What is a genetic disease?
Genetic disease (= “heritable”, “inherited”) is a disease whose underlying basis is due to action of a gene or several genes acting to produce the defect. Genes in general are the biological code for the production of different types of proteins. Some proteins such as collagen are structural proteins while others are enzymes which facilitate various chemical reactions in the body. Very few eye diseases which occur in dogs have been identified as definitely having a genetic cause.
In general most of the retinal degenerations seen in dogs are now known as having a genetic cause. The defective gene codes for an abnormal variant of an enzyme involved in the complicated cascade which converts the energy of light into electrical impulses. The end result of the defective gene is that the light receptor cell dies and the retina degenerates.
Many cataracts are also suspected to have an underlying genetic basis but this is not yet proven. There are a number of well known genetic cataracts in laboratory animals such as rats where the outcome of breeding specific individuals together is highly predictable. Our approach is to assume a cataract to be hereditary unless another specific cause is identified eg trauma, unrelated intraocular inflammation or specific metabolic diseases such as diabetes.
Other diseases such as entropion are more difficult to describe as being truly genetic (i.e. the action of specified genes) but the abnormality usually results from the breeding together of animals with poor conformation where this poor conformation predisposes to the eye disease. Eye certification can still identify poor conformational types which when bred together might result in the abnormality. The heritability of this poor conformation may be very complex involving the action of many different genes often acting in different ways to produce the final result. Some of these diseases where we are unable to put the title “genetic” to them are still described as having a “breed predisposition” i.e. the disease is seen at higher incidence in the breed than the general population at large.
What is a congenital disease?
Congenital disease means that the problem is present from birth. Congenital diseases may or may not be genetic. Where the disease is not genetic it may be the result of an insult to the embryo or foetus which occurred at a very specific time during in utero development. Had the insult occurred a few days either side of this time then the defect might not have occurred.