Bestrophin gene mutations cause canine multifocal retinopathy: a novel animal model for best disease.
OBJECTIVE
Canine multifocal retinopathy (cmr) is an autosomal recessive disorder of multiple dog breeds. The disease shares a number of clinical and pathologic similarities with Best macular dystrophy (BMD), and cmr is proposed as a new large animal model for Best disease.


METHODS
cmr was characterized by ophthalmoscopy and histopathology and compared with BMD-affected patients. BEST1 (alias VMD2), the bestrophin gene causally associated with BMD, was evaluated in the dog. Canine ortholog cDNA sequence was cloned and verified using RPE/choroid 5'- and 3'-RACE. Expression of the canine gene transcripts and protein was analyzed by Northern and Western blotting and immunocytochemistry. All exons and the flanking splice junctions were screened by direct sequencing.


RESULTS
The clinical phenotype and pathology of cmr closely resemble lesions of BMD. Canine VMD2 spans 13.7 kb of genomic DNA on CFA18 and shows a high level of conservation among eukaryotes. The transcript is predominantly expressed in RPE/choroid and encodes bestrophin, a 580-amino acid protein of 66 kDa. Immunocytochemistry of normal canine retina demonstrated specific localization of protein to the RPE basolateral plasma membranes. Two disease-specific sequence alterations were identified in the canine VMD2 gene: a C(73)T stop mutation in cmr1 and a G(482)A missense mutation in cmr2.


CONCLUSIONS
The authors propose these two spontaneous mutations in the canine VMD2 gene, which cause cmr, as the first naturally occurring animal model of BMD. Further development of the cmr models will permit elucidation of the complex molecular mechanism of these retinopathies and the development of potential therapies.
Guziewicz
Karina E
KE
Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Zangerl
Barbara
B
Lindauer
Sarah J
SJ
Mullins
Robert F
RF
Sandmeyer
Lynne S
LS
Grahn
Bruce H
BH
Stone
Edwin M
EM
Acland
Gregory M
GM
Aguirre
Gustavo D
GD
D000369:Aged, 80 and over; D000818:Animals; D015152:Blotting, Northern / Q000662:veterinary; D015153:Blotting, Western / Q000662:veterinary; D002829:Choroid / Q000378:metabolism; D003001:Cloning, Molecular; D018389:Codon, Nonsense / Q000235:genetics*; D004252:DNA Mutational Analysis / Q000662:veterinary; D004195:Disease Models, Animal; D004283:Dog Diseases / Q000235:genetics* / Q000473:pathology; D004285:Dogs; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect / Q000662:veterinary; D015870:Gene Expression; D006801:Humans; D020125:Mutation, Missense / Q000235:genetics*; D009887:Ophthalmoscopy / Q000662:veterinary; D010375:Pedigree; D010641:Phenotype; D010857:Pigment Epithelium of Eye / Q000378:metabolism; D012162:Retinal Degeneration / Q000235:genetics / Q000473:pathology / Q000662:veterinary*; D017422:Sequence Analysis, DNA
D018389:Codon, Nonsense; D005136:Eye Proteins