THE PROBLEM OF OVERLAPPING GLAUCOMA FAMILIES IN THE GLAUCOMA INHERITANCE STUDY IN TASMANIA (GIST)

The Glaucoma Inheritance Study in Tasmania (GIST) is a population surv ey of Australia's island state, Tasmania (population 450,000). Its aim is to find families with autosomal dominant, adult-onset, primary ope n angle glaucoma (POAG) suitable for genetic linkage analysis. POAG is relatively common, affecting around 3% of the Australian population. By finding the large families with POAG and identifying all the descen dants in a captive population, it is possible that there may be overla p of different glaucoma pedigrees. Three of the first thirteen familie s in the study were composed of overlapping pedigrees. In one GIST fam ily, GTas3, there has been intermarriage with other pedigrees with gla ucoma on five occasions. The possibility of multiple genotypes was als o reinforced by the inability to determine a single glaucoma phenotype in this family. When finding large families of POAG for linkage analy sis, researchers must be aware of the risk of affected individuals inh eriting their gene from the alternate parent. Thus, the alternate pare nts or their families must be examined, especially if the phenotype is atypical for the rest of the family.