Cone degeneration

From Dog
Normal (left) versus dystrophy of canine cones[1]

Cone degeneration (hemerolopia) is an autosomal-recessive genetic disease of dogs characterized by 'day blindness' and absence of retinal cone function in adults[2].

This disease, which occurs naturally in the Alaskan Malamute and German Short-Haired Pointer breeds, affects only the cone cells and the rod cells are spared and is similar to the human disease achromatopsia. The missense defect mutation has been located on chromosome 29.

This disease can be diagnosed in dogs from 8 - 12 weeks of age when retinal development is normally complete.

Clinically affected pups show typical signs of hemeralopia, bright-light blepharospasm, photophobia, epiphora, and squinting. Typically, dogs avoid bright light and seek shaded or dark areas. Vision at night is normal.

The retina of the affected dog initially appears normal when examined by an ophthalmologist and initially the ERG (electroretinogram) recording is normal. However, the ERG response from the degenerating cones declines with age and is non-recordable in the mature CD-affected dog.

A differential diagnosis would include progressive retinal atrophy, where night-vision is also affected.

References

  1. Goldstein, A et al An ADAM9 mutation in canine cone-rod dystrophy 3 establishes homology with human cone-rod dystrophy 9. Mol Vis 16:1549-1569
  2. Sidjanin DJ et al (2002) Canine CNGB3 mutations establish cone degeneration as orthologous to the human achromatopsia locus ACHM3. Hum Mol Genet 11(16):1823-1833