Rapid mutation detection by the transgenomic wave analyser DHPLC identifies MYOC mutations in patients with ocular hypertension and/or open angle glaucoma

Age at Glaucoma Diagnosis in Germline Myocilin Mutation Patients: Associations with Polymorphisms in Protein Stabilities

Glaucoma is the leading cause of irreversible blindness worldwide, with elevated intraocular pressure (IOP) as the only known modifiable risk factor. Trabecular meshwork (TM)-inducible myocilin (the MYOC gene) was the first to be identified and linked to juvenile and primary open-angle glaucoma. It has been suggested that mutations in the MYOC gene and the aggregation of mutant myocilin in the endoplasmic reticulum (ER) of TM may cause ER stress, resulting in a reduced outflow of aqueous humor and an increase in IOP. We selected 20 MYOC mutations with experimentally determined melting temperatures of mutated myocilin proteins. We included 40 published studies with at least one glaucoma patient with one of these 20 MYOC mutations and information on age at glaucoma diagnosis. Based on data from 458 patients, we found that a statistically significant but weak correlation was present between age and melting temperature based on various assumptions for age. We therefore conclude that genetic analysis of MYOC mutations alone cannot be used to accurately predict age at glaucoma diagnosis. However, it might be an important prognostic factor combined with other clinical factors for critical and early detection of glaucoma.

Common and rare myocilin variants: Predicting glaucoma pathogenicity based on genetics, clinical, and laboratory misfolding data

Rare variants of the olfactomedin domain of myocilin are considered causative for inherited, early-onset open-angle glaucoma, with a misfolding toxic gain-of-function pathogenic mechanism detailed by 20 years of laboratory research. Myocilin variants are documented in the scientific literature and identified through large-scale genetic sequencing projects such as those curated in the Genome Aggregation Database (gnomAD). In the absence of key clinical and laboratory information, however, the pathogenicity of any given variant is not clear, because glaucoma is a heterogeneous and prevalent age-onset disease, and common variants are likely benign. In this review, we reevaluate the likelihood of pathogenicity for the ~100 nonsynonymous missense, insertion-deletion, and premature termination of myocilin olfactomedin variants documented in the literature. We integrate available clinical, laboratory cellular, biochemical and biophysical data, the olfactomedin domain structure, and population genetics data from gnomAD. Of the variants inspected, ~50% can be binned based on a preponderance of data, leaving many of uncertain pathogenicity that motivate additional studies. Ultimately, the approach of combining metrics from different disciplines will likely resolve outstanding complexities regarding the role of this misfolding-prone protein within the context of a multifactorial and prevalent ocular disease, and pave the way for new precision medicine therapeutics.

A novel MYOC heterozygous mutation identified in a Chinese Uygur pedigree with primary open-angle glaucoma

PURPOSE

To characterize the clinical features of a Chinese Uygur pedigree with primary open-angle glaucoma (POAG) and to identify mutations in two candidate genes, trabecular meshwork inducible glucocorticoid response (MYOC/TIGR) and human dioxin-inducible cytochrome P450 (CYP1B1).

METHODS

Twenty one members from a Chinese Uygur family of four generations were included in the study. All participants underwent complete ophthalmologic examinations. Five were diagnosed as POAG, four as glaucoma suspects, and the rest were asymptomatic. Molecular genetic analysis was performed on all subjects included in the study. All exons of CYP1B1 and MYOC were amplified by polymerase chain reaction (PCR), sequenced and compared with a reference database. The variations detected were evaluated in available family members as well as 102 normal controls. Possible changes in structure and function of the protein induced by amino acid variance were predicted by bioinformatics analysis.

RESULTS

Elevated intraocular pressure and late-stage glaucomatous cupping of the optic disc were found in five patients of this family. A novel heterozygous missense mutation c.1151 A>G in exon 3 of MYOC was found in all five patients diagnosed as POAG and four glaucoma suspects, but not in the rest of the family members and 102 normal controls. This mutation caused an amino acid substitution of aspartic acid to glycine at position 384 (p. D384G) of the MYOC protein. This substitution may cause structural and functional changes of the protein based on bioinformatics analysis. No mutations were found in CYP1B1.

CONCLUSIONS

Our study suggests that the novel mutation D384G of MYOC is likely responsible for the pathogenesis of POAG in this pedigree.

Sequence analysis of MYOC and CYP1B1 in a Chinese pedigree of primary open-angle glaucoma

PURPOSE

To analyze two candidate genes, trabecular meshwork inducible glucocorticoid response (MYOC/TIGR) and human dioxin-inducible cytochrome P450 (CYP1B1), in a Chinese pedigree of primary open-angle glaucoma.

METHODS

In a three-generation family containing 14 members, four of them were patients with primary open-angle glaucoma, one was a glaucoma suspect, and the rest were asymptomatic. All members of the family underwent complete ophthalmologic examinations. Exons of MYOC and CYP1B1 were amplified by polymerase chain reaction, sequenced, and compared with a reference database.

RESULTS

Elevated intraocular pressure and impaired visual field were found in all patients. One MYOC heterozygous mutation G367R, in exon 3 was identified in four patients and the suspect, but not in the rest of the family members. Meanwhile, four single nucleotide polymorphisms in MYOC and CYP1B1 genes were found.

CONCLUSIONS

Although the G367R mutation of MYOC, which causes primary open-angle glaucoma in the form of autosomal dominant inheritance, has been reported in some other ethnicities, it was found in Chinese pedigree for the first time.

Variable clinical spectrum of the myocilin Gln368X mutation in a Dutch family with primary open angle glaucoma

PURPOSE

To describe the clinical phenotype in a family with primary open angle glaucoma harboring a p.Gln368X mutation in MYOC.

MATERIALS AND METHODS

We identified a proband with primary open angle glaucoma and the p.Gln368X MYOC mutation. She and her six siblings were examined clinically, including Heidelberg Retina Tomography II, and venous blood samples were screened for other variants in MYOC, WDR36, OPTN, and CYP1B1.

RESULTS

Four individuals showed the p.Gln368X MYOC mutation, no other genetic variations were assessed. Two of these four siblings had glaucomatous optic disc changes with corresponding visual field losses and abnormal Heidelberg Retina Tomography results by the Moorfields regression analysis, one had abnormal results by the Moorfields regression analysis but no visual field loss, and one showed no glaucomatous signs or symptoms at all. These findings did not correlate with the age of the affected individuals.

CONCLUSION

In the primary open angle glaucoma family described here, we documented a wide range in clinical symptoms, demonstrating a highly variable penetrance of the MYOC p.Gln368X mutation.

Rapid detection of glucose-6-phosphate dehydrogenase gene mutations by denaturing high-performance liquid chromatography

OBJECTIVES

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common inherited disorder worldwide. Different kinds of G6PD mutations may result in variable severity of clinical onset in G6PD-deficient individuals. In this study, a reliable molecular diagnostic method was developed for rapid detection of G6PD gene mutation.

DESIGN AND METHODS

Primers were designed to amplify G6PD gene fragments that were subjected to mutation screening using denaturing high-performance liquid chromatography (DHPLC) analysis. Mutations were identified by their distinct elution peak patterns and were confirmed by DNA sequencing. The assay was further validated against 29 samples from individuals with G6PD deficiency.

RESULTS

A DHPLC-based assay for G6PD mutation detection was established. The 9 common G6PD mutations in the Taiwanese and Chinese population could be distinguished through the analysis of DNA elution patterns. During the validation test with the 29 G6PD deficiency specimens, two additional rare mutations, T517C and C519G, were unveiled. Overall, the DHPLC-based mutation detection was 100% concordant with the DNA sequencing results.

CONCLUSION

Compared to other genotyping techniques, this method requires significantly less technical time to perform and has a greatly increased throughput capacity. Hence, the DHPLC method represents a major technical advance for G6PD genotyping and should benefit G6PD-deficient individuals for proper clinical care.

A common disease haplotype for the Q368STOP mutation of the myocilin gene in Australian and Canadian glaucoma families

PURPOSE

To ascertain whether there is a common disease haplotype for the Q368STOP mutation of the myocilin gene in Australian and Canadian families with primary open-angle glaucoma (POAG).

DESIGN

Family pedigree study.

METHODS

A disease haplotype for the Q368STOP mutation of the myocilin gene has previously been identified in 15 Tasmanian families with POAG. The four microsatellite markers that constitute this 0.14-megabase (Mb) disease haplotype were genotyped in individuals from a large French Canadian family with POAG (family CT) and two unrelated French Canadian individuals with ocular hypertension.

RESULTS

The Tasmanian Q368STOP disease haplotype was identified in affected individuals from family CT, and the same alleles were shared at the four microsatellite markers in the two unrelated French Canadian individuals.

CONCLUSION

The same disease haplotype for the Q368STOP mutation of the myocilin gene was found in both the Tasmanian and French Canadian populations, supporting the view that this mutation arose from a common Caucasian founder.

Novel MYOC gene mutation, Phe369Leu, in Japanese patients with primary open-angle glaucoma detected by denaturing high-performance liquid chromatography

PURPOSE

To screen for mutations in the MYOC gene in Japanese patients with primary open-angle glaucoma (POAG) using denaturing high-performance liquid chromatography (DHPLC).

PATIENTS AND METHODS

Blood samples were collected from 171 patients with POAG and 100 controls from seven institutions in Japan. For high-throughput analysis, seven exonic regions were amplified by polymerase chain reaction using DNA pooled from three patients; each DNA pool was then analyzed chromatographically. For analysis of a small number of samples, 7 exonic regions were amplified separately but simultaneously with annealing at 58 degrees C in each patient and then chromatographed, using 7 wells of the same 96-well plate per sample. When chromatographic patterns were abnormal by either method, the PCR products of the individual samples were sequenced.

RESULTS

Four glaucoma-causing mutations were identified in five POAG patients (2.9%). One missense mutation, Phe369Leu, is new; and three others, Ile360Asn, Ala363Thr, and Thr448Pro, have been reported in Japanese patients. Phe369Leu was associated with adult onset POAG.

CONCLUSIONS

Mutations in the MYOC gene were demonstrated chromatographically in 2.9% of our Japanese POAG patients. The use of pooled DNAs with DHPLC analysis is a time- and labor-saving technique. All mutations detected appear to be specific to Japanese patients.

Low prevalence of MYOC mutations in UK primary open-angle glaucoma patients limits the utility of genetic testing

Primary open angle glaucoma (POAG) affects 1% of people over age 40. Early detection and treatment can prevent blindness, but the disease is often asymptomatic until a late stage. Positive family history is an important risk factor and previous studies indicate that approximately 5% of POAG results from mutations in the myocilin ( MYOC) gene, raising the possibility of identifying individuals genetically predisposed to glaucoma. We collected DNA samples from 426 unselected UK POAG patients and analyzed them for MYOC mutations. The Q368X mutation was found in six patients (1.4%). No other mutations were identified, suggesting that amongst patients unselected for family history, the prevalence of MYOC mutations in the UK is lower than in other populations. Genetic and glaucoma screening was offered to first-degree relatives of these six probands (group 1) and of age/sex-matched mutation-negative controls (group 2). Of 11 group-1 relatives, three carried Q368X, one of whom already had glaucoma. Notably, of the 13 relatives in both groups who were mutation negative, one was already being treated for ocular hypertension. We therefore caution against changing glaucoma surveillance regimens in such individuals and suggest that routine untargeted genetic testing for MYOC mutations in patients with POAG would be of limited value until additional significant genetic risk factors are identified.

Somatic Mutations and Altered Expression of the Candidate Tumor SuppressorsCSNK1ε,DLG1, andEDD/hHYDin Mammary Ductal Carcinoma

We report somatic mutations in three genes (CSNK1 epsilon, encoding the Ser/Thr kinase casein kinase I epsilon; DLG1, encoding a membrane-associated putative scaffolding protein; and EDD/hHYD, encoding a progestin induced putative ubiquitin-protein ligase) in mammary ductal carcinoma. These genes were suspected of playing a role in cancer because loss-of-function mutations in their Drosophila homologues cause excess tissue growth. Using DNA from 82 laser-microdissected tumor samples, followed by microsatellite analysis, denaturing HPLC and direct sequencing, we found multiple somatic point mutations in all three genes, and these mutations showed significant association with loss of heterozygosity of closely linked polymorphic microsatellite markers. For CSNK1 epsilon and DLG1, most of the mutations affected highly conserved residues, some were found repetitively in different patients, and no synonymous mutations were found, indicating that the observed mutations were selected in tumors and may be functionally significant. Immunohistochemical reactivity of each protein was reduced in poorly differentiated tumors, and there was a positive association between altered protein reactivity, loss of heterozygosity, and somatic mutations. There was a statistically significant association of hDlg staining with p53 and Ki67 reactivity, whereas CSK1 epsilon and EDD/hHYD staining levels were associated with progesterone receptor status. The results provide strong indications for a role of all three genes in mammary ductal carcinoma. They also justify additional studies of the functional significance of the changes, as well as a search for additional changes in these and other genes identified from studies on model systems.

A decade of high-resolution liquid chromatography of nucleic acids on styrene-divinylbenzene copolymers

The introduction of alkylated, nonporous poly-(styrene-divinylbenzene) microparticles in 1992 enabled the subsequent development of denaturing HPLC that has emerged as the most sensitive screening method for mutations to date. Denaturing HPLC has provided unprecedented insight into human origins and prehistoric migrations, accelerated the cloning of genes involved in mono- and polygenic traits, and facilitated the mutational analysis of more than a hundred candidate genes of human disease. A significant step toward increased sample-throughput and information content was accomplished by the recent introduction of monolithic poly(styrene-divinylbenzene) capillary columns. They have enabled the construction of capillary arrays amenable to multiplex analysis of fluorescent dye-labeled nucleic acids by laser-induced fluorescence detection. Hyphenation of denaturing HPLC with electrospray ionization mass spectrometry, on the other hand, has allowed the direct elucidation of the chemical nature of DNA variation and determination of phase of multiple alleles on a chromosome.