Primary Open Angle Glaucoma (POAG) is a group of disorders that is resulted from optic nerve damage in the region of the optic nerve head. It has a prevalence of about l % of a predominantly white population over 40 years of age and accounts for 78% of the blindness caused by glaucoma. There is accumulating evidence that genetic predisposition is a major factor in the development of this condition. Accordingly, this study is designed to identify and characterize the genetic factors underlying the adult-onset POAG by genetic linkage analysis and positional mapping. The PI has ascertained multi-generational families by adopting very restrictive diagnostic criteria. A group of 17 adult-onset POAG families with at least 2-3 living affected offspring and one living parent in 2-3 generations (96 meioses, 48 affected) served as the initial screening panel and another 48 families with a minimum of two living affected offspring as the secondary panel. In both panels there are many other normal sibs that are not being used to identify the POAG locus but they will be used for linkage confirmation. The initial screening panel were used to screen the genome at 15-20 cM intervals. After excluding more than 25 candidate gene/regions as likely sites of POAG and after genotyping a total of 215 polymorphic DNA markers, 4 chromosomal locations that may potentially be the sites for different POAG loci were identified. The PI has now proven linkage of one of these sites in a group of adult-onset POAG families (i.e., GLC1B). Further studies are currently underway to confirm the true nature of POAG linkage to the other remaining three sites. Therefore, the specific aims of this proposal are: 1) to investigate the genetic linkage relationship of 65 families to these three potential sites of POAG loci; 2) to search for mutation in a number of GLC1B candidate genes and/or to identify, clone, isolate and characterized the putative GLC1B gene. If linkage of POAG to the three above- mentioned loci is not proven the PI will embark on a second round of a genome-wide search at 5-10 cM intervals in order to identify the chromosomal location of as yet unknown other POAG loci. PRC, gel electrophoresis and silver staining will be used to genotype the DNA markers; LOD scores, sib- pairs, APM and haplotype linkage transmission to analyze the genotypic data; SSCP, heteroduplex and DGGE to search for mutation; GeneBridge 4 Radiation Hybrid Panel and CEPH-Mega YAC clones to narrow down the candidate region; and finally RACE and cDNA selection to isolate potential genes from large DNA fragments. The ever increasing availability of the STRP, STS and EST clones and their respective assignment to the radiation hybrid panels, YACs, BACs, and other Cosmid clones has immensely accelerated the chance of identifying the POAG gene(s).
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