Targeted disruption of the myocilin gene (Myoc) suggests that human glaucoma-causing mutations are gain of function

Glaucoma is a heterogeneous eye disease and a major cause of blindness worl dwide. Recently, primary open angle glaucoma (POAG)-associated mutations ha ve been found in the trabecular meshwork inducible glucocorticoid response gene (TIGR), also known as the myocilin gene (MYOC), at the GLC1A locus on chromosome 1q21-q31. These mutations occurred in a subset of patients with juvenile- and adult-onset POAG and exhibited autosomal dominant inheritance . Ocular expression and its involvement in POAG suggest that TIGR/MYOC may have a role(s) in regulating intraocular pressure (IOP). Here, we report th e generation and analysis of mice heterozygous and homozygous for a targete d null mutation in Myoc. Our study shows that Myoc mutant mice are both via ble and fertile. Our in vivo findings further demonstrate that Myoc is not required for normal IOP or normal ocular morphology. The lack of a discerna ble phenotype in both Myoc-heterozygous and Myoc-null mice suggests that ha ploinsufficiency is not a critical mechanism for POAG in individuals with m utations in MYOC. Instead, disease-causing mutations in humans likely act b y gain of function.