Chromosomal abnormalities and glaucoma: a case of congenital glaucoma with trisomy 8q22-qter/ monosomy 9p23-pter

PURPOSE: To present a case of congenital glaucoma with an unbalanced translocation trisomy 8q22-qter/monosomy 9p23-pter, resulting in trisomy of the GLC1D locus. To perform a literature review of chromosomal abnormalities associated with glaucoma. METHOD: A case report of a family with balanced translocation without glaucoma and unbalanced translocation with congenital glaucoma. PubMed and OMIM databases were searched for reports of chromosomal abnormalities and glaucoma. RESULTS: Other case reports of congenital glaucoma with chromosomal abnormalities in this region were identified. A review of cytogenetics in southeastern Australia found nine cases involving the loss of 9p23 and 10 cases involving mosaicism for trisomy 8, but none had congenital glaucoma. A review of the literature identified reports of glaucoma and chromosomal abnormalities in regions with glaucoma loci mapped by conventional linkage analysis. These include the loci GLC1B, GLC1C, GLC1D, GLC1F, GPDS1, and RIEG2. CONCLUSION: The study of patients with glaucoma and chromosomal abnormalities may help to identify new glaucoma genes. Ophthalmologists can assist with this by requesting cytogenetic studies on congenital and developmental glaucoma cases and interacting with ophthalmic genetics researchers.     

Genetic studies on primary open angle glaucoma

Case work presents the newest studies on molecular genetics in primary open angle glaucoma. The molecular genetics in all types of glaucoma have been a subject of investigations for the last few years. As a result, two loci (GLC3A and GLC3B) have been identified for primary congenital glaucoma, one locus (GLC1A) for juvenile primary open angle glaucoma and further two loci (GLC1B and GLC1C) for adult-onset primary open angle glaucoma. The gene TIGR (trabecular meshwork inducible glucocorticoid response protein) localised in GLC1A was described last year for the first time, thereafter there were trials on mutations within this gene conducted successfully. In this review there are studies presenting the mapping of the first five GLC loci and identification of mutations.     

Glaucoma genetics: where are we? Where will we go?

The understanding of the genetic basis of the glaucomas has advanced rapidly. Mutations in the myocilin gene (previously known as TIGR) at the GLC1A locus on chromosome 1q21-q31 occur in a subset of patients with juvenile- and adult-onset primary open-angle glaucoma. Five other genetic localizations for primary open-angle glaucoma have now been reported. In patients with primary congenital glaucoma, mutations have been found in the CYP1B1 gene on chromosome 2p21. At least one other locus for primary congenital glaucoma is mapped. In the developmental glaucomas, mutations in the PITX2 gene on chromosome 4q25 have been associated with Rieger syndrome, iris hypoplasia, and iridogoniodysgenesis. A second locus for Rieger syndrome resides on chromosome 13q14. Mutations in the FKHL7 gene on chromosome 6p25 have been described in patients with Axenfeld-Rieger anomaly. A new ocular finding of glaucoma in pedigrees with the nailpatella syndrome has been described, and mutations in the LMX1B gene on chromosome 9q34 are now known to underlie nail-patella syndrome. Two loci for the pigment dispersion syndrome have been mapped. This paper provides an overview of recent literature, summarizes developments in glaucoma genetics, and addresses their potential relevance to the clinical management of glaucoma.     

Genetic ground of primary open angle glaucoma

Among basic risk factors for primary open-angle glaucoma (POAG), the leading place takes positive family history. It is generally accepted that this type of glaucoma presents multifactored determination, however pedigrees that follow autosomal dominant way of inheritance are also described. Genetic studies made by linkage analysis enabled to map six loci, linked to development of primary open-angle glaucoma: GLC1A - in 1q21-q31 region, GLC1B - in 2cen-q13 region, GLC1C- in 3q14-q24 region, GLC1D - in 8q23 region, GLC1E- in 10p15-p14 region and GLC1F - in 7q35-q36 region. During last years, in GLC1A locus the TIGR gene that codes for myocilin was cloned and in GLC1E locus the OPTN gene that codes for optineurin was cloned. It was also proved that their mutations are responsible for development of several forms of POAG. Simultaneously it was shown that there are some additional modifier genes, such as CYP1B1 gene, mapped in 2p22-p21 region and coding one of the cytochrome P450 polypeptide, what indicates a possibility of digenic inheritance of POAG.     

湖北地区汉族原发性先天性青光眼患儿CYP1B1基因突变分析

目的研究湖北地区汉族原发性先天性青光眼(primary congenital glaucoma,PCG)患儿CYP1B1基因的突变情况。方法用苯酚-氯仿法从38例原发性先天性青光眼患儿的全血细胞中提取基因组DNA。然后通过聚合酶链反应-单链构象多态性(single-strand conformation polymorphism,PCR-SSCP)银染色法检测CYP1B1基因第2、3外显子的突变情况。结果5例PCG患儿检出CYP1B1基因第3外显子异常DNA片段条带,经测序分析证实为7990C→T,未发现第2外显子存在基因突变。结论CYP1B1基因具有明显的遗传异质性。应用PCR-SSCP技术可初步筛查原发性先天性青光眼患儿CYP1B1基因突变。     

Primary congenital glaucoma: a novel single-nucleotide deletion and varying phenotypic expression for the 1,546-1,555dup mutation in the GLC3A (CYP1B1) gene in 2 families of different ethnic origin

PURPOSE: To present new molecular genetic data on primary congenital glaucoma from 2 families, 1 isolated case and 3 familial cases due to mutations in the cytochrome P-450 1B1 (CYP1B1) gene. METHODS: All diagnoses were made by slit-lamp biomicroscopy, gonioscopy, cornea and optic disk measurements, ultrasound-biometry, and automated static threshold perimetry where possible. Mutation screening was performed by direct sequence analysis of DNA extracted from peripheral blood of the patients and their relatives. RESULTS: For the isolated case, a child of 4 years, a homozygous nucleotide deletion within a tetrad of cytosines (nt622-625, 622delC) was found leading to a predicted nonsense codon 93 truncating the protein by 450 amino acids. For the familial cases, the 3 affected members showed a homozygous mutation 1,546-1,555dupTCATGCCACC for which 9 healthy relatives proved to be heterozygous. The phenotypic expression of these 3 patients varied widely. CONCLUSION: Our results confirm the crucial role of CYP1B1 mutations for congenital glaucoma.     

Confirmation of the adult-onset primary open angle glaucoma locus GLC1B at 2cen-q13 in an Australian family

Primary open-angle glaucoma (POAG) is genetically heterogeneous, with 6 named POAG loci GLC1A-F mapped and genes myocilin (MYOC) and optineurin (OPTN) identified at 2 of the loci. Using penetrance-model-free methods, we screened the POAG loci GLC1A-F in an extended Australian pedigree, using 3-5 markers within each locus. p values of less than 0.05 were obtained empirically using SimWalk2 and exactly using Genehunter for 2 markers within the GLC1B region on chromosome 2. Fine mapping of this region produced p values of 0.01 or less at 5 markers flanked by D2S1897 and D2S2269. The 9 cM haplotype of interest overlaps the original GLC1B region. These results provide supportive evidence for the GLC1B locus on chromosome 2cen-q13 and verify the existence of POAG susceptibility gene in this region, increasing the likelihood of gene identification.     

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, approximately 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.     

Cytochrome P4501B1 mutations cause only part of primary congenital glaucoma in Ecuador

Purpose: To determine the role of cytochrome P4501B1 ( CYP1B1 ) mutations in causing primary congenital glaucoma (PCG) in a cohort of Native Americans from Quito, Ecuador. Materials and methods: Seventeen patients with PCG from 15 Native American families were recruited from the Ophthalmology Clinic at Hospital Metropolitano, Quito, Ecuador. Experienced ophthalmologists examined all affected study subjects. Purified DNA was prepared from peripheral blood samples and CYP1B1 coding exons (exons 2 and 3) were amplified and sequenced. Southern blot was performed only on those affected patients who showed no mutations in the CYP1B1 coding exons. Results: The molecular basis of PCG in two families was determined: two novel mutations (a deletion and a point mutation) and one novel polymorphism in CYP1B1 were identified in addition to a previously described single amino acid substitution. Southern blot analyses on whole genomic DNA from affected individuals in whom no mutations were identified by the direct PCR/sequencing approach did not detect any large rearrangements or mutations outside the coding region. Conclusion: These findings suggest that mutations in CYP1B1 are not a major cause of PCG in this population and that at least one additional locus for this condition is responsible for most cases. Further, the PCG phenotype did not correlate readily with the molecular basis of the disorder, suggesting that careful clinical analysis of the phenotype cannot predict the molecular basis of the disease with accuracy.     

CYP1B1基因突变与原发性开角型青光眼发病关系的研究进展

原发性青光眼包括原发性开角型青光眼（POAG）、原发性闭角型青光眼（PACG）及原发性婴幼儿青光眼（PCG）.目前认为原发性青光眼的发病是遗传因素、环境因素、生活习惯等多种因素综合作用的结果,其中遗传因素,尤其是基因突变,在青光眼的发病过程中起着重要作用.自1997年发现CYP1B1基因为PCG的致病基因以来,关于CYP1B1基因突变与青光眼发病关系的研究成为青光眼遗传和基因研究的热点.随着研究的逐渐深入,许多学者认为CYP1B1基因也是POAG致病基因的候选基因.本研究对近十余年来对CYP1 B1基因的结构和功能以及CYP1B1基因突变与POAG发病及进展关系的研究进展进行总结.     

Glaucoma-associated CYP1B1 mutations share similar haplotype backgrounds in POAG and PACG phenotypes

PURPOSE: To understand the involvement of the CYP1B1 gene in cases of primary open-angle (POAG) and primary angle-closure (PACG) glaucomas and obtain the haplotype background of these mutations. METHODS: The entire coding region of CYP1B1 was screened by resequencing in 224 unrelated cases of POAG (n = 134) and PACG (n = 90) and 200 ethnically matched normal control subjects from Indian populations. Six intragenic single nucleotide polymorphisms (SNPs) in CYP1B1 (-13T>C, R48G, A119S, V432L, D449D, and N453S) were used to generate haplotype data for the cases and controls and linkage disequilibrium (LD) and haplotype analysis were performed with Haploview software, which uses the EM (expectation-maximization) algorithm. RESULTS: The frequency of CYP1B1 mutations was higher among POAG (18.6%; 95% CI, 12.9-26.1) than PACG (11.1%; 95% CI, 6.1-19.3) cases. There was a marked allelic heterogeneity, and the Arg368His was the most prevalent mutation across both the phenotypes. The spectrum of CYP1B1 mutations was largely similar across different POAG populations. Haplotypes generated with intragenic SNPs indicated the C-C-G-G-T-A to be a risk haplotype associated with CYP1B1 mutations in POAG (P = 0.006) and PACG (P = 0.043), similar to that observed in cases of primary congenital glaucoma worldwide. CONCLUSIONS: The results demonstrate an involvement of CYP1B1 in a proportion of POAG and PACG cases that should be explored further. The similar haplotype background of these mutations is indicative of their common origin across multiple glaucoma phenotypes.     

Cytochrome P4501B1 mutations cause only part of primary congenital glaucoma in Ecuador

PURPOSE: To determine the role of cytochrome P450IBI (CYP1B1) mutations in causing primary congenital glaucoma (PCG) in a cohort of Native Americans from Quito, Ecuador. MATERIALS AND METHODS: Seventeen patients with PCG from 15 Native American families were recruited from the Ophthalmology Clinic at Hospital Metropolitano, Quito, Ecuador. Experienced ophthalmologists examined all affected study subjects. Purified DNA was prepared from peripheral blood samples and CYP1B1 coding exons (exons 2 and 3) were amplified and sequenced. Southern blot was performed only on those affected patients who showed no mutations in the CYP1B1 coding exons. RESULTS: The molecular basis of PCG in two families was determined: two novel mutations (a deletion and a point mutation) and one novel polymorphism in CYP1B1 were identified in addition to a previously described single amino acid substitution. Southern blot analyses on whole genomic DNA from affected individuals in whom no mutations were identified by the direct PCR/sequencing approach did not detect any large rearrangements or mutations outside the coding region. CONCLUSION: These findings suggest that mutations in CYPIBI are not a major cause of PCG in this population and that at least one additional locus for this condition is responsible for most cases. Further, the PCG phenotype did not correlate readily with the molecular basis of the disorder, suggesting that careful clinical analysis of the phenotype cannot predict the molecular basis of the disease with accuracy.     

Molecular genetics of open-angle glaucoma, moving from gene localization to predictive testing

It has long been suspected that genetic factors play a role in open-angle glaucoma. Only recently, however, has the molecular basis of such factors begun to be established, with the primary localization of the GLC1A locus for juvenile-onset and early-onset autosomal dominant open-angle glaucoma on chromosome 1q. These findings are clinically significant in that they allow familial screening of individuals at risk for glaucoma before the onset of irreversible visual impairment. A physical map of the GLC1A genomic region is now available, and the actual GLC1A gene might be identified in the near future. Nevertheless, open-angle glaucoma is a genetically heterogeneous entity, and additional loci have been mapped or proposed. Identification of open-angle glaucoma genes should provide invaluable clues to the disorder's pathophysiology. It could also aid in conceiving novel therapeutic agents and broadening the screening of at-risk subjects.     

LTBP2 gene analysis in the GLC3C-linked family and 94 CYP1B1-negative cases with primary congenital glaucoma

Purpose: Primary congenital glaucoma (isolated trabeculodysgensis, PCG) generally presents between birth and 3 years of age. Recently, mutations in Latent Transforming Growth Factor (TGF)-beta Binding Protein 2 (LTBP2) have been reported in several families that were diagnosed with PCG, who actually had a more complex ocular phenotype with ectopia lentis and Marfanoid features. We screened this gene for mutations in the original Turkish GLC3C-linked PCG family and in a group of CYP1B1-negative British PCG cases and their matched normal control subjects.

Methods: The 36-coding exons of the LTBP2 gene were sequenced in 94 familial or sporadic CYP1B1-negative PCG cases and 96 matched normal control subjects.

Results: No disease-causing mutations were identified in the original GLC3C-linked family. Screening of LTBP2 in 94 PCG and 96 control subjects identified three novel synonymous variations (L429L, P680P, S1031S) in 12 PCG and seven control subjects. A novel heterozygous missense mutation (R538W) was also identified in 1 of 90 PCG cases that is unlikely to be disease-causative.

Conclusions: LTBP2 mutations were not found in the Turkish GLC3C-linked PCG family or in 94 British CYP1B1-negative PCG cases. Our data suggest that LTBP2 mutations are not a significant cause for isolated trabeculodysgenesis.     

CYP1B1基因缺失小鼠在高糖皮质激素环境下对青光眼的易感性

目的观察高浓度糖皮质激素对CYP1B1^-/-小鼠青光眼易感性的影响。方法采用成年CYP1B1^-/-小鼠作为实验模型,以同龄C57BL／6J小鼠作为对照。每3天结膜下注射0．04mL倍他米松,用Tonopen眼压（IOP）笔每周定期测定小鼠IOP,于第一次给药前,给药后4、8、12周分别摘除眼球,制备石蜡切片,光学显微镜下观察小鼠视网膜形态和厚度,采用TUNEL法检测视网膜神经节细胞（RGCs）的凋亡。结果与给药前相比,2组小鼠给药后4、8、12周的IOP均较前升高,差异有统计学意义（P〈0．05）;CYP1B1^-/-小鼠的IOP在给药后8周、12周较C57BL／6J小鼠显著升高,差异有统计学意义（P〈0．05）。随着倍他米松注射时间的推移,2组小鼠视网膜纤维层均变薄,各时间组的总体差异有统计学意义（P〈0．05）;且CYP1B1^-/-小鼠视网膜纤维层厚度在给药后8周、12周较C57BL／6J小鼠显著变薄,差异有统计学意义（P〈0．05）。2组小鼠RGCs凋亡的速度与给药前相比均显著增加,差异有统计学意义（P〈0．05）;且CYP1B1^-/-小鼠与C57BL／6J小鼠相比结果更为显著（P〈0．05）。结论在高浓度糖皮质激素的诱导下,CYP1B1^-/-小鼠对青光眼的易感性增加。     

原发性先天性青光眼CYP1B1基因新变异

目的 探讨CYP1B1基因变异在湖南地区原发性先天性青光眼患者中的分布.方法 病例对照研究.收集来自湖南地区的13例原发性先天性青光眼患者的临床资料进行分析,对13例患者的CYP1B1基因编码外显子进行直接测序和聚合酶链反应-限制性内切酶技术检测.结果 13例原发性先天性青光眼患者中,有1例发现一种基因新突变(c.C319G,L107V),是位于外显子2的错义突变.100例正常人中未见L107V突变.同时发现已报道的4种单核苷酸多态位点,分别为R48G、A119S、V432L、D449D.结论 CYP1B1基因L107V突变可能是导致湖南地区原发性先天性青光眼患者的致病原因之一.     

Cytochrome P450 1B1 gene mutations in Japanese patients with primary congenital glaucoma(1)

PURPOSE: To report a novel missense mutation and DNA polymorphism of the CYP1B1gene in Japanese patients with primary congenital glaucoma. METHODS: A series of 11 unrelated patients with primary congenital glaucoma was examined. Patients were followed in the Kagoshima University Hospital between 1979 and 1998. DNA was extracted from leukocytes of the patients, their families, and unrelated healthy individuals. Amplicons spanning the coding regions of the CYP1B1 gene were examined by direct sequencing and enzyme-restriction detection. RESULTS: In the 11 unrelated patients, besides the previously reported insertional mutation (1620 ins G), a novel missense mutation was identified at codons 444 to replace arginine with glutamine (R444Q) in one patient. The novel missense mutation cosegregated in the relevant family as an autosomal recessive pattern and was not found in other patients or control individuals. In addition, five polymorphic sites were found at codons 48, 119, 330, 432, and 449. These polymorphic alleles did not cosegregate with the disease, and they were found in healthy individuals as well. CONCLUSIONS: Approximately 20% of Japanese patients with primary congenital glaucoma may be affected by mutations in the CYP1B1 gene. Further studies are justified to explore whether a relationship exists between the phenotypic expressivity of the disease and the type of mutation.     

原发性先天性青光眼CYP1B1基因变异初步研究

目的了解CYP1B1基因变异在中国原发性先天性青光眼(PCG)患者发病中的作用。方法收集来自不同地区的16例PCG患者,对其CYP1B1基因编码外显子进行直接测序,对照组进行单核苷酸多态性分析。结果在1例PCG患者中发现了一种变异,为8006G>A(R390H)。它是位于外显子III的错义突变。还发现了五种单核苷酸多态性,分别为3793T>G,R48G,A119S,A330S,V432L。结论CYP1B1基因是导致中国人PCG患者的致病基因,但也有其他变异可能和PCG变异有关。     

Identification of R368H as a predominant CYP1B1 allele causing primary congenital glaucoma in Indian patients

PURPOSE. To investigate the predominant mutation in the CYP1B1 gene in patients in India with primary congenital glaucoma (PCG), using PCR-restriction fragment length polymorphism (RFLP) methods and to characterize the molecular defect in two generations of an affected family. METHODS. DNA samples from 146 patients with PCG from 138 pedigrees were analyzed for several distinct mutations in CYP1B1 by PCR-RFLP. RESULTS. PCR-RFLP screening revealed that 30.8% of patients were positive for any one of the six mutations (376insA, 528G-->A, 923C-->T, 959G-->A, 1449G-->A, and 1514C-->A), and 17.8% of the patients were found to have the rarely reported mutation R368H (1449G-->A). All mutations were confirmed by DNA sequencing. CONCLUSIONS. The results suggest extensive allelic heterogeneity in the Indian patients with PCG, with the predominant allele being R368H among the 146 Indian patients tested. It appears possible to use this approach for carrier detection in pedigrees with a positive family history and in population screening. The approach also offers a method for rapid screening of potential carriers and affected individuals.