A sequence change (Arg158Gln) in the leucine zipper-like motif region of the MYOC/TIGR protein

New mutation in the MYOC gene and its association with primary open-angle glaucoma in a Chinese family

Myocilin (MYOC) gene is expressed in many ocular tissues, including the trabecular meshwork, a specialized eye tissue essential in regulating intraocular pressure. Many mutations in MYOC have been detected in primary open-angle glaucoma (POAG). We investigated whether MYOC mutations contributed to the susceptibility to POAG in a Chinese family. In a four-generation family affected with POAG, ocular examinations were performed on all members of the pedigree to determine their disease status, and 200 healthy matched controls were recruited. PCR-restriction fragment length polymorphism (PCR-RFLP) analysis and DNA sequencing were used to determine the mutations in MYOC. Biological software was used to analyze the corresponding proteins for missense mutations. The c.1084G>- was found, for the first time, in four of eight affected patients and in one of two patients with suspected POAG. The c.1006C>T mutation was found in two of eight patients and in one of 19 subjects who were asymptomatic. The frequencies of c.1084G>- and c.1006C>T were 12.82 and 7.69%, respectively, in patients but not in the controls. These data provide additional clues to the pathogenesis of POAG because no other mutation was detected in either group. Our results suggest that the MYOC c.1084G>- may contribute to a genetic predisposition to POAG.

TIGR is upregulated in the chronic glial scar in response to central nervous system injury and inhibits neurite outgrowth

Reactive astrocytes respond to central nervous system (CNS) injury and disease by elaborating a glial scar that is inhibitory to axonal regeneration. To identify genes that may be involved in the astrocytic response to injury, we used differential display polymerase chain reaction and an in vivo model of the CNS glial scar. Expression of the trabecular meshwork inducible glucocorticoid response (TIGR) gene was increased in gliotic tissue compared with the uninjured cerebral cortex. Increased TIGR expression by reactive astrocytes was confirmed by in situ hybridization, quantitative reverse transcriptase-polymerase chain reaction, immunoblot analysis, and immunohistochemistry. Although mutations of the TIGR gene have been implicated in glaucoma, a function for TIGR has not been reported. Since TIGR is secreted, we assessed a possible role in inhibition of neuronal regeneration with an in vitro bioassay and found that this protein is a potent inhibitor of neurite outgrowth. Thus, TIGR is a newly identified component of the CNS glial scar that is likely to contribute to neuronal regenerative failure characteristic of the mammalian CNS.

Prevalence of myocilin mutations in adults with primary open-angle glaucoma in Ghana, West Africa

PURPOSE

Investigators have noted that primary open-angle glaucoma (POAG) in West Africa has an earlier age of onset and appears to be more clinically severe than in the United States and Europe. Primary open-angle glaucoma patients with mutations in myocilin have a similar phenotype. Therefore, we investigated the role of mutations in myocilin in patients with POAG in a West African population.

MATERIALS AND METHODS

Patients seen at the Emmanuel Eye Clinic in Accra, Ghana, were recruited for this study. Informed consent was obtained from all study patients. Glaucoma specialists from the sponsoring institution (PC, LWH, or RRA) ascertained all POAG and control patients. Age-matched unaffected controls were obtained in patients with an IOP < 22 mm Hg and normal-appearing optic nerves. PCR amplification of each of the three myocilin exons was performed. Denaturing high-performance liquid chromatography (Transgenomics Corp.) was used to detect allelic differences and samples demonstrating a mobility shift were sequenced in both directions.

RESULTS

Ninety unrelated affecteds with POAG and 76 control patients were recruited. Four individuals with severe POAG were found to have novel missense mutations in exon 3. Two exhibit an Asp380Asn mutation and two an Arg342Lys mutation. These changes were not detected in 152 ethnically matched control chromosomes. Fourteen affected individuals and eight controls exhibit a translationally silent polymorphism in codon 325 (Thr325Thr).

CONCLUSIONS

A total of 4.4% of patients with POAG have novel disease-associated mutations in myocilin. Mutations in myocilin appear to play a limited role in the pathogenesis of POAG in this region of West Africa.

Genetic basis of glaucoma

The application of molecular genetic techniques to the study of glaucoma has accelerated greatly during the past few years. In addition to localizing and identifying genes for specific types of glaucoma, researchers have begun to characterize the gene products and investigate molecular mechanisms involved in glaucoma. Much research has been focused on the gene expression, protein processing, and mutations of MYOC/TIGR, which is associated with both juvenile-and adult-onset primary open angle glaucoma. Investigations of other glaucoma-related genes, such as PITX2, FOXC1, and CYP1B1, are enabling a better understanding of anterior segment development and its relation to glaucoma.

Analysis of myocilin gene mutations in Japanese patients with normal tension glaucoma and primary open-angle glaucoma

The myocilin gene was identified as a gene (MYOC) that caused primary open-angle glaucoma (POAG). Although a normal tension glaucoma (NTG) patient with the myocilin gene mutation was previously reported, no study using large numbers of patients with NTG has been reported. Single-strand conformation polymorphism analysis and subsequent sequence analysis were performed for genotyping the myocilin gene in 114 unrelated Japanese patients with NTG. One hundred and nineteen patients with POAG and 100 control subjects without glaucoma were studied as reference subjects. Five amino acid sequence changes of the myocilin were identified: Arg46Stop (one NTG), Arg76Lys (four NTG, 10 POAG, seven control), Arg158Gln (one NTG, one POAG, one control) found in only Japanese, Asp208Glu (four NTG, three POAG, one control), Pro481Ser (one control). Pro481Ser was novel. Arg76Lys always occurred with 1-83 from G to A in the promoter as it was reported in Chinese. Although some Japanese patients with NTG had sequence changes of the myocilin gene, there were no apparent specific mutations in patients with NTG.