Genetic basis of CMR1 - is an autosomal recessive inherited eye disorder caused by mutations in the BEST1 gene (Bestrophin 1). In Coton de Tulear dogs, CMR1 manifests due to a specific recessive mutation in the BEST1 gene. Dogs must inherit two copies of the mutated gene (homozygous) to be affected and develop clinical signs; carriers with one copy are asymptomatic but can pass the mutation on. The mutation in BEST1 leads to a truncated or dysfunctional bestrophin protein, which is essential for normal function of the retinal pigment epithelium.
Pathophysiology - the disorder causes multifocal serous retinal detachments manifesting as multiple, discrete circular retinal lesions (or "blisters") in puppies typically between 3 and 4 months of age.These retinal lesions result from fluid accumulation beneath the retina but usually do not worsen over time or cause blindness.The blood-ocular barrier remains intact, and retinal changes are mostly non-progressive.Electroretinography shows minimal decrease in retinal function; some lesions may fade with age but residual retinal changes persist.
Clinical Signs and Breed Specifics - Affected Coton de Tulear puppies present with visible multifocal retinal detachments between 3 to 4 months old. The retinopathy is nonprogressive and usually does not affect vision significantly. Optical coherence tomography and angiography confirm the nature and location of retinal lesions. The disorder has been documented in Coton de Tulears and several other breeds.
Why This Matters to Breeders and Vets - Genetic testing is available to identify carriers and affected dogs, allowing responsible breeding to prevent producing affected puppies. Knowing a dog's CMR1 status helps differentiate CMR from other retinal diseases with similar symptoms. Early diagnosis guides clinical management and stops unnecessary interventions. Carriers are asymptomatic but can pass the mutation on; dogs clear of the mutation cannot pass it.
Summary - Canine Multifocal Retinopathy Type 1 in Coton de Tulears is an autosomal recessive retinal disorder caused by mutations in the BEST1 gene. Affected dogs develop early-life multifocal retinal detachments that are non-progressive and typically do not impair vision seriously. Genetic testing enables carrier and affected dog identification to guide informed breeding and reduce disease incidence in the breed.