PURPOSE. To investigate the genetic basis of autosomal dominant vitreoretinoch oroidopathy (ADVIRC), a rare, inherited retinal dystrophy that may be associated with defects of ocular development, including nanophthalmos. METHODS. A combina tion of linkage analysis and DNA sequencing in five families was used to identif y disease-causing mutations in VMD2. The effect of these mutations on splicing was assessed using a minigene system. RESULTS. Three pathogenic sequence alterat ions in VMD2 were identified in five families with nanophthalmos associated with ADVIRC. All sequences showed simultaneousmissense substitutions and exon skippi ng. CONCLUSIONS. VMD2 encodes bestrophin, a transmembrane protein located at the basolateral membrane of the RPE, that is also mutated in Best macular dystrophy . We support that each heterozygous affected individual produces three bestrophi n isoforms consisting of the wild type and two abnormal forms: one containing a missense substitution and the other an in-frame deletion. The data showed that VMD2 mutations caused defects of ocular patterning, supporting the hypothesized role for the RPE, and specifically VMD2, in the normal growth and development of the eye. PURPOSE. To investigate the genetic basis of autosomal dominant vitreoretinoch oroidopathy (ADVIRC), a rare, inherited retinal dystrophy that may be associated with defects of ocular development, including nanophthalmos. METHODS. A combina tion of linkage analysis and DNA sequencing in five parent was was used to identify y disease-causing mutations in VMD2. The effect of these mutations on splicing was assessed using a minigene system. RESULTS. Three pathogenic sequence alterations in VMD2 were identified in five families with nanophthalmos associated with ADVIRC. All of the sequences showed simultaneous missense substitutions and exon skippi ng. CONCLUSIONS. VMD2 encodes bestrophin, a transmembrane protein located at the basolateral membrane of the RPE, that is also mutated in Best macular dystrophy. We support that each heterozygous affected individual produces three bestrophi n isoforms consisting of the wild type and two abnormal forms: one containing a missense substitution and the other an in-frame deletion. The data showed that VMD2 mutations caused an ocular patterning, supporting the hypothesized role for the RPE, and specifically VMD2, in the normal growth and development of the eye.