Assessment of canine BEST1 variations identifies new mutations and establishes an independent bestrophinopathy model (cmr3)

[摘要] Purpose: Mutations in bestrophin 1 (BEST1)areassociatedwitha group of retinal disorders known asbestrophinopathies in man and canine multifocal retinopathies (cmr)inthedog.To date, the dog is the only large animal model suitablefor the complex characterization and in-depth studies of Best-relateddisorders. In the first report of cmr, the disease wasdescribed in a group of mastiff-related breeds (cmr1) and theCoton de Tulear (cmr2). Additional breeds, e.g., the Lapponianherder (LH) and others, subsequently were recognized with similarphenotypes, but linked loci are unknown. Analysis of the BEST1gene aimed to identify mutations in these additional populations andextend our understanding of genotype–phenotype associations. Methods: Animals were subjected toroutine eye exams, phenotypically characterized, and samples werecollected for molecular studies. Known BEST1 mutations wereassessed, and the canine BEST1 coding exons were amplified andsequenced in selected individuals that exhibited a cmrcompatible phenotype but that did not carry known mutations. Resultingsequence changes were genotyped in several different breeds andevaluated in the context of the phenotype. Results: Seven novel coding variantswere identified in exon 10 of cBEST1. Two linked mutations wereassociated with cmr exclusive to the LH breed (cmr3).Two individuals of Jämthund and Norfolk terrier breeds wereheterozygous for two conservative changes, but these were unlikely tohave disease-causing potential. Another three substitutions were foundin the Bernese mountain dog that were predicted to have a deleteriouseffect on protein function. Previously reported mutations were excludedfrom segregation in these populations, but cmr1 was confirmedin another mastiff-related breed, the Italian cane corso. Conclusions: A third independent caninemodel for human bestrophinopathies has been established in the LHbreed. While exhibiting a phenotype comparable to cmr1 and cmr2,thenovelcmr3 mutation is predicted to be based on adistinctly different molecular mechanism. So far cmr2 and cmr3are exclusive to a single dog breed each. In contrast, cmr1 isfound in multiple related breeds. Additional sequence alterationsidentified in exon 10 of cBEST1 in other breeds exhibitpotential disease-causing features. The inherent genetic and phenotypicvariation observed with retinal disorders in canines is complicatedfurther by cmr3 being one of four distinct genetic retinaltraits found to segregate in LH. Thus, a combination of phenotypic,molecular, and population analysis is required to establish a strongphenotype–genotype association. These results indicate that cmrhas a larger impact on the general dog population than was initiallysuspected. The complexity of these models further confirms thesimilarity to human bestrophinopathies. Moreover, analyses of multiplecanine models will provide additional insight into the molecular basisunderlying diseases caused by mutations in BEST1.

[学科分类] 生物化学/生物物理