Multiple CYP1B1 mutations and incomplete penetrance in an inbred population segregating primary congenital glaucoma suggest frequent de novo events and a dominant modifier locus.

Primary congenital glaucoma (PCG) is an autosomal recessive disorder associated with unknown developmental defect(s) in the anterior chamber. Recently, we reported three distinct mutations in CYP1B1, the gene for cytochrome P4501B1, in 25 Saudi families segregating PCG. For this report, we analyzed 37 additional families and confirmed the initial finding of decreased penetrance. Mutations and intragenic single-nucleotide polymorphisms (SNPs) were also analyzed from direct sequencing of all CYP1B1 coding exons. Eight distinct mutations were identified: G61E, R469W and D374N, the most common Saudi mutations, account for 72, 12 and 7%, respectively, of all the PCG chromosomes. Five additional homozygous mutations (two deletions and three missense mutations) were detected, each in a single family. Affected individuals from five families had no CYP1B1 coding mutations, and each family had a unique SNP profile. The identification of eight distinct mutations in a single gene, on four distinct haplotypes, suggests a relatively recent occurrence of multiple mutations in CYP1B1 in Saudi Arabia. These data demonstrate decreased penetrance of the PCG phenotype in the Saudi population, because 40 apparently unaffected individuals in 22 families have mutations and haplotypes identical to their affected siblings. Two individuals were subsequently diagnosed with glaucoma and two others had abnormal ocular findings that are consistent with milder forms of glaucoma. Analysis of these 22 kindreds suggests the presence of a dominant modifier locus that is not linked genetically to CYP1B1. Linkage and Southern analyses excluded three candidate modifier loci.

Mutations in CYP1B1, the gene for cytochrome P4501B1, are the predominant cause of primary congenital glaucoma in Saudi Arabia.

The autosomal recessive disorder primary congenital glaucoma (PCG) is caused by unknown developmental defect(s) of the trabecular meshwork and anterior chamber angle of the eye. Homozygosity mapping with a DNA pooling strategy in three large consanguineous Saudi PCG families identified the GLC3A locus on chromosome 2p21 in a region tightly linked to PCG in another population. Formal linkage analysis in 25 Saudi PCG families confirmed both significant linkage to polymorphic markers in this region and incomplete penetrance, but it showed no evidence of genetic heterogeneity. For these 25 families, the maximum combined two-point LOD score was 15.76 at a recombination fraction of .021, with the polymorphic marker D2S177. Both haplotype analysis and homozygosity mapping in these families localized GLC3A to a 5-cM critical interval delineated by markers D2S2186 and D2S1356. Sequence analysis of the coding exons for cytochrome P4501B1 (CYP1B1) in these 25 families revealed three distinctive mutations that segregate with the phenotype in 24 families. Additional clinical and molecular data on some mildly affected relatives showed variable expressivity of PCG in this population. These results should stimulate a study of the genetic and environmental events that modify the effects of CYP1B1 mutations in ocular development. Furthermore, the small number of PCG mutations identified in this Saudi population makes both neonatal and population screening attractive public health measures.

A gene for primary congenital glaucoma is not linked to the locus on chromosome 1q for autosomal dominant juvenile-onset open angle glaucoma.

BACKGROUND: Primary congenital glaucoma is an uncommon autosomal recessive condition that results from a developmental defect in the trabecular meshwork and anterior chamber angle, manifesting in the neonatal or infantile period with increased intraocular pressure, corneal enlargement and edema, and optic nerve cupping with consequent loss of vision. Nothing is known about its genetic location. PATIENTS AND METHODS: Linkage analysis was performed in 25 primary congenital glaucoma Saudi Arabian families with six polymorphic DNA markers on chromosome 1q in a region that has shown tight linkage to a locus for autosomal dominant juvenile-onset open angle glaucoma (GLC1A). Twenty-four of these families are highly consanguineous. RESULTS: Each family was shown separately to exclude the 8-centimorgan (cM) interval containing the GLC1A locus. Four families independently demonstrated overlapping regions of exclusion (theta < or = -2) that spanned the entire 8-cM interval. Assignment of a primary congenital glaucoma locus in this region could be excluded by a cadre of 21 families because a primary congenital glaucoma disease locus did not segregate in an autosomal recessive manner on haplotypes constructed with markers in this region. For all families, no affected individuals demonstrated homozygosity of alleles in regions tightly linked to the GLC1A locus. CONCLUSION: These results exclude the 8-cM region on chromosome 1q shown to contain the GLC1A locus from containing a disease locus for primary congenital glaucoma in this population of 25 Saudi Arabian families.

Argon laser trabeculoplasty and pilocarpine effects on outflow facility in the cynomolgus monkey.

PURPOSE: We sought to determine whether and how prior argon laser trabeculoplasty (ALT) alters outflow facility, the pilocarpine-induced facility increase, and the morphology of the trabecular meshwork in cynomolgus monkeys. METHODS: Eleven cynomolgus monkeys underwent unilateral 360 degrees argon laser trabeculoplasty, eight in two 180 degrees sessions (seven 3 months apart, one 11 days apart) and three in a single session. Intraocular pressure (IOP, Golmann ap-planation tonometry), aqueous humor flow rate (AHFR, fluorophotometry), total outflow facility (two-level constant pressure perfusion) and response to intracameral pilocarpine, and morphology (light and scanning/transmission electron microscopy) were determined at various times. RESULTS: Resting total perfusion outflow facility 3 and 6 months after 360 degrees ALT was 30% higher in ALT-treated than in contralateral untreated eyes. There were no consistent or statistically significant differences between ALT-treated and contralateral untreated eyes in (a) IOP or AHFR before ALT, 5 weeks after initial 180 ALT, or 5 weeks after the second 180 ALT; (b) post-intracameral pilocarpine facility, or the dose-dependent facility response to pilocarpine 10 weeks after the initial 180 ALT or 3 and 6 months after the second 180 ALT; or (c) light or electron microscopic appearance of the trabecular meshwork or inner wall of Schlemm's canal 3-17 months after 360 ALT. CONCLUSIONS: This study indicates that (a) ALT alters the biomechanical properties of the monkey trabecular meshwork so as to modestly increase its hydraulic conductivity without affecting the facility response to pilocarpine-induced ciliary muscle contraction; and (b) young healthy monkey outflow tissues exhibit remarkable reparative and homeostatic capabilities.

Muscarinic cholinoceptors in native and cultured human corneal endothelium.

Specific and high affinity binding of the potent muscarinic cholinergic antagonist, [3H]quinuclidinylbenzilate ([3H]QNB) was observed using intact native and cultured adult human corneal endothelium (HCE). Specific binding was proportional to radioligand concentration between 0.03 and 5 nM, indicating a maximal binding capacity (Bmax) of 130 fmol of [3H]QNB/mg protein and a dissociation constant (Kd) of 0.3 nM. Atropine competed effectively with [3H]QNB for binding sites; requiring 3 nM to inhibit 50% of the binding of 1 nM [3H]QNB. Carbachol also competed with [3H]QNB at higher concentrations, but nicotine did not affect [3H]QNB binding at levels up to 1 nM. [3H]QNB binding was also observed in cultured cells of adult human, rabbit, and bovine corneal endothelium. Native and cultured HCE were affinity labelled using tritium-labelled propylbenzilylcholine mustard (PBCM). Separation of the proteins in affinity labelled native and cultured tissue by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) showed that only one protein in each preparation, of 60 and 55 kilodaltons (kDa), respectively, was specifically radiolabelled. These data indicate that the corneal endothelium of human and several animal species exhibit muscarinic cholinoceptors.

Stimulation of cell division by argon and Nd:YAG laser trabeculoplasty in cynomolgus monkeys.

Although laser treatment of the trabecular meshwork is the most common form of surgery for glaucoma, the tissue response to this therapy is still incompletely understood. We applied argon or Nd:YAG laser to the trabecular meshwork of six monkeys. Cell division was identified by injecting tritiated thymidine into the anterior chamber 24 hr after laser application. Autoradiography of tissue sections revealed significantly more labelled cells in eyes treated with laser than in the untreated controls. In addition, cells in neighboring tissues such as iris, ciliary body and sclera showed labelling in association with laser application. Furthermore, comparison of argon-induced lesions with those caused by pulsed Nd:YAG suggests that there are quantitative and qualitative differences in the response of trabecular meshwork and surrounding tissues to these two forms of laser energy.

Histopathology of triamcinolone in the subconjunctiva.

Triamcinolone acetonide (TA) was injected subconjunctivally in nine human eyes one week before trabeculectomy. A biopsy specimen of conjunctiva and subconjunctiva was obtained from the site of drug injection, as well as a site 6 mm from the injection at the time of trabeculectomy. The tissue was evaluated by electron microscopy. TA was similarly injected subconjunctivally in ten normal rabbit eyes. For control purposes, six eyes were injected with the vehicle. Five animals were euthanized at one and two weeks post-injection and subconjunctival biopsy specimens from the drug site, at the margin of the drug site, and 180 degrees away from the drug site were subsequently examined by light and electron microscopy. At the drug site in both humans and rabbits, the subconjunctival fibroblasts were necrotic, the collagen fibers were altered in appearance, and there was infiltration of macrophages. The control site was unremarkable. These local morphologic changes may explain, in part, the mechanism(s) of action of injected TA.

The effect of preoperative subconjunctival triamcinolone administration on glaucoma filtration. I. Trabeculectomy following subconjunctival triamcinolone.

Trabeculectomies were performed on 15 eyes because of uncontrolled glaucoma despite the maximum use of tolerated antiglaucoma medication. We considered all of these eyes to be at increased risk for episcleral cicatricial closure for one of the following reasons: neonatal glaucoma, a patient of age 40 years or less, previously failed glaucoma filtration surgery, or aphakia. A standard operation was performed except that triamcinolone acetonide (4 mg) was injected subconjunctivally at the intended trabeculectomy site one week before surgery in 12 eyes, the day of surgery in two eyes, and two days prior to surgery in one eye. During the follow-up period of six to 16 months, 14 of 15 eyes had an intraocular pressure (IOP) of 18 mm Hg or less. The average IOP for these 14 eyes was 12.4 +/- 4.6 (mean +/- 1 SD), and only three of the 14 required any antiglaucoma medication. One eye was a surgical failure. All eyes with controlled IOP had diffuse microcystic filtration blebs by slitlamp examination. The postoperative visual acuity was within one line of the preoperative level in all eyes, except for the one failure. The use of triamcinolone did not appear to add any additional risks to the surgical procedure or to the postoperative period.

Can macrophages cause obstruction to aqueous outflow in rabbits?

We describe a technique by which large numbers of peritoneal macrophages can be harvested without harming the experimental animal. The macrophages can be reintroduced into the same animal avoiding possible immune reactions associated with injection of foreign cells or other antigenic materials. In an attempt to obstruct aqueous outflow rabbit peritoneal macrophages engorged with mineral oil were injected intracamerally in the same rabbit's eye. The number of cells per single injection varied from 4.0 X 10(4) to 1.4 X 10(6) in eight rabbits. In three animals daily injections of 1 X 10(6) cells were performed. Using the Perkins applanation tonometer daily and hourly, no pressure elevation could be detected.

Metastatic carcinoma of the iris simulating iridocyclitis.

A 46-year-old woman with a history of breast carcinoma and no known metastatic disease presented with iridocyclitis and secondary glaucoma. Intraocular inflammation and pressure elevation persisted despite standard medical therapy, and paracentesis was performed. Cytological examination of the aspirate revealed adenocarcinoma. Subsequent studies disclosed no evidence of extraocular metastasis. Two courses of radiation therapy to the involved eye resulted in a dramatic reduction in intraocular inflammation and allowed temporary control of the intraocular pressure. Ultimately, however, progressive glaucoma necessitated enucleation. This case confirms previous statements that iridocyclitis may be the initial clinical manifestation of metastatic malignancy. In addition, this report emphasises the importance of paracentesis in the diagnostic evaluation of selected cases of anterior uveitis of unknown aetiology.

Congenital glaucoma unresponsive to conventional therapy: a clinicopathological case presentation.

A clinicopathological case report of a black male with congenital glaucoma is presented. The child died at age three months of the Sudden Infant Death Syndrome. The clinical course was characterized by persistent corneal clouding and elevated intraocular pressure in spite of vigorous medical and surgical therapy. Histopathological findings included corneal enlargement, marked hypoplasia of the canal of Schlemm, poorly developed scleral spur, insertion of the ciliary musculature directly into the trabecular meshwork anterior to the scleral spur, and anterior displacement of the iris root. There was also anomalous dispersion of the sphincter muscle of the iris from the pupillary margin almost to the iris root, and attachment of some ciliary processes to the posterior surface of the iris. A poor clinical response to conventional glaucoma therapy, including trabeculotomy, goniotomy, trabeculectomy and medical therapy, supports the belief that the marked hypoplasia of Schlemm's canal was a major factor contributing to the elevated intraocular pressure. Furthermore, the multiplicity of abnormalities of anterior chamber angle structures suggests that some cases of congenital glaucoma may result from an early and extensive disorder in the formation of anterior segment tissues.

Risk factors for rate of progression of glaucomatous visual field loss: a computer-based analysis.

Factors affecting the progression of visual field loss were examined in 57 patients with bilateral open angle glaucoma. patients who already had marked visual field loss experienced further field loss at a greatly accelerated rate. Family history of glaucoma, sex, and initial registration intraocular pressure were also important prognostic factors for progressive visual field loss, whereas age and systemic blood pressure were not found to affect rate of visual field loss. Follow-up data from these patients were drawn from a computer-based clinic record system that may serve as a prototype for the collection of information on the natural history of ophthalmic diseases.

The role of gonio-photocoagulation in neovascularization of the anterior chamber angle.

Gonio-photocoagulation is a name applied to direct laser therapy to neovascular vessels in the anterior chamber angle in progressive anterior segment neovascularization. The technique is useful not in altering the stimulus to anterior segment neovascularization, but in immediately altering the product of the stimulus, the new vessels in the angle. The goal is to halt immediately progression toward angle closure and severe neovascular glaucoma. A recommended protocol is presented for incorporation of this technique into a prophylactic regimen for neovascular glaucoma in conjunction with retinal therapy to alter the stimulus.

SEM of the ciliary processes after paracentesis.

Corneal perforation and withdrawal of aqueous humor (paracentesis) represents a practical means for producing controlled trauma to the eye. The sequence of events triggered by paracentesis has been carefully studied by in vivo and in vitro microscopy and other means. These observations have proven especially helpful in elucidating the physiology and pharmacology of ocular trauma. Scanning electron microscopy of the ciliary processes of the rabbit has proven a sensitive indicator of the response to prostaglandin, a mediator of the paracentesis reaction. We used SEM to invetigate changes in the ciliary processes induced by paracentesis. We also examined the opposite eye for a consensual response. The effect of prior treatment with aspirin or nerve block was assessed in both the traumatized eye and the fellow eye. In an untreated animal, a consensual response to trauma was present and demonstrable by scanning electron microscopy. The direct response was more effectively blocked by aspirin than by local anesthesia. Both pretreatments were effective in reducing the consensual reaction.

Scanning electron microscopy of trabeculectomy specimens in open-angle glaucoma.

We examined trabeculectomy specimens obtained at the time of surgery for inadequately controlled open-angle glaucoma by scanning electron microscopy. Of the 50 specimens ten included a broad area of the trabecular meshwork. In these ten specimens the meshwork was obscured by material. We believe the degree of occlusion was significant in these specimens, which would lead to obstruction of aqueous outflow. No similar material was found in control specimens from persons of similar age.

Effects of panretinal photocoagulation on rubeosis iridis, angle neovascularization, and neovascular glaucoma.

Ninety-three patients received ruby laser panretinal photocoagulation in one eye for diabetic retinopathy and we examined them at an average time of 7.1 years later. In 14 patients, the untreated eye developed rubeosis iridis and the contralateral treated eye did not. In seven patients, the untreated eye developed angle neovascularization and the contralateral eye did not. The untreated eye developed neovascular glaucoma and the contralateral treated eye did not in four patients. Our findings suggest that eyes with proliferative retinopathy that received panretinal photocoagulation are less likely to develop rubeosis iridis, angle neovascularization, and probably neovascular glaucoma, than those eyes not receiving panretinal photocoagulation.

Goniophotocoagulation for neovascular glaucoma.

A new treatment, goniophotocoagulation, for neovascularization of the anterior chamber angle has been applied with the argon laser to 21 eyes of 20 patients. Three of the eyes had neovascularization related to central retinal vein occlusion. In the other 18 eyes the neovascularization was related to diabetic retinopathy. A specific protocol has been followed since January 1973. The results so far indicate that closure of the angle and progression of the usual chain of pathologic events in neovascular glaucoma were prevented in 10 (77%) of the 13 eyes having an average follow-up of 22 months. We believe that goniophotocoagulation of the angle deserves more extensive, judicious, and carefully monitored clinical use. Our results suggest that this new technique is safe and reasonably effective in preventing progressive neovascularization of the angle, synechial closure, and severe nonvascular glaucoma.