Title

Positional mapping and molecular cloning of an adult-onset primary open angle glaucoma (POAG) gene

Date of Completion

January 2005

Keywords

Biology, Molecular|Biology, Genetics|Health Sciences, Ophthalmology|Engineering, Biomedical

Degree

Ph.D.

Abstract

Glaucoma is a leading cause of blindness in virtually every country. This disease is usually asymptomatic until the late stages, by which time significant and irreversible optic nerve damage has already taken place. Therefore, development of an accurate diagnostic test for presymptomatic detection of at risk individuals is an urgent requisition. The mapping, cloning and identification of novel mutations involved in the etiology of glaucoma would provide a significant opportunity for presymptomatic diagnosis, improved prognosis, and better understanding of the etiology of this blinding condition. During the course of this study, and by virtue of genetic linkage study, a new POAG locus (designated as GLC1G) was identified on 5q22.1. Mutation screening of 7 candidate genes from the GLC1G critical region (∼2-Mb between D5S1466 and D5S2051) revealed only one significant alteration in the WDR36 (WD40-Repeat 36) gene. Further screening of this gene in a total of 130 POAG families revealed 24 DNA variations. Overall, 4 mutations (N355S, A449T, R529Q and D658G) were identified in 17 (5.02%--6.92%) unrelated POAG subjects: 11 with high-pressure and 6 with low-pressure glaucoma. These mutations were absent in a minimum of 200 normal control chromosomes. They were also conserved between WDR36 orthologues in mice, rats, dogs, chimps and humans. WDR36 is a novel gene with 23 exons that encodes for 951-amino acids and a protein with multiple G-beta WD40 repeats. By Northern blotting, 2 distinct mRNA transcripts of 5.9-kb and 2.5-kb were observed in the human heart, placenta, liver, skeletal muscle, kidney and pancreas. WDR36 gene expression in the lens, iris, sclera, ciliary muscles, ciliary body, trabecular meshwork, retina, and optic nerve were established by RT-PCR. In mice, two transcripts of 3.5-kb and 2.9-kb showed analogous expression patterns to humans. mRNA expressions were detected in 7-, 11-, 15- and 17-day-old developing mouse embryos. In summary, WDR36 is a novel causative gene for Adult-Onset POAG at the GLC1G locus. Although the in-vivo function of WDR36 is yet unknown, identification of this gene provides an opportunity for presymptomatic diagnosis of at-risk individuals and the study of the biochemical pathways involved in the pathogenesis of this group of optic neuropathies. ^