performed on his left eye. After successful surgery of his left eye, the best-corrected visual acuity (BCVA) was obviously improved from 2 to 0.5 (LogMAR). A transient elevation of intraocular pressure (IOP) was controlled with medication.

CONCLUSIONS

Through genetic testing, a known pathogenic mutation NM_153427.2:c.272G > A was detected on the PITX2 gene; and an unknown mutation NM_001453.2:c.1063C > T was detected on FOXC1 gene. For the ARS patient with complicated cataract, the visual acuity was increased by phacoemulsificasion in combination with microincision.

Childhood glaucoma genes and phenotypes: Focus on FOXC1 mutations causing anterior segment dysgenesis and hearing loss

Childhood glaucoma is an important cause of blindness world-wide. Eleven genes are currently known to cause inherited forms of glaucoma with onset before age 20. While all the early-onset glaucoma genes cause severe disease, considerable phenotypic variability is observed among mutations carriers. In particular, FOXC1 genetic variants are associated with a broad range of phenotypes including multiple forms of glaucoma and also systemic abnormalities, especially hearing loss. FOXC1 is a member of the forkhead family of transcription factors and is involved in neural crest development necessary for formation of anterior eye structures and also pharyngeal arches that form the middle ear bones. In this study we review the clinical phenotypes reported for known FOXC1 mutations and show that mutations in patients with reported ocular anterior segment abnormalities and hearing loss primarily disrupt the critically important forkhead domain. These results suggest that optimal care for patients affected with anterior segment dysgenesis should include screening for FOXC1 mutations and also testing for hearing loss.

Molecular characterization of Axenfeld-Rieger spectrum and other anterior segment dysgeneses in a sample of Mexican patients

BACKGROUND

Anterior segment dysgenesis (ASD) and Axenfeld-Rieger spectrum (ARS) are mainly due to PITX2 and FOXC1 defects, but it is difficult in some patients to differentiate among PITX2-, FOXC1-, PAX6- and CYP1B1-related disorders. Here, we set out to characterize the pathogenic variants (PV) in PITX2, FOXC1, CYP1B1 and PAX6 in nine unrelated Mexican ARS/ASD patients and in their available affected/unaffected relatives.

MATERIALS AND METHODS

Automated Sanger sequencing of PITX2, FOXC1, PAX6 and CYP1B1 was performed; those patients without a PV were subsequently analyzed by Multiplex Ligation-dependent Probe Amplification (MLPA) for PITX2, FOXC1 and PAX6. Missense variants were evaluated with the MutPred, Provean, PMUT, SIFT, PolyPhen-2, CUPSAT and HOPE programs.

RESULTS

We identified three novel PV in PITX2 (NM_153427.2:c.217G>A, c.233T>C and c.279del) and two in FOXC1 [NM_001453.2:c.274C>T (novel) and c.454T>A] in five ARS patients. The previously reported FOXC1 c.367C>T or p.(Gln123*) variant was identified in a patient with ASD. The ocular phenotype related to FOXC1 included aniridia, corneal opacity and early onset glaucoma, while an asymmetric ocular phenotype and aniridia were associated with PITX2. No gene rearrangements were documented by MLPA analysis, nor were any PV identified in PAX6 or CYP1B1.

CONCLUSIONS

Heterozygous PV in the PITX2 and FOXC1 genes accounted for 66% (6/9) of the ARS/ASD cases. The absence of PAX6 or CYP1B1 abnormalities could reflect our small sample size, although their analysis could be justified in ARS/ASD patients that present with congenital glaucoma or aniridia.

Corneal endothelial cell density and cardiovascular mortality: A Global Survey and Correlative Meta-Analysis

Based on embryological commonalities between eye and heart development, a global, country-specific meta-analysis of normal, adult corneal endothelial cell density (ECD) was performed and correlated against mortality rates secondary to diseases affecting cardiac neural crest cell (CNCC)-derived cardiovascular structures. A country-specific survey of ECD was performed by searching PubMed for studies reporting ECD datasets from normal adults. All eligible datasets were assigned a country of origin. Country-specific weighted mean ECD were calculated based on dataset n. Country-specific disease mortality rates were obtained from the World Health Organization. The correlations between weighted mean ECD and mortality rates secondary to diseases affecting CNCC-derived cardiovascular structures were calculated. As controls, correlations between ECD and noncardiovascular disease mortality were examined. Pearson correlation coefficients (r) corresponding to P-value < 0.05 were considered significant. Three hundred ninety-two datasets (39,762 eyes) from 267 source-studies were assigned to 42 countries. Significant correlations were found between ECD and mortality due to coronary heart disease (r = -0.39, P = 0.011), hypertension (r = -0.33, P = 0.033), and all-cause cardiac disease (r = -0.36, P = 0.019). No significant correlations were found between ECD and mortality secondary to the control conditions: inflammatory heart disease (mesoderm-derived tissues) (r = -0.12, P = 0.45), diabetes (r = -0.13, P = 0.41), lung disease (r = -0.21, P = 0.18), liver disease (r = -0.13, P = 0.41), renal disease (r = -0.10, P = 0.53), lung cancer (r = 0.02, P = 0.90), pancreatic cancer (r = 0.24, P = 0.13), malnutrition (r = -0.07, P = 0.66), or all-cause mortality (r = 0.04, P = 0.81). Negative correlations exist between ECD and mortality due to coronary artery disease and hypertension. On a population-based level, adult ECD is correlated to mortality from certain cardiovascular diseases. Clin. Anat. 31:927-936, 2018. © 2018 Wiley Periodicals, Inc.

The transcription factor Foxc1a in zebrafish directly regulates expression of nkx2.5, encoding a transcriptional regulator of cardiac progenitor cells

Cardiogenesis is a tightly controlled biological process required for formation of a functional heart. The transcription factor Foxc1 not only plays a crucial role in outflow tract development in mice, but is also involved in cardiac structure formation and normal function in humans. However, the molecular mechanisms by which Foxc1 controls cardiac development remain poorly understood. Previously, we reported that zebrafish embryos deficient in foxc1a, an ortholog of mammalian Foxc1, display pericardial edemas and die 9-10 days postfertilization. To further investigate Foxc1a's role in zebrafish cardiogenesis and identify its downstream target genes during early heart development, we comprehensively analyzed the cardiovascular phenotype of foxc1a-null zebrafish embryos. Our results confirmed that foxc1a-null mutants exhibit disrupted cardiac morphology, structure, and function. Performing transcriptome analysis on the foxc1a mutants, we found that the expression of the cardiac progenitor marker gene nkx2.5 was significantly decreased, but the expression of germ layer-patterning genes was unaffected. Dual-fluorescence in situ hybridization assays revealed that foxc1a and nkx2.5 are co-expressed in the anterior lateral plate mesoderm at the somite stage. Chromatin immunoprecipitation and promoter truncation assays disclosed that Foxc1a regulates nkx2.5 expression via direct binding to two noncanonical binding sites in the proximal nkx2.5 promoter. Moreover, functional rescue experiments revealed that developmental stage-specific nkx2.5 overexpression partially rescues the cardiac defects of the foxc1a-null embryos. Taken together, our results indicate that during zebrafish cardiogenesis, Foxc1a is active directly upstream of nkx2.5.

A Novel Mutation in FOXC1 in a Lebanese Family with Congenital Heart Disease and Anterior Segment Dysgenesis: Potential Roles for NFATC1 and DPT in the Phenotypic Variations

Congenital heart diseases (CHDs) are still the leading cause of death in neonates. Anterior segment dysgenesis is a broad clinical phenotype that affects the normal development of the eye, leading in most of the cases to glaucoma which is still a major cause of blindness for children and adolescents. Despite tremendous insights gained from genetic studies, a clear genotype–phenotype correlation is still difficult to draw. In Lebanon, a small country with still a high rate of consanguineous marriages, there are little data on the epidemiology of glaucoma amongst children with or without CHD. We carried out whole exome sequencing (WES) on a family with anterior segment dysgenesis, and CHD composed of three affected children with glaucoma, two of them with structural cardiac defects and three healthy siblings. The results unravel a novel mutation in FOXC1 (p. R127H) segregating with the phenotype and inherited from the mother, who did not develop glaucoma. We propose a digenic model for glaucoma in this family by combining the FOXC1 variant with a missense variant inherited from the father in the dermatopontin (DPT) gene. We also unravel a novel NFATC1 missense mutation predicted to be deleterious and present only in the patient with a severe ocular and cardiac phenotype. This is the first report on FOXC1 using WES to genetically characterize a family with both ocular and cardiac malformations. Our results support the usage of such technology to have a better genotype–phenotype picture for Mendelian-inherited diseases for which expressivity and penetrance are still not answered.

Primary congenital and developmental glaucomas

Glaucoma is the leading cause of irreversible blindness worldwide. Although most glaucoma patients are elderly, congenital glaucoma and glaucomas of childhood are also important causes of visual disability. Primary congenital glaucoma (PCG) is isolated, non-syndromic glaucoma that occurs in the first three years of life and is a major cause of childhood blindness. Other early-onset glaucomas may arise secondary to developmental abnormalities, such as glaucomas that occur with aniridia or as part of Axenfeld-Rieger syndrome. Congenital and childhood glaucomas have strong genetic bases and disease-causing mutations have been discovered in several genes. Mutations in three genes (CYP1B1, LTBP2, TEK) have been reported in PCG patients. Axenfeld-Rieger syndrome is caused by mutations in PITX2 or FOXC1 and aniridia is caused by PAX6 mutations. This review discusses the roles of these genes in primary congenital glaucoma and glaucomas of childhood.

The rare Axenfeld-Rieger syndrome with systemic anomalies: A case report and brief review of literature

RATIONALE

Axenfeld-Rieger syndrome (ARS) is a rare autosomal dominant disorder with ocular anterior segment dysgenesis and systemic anomalies.

PATIENT CONCERNS

A 28-year-old Chinese Han female was referred to Beijing Tongren Eye Center for progressive decrease of the visual acuity on her right eye in the past month.

DIAGNOSES

The patient was diagnosed as ARS with retinal detachment based on series of ophthalmic examinations performed.

INTERVENTIONS

A pars plana vitrectomy was performed to manage the retinal detachment.

OUTCOMES

Her best-corrected visual acuity was slightly improved after surgery.

LESSONS

ARS is a developmental defect of ocular anterior segment with various clinical manifestations which might cause misdiagnosis.

Novel FOXC2 Mutation in Hereditary Distichiasis Impairs DNA-Binding Activity and Transcriptional Activation

Distichiasis presents as double rows of eyelashes arising from aberrant differentiation of the meibomian glands of the eyelids, and it may be sporadic or hereditary. FOXC2 gene mutations in hereditary distichiasis are rarely reported. Here, we examined two generations of a Chinese family with hereditary distichiasis but without lymphedema or other features of LD syndrome. The FOXC2 gene was amplified and sequenced in all family members. Subcellular localization and luciferase assays were performed to assess the activity of the mutant FOXC2 protein. Clinical examinations showed distichiasis, lower eyelid ectropion, congenital ptosis and photophobia in all affected individuals. Sequence analysis revealed a novel frameshift mutation, c.964_965insG, in the coding region of the FOXC2 gene. This mutation caused protein truncation due to the presence of a premature stop codon. A fluorescence assay showed that this mutation did not change the nuclear localization of the protein. However, it impaired DNA-binding activity and decreased transcriptional activation. This is the first report of a FOXC2 mutation in hereditary distichiasis in the Chinese population. The findings of our study expand the FOXC2 mutation spectrum and contribute to the understanding of the genotype-phenotype correlation of this disease.

Search for Rare Copy-Number Variants in Congenital Heart Defects Identifies Novel Candidate Genes and a Potential Role for FOXC1 in Patients With Coarctation of the Aorta

Background—

Congenital heart defects are the most frequent malformations among newborns and a frequent cause of morbidity and mortality. Although genetic variation contributes to congenital heart defects, their precise molecular bases remain unknown in the majority of patients.

Methods and Results—

We analyzed, by high-resolution array comparative genomic hybridization, 316 children with sporadic, nonsyndromic congenital heart defects, including 76 coarctation of the aorta, 159 transposition of the great arteries, and 81 tetralogy of Fallot, as well as their unaffected parents. We identified by array comparative genomic hybridization, and validated by quantitative real-time polymerase chain reaction, 71 rare de novo (n=8) or inherited (n=63) copy-number variants (CNVs; 50 duplications and 21 deletions) in patients. We identified 113 candidate genes for congenital heart defects within these CNVs, including BTRC , CHRNB3 , CSRP2BP , ERBB2 , ERMARD , GLIS3 , PLN , PTPRJ , RLN3 , and TCTE3 . No de novo CNVs were identified in patients with transposition of the great arteries in contrast to coarctation of the aorta and tetralogy of Fallot ( P =0.002; Fisher exact test). A search for transcription factor binding sites showed that 93% of the rare CNVs identified in patients with coarctation of the aorta contained at least 1 gene with FOXC1-binding sites. This significant enrichment ( P <0.0001; permutation test) was not observed for the CNVs identified in patients with transposition of the great arteries and tetralogy of Fallot. We hypothesize that these CNVs may alter the expression of genes regulated by FOXC1. Foxc1 belongs to the forkhead transcription factors family, which plays a critical role in cardiovascular development in mice.

Conclusions—

These data suggest that deregulation of FOXC1 or its downstream genes play a major role in the pathogenesis of coarctation of the aorta in humans.

Forkhead box transcription factors in embryonic heart development and congenital heart disease

Embryonic heart development is a very complicated process regulated precisely by a network composed of many genes and signaling pathways in time and space. Forkhead box (Fox, FOX) proteins are a family of transcription factors characterized by the presence of an evolutionary conserved "forkhead"or "winged-helix" DNA-binding domain and able to organize temporal and spatial gene expression during development. They are involved in a wide variety of cellular processes, such as cell cycle progression, proliferation, differentiation, migration, metabolism and DNA damage response. An abundance of studies in model organisms and systems has established that Foxa2, Foxc1/c2, Foxh1 and Foxm1, Foxos and Foxps are important components of the signaling pathways that instruct cardiogenesis and embryonic heart development, playing paramount roles in heart development. The previous studies also have demonstrated that mutations in some of the forkhead box genes and the aberrant expression of forkhead box gene are heavily implicated in the congenital heart disease (CHD) of humans. This review primarily focuses on the current understanding of heart development regulated by forkhead box transcription factors and molecular genetic mechanisms by which forkhead box factors modulate heart development during embryogenesis and organogenesis. This review also summarizes human CHD related mutations in forkhead box genes as well as the abnormal expression of forkhead box gene, and discusses additional possible regulatory mechanisms of the forkhead box genes during embryonic heart development that warrant further investigation.

Glaucoma Genes and Mechanisms

Genetic studies have yielded important genes contributing to both early-onset and adult-onset forms of glaucoma. The proteins encoded by the current collection of glaucoma genes participate in a broad range of cellular processes and biological systems. Approximately half the glaucoma-related genes function in the extracellular matrix, however proteins involved in cytokine signaling, lipid metabolism, membrane biology, regulation of cell division, autophagy, and ocular development also contribute to the disease pathogenesis. While the function of these proteins in health and disease are not completely understood, recent studies are providing insight into underlying disease mechanisms, a critical step toward the development of gene-based therapies. In this review, genes known to cause early-onset glaucoma or contribute to adult-onset glaucoma are organized according to the cell processes or biological systems that are impacted by the function of the disease-related protein product.