Multiocular defect is an inherited syndrome with affected dogs presenting with multiple and various ocular abnormalities. A mutation in COL11A1 causes MOD in the Old English Sheepdog breed. Clinical signs in affected dogs include cataract, microphakia, macrophthalmos, lens coloboma, retinal folds and detachment, vitreous anomalies/degeneration and persistent pupillary membranes, although not all affected dogs display all of these abnormalities Heterozygous dogs might have fewer clinical signs than homozygous dogs and/or a later onset of disease.
The single nucleotide substitution in the gene called COL11A1 that causes Multiocular Defect in Old English Sheepdog is autosomal dominant. This means that dogs that carry one or two copies of the mutation (heterozygotes and homozygotes respectively) will almost certainly develop Multiocular Defect during their lives. They will also pass the mutation on to all (for homozygotes) or about half (for heterozygotes) of any offspring they have. Breeding dogs that will not develop Multiocular Defect should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Heterozygotes (“carriers”) should not be bred from, even if they are mated to a dog that has also been tested and is clear of the COL11A1 mutation (i.e. carry no copies of the mutation). If a heterozygote is mated to a clear dog approximately half of the resulting puppies will also be heterozygous and will develop Multiocular Defect caused by the COL11A1 mutation during their lifetime.