Congenital Hereditary Cataracts (CHC) in Dogs

The miniature Schnauzer dog breed is one of several breeds that have elevated risk factors for developing hereditary cataracts, and dogs of the breed can undergo eye screening to look for the signs of cataracts prior to breeding, in order to minimise the risk of producing litters that will in turn suffer from cataracts.

Congenital hereditary cataracts or CHC are just one of a great many different types of cataracts that can affect dogs, and as the name implies, this form of cataracts is hereditary, or passed on from dog to dog through the breed line. However, unlike many of the other forms of cataracts, researchers have been unable to isolate the gene mutation that causes this type of cataracts in the miniature Schnauzer so far, and so it is not possible to DNA test dogs to find out their risk factors.

In this article, we will look at congenital hereditary cataracts in the miniature Schnauzer in more detail, including how this type of cataracts occur, what sort of dogs develop them, and how dogs are tested for CHC. Read on to learn more.

What are congenital hereditary cataracts?

Cataracts are a cloudiness that forms over the lens of the eye, and which may affect either one eye alone or both at once. Cataracts are not usually painful, but they do go a great way towards obscuring vision, and can lead to total blindness in the dog as they progress.

A congenital disorder means a problem or disorder that develops or is present in the dog before they are born, and hereditary means something that is inherited, due to the combination of genes that the dog receives from both of their parents.

Congenital hereditary cataracts are therefore cataracts that are caused by inheritance from the dog’s parentage, that have the markers or flaws in place to develop even before the puppy is born, and so, that may potentially begin to show symptoms in the pup while they are still young. This is reasonably uncommon for cataracts as a whole, as they are usually considered to be a disease associated with aging.

What sort of dogs can develop congenital hereditary cataracts?

A reasonably large number of dog breeds have risk factors or a predisposition to hereditary cataracts or HC, but it is important to note that this is not the same as the congenital hereditary cataracts or CHC that has been identified as a problem in the miniature Schnauzer breed.

Cataracts are not contagious and cannot be caught or passed from dog to dog-but if a miniature Schnauzer pup inherits the markers of CHC, they are apt to develop cataracts themselves, potentially while still very young.

Both male and female pups are equally likely to be affected, and pups are sometimes only a few weeks old when the first signs of cataract development begin to show up.

How to identify cataract development

Cataracts produce visible changes to the surface of the eye that can be seen, but that can be hard to spot during their very early stages of development. Because congenital hereditary cataracts are a known risk for the Miniature Schnauzer breed, breeders and owners of such dogs should remain vigilant to the early warning markers of the condition.

Changes to the surface of the eye, including the eye beginning to appear paler in colour and of course, the signature clouding or opacity of the lens itself indicate the potential development of congenital hereditary cataracts, and this is something to watch out for in dogs of the breed from a young age.

Health testing for the miniature Schnauzer

For many forms of canine cataracts, the exact genetic mutation or fault that causes their development has been mapped out, which allows researchers to identify the root cause of the problem and devise a DNA test to screen dogs for their risk factors and status.

However, the exact gene that causes congenital hereditary cataracts in the miniature Schnauzer has not as yet been identified, which means that DNA testing and returning a definitive result of the dog’s status is not currently possible. Researchers think that the condition is passed on by autosomal recessive heredity-which means that genes from both sides of the parentage would dictate the dog’s status-but even this is not a given.

In order to perform health testing for congenital hereditary cataracts in the miniature Schnauzer, eye screening has to be carried out on the dog, and this is something that may have to be carried out more than once in the life of the dog. Eye screening should be performed in accordance with The Kennel Club and British Veterinary Association protocols, who collate test results as part of their research.

Prior to breeding, potential parent dogs can undergo eye screening for congenital hereditary cataracts, and this is mandatory for breeders that register pedigree miniature Schnauzers with The Kennel Club under the Assured Breeder Scheme, as well as a condition of membership of many miniature Schnauzer clubs and organisations.

The screening should be performed on parent dogs within the twelve months prior to mating-which means that dogs that are bred more than once may have to be tested each time.

Additionally, once a litter has been born, the pups too should undergo eye screening for the presence of congenital hereditary cataracts between the ages of five and eight weeks old, before they go on to their new homes.

Eye screening does not guarantee that the dog will not develop congenital hereditary cataracts later in life-which is why dogs may need to undergo screening several times throughout their lives. However, screening of pups and prior to breeding and returning a clear result greatly reduces the chances of breeding from dogs that have the condition, and so, helps to breed this fault out of the wider gene pool.

The Animal Health Trust is one of the organizations that undertakes research into congenital hereditary cataracts in the miniature Schnauzer, and the Trust is currently inviting owners of miniature Schnauzers to submit DNA samples for inclusion within their research, both from dogs with the condition and those that are clear of it.