Screening for mutations of Axenfeld-Rieger syndrome caused by FOXC1 gene in Japanese patients

PURPOSE

Mutations in the forkhead transcription factor gene (FOXC1) have been recently shown to cause some cases of juvenile glaucoma associated with a variety of anterior-segment anomalies. The purpose of this study was to investigate the clinical features of Axenfeld-Rieger syndrome caused by FOXC1 mutations in Japanese patients.

PATIENTS AND METHODS

After informed consent was obtained, genomic DNA was isolated from peripheral blood. The DNA-sequence changes were analyzed using single-strand conformation polymorphism analysis and automated sequencing in six Japanese probands with Axenfeld-Rieger syndrome.

RESULTS

The authors identified four mutations: pedigree 1 (26-47ins22), 2 (Ile91Ser), 3 (286ins1), and 4 (Arg127His). Two pedigrees showed new mutations in FOXC1. In pedigrees 1,2, and 4, younger generations had iris hypoplasia with severe early-onset glaucoma, whereas their parents had posterior embryotoxon without glaucoma. Pedigree 3 had a single affected person with iris hypoplasia and posterior embryotoxon with a mild increase of intraocular pressure.

CONCLUSION

Four different FOXC1 mutations were found in four of six Japanese pedigrees with Axenfeld-Rieger syndrome. This was a new mutation in two pedigrees that was not found in earlier generations. This study confirms that mutations in this gene cause maldevelopment of the anterior segment of the eye.

Rate of visual field loss and long-term visual outcome in primary open-angle glaucoma

PURPOSE

To evaluate long-term visual field outcome in primary open-angle glaucoma.

METHODS

In this retrospective cohort study, 40 eyes of 40 patients with primary open-angle glaucoma with elevated intraocular pressure and a minimum of 8-year longitudinal series of visual fields were plotted with Goldmann perimeter. Eyes with any other ocular disease except cataract were excluded. Manual grid templates were used to quantify the visual fields. Linear regression was performed to estimate the rate of visual field decline. Pertinent clinical factors were evaluated for statistical association with the rate of decline. Long-term clinical outcome including visual acuity, rate of legal blindness, and rate of medical and surgical interventions was also measured.

RESULTS

In the 40 eyes studied, with a mean follow-up of 14 years, the visual field score decreased at the rate of -1.5% per year. Overall, 68% showed significant decrease, and the rate of decrease among these eyes was -2.1% per year. Five eyes became legally blind from glaucoma; the cumulative rate of blindness from glaucoma was 19% at 22 years. Higher intraocular pressure and greater number of antiglaucoma medications on initial presentation were associated with faster and slower deterioration of visual field (compared with the average), respectively.

CONCLUSIONS

With standard glaucoma therapy, the rate of visual field loss in primary open-angle glaucoma is slow. Lower intraocular pressure and more antiglaucoma medications are associated with slower visual field decline. Legal blindness from glaucoma is 19% over a follow-up of 22 years.

Long-term results of eyes with penetrating keratoplasty and glaucoma drainage tube implant

PURPOSE

To present long-term results of eyes with penetrating keratoplasty (PK) and glaucoma tube implant.

DESIGN

Retrospective, noncomparative, interventional case series.

PARTICIPANTS

We retrospectively reviewed medical records of all patients who underwent both PK and glaucoma tube implant (Baerveldt or Ahmed) at the University of Iowa between July of 1988 and December of 1997 (55 eyes).

METHODS

Success of the tube implant or PK was evaluated using Kaplan-Meier survival analysis. Association of relevant clinical factors with glaucoma or corneal graft outcome was evaluated using log-rank test or Cox proportional hazard regression analysis. The factors evaluated were glaucoma and cornea diagnoses; prior, simultaneous, and subsequent surgeries; type of tube implant; relative timing of surgeries; and postsurgical complications.

MAIN OUTCOME MEASURES

Glaucoma outcome was assessed by postoperative intraocular pressure (IOP), number of medications, and need for further glaucoma surgery. Corneal outcome was assessed by graft rejection, failure, and Snellen visual acuity. Surgical procedures before and during the study period, and their complications were evaluated.

RESULTS

The mean preoperative intraocular pressure was 29.8 mmHg with an average of 2.9 medications. At last postoperative follow-up, the mean IOP decreased to 14.3 mmHg with 0.7 medication. The tube implant successfully controlled glaucoma in 45 eyes (82%) at 3 years. More severe postsurgical complications were associated with greater glaucoma failure. Graft rejection occurred in 17 eyes, and 7 of these progressed to failure. Nonimmunologic graft failure occurred in an additional 17 eyes (31%). The remaining 31 eyes (56%) had a clear graft. The corneal grafts remained clear in 70% and 55% of eyes at 2 and 3 years, respectively. Corneal graft failure was associated with glaucoma and cornea diagnoses groups, type of tube implant, and relative timing of the two surgeries. Complications occurred in 23 eyes (42%), and 10 of these were serious.

CONCLUSIONS

A drainage tube implant can successfully control glaucoma in a majority (82%) of keratoplasty eyes at 3 years. However, the success of corneal grafts is low (55%) at 3 years. Postsurgical complications are not uncommon and are associated with poor glaucoma outcome. Other clinical factors are associated with poor graft outcome.

Non-secretion of mutant proteins of the glaucoma gene myocilin in cultured trabecular meshwork cells and in aqueous humor

Until recently, very little was known about the molecular mechanisms responsible for the development of glaucoma, a leading cause of blindness worldwide. Mutations in the glaucoma gene myocilin (MYOC, GLC1A) are associated with elevated intraocular pressure and the development of autosomal dominant juvenile glaucoma and a subset of adult-onset glaucoma. MYOC is expressed in the trabecular meshwork (TM), a tissue responsible for drainage of aqueous humor from the eye, and the tissue involved in elevated intraocular pressure associated with glaucoma. To better understand the role of MYOC in glaucoma pathogenesis, we examined the expression of normal and mutant myocilin in cultured ocular (TM) and non-ocular cells as well as in the aqueous humor of patients with and without MYOC glaucoma. Normal myocilin was secreted from cultured cells, but very little to no myocilin was secreted from cells expressing five different mutant forms of MYOC. In addition, no mutant myocilin was detected in the aqueous humor of patients harboring a nonsense MYOC mutation (Q368X). Co-transfection of cultured cells with normal and mutant myocilin led to suppression of normal myocilin secretion. These studies suggest that MYOC glaucoma is due either to insufficient levels of secreted myocilin or to compromised TM cell function caused by congestion of the TM secretory pathway.

Evaluation of the myocilin (MYOC) glaucoma gene in monkey and human steroid-induced ocular hypertension

PURPOSE

Glucocorticoid-induced ocular hypertension (the steroid response) may result in optic nerve damage that very closely mimics the pathologic course of primary open angle glaucoma (POAG). In addition, patients with glaucoma and their relatives are much more likely to exhibit the steroid response than unaffected individuals, suggesting a potential link between the steroid response and POAG. Recently, the expression of a gene (MYOC) in the trabecular meshwork was shown to be steroid-induced. MYOC variations thought to be disease-causing also were found in 3% to 5% of POAG cases. The purpose of this study was to determine whether some variations in MYOC might be involved in steroid-induced ocular hypertension.

METHODS

Seventy human steroid responders and 114 control subjects were screened for variations in the coding sequence and promoter of MYOC. Also, topical doses of dexamethasone (DEX) were administered to cynomolgus monkeys to determine their steroid responsiveness, and the MYOC orthologue was cloned from the cynomolgus monkey.

RESULTS

Overall, 109 instances of 20 different sequence variations were identified in the human myocilin gene. However, only four of these (each observed in a single individual) met the study criteria for a possible phenotype-altering variation. Three of these were present in steroid responders and one in a control patient, a distribution that was not statistically significant (P: = 0.3). In addition, the allele frequency of a closely flanking marker was compared between the steroid responders and the control subjects, and no evidence for linkage disequilibrium was observed. Reproducible and reversible ocular hypertension was induced in approximately 40% of the monkeys treated with DEX, similar to that seen in man. Ten monkeys were screened for MYOC mutations with single-strand conformation polymorphism (SSCP) analysis. Overall, 37 instances of 13 different sequence variations were observed. Four of these changes met the study criteria for a possible phenotype-altering variation, and these were equally distributed between responder and nonresponder monkeys.

CONCLUSIONS

This study identified no statistically significant evidence for a link between MYOC mutations and steroid-induced ocular hypertension.

Localization of MYOC transcripts in human eye and optic nerve by in situ hybridization

PURPOSE

To evaluate MYOC (myocilin) gene expression at the RNA level in normal intact human eyes and optic nerve using in situ hybridization.

METHODS

Normal human eyes and optic nerves from donors 62 to 83 years of age with no history of glaucoma were fixed, embedded in paraffin, and sectioned. Sections were hybridized with (35)S-labeled sense and antisense riboprobes derived from a full-length MYOC cDNA.

RESULTS

High levels of MYOC expression were observed throughout the trabecular meshwork as well as in the most anterior nonfiltering meshwork (Schwalbe's line), in the scleral spur, and in the endothelial lining of Schlemm's canal. MYOC transcripts were also detected in the anterior corneal stroma, in the ciliary muscle, beneath the anterior border of the iris, in the iris stroma, and in the sclera. Expression in the retrolaminar region of the optic nerve was present in the pial septa that divide the nerve fiber bundles, in the perivascular connective tissue surrounding the central retinal vessels, and in the dura mater, arachnoid, and pia mater of the meningeal sheath surrounding the optic nerve.

CONCLUSIONS

MYOC gene expression in the trabecular meshwork, Schlemm's canal, scleral spur, and ciliary muscle indicates a structural or functional role for myocilin in the regulation of aqueous humor outflow that may influence intraocular pressure. MYOC expression in the optic nerve suggests that changes in the structural, metabolic, or neurotropic support of the optic nerve may influence its susceptibility to glaucomatous damage.

Rieger syndrome: a clinical, molecular, and biochemical analysis

Rieger syndrome (RIEG 1; MIM 180500) is an autosomal dominant disorder of morphogenesis. It is a phenotypically heterogeneous disorder characterized by malformations of the eyes, teeth, and umbilicus. RIEG belongs to the Axenfeld-Rieger group of anomalies, which includes Axenfeld anomaly and Rieger anomaly (or Rieger eye malformation), which display ocular features only. Recently, mutations in the homeodomain transcription factor, PITX2, have been shown to be associated with Rieger syndrome. This review discusses the clinical manifestations of Rieger syndrome and how they correlate with the current molecular and biochemical studies on this human disorder.

Correlation of automated visual field parameters and peripapillary nerve fiber layer thickness as measured by scanning laser polarimetry

PURPOSE

To correlate Humphrey visual field mean sensitivity and peripapillary nerve fiber layer thickness as measured by scanning laser polarimetry.

METHODS

The authors studied 54 eyes of 34 patients who visited a university-based glaucoma clinic and had undergone scanning laser polarimetry and Humphrey perimetry within 6 months. The study population included normal patients and those with glaucoma, ocular hypertension, and glaucoma suspect. The authors correlated visual field sensitivity with peripapillary nerve fiber thickness, and visual field mean deviation with the average deviation from the normal nerve fiber layer thickness. They also correlated the visual field mean deviation with all available GDx Nerve Fiber Analyzer parameters.

RESULTS

The visual field mean sensitivity and deviation showed a bilinear correlation to peripapillary nerve fiber layer thickness. The visual field mean sensitivity changed little when the nerve fiber layer thickness was greater than 70 microm. The nerve fiber layer thickness below this level was associated with a rapid decrease in the visual field sensitivity. Similarly, the visual field mean deviation was close to 0 dB when the nerve fiber layer was within -10 microm of the normal value; below this thickness, the mean deviation became substantially more negative. There was a large individual variability around the bilinear fit. Of the scanning laser polarimetry parameters, a calculated index, referred to as the number, had the highest correlation with the Humphrey mean deviation.

CONCLUSION

The bilinear correlation and its variability between the scanning laser polarimetry and visual field parameters make it difficult to predict the result of one from the other. In general, the correlation between the two is better when there is a significant visual field defect than when the visual field is close to normal.

Axenfeld-Rieger syndrome in the age of molecular genetics

PURPOSE

To review the molecular genetics of Axenfeld-Rieger syndrome and related phenotypes and to discuss how this information might affect the way that we classify these disorders.

METHODS

A review of historical and recent literature on Axenfeld-Rieger syndrome and related disorders. The review includes clinical and molecular genetic literature relevant to these phenotypes.

RESULTS

Three chromosomal loci have recently been demonstrated to link to Axenfeld-Rieger syndrome and related phenotypes. These loci are on chromosomes 4q25, 6p25, and 13q14. The genes at chromosomes 4q25 and 6p25 have been identified as PITX2 and FKHL7, respectively. Mutations in these genes can cause a wide variety of phenotypes that share features with Axenfeld-Rieger syndrome. Axenfeld anomaly, Rieger anomaly, Rieger syndrome, iridogoniodysgenesis anomaly, iridogoniodysgenesis syndrome, iris hypoplasia, and familial glaucoma iridogoniodysplasia all have sufficient genotypic and phenotypic overlap that they should be considered one condition.

CONCLUSIONS

Axenfeld-Rieger syndrome is a term that can be used to describe a variety of overlapping phenotypes. To date, at least three known genetic loci can cause these disorders. The single most important feature of these phenotypes is that they confer a 50% or greater risk of developing glaucoma. Currently there is a fairly arbitrary grouping of disorders into small categories. Considering all of these phenotypes under the heading of Axenfeld-Rieger syndrome will allow easier communication between clinicians and scientists and eliminate arbitrary and confusing subclassification.

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.

Haploinsufficiency of the transcription factors FOXC1 and FOXC2 results in aberrant ocular development

Anterior segment developmental disorders, including Axenfeld-Rieger anomaly (ARA), variably associate with harmfully elevated intraocular pressure (IOP), which causes glaucoma. Clinically observed dysgenesis does not correlate with IOP, however, and the etiology of glaucoma development is not understood. The forkhead transcription factor genes Foxc1 (formerly Mf1 ) and Foxc2 (formerly Mfh1 ) are expressed in the mesenchyme from which the ocular drainage structures derive. Mutations in the human homolog of Foxc1, FKHL7, cause dominant anterior segment defects and glaucoma in various families. We show that Foxc1 (+/-)mice have anterior segment abnormalities similar to those reported in human patients. These abnormalities include small or absent Schlemm's canal, aberrantly developed trabecular meshwork, iris hypoplasia, severely eccentric pupils and displaced Schwalbe's line. The penetrance of clinically obvious abnormalities varies with genetic background. In some affected eyes, collagen bundles were half normal diameter, or collagen and elastic tissue were very sparse. Thus, abnormalities in extracellular matrix synthesis or organization may contribute to development of the ocular phenotypes. Despite the abnormalities in ocular drainage structures in Foxc1 (+/-)mice, IOP was normal in almost all mice analyzed, on all genetic backgrounds and at all ages. Similar abnormalities were found in Foxc2 (+/-)mice, but no disease-associated mutations were identified in the human homolog FKHL14 in 32 ARA patients. Foxc1 (+/-)and Foxc2 (+/-)mice are useful models for studying anterior segment development and its anomalies, and may allow identification of genes that interact with Foxc1 and Foxc2 (or FKHL7 and FKHL14 ) to produce a phenotype with elevated IOP and glaucoma.

Combination of autologous blood injection and bleb compression sutures to treat hypotony maculopathy

PURPOSE

To report successful use of a combination of autologous blood injection and bleb compression sutures to treat overfiltration with hypotony maculopathy after trabeculectomy with mitomycin C.

METHODS

Two patients underwent the combined procedure and were followed until visual acuity and intraocular pressure (IOP) were stable over three consecutive visits (4 to 9 months).

RESULTS

Both patients experienced improvement in visual acuity both subjectively and objectively, and both patients had an elevation in IOP that persisted over three consecutive visits.

CONCLUSIONS

Combination autologous blood injection and bleb compression suture placement may be an effective means of treating hypotony maculopathy after trabeculectomy with mitomycin C.

Myositis associated with a Baerveldt glaucoma implant

PURPOSE

To describe a case of myositis in the presence of a Baerveldt glaucoma implant.

METHOD

Case report.

RESULTS

A 41-year-old black woman developed myositis after placement of a Baerveldt glaucoma implant. Echography demonstrated migration of the seton plate against the medial rectus muscle insertion. Myositis resolved after removal of the Baerveldt glaucoma implant.

CONCLUSION

The Baerveldt glaucoma implant may have precipitated myositis in this patient.

Expression of the Mf1 gene in developing mouse hearts: implication in the development of human congenital heart defects

The transcription factor FKHL7 gene has recently been associated with the anterior segment dysgenesis disorder of the eye known as Axenfeld-Rieger anomaly (ARA). A growing body of evidence indicates that mutations in FKHL7 cause not only defects in the anterior segment of the eye but defects in the heart valves and septa as well. In order to evaluate its contribution to normal heart septation and valve formation, expression of the mouse homologue Mf1 in embryonic hearts was analyzed by in situ hybridization. A weak but significant level of Mf1 expression could be detected in the endocardium of mouse embryos as early as day 8.5 post-conception (p.c.). Mf1 expression was undetectable in the hearts of day 9.5 p.c. embryos, but by day 10.5-11 p.c., Mf1 transcripts could be found again in the endocardium of both the atrium and ventricle and a relatively strong signal was observed in the dorsal portion of the septum primum, in what appeared to be the spinal vestibule. At day 13 p.c. when aortic and pulmonary trunks are separated, relatively more Mf1 transcripts were detected in the leaflets of aortic, pulmonary, and venous valves, the ventral portion of the septum primum, as well as in the single layer of cells on the edges of the atrioventricular cushion tissues. Surprisingly, there was no signal detected in the developing interventricular septum. At day 15 p.c., overall Mf1 signals were greatly decreased. However, significant levels of expression could still be observed in the atrial septum, the tricuspid valve, the mitral valve, and in the venous valve but not in the interventricular septum. The temporal and spatial expression patterns of the Mf1 gene in developing mouse hearts suggest that Mf1 may play a critical role in the formation of valves and septa with the exception of the interventricular septum. This is further supported by our studies showing that mutations in the FKHL7 gene were associated with defects in the anterior segment of the eye as well as atrial septal defects or mitral valve defects. Dev Dyn 1999;216:16-27.

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.

Analysis of myocilin mutations in 1703 glaucoma patients from five different populations

A glaucoma locus, GLC1A, was identified previously on chromosome 1q. A gene within this locus (encoding the protein myocilin) subsequently was shown to harbor mutations in 2-4% of primary open angle glaucoma patients. A total of 1703 patients was screened from five different populations representing three racial groups. There were 1284 patients from primarily Caucasian populations in Iowa (727), Australia (390) and Canada (167). A group of 312 African American patients was from New York City and 107 Asian patients from Japan. Overall, 61 different myocilin sequence variations were identified. Of the 61 variations, 21 were judged to be probable disease-causing mutations. The number of probands found to harbor such mutations in each population was: Iowa 31/727 (4.3%), African Americans from New York City 8/312 (2.6%), Japan 3/107 (2.8%), Canada 5/167 (3.0%), Australia 11/390 (2.8%) and overall 58/1703 (3. 4%). Overall, 16 (76%) of 21 mutations were found in only one population. The most common mutation observed, Gln368Stop, was found in 27/1703 (1.6%) glaucoma probands and was found at least once in all groups except the Japanese. Studies of genetic markers flanking the myocilin gene suggest that most cases of the Gln368Stop mutations are descended from a common founder. Although the specific mutations found in each of the five populations were different, the overall frequency of myocilin mutations was similar ( approximately 2-4%) in all populations, suggesting that the increased rate of glaucoma in African Americans is not due to a higher prevalence of myocilin mutations.

Control of intraocular pressure after trabeculectomy

Control of intraocular pressure (IOP) is the goal of trabeculectomy, and pursuit of this goal does not end with the completion of the surgical procedure. Proper postoperative management of the trabeculectomy patient requires an understanding of possible events that alter IOP and knowledge of the treatments to control IOP. Recent changes in surgical technique, including the use of antimetabolites, have provided new challenges in the postoperative management of trabeculectomy patients. Interventions are described to restore the flow of aqueous to the filtering bleb in the early postoperative period, to manage flat anterior chambers with both high and low intraocular pressures, to manage a failing filtering bleb, and to manage hypotony. Herein we discuss current methods for controlling IOP in the postoperative period.

The forkhead transcription factor gene FKHL7 is responsible for glaucoma phenotypes which map to 6p25

A number of different eye disorders with the presence of early-onset glaucoma as a component of the phenotype have been mapped to human chromosome 6p25. These disorders have been postulated to be either allelic to each other or associated with a cluster of tightly linked genes. We have identified two primary congenital glaucoma (PCG) patients with chromosomal anomalies involving 6p25. In order to identify a gene involved in PCG, the chromosomal breakpoints in a patient with a balanced translocation between 6p25 and 13q22 were cloned. Cloning of the 6p25 breakpoint led to the identification of two candidate genes based on proximity to the breakpoint. One of these, FKHL7, encoding a forkhead transcription factor, is in close proximity to the breakpoint in the balanced translocation patient and is deleted in a second PCG patient with partial 6p monosomy. Furthermore, FKHL7 was found to harbour mutations in patients diagnosed with Rieger anomaly (RA), Axenfeld anomaly (AA) and iris hypoplasia (IH). This study demonstrates that mutations in FKHL7 cause a spectrum of glaucoma phenotypes.

A novel homeobox gene PITX3 is mutated in families with autosomal-dominant cataracts and ASMD

We report here the identification of a new human homeobox gene, PITX3, and its involvement in anterior segment mesenchymal dysgenesis (ASMD) and congenital cataracts in humans. The PITX3 gene is the human homologue of the mouse Pitx3 gene and is a member of the RIEG/PITX homeobox gene family. The protein encoded by PITX3 shows 99% amino-acid identity to the mouse protein, with 100% identity in the homeodomain and approximately 70% overall identity to other members of this family. We mapped the human PITX3 gene to 10q25 using a radiation-hybrid panel. A collection of 80 DNA samples from individuals with various eye anomalies was screened for mutations in the PITX3 gene. We identified two mutations in independent patients. A 17-bp insertion in the 3'-end of the coding sequence, resulting in a frame shift, occurred in a patient with ASMD and cataracts, and a G-->A substitution, changing a codon for serine into a codon for asparagine, in the 5'-end of the gene occurred in a patient with congenital cataracts. Both mutations cosegregate with the disease phenotype in families, and neither were found in up to 300 control individuals studied. Further expression analysis of Pitx3 in the mouse supports a unique role in early ocular development, with later expression extending to the midbrain, tongue, incisors, sternum, vertebrae and limbs. These data strongly suggest a role for PITX3 in ASMD and cataracts and provide new evidence of the contribution of the RIEG/PITX gene family to the developmental program underpinning normal eye formation.

Clinical features associated with mutations in the chromosome 1 open-angle glaucoma gene (GLC1A)

BACKGROUND

A substantial proportion of cases of glaucoma have a genetic basis. Mutations causing glaucoma have been identified in the chromosome 1 open-angle glaucoma gene (GLC1A), which encodes a 57-kd protein known as myocilin. The normal role of this protein and the mechanism by which mutations cause glaucoma are not known.

METHODS

We screened 716 patients with primary open-angle glaucoma and 596 control subjects for sequence changes in the GLC1A gene.

RESULTS

We identified 16 sequence variations that met the criteria for a probable disease-causing mutation because they altered the predicted amino acid sequence and they were found in one or more patients with glaucoma, in less than 1 percent of the control subjects. These 16 mutations were found in 33 patients (4.6 percent). Six of the mutations were found in more than 1 subject (total, 99). Clinical features associated with these six mutations included an age at diagnosis ranging from 8 to 77 years and maximal recorded intraocular pressures ranging from 12 to 77 mm Hg.

CONCLUSIONS

A variety of mutations in the GLC1A gene are associated with glaucoma. The spectrum of disease can range from juvenile glaucoma to typical late-onset primary open-angle glaucoma.

Characterization and comparison of the human and mouse GLC1A glaucoma genes

The GLC1A gene (which encodes the protein myocilin) has been associated with the development of primary open angle glaucoma. Bacterial artificial chromosomes containing the human GLC1A gene and its mouse ortholog were subcloned and sequenced to reveal the genomic structure of the genes. Comparison of the coding sequences of the human and mouse GLC1A genes revealed a high degree of amino acid homology (82%) and the presence of several conserved motifs in the predicted GLC1A proteins. The expression of GLC1A was examined by Northern blot analysis of RNA from adult human tissues. GLC1A expression was observed in 17 of 23 tissues tested, suggesting a wider range of expression than was recognized previously. The comparison of the human and mouse GLC1A genes suggests that the mouse may be a useful model organism in studying the molecular pathophysiology of glaucoma.