HSF4 - Hereditary Cataract
Hereditary cataract in the Australian Shepherd (HC) is an inherited eye disease that is caused by a mutation in the HSF4 gene. This genetic defect is inherited as an autosomal dominant trait. Catarct is also known as "cataract" and is one of the most common causes of clouding of the lens and blindness in dogs. The symptoms usually appear at a young age, the progression of the disease is bilaterally symmetrical and, without treatment, always ends with complete blindness. The only effective treatment option is surgery. The mutation underlying the defect can be detected using a DNA test. HC is inherited in an autosomal dominant manner, which means that one affected allele leads to this disease. The severity of the disease increases if the dog is hereditary for the mutation, ie has two affected alleles.
There are three genotypes:
1. Genotype N / N (homozygous healthy): This dog does not carry the mutation and will not develop HC. He cannot pass the mutation on to his offspring.
2. Genotype N / HC (heterozygous carrier): This dog carries a copy of the mutated gene. Due to the dominant inheritance, the dog has a high risk of developing HC.
3. Genotype HC / HC (homozygous affected): This dog carries two copies of the mutated gene and has an extremely high risk of developing HC. He will pass 100% of the mutation on to his offspring.
A DNA test enables direct detection of the responsible mutation. The DNA analysis is possible regardless of the age of the animal and can already be carried out on puppies. Not only is it possible to differentiate between affected and mutation-free animals, the genetic test can also be used to identify clinically normal carriers, which is of great importance for breeding. In order to offer maximum test reliability, each sample is examined in two independent test approaches.
CEA - Collie Eye Anomalie / CH - Choroidal Hypoplasia:
This is a widespread developmental disorder of the choroid in Collies and Shelties, which can also occur in the related Australian Shepherd. In CH there is an underdevelopment (hypoplasia) of the eye tissue layer (choroid). This looks pale and thin, almost transparent, and the blood vessels can easily be seen in these "thin" regions. In the vast majority of cases, the clinical impact is minor. In individual cases, however, the affected animal can become blind at the age of a few weeks to months. The change can be seen most clearly in puppies between 6 and 8 weeks of age and often manifests itself only as a light red discoloration next to the optic disc. However, malformations of the optic nerve, so-called colobomas, can also occur (see below). In severe cases, bleeding and retinal detachment occur. Treatment is not possible.
Cataracts - cataracts:
As in humans, a distinction is made in dogs between old age cataracts, which appear later in life, acquired cataracts due to an injury, and inherited cataracts, which in dogs usually appear within the first 6 to 7 years of life.
About 1/3 of all Aussies carry the genes for cataracts. There are different types of cataract (in humans there are 13 types). In the case of a genetic cataract, the lens opacity typically occurs on the back of the lens and also changes very quickly. The disease usually occurs between the ages of 18 months and 7 years.
Aging cataract is due to a natural aging process and leads to lens opacity that starts in the center of the lens and progresses slowly. An occurrence before the age of 7 can be ruled out. An annual eye examination should therefore be compulsory up to the age of 9 years. If a small, punctiform cataract is found in a dog, this can be harmless. One should wait a year and see if changes occur.
Often one reads terms in connection with cataract diseases that can be misleading for the layperson. Cataract diseases are usually classified according to the following criteria:
Time of creation:
The congenital cataract is already present in the newborn puppy, but mostly only visible at the age of 12 weeks. Usually both eyes are affected. In various breeds, an inherited defect can be the cause of congenital cataracts, but it is usually not hereditary.
The juvenile cataract, which usually occurs up to the age of 6 years, is often of hereditary origin, ie inherited.
Senile cataracts occur at an advanced age in dogs and are often the result or accompanying symptom of nucleosclerosis (clouding of the lens).
Localization of the cloudiness:
The total cataract affects all lens structures, while the partial cataract is restricted to certain areas of the lens.
The main criterion is the distinction between hereditary (inherited) and non-hereditary causes.
Primary hereditary cataracts are not related to other diseases. As a rule, they do not develop until the first few years of life (juvenile cataracts) and are only rarely congenital (congenital).
Secondary cataracts are not hereditary, but can be triggered by a number of causes. These include metabolic influences (metabolic disorders, e.g. diabetes mellitus, hypocalcemia), toxic influences, nutritional errors, trauma and radiation. Cataracta complicata occurs as a side effect of other eye diseases, which in turn can be hereditary, such as PRA (see below).
A distinction is made between incipient, immature, mature and overripe cataracts. A genetic test is now also available for one form of hereditary cataract mutation, but its informative value is limited due to the many different types of cataract.
There is a genetic test for a hereditary form of cataract (see link list: Animal Health Trust). The test can be used to determine whether the dog carries a gene mutation that he can inherit and that significantly increases the risk of developing cataracts. In contrast to other diseases, it is sufficient that the dog is the carrier of this mutation, so it does not have to be contained twice in the genome.
Distichia are individual hairs that arise from the openings of the glands on the edge of the eyelid, where there are usually no hairs. Distichia can irritate the cornea because they constantly irritate and, in extreme cases, damage a cornea until it breaks through. They are often so small that they cannot be seen with the naked eye. Individual hairs are called distichiae, and a whole series of hairs is called the "second row of eyelashes".
If a Rollied causes permanent irritation of the eye, an operation must be carried out.
Part of the eye (e.g. iris, lens) is missing from birth. Depending on the size and type, this can lead to impaired vision or to an over-sensitivity to bright light. The disease is usually one-sided, Merles are more often affected.
PRA - Progressive Retinal Atrophy:
This is a degenerate fundus. The disease first begins with night blindness, then day blindness and often cataracts as well. This disease is rare in the Aussie and is usually caused by trauma and is unlikely to be inherited.
For a hereditary form of PRA (progressive rod-cone degeneration) there is a genetic test that is very informative. The test can be used to determine whether the dog itself and its offspring can develop prcd-PRA.
PPM - Persistent Pupillary Membrane / MPP - Membrana Pupillaris Persistens:
During the development of the eye before birth, the later pupil is covered by a pigmented vascular network, which regresses at the time of birth. In puppies that have just opened their eyes, you can often still see fine remnants of this network. If pigmented tissue strands are also visible later, this is called PPM. They usually have little or no effect on the dog's eyesight unless the lens is affected.
In the course of the development of the retina there are occasional disturbances. Such undesirable developments can only affect small parts of the retina and are then recognizable as wrinkles that have little effect on vision. However, if larger areas are affected, the visual disturbances can be significant. Treatment is not possible. In the Aussie, retinal dysplasias often occur in connection with CEA - otherwise they are usually unproblematic.
CMR - Canine Multifocal Retinopathy:
This disease was recently diagnosed in an Australian Shepherd for the first time. So far it has only been known to occur in a few breeds such as Cane Corso, Mastiff, Pyrenees Mountain Dog, Coton de Tulear, Lapland Reindeer Dog and Perro de Presa Canario.
The CMR develops very early, usually before the fourth month of life. It manifests itself, among other things, by detachments of the retina that become visible as gray-pink spots. These lesions, which are similar to vesicles, are of different sizes and deformed and can be seen very well in both eyes of the affected dogs. Some vesicles on the retina can recede without permanent consequences, while others form permanent scars. Despite the strong retinal changes, impairments in the eyesight of the affected dogs are only to be expected at an advanced age.
It is an inherited disease that appears to be passed on in an autosomal recessive manner. So it is to be treated in breeding like the MDR1 defect. Carriers of the disease do not get sick, only if there are two copies does the disease break out. A DNA test was developed in collaboration with Optigen and is now available to all Aussie owners.