The human BEST1 gene (OMIM 607854; previously

known as VMD2) was mapped on the long arm of chromo-some 11q12-q13 and found to be causative for Best vitel-liform macular dystrophy (BVMD) in 1998 by linkage and sequencing studies of families affected by BVMD [1]. The gene consists of 11 exons that encode a 585-amino acid transmembrane protein, bestrophin-1, which localizes to the basolateral membrane of RPE cells [2]. To date, more than 200 different BEST1 mutations have been identified, most of which are missense mutations located in the N-terminal half of the protein (HGMD). These mutations are associated with at least four clinically distinguishable degenerative human eye diseases, collectively referred to as bestrophinopathies: BVMD or Best disease (OMIM 153700), autosomal reces-sive (ar) bestrophinopathy (ARB, OMIM 611809), autosomal dominant (ad) vitreoretinochoroidopathy (OMIM 193220)