Clinical phenotype of juvenile-onset primary open-angle glaucoma linked to chromosome 1q

Gonioscopy-Assisted Transluminal Trabeculotomy for Myocilin-Associated Juvenile Open-Angle Glaucoma: A Case Series of 8 Eyes Over 2.2 to 4.1 Years

OBJECTIVE

Mutations within the myocilin (MYOC) gene are the first known single-gene cause of both primary open-angle glaucoma and juvenile open-angle glaucoma (JOAG). Subsequent studies have shown these mutations cause trabecular meshwork dysfunction, resulting in markedly elevated intraocular pressures (IOPs) at young ages. Angle-based procedures, like gonioscopy-assisted transluminal trabeculotomy (GATT), bypass the trabecular meshwork, and as such, are hypothesized to be particularly effective in this angle-based disease. The purpose of this case series is to evaluate the efficacy of GATT for MYOC-associated JOAG.

DESIGN

A retrospective chart review was performed evaluating patients under the age of 18 years with known MYOC-associated JOAG who underwent GATT. A total of 8 eyes of 4 children are included.

PARTICIPANTS

All participants had a strong family history of MYOC glaucoma.

METHODS

All patients underwent a thorough clinical evaluation, including visual acuity, slit lamp examination, optic nerve fundoscopy, and IOP measurements by Goldmann applanation. Most patients also underwent 24-2 Swedish Interactive Thresholding algorithm (SITA) standard Humphrey visual fields and fundus photography, and all patients had retinal nerve fiber layer OCT.

MAIN OUTCOME MEASURES

Main outcome measures include IOP and number of medications. Additional measures include visual acuity, optic nerve photos, visual field testing, and OCT.

RESULTS

Following 360° GATT, all 8 eyes of 4 children had a mean drop in IOP of 26 mmHg (68%), and all were able to stop glaucoma medications entirely. Our patients were followed up between 2.2 and 4.1 years with no evidence of decreasing efficacy or glaucomatous progression. All patients maintain 20/20 visual acuity or better in both eyes, and glaucoma has stabilized on all available ancillary testing (OCT, Humphrey visual field, and optic nerve photos). One patient (patient 4) had a notable reversal of cupping.

CONCLUSIONS

In MYOC-associated JOAG, the pathology is concentrated at the trabecular meshwork (TM), lending itself well to angle-based surgeries, especially GATT. Gonioscopy-assisted transluminal trabeculotomy is particularly effective in children with MYOC JOAG, allowing them to avoid, or at least delay, the need for more invasive surgeries like trabeculectomy and tube shunt surgeries with over 4 years of follow-up. To date, this is the first genetically directed glaucoma surgery available.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Juvenile-onset open-angle glaucoma - A clinical and genetic update

Juvenile-onset open-angle glaucoma (JOAG) is a subset of primary open-angle glaucoma that is diagnosed before 40 years of age. The disease may be familial or non-familial, with proportions varying among different populations. Myocilin mutations are the most commonly associated. JOAG is characterized by high intraocular pressures (IOP), with many patients needing surgery. The mean age at diagnosis is in the 3rd decade, with a male preponderance. Myopia is a common association. The pathophysiology underlying the disease is immaturity of the conventional outflow pathways, which may or may not be observed on gonioscopy and anterior segment optical coherence tomography. The unique optic nerve head features include large discs with deep, steep cupping associated with high IOP-induced damage. Progression rates among JOAG patients are comparable to adult primary glaucomas, but as the disease affects younger patients, the projected disability from this disease is higher. Early diagnosis, prompt management, and life-long monitoring play an important role in preventing disease progression. Gene-based therapies currently under investigation offer future hope.

Outcomes of gonioscopy-assisted transluminal trabeculotomy in juvenile-onset primary open-angle glaucoma

PURPOSE

To report the outcomes of gonioscopy-assisted transluminal trabeculotomy (GATT) for juvenile-onset primary open-angle glaucoma (JOAG).

METHODS

A consecutive case series of JOAG patients who underwent GATT was reviewed with follow-up period of up to 18 months. Intraocular pressure (IOP), number of glaucoma medications and success rate were compared between eyes with and without prior glaucoma surgery, and between mild-to-moderate and severe cases defined based on Humphrey Visual Field mean deviation.

RESULTS

In total, 59 eyes of 48 patients were included. Overall, IOP was reduced from 26.5 ± 9.0 mmHg on 3.7 ± 0.9 medications preoperatively to 14.7 ± 3.0 mmHg on 0.7 ± 1.2 medications at 12 months and to 14.1 ± 2.3 mmHg on 0.4 ± 0.8 medications at 18 months postoperatively (P < 0.001). The complete and qualified success rates were 70.8% and 81.2% at 12 months, and 58.6% and 81.2% at 18 months, respectively. Eyes with and without prior glaucoma surgery did not differ significantly in terms of postoperative IOP, glaucoma medication and success rate. In addition, GATT was effective for both mild-to-moderate and severe cases; the latter achieved a surgical success of 79.1%.

CONCLUSIONS

GATT is effective for JOAG. In particular, this case series suggests that GATT is promising in treating severe JOAG and those with prior glaucoma surgery.

Prevalence and Clinical Characteristics of Childhood Glaucoma at a Tertiary Care Children's Hospital

PRECIS

Glaucoma suspect was the most prevalent category in this study followed by glaucoma associated with acquired ocular anomaly and juvenile open-angle glaucoma. Primary congenital glaucoma was diagnosed in only 3% of the population studied.

PURPOSE

To describe the prevalence and clinical characteristics of childhood glaucoma diagnosed over a 10-year period among patients aged 18 years or below who were seen at a tertiary care children's hospital using the new Childhood Glaucoma Research Network classification system.

METHODS

Medical records of all patients aged 18 years or below (n=108) who were diagnosed with glaucoma between January 1, 2008 through September 30, 2018 were reviewed. Data collected included demographics (age at diagnosis, sex, and family history of glaucoma), intraocular pressure, disc-to-cup ratio, retinal nerve fiber layer thickness, and refractive errors. Clinical characteristics of each patient were evaluated according to the criteria established by Childhood Glaucoma Research Network. Categorical distributional equivalence comparisons were performed using the Pearson χ test. A P-value <0.05 was defined as statistically significant.

RESULTS

A total of 108 patients with a diagnosis of childhood glaucoma or glaucoma suspect were included in this study. Sixty-four percent of these patients were males (P<0.0001). The mean age at the time of diagnosis was 7.07±5.4 years. "Glaucoma suspect" was the most prevalent category (46%, P=0.0002), followed by glaucoma associated with the acquired ocular anomaly (20%) and juvenile open-angle glaucoma (16%). Primary congenital glaucoma represented 3% and all these patients were males. Sixty-nine percent of the patients had bilateral involvement (P=0.0073). The highest intraocular pressure recorded in the study was 57 mm Hg, the largest cup-to-disc ratio was 0.96, and the lowest retinal nerve fiber layer measurement was 39 μm. Ninety-two percent of the patients had refractive errors and 85% of them had astigmatism.

CONCLUSIONS

Establishing a pattern and the associated clinical characteristics of childhood glaucoma at tertiary care children's hospitals will help in developing collaborative research efforts and effective treatment/management strategies for children with these rare groups of disorders.

The Genetic and Endoplasmic Reticulum-Mediated Molecular Mechanisms of Primary Open-Angle Glaucoma

Glaucoma is a heterogenous, chronic, progressive group of eye diseases, which results in irreversible loss of vision. There are several types of glaucoma, whereas the primary open-angle glaucoma (POAG) constitutes the most common type of glaucoma, accounting for three-quarters of all glaucoma cases. The pathological mechanisms leading to POAG pathogenesis are multifactorial and still poorly understood, but it is commonly known that significantly elevated intraocular pressure (IOP) plays a crucial role in POAG pathogenesis. Besides, genetic predisposition and aggregation of abrogated proteins within the endoplasmic reticulum (ER) lumen and subsequent activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-dependent unfolded protein response (UPR) signaling pathway may also constitute important factors for POAG pathogenesis at the molecular level. Glaucoma is commonly known as a ‘silent thief of sight’, as it remains asymptomatic until later stages, and thus its diagnosis is frequently delayed. Thereby, detailed knowledge about the glaucoma pathophysiology is necessary to develop both biochemical and genetic tests to improve its early diagnosis as well as develop a novel, ground-breaking treatment strategy, as currently used medical therapies against glaucoma are limited and may evoke numerous adverse side-effects in patients.

Estimating the age of the p.Cys433Arg variant in the MYOC gene in patients with primary open-angle glaucoma

The aim of this study was to estimate the age of the Cys433Arg (c.1297T>C, p.Cys433Arg) variant by comparing the genotypes of individuals affected and not affected by primary open angle glaucoma juvenile onset (JOAG). Our sample consisted of 35 JOAG-affected individuals from three families, 16 unrelated patients with the MYOC p.Cys433Arg variant and 16 unaffected individuals. Genomic DNA was amplified by PCR; nine short tandem repeats were genotyped through automated electrophoresis and three single nucleotide polymorphisms through Sanger sequencing. The determination of haplotypes was performed using Arlequin software and age estimation was performed using DMLE+ 2.3 and BDMC21 softwares. Four markers constituted the haplotypes associated with the p.Cys433Arg variant. The software DMLE+2.3 predicted an age of 43 generations for this variant with a 95% confidence interval ranging from 28 to 76 generations (560-1520 years) and BDMC21 predicted an age of 59 generations (1180 years) (95% CI: 40 to 100).

Genetics and genetic testing for glaucoma

PURPOSE OF REVIEW

In recent decades, investigators have identified numerous genes and genetic factors that cause or contribute risk for glaucoma. These findings have increased our understanding of disease mechanisms, provided us with new diagnostic tools, and may allow for development of improved therapies for glaucoma. However, genetic testing is most useful when it is reserved for appropriate patients. The purpose of this article is to review key points and recent developments regarding the genetics and genetic testing for glaucoma and to provide recommendations for when genetic testing may be warranted.

RECENT FINDINGS

Large genome-wide association studies have identified multiple new susceptibility loci associated with primary open angle glaucoma and primary angle closure glaucoma.

SUMMARY

Several glaucoma-causing genes and genetic risk factors for glaucoma have been discovered. As a result, there are specific clinical scenarios in which genetic testing is warranted. In select cases (i.e., familial juvenile open angle glaucoma), genetic testing can serve as a powerful tool to improve diagnostic accuracy, efficiency of disease surveillance, and selection of treatment, enabling physicians to better optimize care for their patients.

Clinical and genetic characterization of a large primary open angle glaucoma pedigree

PURPOSE

To both characterize the clinical features of large primary open angle glaucoma (POAG) pedigree from a village in southern India and to investigate the genetic basis of their disease.

MATERIALS AND METHODS

Eighty-four members of a large pedigree received complete eye examinations including slit lamp examination, tonometry, gonioscopy, and ophthalmoscopy. Some were further studied with perimetry. Those diagnosed with POAG were tested for disease-causing mutations in the myocilin and optineurin genes with Sanger sequencing.

RESULTS

Fourteen of 84 family members were diagnosed with POAG, while eight were clinically judged to be POAG-suspects. The family structure and the pattern of glaucoma in the pedigree are complex. Features of glaucoma in this pedigree include relatively early age at diagnosis (mean 50 ± 14 years) and maximum intraocular pressures ranging from 14 to 36 mm Hg with a mean of 23 mm Hg ± 6.5 mm Hg. Patients had an average central corneal thickness (mean 529 ± 37.8 microns) and moderate cup-to-disc ratios (0.74 ± 0.14). No mutations were detected in myocilin, optineurin, or TANK binding kinase 1 (TBK1).

CONCLUSIONS

We report a five-generation pedigree with a complex pattern of POAG inheritance that includes 22 POAG patients and glaucoma suspects. Although the familial clustering of POAG in this pedigree is consistent with dominant inheritance of a glaucoma-causing gene, mutations were not detected in genes previously associated with autosomal dominant glaucoma, suggesting the involvement of a novel disease-causing gene in this pedigree.

Common and rare genetic risk factors for glaucoma

The characterization of genes responsible for glaucoma is the critical first step toward the development of gene-based diagnostic and screening tests, which could identify individuals at risk for disease before irreversible optic nerve damage occurs. Early-onset forms of glaucoma affecting children and young adults are typically inherited as Mendelian autosomal dominant or recessive traits whereas glaucoma affecting older adults has complex inheritance. In this report, we present a comprehensive overview of the genes and genomic regions contributing to inherited glaucoma.

Primary open-angle glaucoma genes

A substantial fraction of glaucoma has a genetic basis. About 5% of primary open angle glaucoma (POAG) is currently attributed to single-gene or Mendelian forms of glaucoma (ie glaucoma caused by mutations in myocilin or optineurin). Mutations in these genes have a high likelihood of leading to glaucoma and are rarely seen in normal subjects. Other cases of POAG have a more complex genetic basis and are caused by the combined effects of many genetic and environmental risk factors, each of which do not act alone to cause glaucoma. These factors are more frequently detected in patients with POAG, but are also commonly observed in normal subjects. Additional genes that may be important in glaucoma pathogenesis have been investigated using quantitative traits approaches. Such studies have begun to identify genes that control the magnitude of important quantitative features of glaucoma that may also be important risk factors for POAG, such as central corneal thickness. Each of these different approaches to study glaucoma genetics is providing new insights into the pathogenesis of POAG.

Glaucoma: genes, phenotypes, and new directions for therapy

Glaucoma, a leading cause of blindness worldwide, is characterized by progressive optic nerve damage, usually associated with intraocular pressure. Although the clinical progression of the disease is well defined, the molecular events responsible for glaucoma are currently poorly understood and current therapeutic strategies are not curative. This review summarizes the human genetics and genomic approaches that have shed light on the complex inheritance of glaucoma genes and the potential for gene-based and cellular therapies that this research makes possible.

Myocilin protein levels in the aqueous humor of the glaucomas in selected canine breeds

OBJECTIVE

To compare aqueous humor myocilin protein levels in dogs with the primary glaucomas to those with the secondary glaucomas, primary cataracts, and diabetic cataracts.

MATERIALS AND METHODS

Four groups were selected, based on diagnosis by the attending veterinary ophthalmologists and included: primary glaucoma (primary open-angle glaucoma (POAG) and primary closed angle glaucoma (PCAG); n = 155); secondary glaucoma (n = 94); primary (presumed inherited) cataract (n = 142), and diabetic cataract (n = 83). A total of 474 samples (187 males, 263 females, 24 unreported) with average ages of 117 months for the males and 101 months for the females were analyzed. Myocilin protein was measured using the Coomassie staining and Western blot methods relative to a myocilin control.

RESULTS

Differences were seen between nonglaucomatous (cataractous) and glaucomatous dogs with myocilin levels in glaucomatous eyes being many times higher than those in the cataractous dogs. Primary glaucomatous dogs were found to have an aqueous humor myocilin protein level of 17.30 +/- 1.03 units. Secondary glaucomas had the highest level of myocilin in the aqueous humor with 19.27 +/- 1.41 units. Diabetic cataractous dogs had the lowest levels of myocilin reported with 6.60 +/- 0.88 (mean +/- SEM) units. Normal (cataractous) dogs had a myocilin level in the aqueous humor of 8.05 +/- 0.86 units.

CONCLUSION

Aqueous humor protein levels were elevated, relative to the myocilin control, in both the primary and secondary glaucoma groups compared to the cataract and diabetic cataract groups. Like in the Beagle POAG, aqueous humor myocilin protein levels are increased. Further studies are indicated to investigate the exact role of the aqueous humor myocilin protein in the genesis in increased IOP in these primary glaucomatous breeds.

Advanced juvenile open-angle glaucoma in an 8-year-old Haitian girl

BACKGROUND

Glaucoma can afflict infants and children in several ways. Conditions such as inflammation or trauma can contribute to elevated intraocular pressure in secondary glaucoma, whereas congenital abnormalities of the trabecular meshwork development can result in infantile glaucoma. Lesser known, however, is juvenile open-angle glaucoma, which afflicts children and young adults in a manner similar to primary open-angle glaucoma, with no identifiable trabecular meshwork abnormalities or other secondary causes.

CASE REPORT

An 8-year-old Haitian girl was referred for suspicion of a left optic neuropathy. Examination found markedly elevated intraocular pressure with open angles and advanced glaucomatous neuropathy in each eye without evidence of signs of infantile or secondary glaucoma. Medical therapy was instituted before surgical consultation. Clinical features of patients with juvenile open-angle glaucoma are presented along with a discussion of genetic expression and management of the condition.

CONCLUSIONS

Juvenile open-angle glaucoma, although uncommon, can cause significant visual morbidity in children. In that children represent a unique and atypical glaucoma population with special therapeutic needs, all treatment options must be clearly understood.

Role of CYP1B1 in Glaucoma

Glaucoma is a leading cause of blindness, estimated to affect 60 million people by 2010, and represents a heterogeneous group of neurodegenerative disease. The two major types of glaucoma include primary open-angle glaucoma (POAG) and primary congenital glaucoma (PCG). A genetically heterogeneous group of developmental disorders known as anterior segment dysgenesis (ASD) have been reported to be associated with increased intraocular pressure (IOP) and glaucoma. These include Peters' anomaly, Rieger's anomaly, aniridia, iris hypoplasia, and iridogoniodysgenesis. Genetic linkage analysis and mutation studies have identified CYP1B1 as a causative gene in PCG, as a modifier gene in POAG, and, on rare occasions, as causative gene in POAG as well as in several ASD disorders. CYP1B1-deficient mice exhibit abnormalities in their ocular drainage structure and trabecular meshwork that are similar to those reported in human PCG patients. Accordingly, it is speculated that diminished or absent metabolism of key endogenous CYP1B1 substrates adversely affects the development of the trabecular meshwork. CYP1B1 protein is involved in the metabolism of steroids, retinol and retinal, arachidonate, and melatonin. The conserved expression of CYP1B1 in both murine and human eyes, its higher expression in fetal than adult eyes, and its biochemical properties are consistent with this hypothesis. The exact role of CYP1B1 in the pathogenesis of glaucoma and other ASD disorders remains to be elucidated.

Gene mapping for primary open angle glaucoma

Primary open angle glaucoma (POAG) is a leading cause of visual impairment and blindness worldwide. To date, at least 20 genetic loci for POAG have been reported. Only 3 causative genes are identified from these loci: myocilin (MYOC), optineurin (OPTN) and WD repeat domain 36 (WDR36), which together account for less than 10% of POAG. Only a portion of POAG follows Mendelian inheritance, and a considerable fraction results from a large number of variants in several genes, each contributing small effects. Over the past 10 years, there has been vigorous research on mapping the POAG genes. The main technological approaches are functional cloning, family linkage analysis, genome-wide scan, case-control association study, and microarray analysis. Association studies found 16 genes related to POAG, but reports on glaucoma-causing effects of these genes are conflicting. Ten microarray gene expression studies related to POAG have been published. A number of genes potentially related to POAG have been identified, and they provide a good resource to select candidate genes for mutation analysis in association studies. While linkage studies remain a mainstay, the current trend is to use genome-wide association studies to map genes for POAG. This review gives an overview of the efforts in the past decade to identify the POAG genes through linkage studies, genome-wide scans, case-control association studies and microarray studies. In the near future such comprehensive studies are expected to greatly advance our understanding of the genetic basis of POAG and provide information for effective glaucoma therapy.

Clinicopathologic correlation and genetic analysis in a case of posterior polymorphous corneal dystrophy

PURPOSE

To evaluate the clinical history, histopathology, and genetics of posterior polymorphous corneal dystrophy (PPMD) in a woman with a prominent retrocorneal membrane.

DESIGN

Observational case report and genetic analysis of her family, UM:139.

METHODS

Records were reviewed from a case and associated family members. The diagnosis of PPMD was based on clinical examination, immunohistochemical staining, electron microscopy, and screening of genetic markers from regions previously reported to be associated with PPMD.

RESULTS

Over 17 years, the proband with PPMD had 25 ocular procedures performed for glaucoma, cataract, cornea, retina, and postoperative problems. A prominent retrocorneal membrane grew onto the crystalline lens and intraocular lens (IOL). Histopathology revealed stratified epithelial-like cells on iris from an iridectomy and stratified corneal endothelium on a corneal button. Electron microscopy on the cornea revealed microvilli, tonofilaments, and desmosomes consistent with endothelial transformation, which was confirmed by positive anticytokeratin (CK) AE1/AE3 and CAM 5.2 immunoreactivity. Negative immunoreactivity in epithelium and positive in endothelium with anti-CK 7 supported the diagnosis of PPMD rather than epithelial downgrowth. Multiple relatives were affected with PPMD with apparent autosomal dominant inheritance, but surprisingly, the PPMD, congenital hereditary endothelial dystrophy 1 (CHED1) and CHED2 loci on chromosome 20 and the collagen, type VIII, alpha-2 (COL8A2) gene were excluded by linkage and haplotype analyses.

CONCLUSIONS

We are unaware of previous PPMD reports describing the unusual feature of a retrocorneal membrane extending onto the crystalline lens and IOL. In addition, this family suggests another PPMD locus.

Septuagenarian's phenotype leads to ascertainment of familial MYOC gene mutation

PURPOSE

To report a family with a myocilin (MYOC) gene mutation ascertained on the basis of the phenotype of the 71-year-old proband with juvenile-onset primary open-angle glaucoma (JOAG).

PATIENTS AND METHODS

A thorough patient history of the proband and review of medical records revealed that a filtering procedure performed 50 years before had controlled the intraocular pressure (IOP) and prevented optic disc damage and visual field loss until the bleb failed after cataract surgery. Patient characteristics and history led to suspicion of a mutation in the MYOC gene. Mutation screening and clinical evaluation of the proband and family members were undertaken.

RESULTS

A Val426Phe mutation was found in the JOAG proband and in 3 other blood relatives with glaucoma. The mutation was not present in unaffected relatives.

CONCLUSIONS

A functioning filtering procedure performed 50 years before the current study was all that was needed to prevent glaucomatous damage and control IOP in the proband. Once the bleb failed, increased IOP led to damage in a relatively brief period of time. Although not every JOAG patient has the MYOC mutation, there is a somewhat typical MYOC phenotype that may predict an increased chance of harboring a MYOC mutation. Use of such phenotype information in evaluating whether to screen older patients can lead to identification of families at risk for open-angle glaucoma.

A case-control comparison of the clinical characteristics of glaucoma and ocular hypertensive patients with and without the myocilin Gln368Stop mutation

PURPOSE

To determine whether primary open-angle glaucoma (POAG) and ocular hypertensive (OHT) patients who harbor the myocilin Gln368Stop mutation differ in phenotype or clinical course from patients without the mutation.

DESIGN

Case-control study.

METHODS

A retrospective case-control study compared all known POAG patients (n = 18) and OHT patients (n = 4) harboring the Gln368Stop mutation evaluated by the University of Iowa Glaucoma Service with control patients from the same population. Patients and control subjects were matched for diagnosis, age, sex, and race and were compared for phenotype and clinical course.

RESULTS

Mean age of disease onset and mean peak intraocular pressures (IOPs) of cases were similar to those reported by other studies. There was no statistically significant difference between cases and controls for the following variables: age at onset, peak intraocular pressure, Snellen visual acuity, number of medications, Humphrey visual field (HVF) mean deviation, HVF pattern deviation, number of filtering surgeries performed, time intervals from diagnosis to argon laser trabeculoplasty (ALT), diagnosis to first filtering surgery, ALT to first filtering surgery, and percent change in IOP after ALT and after first filtering surgery.

CONCLUSIONS

There is no statistically significant difference between the onset and clinical course of POAG and OHT caused by the Gln368Stop mutation and POAG and OHT not associated with the mutation.

Myocilin and glaucoma: facts and ideas

Mutations in the MYOC gene that encodes for myocilin are causative for some forms of juvenile and adult-onset primary open-angle glaucoma (POAG). Myocilin is a secreted 55-57kDa glycoprotein that forms dimers and multimers. Characteristic structural motifs include a myosin-like domain, a leucine zipper region and an olfactomedin domain. Most of the mutations that have been identified in patients with POAG are localized in the olfactomedin domain, which is highly conserved among species. In the eye, myocilin is expressed in high amounts in the trabecular meshwork (TM), sclera, ciliary body and iris, and at considerable lower amounts in retina and optic nerve head. Secreted myocilin is present in the aqueous humor. In the TM, myocilin is found within the cytoplasm of TM cells and in the juxtacanalicular region in association with fibrillar extracellular matrix components. Since patients with mutations in myocilin may have high intraocular pressures, the role of myocilin for aqueous humor outflow has been investigated and conflicting results have been obtained. Recombinant myocilin increases outflow resistance in perfused anterior segment organ cultures, while overexpression of myocilin after viral gene transfer appears to reduce outflow resistance. In TM cells, the expression of myocilin is induced upon treatment with dexamethasone at a time course similar to that observed in steroid-induced glaucoma. Other factors that induce myocilin expression are transforming growth factor-beta and mechanical stretch. Promoter elements that are important for the glucocorticoid induction have not been identified, but it has been shown that upstream stimulatory factor is critical for the basal promoter activity of MYOC. Mice with a targeted disruption of the myocilin gene do not express a phenotype, indicating that the glaucomatous phenotype in humans is not because of a loss-of-function effect. Experimental studies show that mutated myocilin is not secreted, but appears to accumulate in the cells. Such an accumulation might interfere with TM function and lead to impaired outflow resistance, but, so far, experimental evidence for such a scenario is lacking. In addition, the normal function(s) of myocilin is (are) still elusive.

Inheritance of open-angle glaucoma in the Barbados family study

The majority of genetic studies on open-angle glaucoma (OAG) have been conducted in primarily white populations, with investigations of inheritance patterns largely based on self-reported information. The Barbados Family Study of Open-Angle Glaucoma (BFSG) is the first study to investigate the transmission pattern(s) for OAG in a predominantly black population, based on standardized examinations. Each BFSG participant received a comprehensive examination including anthropometric and other measurements, best-corrected visual acuity, perimetry, tonometry, lens gradings, fundus photography, venipuncture, an extensive interview including ocular, medical and family history information and a comprehensive ophthalmologic evaluation. Conservative criteria were used to define glaucoma status, including the presence of both visual field defects and optic disc damage. The study included 207 OAG-affected probands (median age: 68 years) and 1,056 of their relatives (median age: 47 years). Among the relatives examined 10% (n = 106) had OAG and 13% (n = 141) had probable OAG. Segregation analyses were performed to determine the mode of inheritance for glaucoma in these families. The results indicate that transmission of OAG or probable OAG is most likely due to a major codominant gene. Both age and gender are shown to be significant factors as well; with an increase in risk being associated with each year of age over 54 years and an increase in risk for all ages and genotypes observed in males. These analyses do not, however, preclude the possible existence of an environmental component or other genetic determinants in OAG. Further evidence for the existence of a major gene may be obtained by additional follow-up of the relatively young cohort of relatives, as well as ongoing linkage analyses.

The role of myocilin/TIGR in glaucoma: results of the Glaucoma Research Foundation catalyst meeting in Berkeley, California, March 2000

Approximately 3 years ago, the first major (biochemical, molecular biologic, and biologic) insight into primary open-angle glaucoma was the finding that mutations in the myocilin (MYOC/TIGR) gene were related to certain forms of juvenile onset of this disease. Since then, a great deal of work has been done to determine the possible mechanisms by which MYOC/TIGR might cause not only juvenile but also adult-onset primary open-angle glaucoma. To assess the current knowledge and those areas in which more research is necessary, a meeting of scientists was held by the Glaucoma Research Foundation of San Francisco, California in the spring of 2000. This meeting attempted to concentrate on the MYOC/TIGR protein rather than the genetics of this gene. Possible functions and roles of this protein intracellularly and extracellularly were critically examined and discussed. Normal transcriptional and translational events and the effect of mutations on these events were explored. The discussions yielded insight not only in those areas in which important information is known but also in vital areas in which little is currently understood. This review attempts to summarize the current knowledge regarding MYOC/TIGR and to elucidate the points that the people attending the meeting thought needed further study.

Age-dependent prevalence of mutations at the GLC1A locus in primary open-angle glaucoma

PURPOSE

To screen a population with primary open-angle glaucoma for mutations in the gene that encodes the trabecular meshwork inducible glucocorticoid response protein (TIGR), also known as myocilin (MYOC).

METHODS

Ophthalmologic information was collected for study subjects with primary open-angle glaucoma and their relatives. Mutation screening of 74 primary open-angle glaucoma probands was conducted by sequencing TIGR/MYOC coding sequence and splice sites.

RESULTS

In 23 families we detected 13 nonsynonymous sequence changes, nine of which appear to be mutations likely to cause or contribute to primary open-angle glaucoma. Two mutations, Arg272Gly and Ile499Ser, and one nonsynonymous sequence variant, Asn57Asp, are novel. We found mutations in nine of 25 juvenile glaucoma probands (36%) and two of 49 adult-onset glaucoma probands (4%). Age classification of families rather than individual probands revealed mutations in three of nine families with strictly juvenile primary open-angle glaucoma (33%), and no mutations in 39 families with strictly adult-onset primary open-angle glaucoma (0%). In families with mixed-onset primary open-angle glaucoma containing both juvenile primary open-angle glaucoma and adult-onset primary open-angle glaucoma cases, we found mutations in eight of 26 families (31%).

CONCLUSIONS

Our data suggest that Gly252Arg, Arg272Gly, Glu323Lys, Gln368STOP, Pro370Leu, Thr377Met, Val426Phe, Ile477Asn, and Ile499Ser are likely to play roles that cause or contribute to the etiology of autosomal dominant primary open-angle glaucoma. Our finding of more TIGR/MYOC mutations in families with mixed-onset primary open-angle glaucoma than in the families with strictly adult-onset primary open-angle glaucoma implies that the presence of relatives with juvenile primary open-angle glaucoma in a family could be used as a basis for identifying a subset of the population with adult-onset primary open-angle glaucoma with higher prevalence of TIGR/MYOC mutations. To address this issue, and to refine estimations of mutation prevalence in these age-defined subpopulations, prospective study of a larger population ascertained entirely through adult-onset primary open-angle glaucoma probands will be needed.

Regulation of human myocilin/TIGR gene transcription in trabecular meshwork cells and astrocytes: role of upstream stimulatory factor

BACKGROUND

Mutations in the myocilin (MYOC)/TIGR gene are responsible for autosomal-dominant juvenile primary open-angle glaucoma (POAG). In patients with non-autosomal-dominant POAG, such mutations are rare, but the expression of MYOC/TIGR in the trabecular meshwork (TM) of the eye is considerably higher than in normals. We performed transfection, DNAse I footprinting, mutagenesis and electrophoretic mobility shift assays (EMSA) to identify elements responsible for the basal transcription of MYOC/TIGR in TM cells and astrocytes.

RESULTS

DNAse I footprinting experiments of the human MYOC/TIGR promoter showed a major protected area between nt -106 to -77, which was not conserved in the homologous region of the mouse myoc/tigr promoter. In addition, the TATA-box was protected, as well as at least three downstream sites, including an AP-1-like sequence. Deletion of the -106 to -77 region caused a substantial loss of functional promotor activity in all cell types. Site-directed mutagenesis and EMSA experiments revealed the presence of two regulatory elements in the -106 to -77 region. Each of these cis-elements is essential for minimal promoter activity. The 5'-half of the region contains a sequence with similarities to NF-kappaB-related sites, however, binding of NF-kappaB could not be confirmed by EMSA. The 3'-half contains a canonical E-box sequence. EMSA experiments showed that the upstream regulatory factor (USF) was binding to the E-box sequence and that the binding can be supershifted by specific antibodies.

CONCLUSIONS

Several DNA-protein binding elements contribute to a transcription of MYOC/TIGR, and USF is critically required for its basal transcription in trabecular meshwork cells and astrocytes.

A cellular assay distinguishes normal and mutant TIGR/myocilin protein

Glaucoma is a blinding eye disease that affects approximately 70 000 000 people world-wide. Mutations in the gene TIGR / MYOC have been shown to cause the most common form of the disease, primary open angle glaucoma, in selected families. Amino acid sequence variants of the gene have been found in 2-4% of sporadic primary open angle glaucoma cases. Most variants are rare and it is often difficult to definitively distinguish between a deleterious mutation and a benign variant solely on the basis of relative frequencies in patient and control groups. The function of the TIGR/myocilin protein is unknown and an assay to functionally classify variants is lacking. We sought to develop a biochemical assay to distinguish different forms of TIGR/myocilin. We investigated the Triton X-100 detergent solubility characteristics of mutant and normal forms of the protein, expressed by transfection in cultured cells. We observed a clear difference in the behavior of the two types of TIGR/myocilin; all confirmed mutant proteins tested were substantially Triton insoluble, while normal protein and controls were completely soluble. We also tested seven ambiguous variant proteins and classified them as mutant or normal on the basis of their Triton solubility. The results in some cases validated, and in other cases contradicted, earlier classifications of these variants. To our knowledge, Triton solubility is the first example of a general difference in the properties of mutant and normal forms of TIGR/myocilin. The assay we have developed will be useful for discerning protein functional information from the location of mutations, will aid genetic counseling of individuals with TIGR/myocilin variants and may provide a clue to understanding a mechanism by which mutations in TIGR / MYOC cause glaucoma.

Molecular basis of open-angle glaucoma in Italy

Glaucoma is a group of ocular diseases characterized by an optic neuropathy in which degeneration of retinal ganglion cells leads to a characteristic excavation of the optic nerve head. Primary open-angle glaucoma (POAG) can be subdivided into two groups according to age of onset:- 1. the more common middle- to late-age onset, chronic open-angle glaucoma (COAG) diagnosed after the age of 40 years; 2. the rarer juvenile open-angle glaucoma (JOAG), which is diagnosed between the age of 3 years and early adulthood. Recently, the gene coding for the trabecular meshwork-induced glucocorticoid response protein (TIGR), located in chromosome 1 (1q23-25), was found mutated in patients affected by POAG. In this work we describe the clinical and molecular genetic features of several Italian families affected by autosomal dominant POAG, collected in various regions of Italy.

Cosegregation of open-angle glaucoma and the nail-patella syndrome

PURPOSE

To evaluate two families ascertained only for the presence of glaucoma in which both nail-patella syndrome and glaucoma occur in several generations and to determine whether the two diseases are genetically related.

METHODS

Ophthalmologic examinations and orthopedic examinations were performed. DNA samples from family members were screened with a microsatellite repeat marker at the argininosuccinate synthetase (ASS) locus at 9q34, and linkage analysis was performed.

RESULTS

Six patients with open-angle glaucoma were found among 13 patients with nail-patella syndrome in family UM:47. Seven patients with glaucoma were found among 11 patients with nail-patella syndrome in family UM:65. In both families, all individuals with glaucoma also had nail-patella syndrome. Two-point linkage analysis resulted in a lod score of 2.98 at a recombination fraction of 0.00 for open-angle glaucoma and nail-patella syndrome.

CONCLUSIONS

Linkage results presented here provide strong evidence that the orthopedic and nail anomalies in these two families result from the same nail-patella syndrome locus that has been previously linked to markers at 9q34. These data provide indirect evidence for a possible glaucoma locus at 9q34 and do not allow us to distinguish whether the glaucoma is the result of the nail-patella syndrome mutation or whether there is a separate locus responsible for glaucoma in these families. These studies suggest a need for ophthalmologic examination of individuals with nail-patella syndrome.

Genetic heterogeneity of primary open angle glaucoma and ocular hypertension: linkage to GLC1A associated with an increased risk of severe glaucomatous optic neuropathy

The GLC1A locus for autosomal dominant juvenile and middle age onset primary open angle glaucoma (OAG) has been mapped to chromosome 1q21-q31. OAG, however, is a heterogeneous disease. We tested linkage of OAG and ocular hypertension (OHT), a major risk factor for OAG, to GLC1A in eight French families with multiple cases of juvenile and middle age onset OAG. There was strong evidence of genetic heterogeneity, four families being linked to GLC1A and two or three others being unlinked, depending on whether the complete OAG phenotype was analysed alone or jointly with OHT. Peak intraocular pressure (IOP) did not differ significantly between the two groups of families, while linkage to GLC1A conferred a highly increased risk of developing OAG and of having severe glaucomatous optic neuropathy. Testing linkage of familial OAG to GLC1A may therefore have prognostic value too.

Juvenile glaucoma linked to the GLC1A gene on chromosome 1q in a Panamanian family

PURPOSE

To characterize clinically and genetically autosomal dominant juvenile-onset primary open-angle glaucoma in a Panamanian family.

METHODS

Twenty members of a six-generation family underwent ophthalmologic examination and genetic screening with markers near the GLC1A gene on chromosome 1q.

RESULTS

Linkage analysis disclosed evidence linking primary open-angle glaucoma in this family to the GLC1A gene on chromosome 1q, with a maximum lod score of 3.75 for marker D1S431 at an estimated recombination fraction of 0.00.

CONCLUSIONS

This is the first report of a Panamanian family in which primary open-angle glaucoma is linked to the GLC1A gene on chromosome 1q.

Genetic heterogeneity in Hispanic families with autosomal dominant juvenile glaucoma

A gene for autosomal dominant, juvenile-onset, primary open angle glaucoma (GLCIA) has been previously mapped to 1q21-31 in several Caucasian pedigrees. We studied two Hispanic families with this disease to determine if their disease genes also map to this region. Individuals were considered as being affected if they had 1OP > 30 mmHg (without treatment) and glaucomatous optic nerve damage or visual field defects. Persons older than 40 years with intraocular pressures < or = 21 mmHg and no evidence of optic nerve damage or visual field loss were scored as unaffected. Individuals not falling into these two categories were considered unknown. Genomic DNA was extracted from blood samples and subjected to PCR-based microsatellite marker analysis. Computer-based linkage analysis was used to determine if the disease gene mapped to chromosome 1q2I-31. In the family from the Canary Islands, the disease gene was linked to the chromosome 1q2I-31 region previously identified by other researchers. Markers D1S212 and D1S218 produced maximum lod scores of 3.38 and 2.99, respectively. In the family from the Balearic Islands, the disease gene was excluded from this region by genetic linkage analysis. Haplotype analysis also excluded the disease gene from chromosome 1q21-31. Our Hispanic families showed genetic heterogeneity with respect to autosomal dominant, juvenile-onset, primary open angle glaucoma.

Probable exclusion of GLC1A as a candidate glaucoma gene in a family with middle-age-onset primary open-angle glaucoma

PURPOSE

To determine whether an adult-onset variety of primary open-angle glaucoma in family UM:POAG1 is linked to the previously mapped GLC1A juvenile-onset primary open-angle glaucoma locus on chromosome 1q or whether linkage can be excluded.

METHODS

Microsatellite repeat markers from the 9 cM D1S196 to D1S218 interval containing the GLC1A gene were amplified by polymerase chain reaction from DNA samples collected from 11 members of one sibship in family UM:POAG1. Haplotype analysis was carried out, including calculation of the probability that the observed data would have been obtained if the underlying cause of primary open-angle glaucoma in this family were a defect in a gene located in the tested interval. Linkage analysis was carried out under an autosomal dominant model for GLC1A glaucoma.

RESULTS

In family UM:POAG1, primary open-angle glaucoma was diagnosed in six surviving and one deceased member of a sibship of 13 individuals during the fifth or sixth decade of life. Glaucoma in this family has a later average age at diagnosis and significantly less elevation in intraocular pressure than GLC1A glaucoma so far described. Haplotype analysis, using a population prevalence up to 0.9%, shows that it is unlikely that the reported data would have been observed if primary open-angle glaucoma in this pedigree were due to the GLC1A locus on chromosome 1q21-q31. Linkage analysis under the juvenile glaucoma autosomal dominant model allowed exclusion of linkage across the entire GLC1A genetic inclusion interval, with a maximum lod score in the interval of -3.28.

CONCLUSION

The most likely interpretation of these observations is that a defect in the GLC1A glaucoma gene is not responsible for adult-onset primary open-angle glaucoma in family UM:POAG1. This suggests the existence of at least two primary open-angle glaucoma genes, the previously reported GLC1A gene on chromosome 1q and another gene located elsewhere in the genome. Diagnosis of UM:POAG1 glaucoma between 42 and 57 years of age also raises questions regarding the relation of the glaucoma present in this family to the common later-age-onset form of the disease.