Genetic Health -Cataracts Fall Issue 2005

GENETIC HEALTH - Cataracts
by Sharon Schaefer

Cataracts are the most common disease of the lens of the eye and are an inherited eye disorder. Cataracts occur as an aging change in the eyes of dogs (after age 9-10) and people; a few cataracts result from injury, toxins, or diseases such as diabetes; but the vast majority of cataracts is an inherited problem. In most breeds the genetics producing cataracts is not yet defined. In those breeds where the inheritance has been established it varies from autosomal recessive to autosomal dominant to incomplete dominance with variable expressivity. This indicates that we need to carefully study and track the occurrence of cataracts in Icelandics to begin to establish our own breed pattern.

There are also breed differences in the age of onset, degree of symmetry between eyes, rate of progression, and actual abnormalities seen on the lens. This again is information we need to gather and study in Icelandics who have cataracts. Cataracts present before 8 weeks of age are called congenital (considered at birth), cataracts appearing up to 4 years of age are considered juvenile or developmental, and after this they're called later onset cataracts. Various breeds may be prone to only one or all three of these types. In different breeds having cataracts, some may occur in only one eye while in other breeds it will be both eyes. In some breeds the original cataract (independent of age of onset) will never change very much and in other breeds it will continue to grow leading to blindness. Probably through their superior senses of smell and hearing, dogs are very good at compensating for vision problems. If they are kept in a familiar environment, owners may be unaware of considerable vision loss.


The American College of Veterinary Ophthalmologists controls certification for freedom from heritable eye diseases. Clearances for vision must be performed annually by a board certified veterinary ophthalmologist and not by a local veterinarian. Both the Canine Eye Registration Foundation (CERF) and the Institute for Genetic Disease Control in Animals (GDC) offer certification on an annual basis if the appropriate form and fee is forwarded to them. CERF is a closed registry and failed reports are completely confidential (up-to-date 'clear' reports may be accessed on the website). The research copy of the CERF form is always forwarded to the Veterinary Medical Database of CERF for breed information (individual identity is confidential). This data is used to form the C.E.R.F. data base which is useful in researching trends in eye disease and breed susceptibility.


CERF charges $10.50US for each new entry and $8.00US for recertification with a kennel rate for 10 or more sent back to same owner of $7.50 each. GDC maintains an open registry (all reports are publicly shared) of inherited eye diseases so breeders can track families more easily (KIN report available). There is no charge for entering an Affected Dog into the GDC database. Fee for a first Unaffected is $10US with annual updates $5US. Three or more littermates or related dogs entered at once are $25US.


The general breeding recommendation concerning cataracts is not to use affected dogs (and sometimes their parents and siblings) and to examine close relatives. Considering the small gene pool available to Icelandic breeders at the moment, all close relatives of an affected dog should be examined annually and breeding decisions made with care. Certainly dogs which are affected with cataracts should not be bred so breeders need to have annual eye examinations on all their stock. Breed associations need to develop recommendations and guidelines for their members anticipating future difficulties. If cataracts are discovered in a dog at 5 years of age it will probably already have a couple of generations of potential carriers produced.

These offspring need to be tracked even more carefully and possibly removed from the reproductive pool?


If we are lucky enough to have cataracts in Icelandics which are autosomal dominant and early onset they can be fairly easily bred away from! Sharing annual eye results and pedigree information internationally can help all Icelandic fanciers learn the patterns of cataract occurrence in our breed so more informed breeding decisions may be made in the future.


References
Canine Inherited Diseases Database, www.upei.ca/~cidd
Canine Eye Registry Foundation, www.vmdb.org/cerf.html
Institute for Genetic Disease Control in Animals, www.gdcinstitute.org