Juvenile-onset Primary Open-angle Glaucoma Research Articles

Genetic analysis of an Indian family with members affected with juvenile-onset primary open-angle glaucoma

Purpose: Glaucoma is the second leading cause of blindness. In India, ~1.5 million people are blind due to glaucoma. Mutations in the MYOC gene located at the GLC1A locus on chromosome 1q21–q31 have been found in patients with juvenile-onset primary open-angle glaucoma (J-POAG). The purpose of the present study was to identify the genetic cause of glaucoma in a four-generation Indian family affected with J-POAG. Methods: Peripheral blood samples were obtained from individuals for genomic DNA isolation. To determine if this family was linked to the GLC1A locus, haplotyping analysis was carried out using microsatellite markers from the GLC1A candidate region. Exon-specific primers from exon 3 of the MYOC gene were used to amplify DNA samples from individuals. Mutation analysis was carried out using PCR-SSCP and DNA sequence analyses. Results: Pedigree analysis suggested that glaucoma in this family segregated as an autosomal dominant trait. Of six patients, five had J-POAG and one had adult-onset POAG (A-POAG). Haplotype analysis suggested linkage of this family to the GLC1A locus. Mutation and sequence analyses showed a novel missense mutation, c.821C > G (p.P274R), in the C-terminal olfactomedin domain coded by exon 3 of the MYOC gene. One patient was found to be homozygous for this mutation with a severe phenotype. Conclusions: This study reports a novel missense mutation in a four-generation Indian family with all but one member affected with J-POAG. The total number of mutations described so far in the MYOC gene, including the one reported here, is 59 with a clustering of 52 mutations in exon 3.

Molecular Cloning and Expression Profile of Rat Myocilin

Myocilin is known to be associated with the pathogenesis of juvenile-onset primary open angle glaucoma. The tissue distribution of myocilin transcripts has been analyzed in both humans and mice, and a high level of expression in the retina and skeletal muscle has been reported. The functions of myocilin in these tissues are unknown. We isolated rat myocilin cDNA and examined the expression pattern of myocilin, including its expression in endocrine organs, using Northern blot analysis. The rat myocilin cDNA sequence has two in-frame initiation codons, the upstream and downstream ATGs corresponding to the initiation codon of human and murine myocilin, respectively. It is most likely that the first ATG is a translational initiation codon, since 8 of 13 amino acid residues deduced from the rat cDNA sequence between the first and the second ATGs are the same as those in human myocilin. The open reading frame encodes 502 amino acids. Rat myocilin also has both a myosin-like domain and an olfactmedin-like domain, which have been identified in human and murine myocilin. Northern analysis of rat myocilin mRNA revealed substantial expression in the thyroid gland, as well as in the retina and muscle. No transcripts were detected in other endocrine glands, including the adrenal gland, pituitary, and testis. Myocilin may play an important role in thyroid function. Further study of the expression and role of myocilin in the thyroid is required.

The genetics of open-angle glaucoma: the story of GLC1A and myocilin.

A linkage analysis study was performed on a single large family with juvenile-onset primary open-angle glaucoma (POAG). This led to the recognition that there was a region of chromosome 1q that harboured a gene for juvenile-onset POAG. This chromosomal site was called GLC1A. It was discovered that a gene that produces the protein myocilin resides within this interval and that mutations in myocilin caused most cases of autosomal dominant juvenile-onset POAG. More importantly myocilin mutations also cause up to 4.6% of cases of adult-onset POAG. The prevalence of myocilin mutations is similar regardless of race or geographic location. There are widely variable glaucoma phenotypes depending on the specific mutation in myocilin. Myocilin is expressed in multiple tissues throughout the eye and in many other organs. In the trabecular meshwork the production of myocilin can be induced by the application of topical corticosteroids. The exact function of myocilin in health and disease remains a mystery.

Optic nerve head appearance in juvenile-onset chronic high-pressure glaucoma and normal-pressure glaucoma

Objective To evaluate the appearance of the optic nerve head in chronic high-pressure glaucoma and normal-pressure glaucoma. Design Clinic-based cross-sectional study. Participants The study included 52 eyes with normal-pressure glaucoma and 28 eyes with juvenile-onset primary open-angle glaucoma that served as models for chronic high-pressure glaucoma. Methods Color stereo optic disc photographs and wide-angle retinal nerve fiber layer photographs were morphometrically examined. Main outcome measures Localized retinal nerve fiber layer defects; parapapillary chorioretinal atrophy; disc hemorrhages; optic cup shape; retinal arteriole narrowing. Results Both study groups did not vary significantly in count of localized retinal nerve fiber layer defects, size of parapapillary atrophy, optic cup depth, steepness of disc cupping, rim/disc area ratio, diameter of retinal arterioles, and frequency and degree of focal retinal arteriole narrowing. In normal-pressure glaucoma versus juvenile open-angle glaucoma, localized retinal nerve fiber layer defects were significantly broader, disc hemorrhages were found significantly more often and were larger, and neuroretinal rim notches were present more frequently and were deeper. Conclusions Chronic high-pressure glaucoma and normal-pressure glaucoma show morphologic similarities in the appearance of the optic nerve head. The lower frequencies of detected disc hemorrhages and rim notches in high-pressure glaucoma may be due to a smaller size of hemorrhages and localized retinal nerve fiber layer defects in high-pressure glaucoma. Both glaucoma types have morphologic features in common, suggesting that they may possibly belong to a spectrum of the same pathologic process.

Novel mutations in the myocilin gene in Japanese glaucoma patients.

Myocilin is a gene responsible for juvenile onset primary open angle glaucoma (POAG) mapped as the GLC1A locus and, many mutations have been reported worldwide. Some mutations were found not only in patients with juvenile onset POAG, but also in patients with late onset POAG and in patients with normal tension glaucoma. To investigate the mutation prevalence in Japan, we performed a mutation analysis in 140 unrelated Japanese patients. We have identified the 10 sequence variants, of which four were highly probable for disease-causing mutations (Arg46ter, Arg158Gln, Ile360Asn, and Ala363Thr), and six polymorphisms (Gln19His, Arg76Lys, Asp208Glu, Val439Val, Arg470His, and Ala488Ala). Thus, myocilin mutations were found at the rate of 4/140 (2.9%) probands, similar to previous reports with other ethnic populations.

Expression of the TIGR gene in the iris, ciliary body, and trabecular meshwork of the human eye

Mutations in the the glaucoma gene GCL1A, also known as trabecular meshwork glucocorticoid response (TIGR) or myocilin (Myoc), have been shown to be associated with juvenile-onset primary open-angle glaucoma. Very little is known about the pattern of expression of the TIGR gene in human ocular tissues. In-situ hybridization experiments demonstrated the localization of TIGR mRNA in cells throughout the iris, ciliary muscle, and the filtering portion of the trabecular meshwork of normal eye donors. The expression of TIGR protein was investigated by Western blot using an epitope-directed antibody to the carboxy terminus region of TIGR. This antibody was able to distinguish a recombinant TIGR fusion protein from a truncated TIGR form containing the naturally occurring Gln 368 ?stop mutation. In tissue extracts from the iris, ciliary body, and trabecular meshwork, the antibody recognized a major protein band of 57-kDa molecular mass. Deglycosylation treatment with PNGase F, NANase II, and O-glycosidase indicated that the 57-kDa protein in these tissues was unglycosylated. In agreement with this observation, in coupled in-vitro transcription/translation systems, the 57-kDa TIGR protein was unaffected by the presence of the processing and glycosylation activities of canine pancreatic microsomal membranes. These findings support the view that the expression of TIGR mRNA in cells of the iris, ciliary body, and trabecular meshwork correlates with that of TIGR protein, and that the 57-kDa TIGR protein was unglycosylated. These results, which are in contrast with earlier reports, raise the possibility that the TIGR protein might be processed into distinct forms in a tissue-specific manner.

Morphology of the optic papilla in glaucoma. I. Primary open-angle glaucoma

Previous studies have shown that the chronic open-angle glaucomas form a heterogeneous spectrum of diseases which have in common an open anterior chamber angle and glaucomatous optic nerve damage. Purpose of this study was to evaluate whether the appearance of the optic disc differs among the various types of primary open-angle glaucoma. Color stereo optic disc photographs of 683 patients with primary open-angle glaucoma (POAG), and 481 normal eyes were morphometrically evaluated. Morphologic characteristics of the glaucoma types were as follows: Highly myopic POAG: secondary macrodiscs with abnormal shape; shallow, flat, concentric disc cupping; low frequency of disc hemorrhages; large parapapillary atrophy or myopic crescent; medium to low intraocular pressure. Juvenile-onset POAG: Optic disc of normal size and shape; deep and steep disc cupping; low frequency of broad rim notches or large disc hemorrhages; small parapapillary atrophy; high minimal and maximal intraocular pressure measurements. Age-related atrophic POAG: Optic disc of normal size and shape; shallow, flat and concentric disc cupping; medium to low frequency of disc hemorrhages; large parapapillary atrophy; medium to low intraocular pressure. Eyes with normal-pressure glaucoma: Optic disc of normal size and shape; deep and steep cupping; relatively small parapapillary atrophy; high frequency of disc hemorrhages and rim notches. These characteristics in the appearance of the optic disc may be helpful for clinical diagnosis and therapy and may give pathogenetic hints.

Expression pattern and in situ localization of the mouse homologue of the human MYOC ( GLC1A) gene in adult brain

The MYOC ( GLC1A) gene has recently been associated with both juvenile-onset primary open angle glaucoma (JOAG) and typical late-onset primary open angle glaucoma (POAG). As a result, much scrutiny has been focused on the pathology of these diseases. In order to better understand the pathophysiology of POAG, we have been developing a mouse model of the disease. As a step in this development, we have investigated the expression pattern of Myoc transcripts in embryonic and adult mouse tissue using Northern blot and in situ hybridization analyses. Myoc transcripts were found in high levels in adult eye, heart, brain, skeletal muscle and testis and to a lesser extent in lung and kidney. They were also present, albeit in very low amounts, during mouse embryogenesis. We present new evidence using in situ hybridization analysis that Myoc transcripts were present in widespread regions of the adult brain including the ependymal lining of the third and fourth ventricles, in the choroid plexus, the zonal layer of the junction of the inferior and superior colliculi, the neurons of the habenula, the piriform cortex, the median pre-optic nucleus of the hypothalamus, the olfactory tubercle, and in the inferior olive. In a functional sense, Myoc expression in the ependyma and choroid plexus, two regions of the brain involved in cerebrospinal fluid synthesis and resorption, parallels Myoc expression in the ciliary body and trabecular meshwork of the anterior segment of the eye where aqueous humor synthesis and outflow occur.

Novel TIGR/MYOC mutations in families with juvenile onset primary open angle glaucoma.

Mutations in the trabecular meshwork induced glucocorticoid response protein (TIGR) or myocilin (MYOC) has recently been shown to cause juvenile onset primary open angle glaucoma (JOAG). In this study, we...

Novel trabecular meshwork inducible glucocorticoid response mutation in an eight-generation juvenile-onset primary open-angle glaucoma pedigree

Objective This study aimed to update a large kindred with juvenile-onset primary open-angle glaucoma (POAG) first described in 1940 and to identify the underlying genetic cause of the disease. Design Molecular genetic study of a single kindred, including clinical examination, retrospective review of clinical and family history records, linkage analysis, and mutation screening. Participants The retrospective review included 957 members of a single large family. The linkage study included 40 members of 1 branch of the family in which juvenile-onset POAG is segregating in an autosomal-dominant pattern. Mutation screening included 15 at-risk family members with juvenile-onset POAG, probands of 40 families with adult-onset POAG, probands of 11 additional unrelated juvenile-onset POAG families, and 43 unrelated normal control subjects. Intervention Clinical and family history records were obtained, ophthalmologic examinations were performed, and blood samples were drawn for use in genotyping. Main outcome measures Allele sizes of microsatellite repeat genetic markers from the vicinity of the GLC1A glaucoma gene on chromosome 1q were assigned based on size fractionation of DNA fragments generated by polymerase chain reaction (PCR). Linkage was established by the method of lod scores. Mutations were identified by determination of the DNA sequence of PCR products amplified from the trabecular meshwork inducible glucocorticoid response (TIGR) gene. Glaucoma status for purposes of linkage and mutation analysis was based on a combination of ophthalmologic examination, clinical records, family history, and previously published information. For some individuals reported in the pedigree, but not included in the genotyping studies, less information was available as presented in the text and tables. Results Autosomal-dominant POAG was confirmed or reported for 78 members of an 8-generation family. Linkage analysis showed significant evidence for linkage of juvenile-onset POAG in one branch of the family to D1S452 (maximum lod score of 6.42 at a recombination fraction of 0.00) and other markers in the vicinity of the GLC1A gene on chromosome 1q. Screening of the TIGR gene identified a mutation that results in substitution of asparagine for isoleucine at codon 477 near the carboxyterminal end of the protein. Conclusions The authors’ findings strongly suggest that the juvenile-onset POAG locus in this family is the GLC1A locus and that the underlying cause of the disease is the lle477Asn TIGR mutation that cosegregates with juvenile-onset POAG in one branch of this large family. Lack of samples from deceased individuals prevented the authors from determining whether reported adult-onset cases in this family could also be attributed to the lle477Asn TIGR mutation. Absence of the lle477Asn TIGR mutation from other juvenile- and adult-onset POAG families implies that this TIGR mutation is not a common cause of glaucoma.

Mouse Myocilin (Myoc) Gene Expression in Ocular Tissues1

Human myocilin is identical to TIGR (trabecular meshwork inducible glucocorticoid response) which is responsible for the pathogenesis of juvenile-onset primary open angle glaucoma (GLC1A). We have isolated cDNA for mouse myocilin (Myoc) and investigated mouse myocilin gene expression in ocular tissues within situRNA hybridization. Hybridization signals were observed in the iris, ciliary body, trabecular meshwork, sclera, and retina in the mouse eye. The marked signals were seen in trabecular meshwork cells and the anterior portion of sclera. These findings suggest that myocilin mutation could affect the capacity of aqueous outflow and cause elevation of the intraocular pressure which is involved in the pathogenesis of glaucoma.

Recurrent mutations in a single exon encoding the evolutionarily conserved olfactomedin-homology domain of TIGR in familial open-angle glaucoma.

Primary open-angle glaucoma (POAG) is a highly prevalent cause of irreversible blindness which associates cupping of the optic disc and alteration of the visual field, elevation of intraocular pressure being a major risk factor. Provided diagnosis is made at an early stage, treatments are available to prevent visual impairment. A locus, GLC1A, has been mapped on chromosome 1q23-q25 in several families affected with juvenile-onset POAG (JOAG) and also in some families affected with juvenile and middle-age onset POAG. Recently, three mutations of the TIGR (Trabecular meshwork-Induced Glucocorticoid Response) gene were shown to be responsible for the disease in several American families and in unrelated POAG patients. We now describe five new mutations in eight French families. All mutations known to date appear to concentrate in the evolutionarily conserved C-terminal domain of TIGR which bears homology to frog olfactomedin, an extracellular matrix glycoprotein of the olfactory epithelium, to rat and human neuronal olfactomedin-related proteins and to F11C3.2, a protein from Caenorhabditis elegans . Moreover, this conserved domain of TIGR is encoded by a single exon to which mutation screening could be limited. Surprisingly, the TIGR message, which is abundantly transcribed in the trabecular meshwork and also in the ciliary body and the sclera, is not expressed in the optic nerve whose degeneration is, however, the primary lesion of POAG.

Recent advances in molecular genetics of glaucomas.

Glaucomas are a heterogeneous group of eye conditions with manifestation from as early as birth to very late age of onset in life. The primary type of these conditions affecting children and juveniles are less frequent, but the prevalence of glaucomas affecting older people of > or = 70 years progressively rises to approximately 5%. The molecular genetics of three types of glaucoma have been the subject of investigation in the last few years. As a result, two loci (GLC3A and GLC3B) have been identified for primary congenital glaucoma, one locus (GLC1A) for juvenile-onset primary open angle glaucoma and a further two loci (GLC1B and GLC1C) for late-onset chronic open angle glaucoma. Early this year, the first set of mutations was described in the CYP1B1 (Cytochrome P4501B1) and TIGR (Trabecular meshwork Inducible Glucocorticoid Response Protein) genes for the GLC3A and GLC1A-linked families, respectively. The mapping of different types of glaucoma and mutation identification in these two genes are the focus of this review.

Juvenile Glaucoma Linked to the GLC1A Gene on Chromosome 1q in a Panamanian Family

To characterize clinically and genetically autosomal dominant juvenile-onset primary open-angle glaucoma in a Panamanian family. Twenty members of a six-generation family underwent ophthalmologic examination and genetic screening with markers near the GLC1A gene on chromosome 1q. 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. This is the first report of a Panamanian family in which primary open-angle glaucoma is linked to the GLC1A gene on chromosome 1q.

Recombinational and Physical Mapping of the Locus for Primary Open-Angle Glaucoma (GLC1A) on Chromosome 1q23–q25

Primary open-angle glaucoma (POAG) is a leading cause of irreversible blindness in industrialized countries. A locus for juvenile-onset POAG,GLC1A,has been mapped to 1q21–q31 in a 9-cM interval. With recombinant haplotypes, we have now reduced theGLC1Ainterval to a maximum of 3 cM, between theD1S452/NGA1/D1S210andNGA5loci. These loci are 2.8 Mb apart on a 4.7-Mb contig that we have completed between theD1S2851andD1S218loci and that includes 96 YAC clones and 48 STSs. The newGLC1Ainterval itself is now covered by 25 YACs, 30 STSs, and 16 restriction enzyme site landmarks. The lack of aNotI site suggests that the region has few CpG islands and a low gene content. This is compatible with its predominant cytogenetic location on the 1q24 G-band. Finally, we have excluded important candidate genes, including genes coding for three ATPases (ATP1B1, ATP2B4, ATP1A2), an ion channel (VDAC4), antithrombine III (AT3), and prostaglandin synthase (PTGS2). Our results provide a basis to identify theGLC1Agene.

Identification of a new ‘TIGR’ mutation in a family with juvenile-onset primary open angle glaucoma

Positional mapping of families segregating for juvenile-onset primary open angle glaucoma (JOAG) has previously identified a locus (GLC1A) for this condition on the long arm of chromosome 1. Recently, three mutations in the TIGR gene (Trabecular meshwork Inducible Glucocorticoid Response protein) have been described in a total of ten familial, three sporadic, and one normal subject. One of the familial cases has also been indicated to be of an adult-onset type. Herein, we report the identification of a new mutation in the TIGR gene in a six generation well-documented Edinburgh family with JOAG. We have sampled and screened the living affected members of this family and identified an ‘A’-to-‘G’ transition at amino acid 337 that has changed the glutamine (Gin) to arginine (Arg). This newly identified mutation resides 27 amino acids 5-prime from the previously reported mutation of Gly-to-Val. This mutation created a new MspI restriction site that has co-segregated perfectly with inherited affected haplotype of the pedigree and, furthermore, it has not been observed in 142 chromosomes of randomly selected subjects of the same population. This report, therefore, confirms the role of the TIGR gene in the etiology of JOAG and adds a new mutation to the three reported previously.

Probable Exclusion of GLC1A as a Candidate Glaucoma Gene in a Family with Middle-age-onset Primary Open-angle Glaucoma

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. 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. 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. 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.

Clinical Phenotype of Juvenile-onset Primary Open-angle Glaucoma Linked to Chromosome 1q

Purpose: Recent reports have suggested that a gene responsible for juvenile-onset primary open-angle glaucoma exists on the long arm of chromosome 1 (1 q). This report describes a previously unpublished family (UM:JG3) in which juvenile-onset glaucoma is segregating in an autosomal dominant manner. The clinical features in this family were compared with those seen in other pedigrees with this condition. Linkage analysis was performed to evaluate whether a glaucoma-causing gene in UM:JG3 is linked to genetic markers on chromosome 1 q.Methods: Affected family members, their siblings, children, and spouses were examined to identify the presence of glaucoma. Linkage studies were performed using short tandem repeat polymorphisms from chromosome 1 q. Results of these studies were compared with those found for other families in which juvenile-onset primary open-angle glaucoma is linked genetically to the same chromosome 1 q region.Results: The UM:JG3 family includes 22 affected individuals over five generations, including 12 still living. The average age at diagnosis for living affected individuals was 26 years. An association between myopia and glaucoma was observed in this family, but the glaucoma was not associated with iris processes or other structural anomalies. The clinical course of disease and response to treatment were similar to other families with this disease. The disease phenotype in this family is linked to markers on chromosome 1 q with a maximum lod score of 3.52 at a recombination fraction of 0.00 for marker D1 S433. Haplotype analysis suggests the gene responsible for glaucoma in this family is located in an 8-cM region between markers D1S445 and D1S218.Conclusions: The glaucoma in UM:JG3 is linked to markers on chromosome 1q, with a candidate interval smaller than that in previous reports. In individuals with juvenile-onset open-angle glaucoma linked to chromosome 1 q, the phenotype can range from mild ocular hypertension to blindness, resulting from marked elevations in intraocular pressure, with age at diagnosis ranging from 6 to 62 years. However, most affected individuals display a characteristic phenotype that includes onset in the first three decades of life, unusually high intraocular pressures, and the need for surgical therapy to prevent loss of vision. Whether differences in expression among families is due to allelic heterogeneity remains to be determined.