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Short intro to theories of heredity
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One thing you have to remember when talking about hereditary diseases and breeding is that every organism, from fruit flies to our self, carries about 5 lethal (potentially harmful or deadly) genes. So if you hear someone that says, “ there are no diseases in my dogs line” or “ my dog is out of genetically clean line” you can be pretty sure that the owner/breeder isn’t very serious about breeding. There are NO such things as genetically clean line. Every line has it particularly problem and that goes for ALL breeds - and please remember that the vast majorities of diseases is caused by action of two parties, meaning both sire and dam, so if someone tells you "my girls line are clean of that, so it must be cause by bad genes from the dog" you can be pretty that the breeder is either very ignoranced or worsed: not give a d.. about serious breeding! The Australian Shepherd is primarily bred on the basis of other shepherds. You can therefore expect the Aussie to be affected by genetic diseases affecting them. The diseases most often affecting the Aussie are eye diseases, especially cataract, epilepsy and CHD.
The eye The cornea, a colorless, transparent membrane, covers the part of the eye facing the outer world. The colored iris is placed beneath this membrane and is penetrated by the pupil, the black hole in the eye that acts as the `entries hole´ for light. Behind the iris is the lens hung in a lens-ligament, which enables movement of the lens when focusing. The back of the eye consist of 3 layers, outermost the sclera that is responsible for keeping the round shape of the eye. A pigmented membrane called choriodea is placed between the sclera and the retina. It consisted of numerous small vessels and a reflecting layer called tapetum lucidum, which reflects received light so the overall effectiveness of retina is increased. Reflection from the eyes by flash or car light is due to reflection from tapetum lucidum. Inmost to the centre of the eye, you find the retina, a transparent and light-sensitive membrane. It consists of 2 types of pigmented cells, optical cells and nerve cells. The optical cells consist of 2 types of cells, rods and cones. They absorb the received light and the nerve cells convert this light in to images in the brain. Rods absorb all light in the visible spectrum and can thereby not distinguish between colors. The cones on the other hand exist in several types, which each absorbs a specific color. They need a great deal of light and do thereby not function in darkness. The following article is a short intro to the eye diseaeses that affects the Aussie - also see below:
Can You See?: Inherited Eye Disease in Aussies
Cataract
is a degeneration of the lens and is the most common eye disease in the
Australian shepherd. It usually starts as small muddy dots on the lens
and progresses to involve larger and larger areas of the lens. The dog
will be completely blind when most of the lens is infected, this will be
visible as a whitish or bluish silvering of the lens. Hereditary
cataracts in Aussies always affect both eyes at the same time. It is
hard to say how fast the dog will be completely blind, in some dogs it
progresses very slowly, on others very fast. Most often though, signs of
hereditary cataract will appear when the dog is about 4 – 5 years of
age.
A special kind of cataract, juvenile cataract, can be detected in even
very young puppies and the dog will in most cases be blind before he
turns 4 years of age.
Even though it is possible to operate a dog for cataract, should one be
very careful when breeding, cataract is probably inhered autosomal
recessive and can for that reason be carried in many generations with
out causing any problems. To complicate things is cataract in Aussies
believed to be composed of two different types. Dogs affecting with
cataract, related dogs or dogs that has produced cataract should never
be used for breeding.
Cataract can also be caused by damages to the eye, it can be due
to diseases like diabetic and age, but unlike hereditary cataract does
it, almost never, start simultaneously in both eyes.
CEA
(Collie Eye Anomaly) is an assembling of several diseases affecting
retina and the optical nerve. It is a bilateral disease, which means
that the dog is affected simultaneously on both eyes. CEA is divided in
4 degrees; the first degree cause only minor optical problems and the
fours degree blindness. It is very important to remember that even
though the dog `only´ are affected by the first degree is it perfectly
cable of producing puppies with the fours degree. 1.
degree: Vessle torturous, small areas of choroidal hypoplisia 2.
degree: Choroidal hypoplisia and coloboma 3.
degree: Retinal detachment 4.
degree: Intra ocular haemorrhage CEA is properly transmitted autosomalt recessive and is more common in the showdogs than the workingdogs. Dogs that have produced or is related to individuals with CEA should not be used for breeding. It is now possible to test your dog gentically for CEA, so high risk should be tested before entering any breeding program. For further info: OptiGen Vessle
Totuosity Vessle
Totuosity occur when the small vessels in choroids plexex is shaded. Choroidal
Hypoplasia This
disease is caused by an inadequacy development of the choroids plexex.
It often means fewer vessels in choriodea or losing of pigmentation due
to lacking or abnormal cells in tapetum lucidum. Choroidal Hypoplasia
will normally not cause the dog sever defect in regards to vision. It is
possible to detect this eye disease when the pup is about 6 weeks of age
and it will not change worth mentioning from this time. Some young
puppies though, are cable of replace the lacking pigment. This is called
`go-normal´, the dog looks perfectly normal when grown but can produce
puppies affected by CEA in the fours degree. That is why it is so
important that an ophthalmologist checks the puppies’ eyes before they
turn 10 weeks of age. Coloboma
Coloboma
is a defect in sclera and emergence already during development of the
embryo. The choriodiale tissue around the optical nerve become
underdeveloped and there can occur a regular hole in the nerve. The
underlying retina and vessels can be squished out of this hole and form
a hernia. Small colomobas does usually not cause major disturbers to
vision, but larger ones will cause black spots in field of vision and at
worst Retinal Detachment. Checking the puppies eyes between 6 – 7
weeks of age is a very good idea, as some small colobomas can heel
themselves. Retinal
Detachment Is
a diseases caused by detachment of retina from the tissue beneath.
Reduction of vision depends of the degree of detachment; complete
detachment will however cause complete blindness, usually due to
intra-ocular haemorrhage.
Disticiasis
is a hereditary defect that are caused by over-numbered or misplaced
hears at the edge of the eyelid. These hairs will grow inwards towards
the eye and cause symptoms like running, etching and red eyes and/or
wounds. It is possible to treat this disease by removal of the hairs; it
can however often take quite some time to remove all of them. It is not know how this disease is transmitted but one should not use affected animals in the breeding.
Iris Coloboma is a regular hole in the dog’s iris The dog is fully ably to see, but light is able to enter the eye through the hole, something that hamper the dog in doing his work. Big coloboma can been seen as black dots in the eye, sometime it even looks like the dog has two pupils. It is not know how this disease is inherited, but one should not use dogs know to produce this disease.
PPM
is short for Persistent Pupil Membrane and is an eye disease that arises
in the embryonic stages. During development of the eye does iris create
a membrane from with the pupil is developed. The pupil will first
develop after the pup has been born and it is quite common that you can
se string of this membrane in young pups. They will normally disappear
before the age of 8 weeks; the presents of membrane stings after this
age is normally viewed as a hereditary defect.
The
must common form of PPM is a sting that stretches from one point in the
iris to another point. These strings can sometime pass the pupil or
worse fasten to the lens. It is not know how PPM is inherited but dogs that suffers from PPM should not be use for breeding.
PRA
(Progressive Retinal Atrophy) is a slowly progressive degeneration of
the rods and cones in retina. All dogs diagnosed with PRA will
eventually become blind. The first symptoms to be noted are night
blindness, but later on blindness at daytime will appear too. 2 types of
PRA exist. The first is characterised by an underdevelopment of the rods
and cones, which can cause a reduction in vision in puppies as young as
12 weeks. The dog will be completely blind before it is 2 years old. The
other form of PRA do first start develop when the dog is about 4 – 7
years of age and is caused by degeneration of the rods and cones. The
rods that are responsible for vision in twilight and dusk are the fist
to be destroyd, later degeneration of the cones take place, like
reduction in the vessels in choriodea and increased reflection from
tapetum lucidum can be observed too. It is individual when the dog is
affected by PRA and have long it takes before it becomes completely
blind.
It is relatively rare that an Aussie is affected by PRA, but one
should be very careful due to the diseases being transmitted autesomal
recessive.
CHD
is a disease affecting young dogs by abnormal development of the hip
joint, either by loosening of the hip joint, irregular shape of the
femoral head or shallowness of the hip sockets. The dog does not
necessary show any symptoms of CHD, but if they do it will usually be as
lameness and difficulties standing and walking after getting up. It will
in the long run disable the dog completely. The dogs are apparently born normally and will first develop CHD later in their life. CHD is transmitted polygenic, meaning it is caused by the influence of many genes, but it can also be caused by traumas like falls, over-feeding and over-exercise of the young dog. It is believe that the hereditary faktor is about 30-40 %. It is very important that every dog entering a breeding program has it hips x-rayed around the age of 1½ - 3 years (when using the traditional method). PennHIP on the other hand is a new method, which can be used from the age of 4 months. Due to the complicated transmission of CHD, are two dogs cleared from CHD, perfectly cable of producing puppies with this disease, especially if there is a history of CHD in the two parents ancestors. It is therefore a good idea to check the hips on the grandparents too. It has however been proved that mating between two dogs rated with A has a propertional better chance of producing pups without CHD. In order for the breeders to eliminate CHD would be a good idea to x-ray all the pups in a litter not just the ones used for breeding. Another reason for this is that Aussies generally are a very tough breed and can tolerate a lot more pain without a murmur than other breeds. Detecting problems can therefore sometimes only be seen when the dysphasia is really hurting the dog. An investigation amongst nearly 10.000 Aussies in USA revealed that 6,5 % of the Aussies suffered from CHD. In USA though, are dogs used for breeding primarily the only dogs examined. The correct percentage from the whole Aussie population is therefore properly higher than this.
Elbow Dysplasia is properly cause by abnormal growth rates of the 3 bones that make up the elbow joint: humerus, ulna and radius. Minor cases will cause symptoms like rheumatism. In more severe cases will the changes in the bones, especially humerus and ulna, cause a disease called Osteochondritis dissecans, OCD. The most common causes of OCD are fragmentation of the tuberosities (out-growths on the bones that act to fasten muscles) or lack of unifying of these. These fragments can loosen and place themselves in the joint. A peace of humerus can also die and loosen, a disease call humeral condyle. OCD will in severe cases causes lameness and difficulties in getting up and walking. An examination of OCD in Rottweiler, showed that OCS affected the dogs twice as often as the bitches.
It is possible to remove the
loose fragment from the joint by surgery and about 50 % of the dogs will
recover. The higher grow rate of the joint is apparently under genetic
influence, so dogs affected by ED should not be used for breeding. The
environment can like CHD cause ED. Young dogs should therefore not be
put through over-exercise, jumping and falls, like you should be careful
with the weight of the young dog. ED has been diagnosed in Denmark.
Patella
luxation is loosening or dislocation of the patella (kneecap). The
normal position for the kneecap is in a groove in the middle of femur (thigh
bone). It is usually held in place partly by this groove and partly by a
tendon, patella ligament, which stretch from the middle of the kneecaps
underneath to the tibia (shin bone). The
muscles from the thigh are placed on top of the kneecap and are being
held in place either directly or indirectly. It is these muscles that
are used for stretching the leg.
Patella Luxation is normally divided into to categories,
MLP, Medially Luxation Patella that is present at the time of birth and
LLP, Laterally Luxation Patella, which is caused by damages. MLP are
usually affecting smaller breeds and is hereditary. Dislocation of the
kneecap normally happens towards the inside of the leg and at the same
time on both legs. Many dogs learn to compensate when walking by pushing
the leg forward, so the kneecap fall into place. Even though some dogs
are able to live with this disease their whole life, will it in most
cases, cost damages on joints and tendons. Even though the Aussie isnåt
a smal breed, has MLP been diagnosed in USA.
Von Willebrand Von
Willebrand is the most common haemophilia in the Aussies, but still
pretty rarely seen.
In order better to understand what von Willesbrand is must
it be explain how normal clotting of blood functions.
When tissues are destroy (wounds and so on) the organism
normally will response by creating an impermeable blood coagel. This
plug is formed by the release of some special compounds from the blood.
These compounds attracts thrombocytes (platelets), make them stick to
the edge of the wound and at the same time stimulating contractions of
the vessels. This will reduce the bleeding. Here after will both the
edge of the wound and the platelets secrete some other compounds that
transform fibrinogen, a protein dissolved in the blood, to fibrin which
are insoluble. Molecules of fibrin stick to each other and the edge of
the wood and create the blood coagel. Other factors will then again be
responsible for dissolving the coagel when tissue has been made.
The bloods ability to clot is caused by several of
factors, 13 to be precise. Missing of just one of them will have severe
consequences like uncontrolled bleeding. Von Willebrand is cause by
malfunction of the vWD factor. This factor is created by the edge of the
wound and attracts the platelets as well as speeding up the heeling
process. The factor must also be involved in creation of the platelets
as a dramatic drop in platelets can be observed in the heterozygous (carriers
of the diseases). The symptoms of von Willebrand are bleeding,
especially of the mucous membranes. Prolong bleeding can therefore be
observed in connection with heat, whelping, nosebleed, secondary
dentition, blood in the stole and so on.
Symptoms can often be confused with the symptoms of
hypothyroidism, as reduced platelets function too can arise in this
disease. Dogs will therefore often response positive to thyroxin
treatment and this it is also the only treatment available today.
Three types of von Willebrand exist I, II and III, where
type I is being the less severe and type III causes massive bleedings.
Type I is the most common type diagnosed and is properly transmitted
austosomalt with incomplete dominance. IT is possible to test if the dog
should be a carrier, as heterozygous has a reduced platelets contains. Besides von Willebrans have two other haemophilias been diagnosed in the Aussies: hemophilia A (malfunction of the VIIIC factor) and hemophilia B (malfunction of the IX factor). Both A and B are sex-linked, meaning that the gene in question resides on one of the sex chromosomes; in this place on chromosome X. This means that the males (XY) only will need one gene, to develop the diseases; while bitches (XX) will have to have the gene from both parents. A bitch can therefore be carrier with out be affected of the disease and still transmitted it to 50 % percents of her sons.
Demodecosis Demodecosis
are causes by the ectoparasite Demodex canis, which live in the
hair follicles of every healthy dog (and people for that matter). The
puppies are infected shortly after birth, but the mite will only
multiply to population that cause problems in a few dogs. It is not know
what causes some dog to be affected and others not, but a lower immune
system could have an effect, especially because the disease seems to be
hereditary.
Two types of demodecosis exist; localizes and generalize
demodecosis. Localized
demodecosis primarily affects young dogs under the age of one. The dog
will show signs of itching, blushing and scaly areas on head and
forelegs and infection of the ear canal with plenty sticky earwax. It is
possible to get to the disease in this stadium by medicine and medicine
bathes. Adding extra vitamin E to the dogs diet should have useful
effect too. Some dogs are cable of recovery by themselves, presumably
when their immune system is completely developed. If this happens before
the dog turn one year of age, are this symptomes not regarded as a
hereditary form of demodecosis.
If the mites however are left on their own in this stage, the
disease can develop into the next stage, generalize demodecosis, where
the dog loose larger and larger areas of fur in head, legs, and body. As
the number of mites increase, the skin will develop wounds and scabs.
At
last, a variation of demodecoses exist that only attacks the paws of
especially older dogs.
Diagnosis of demodecoses is easy done by scraping a tissue sample
from the skin. Due to the hereditary transmission one should not breed
animals that are suffering of demodecosis, like combination that has
produces demo shouldn't be repeated.
Hypothyroidism Hypothyroidism
is a disease caused by degeneration of the thyroidea. This gland
produces the iodic hormone thyroxin that increases metabolism. The
symptoms normally start developing when the dog is around 2 – 3 years
of age. At first the symptoms comes and gos due to the gland still is
able to produce some hormone. The typical signs in this stage are
irritated skin and lack of appetite. These symptoms can easily be
confused with allergy, so it would be a good idea to ask the vet to take
a blood sample and check the dogs blood content of FSH (a hormone in the
brain) and thyroxin (both T3, T4 and free T4). When the dog is about 6
– 7 years of age the gland will be completely warn out and symptoms
like gaining weight, reluctant to exercise, dry and dull coat, loss of
hair, smelling coat, bleary eyes and rigid joins can occur. The dog can
also shows some behaviour-like changes like increased aggression. If the
dog is not put under medically supervision it will die. Hypothyroidism is common among the shepherds and therefore also seen among the Aussies. The diseases has unfortunately started to increase in frequence. This i due to lack of concern amonst a lot of breeders. Dogs used for breeding should be examined at least every second year to make sure that the T3, T4, free T4 and TSH values lays within the normal range and that the dogs isn't producing antibodies against thyreoidea. Both affected and also related dogs should never be a part of any breeding program.
Lupus Lupus
is an autoimmune disease, which means that the immune system is trying
to destroy the body’s own cells. 2 types of lupus have been
ascertained in dogs: Systemic Lupus Erythematosus, SLE and Cutaneous
Lupus Erythematoses, CLE (Discoid lupus).
SLE is a rare immune response affecting large portion of the body.
Generally inflammation of joint, failure of the muscles, skin diseases,
anaemia and kidney diseases are symptoms generally occurring. The dog
can also show temporary lameness in different places, one day the right
hind leg, the next day left foreleg. The first symptoms to be detected
are usually losing of pigmentation on the nose and ticking of the pads.
Later will general weakness, pale gums due to anaemia, increased thirst
and urination appear. It is often quite difficult to give the right
diagnose because SLE display the same symptoms like cancer and medically
reactions. The dog has in order to survive be on lifelong medicine, but
unfortunately will he often start responding towards this medicine.
CLE is considered as a lesser severe type of SLE. Like SLE will
the disease starts by loosing of pigmentation on the nose. As the
diseases develop can wounds occur on the nose and possibly also on the
ears. The dog is generally very sensitive against UV light, which seems
to worsen the wounds.
It is not know have SLE or CLE is transmitted, but one should
never breed dog affected by this disease, like related individuals
shouldn’t be used for breeding.
Epilepsy Epilepsy
among dogs are, just like humans, characterised by the dog suffering
from epileptics seizures. The seizures are cost by a brain defect that
stimulate all the muscles in the body to contract at the same time.
Diagnoses epilepsy in dogs is complicated process based on exclusion of
other diseases; measuring brain activities by electrodes is not possible
in dogs. Even though no seizures are alike, is a pattern recognized:
The seizures are told to be painless (accordingly from statements from humans), this is properly due to the fact that the brain disconnect so to speak. This should not make any one believe that epilepsy is a disease that one can take lightly. First of all will epilepsy affect the dog's mind and moods tremendously and secondly the seizures can be so severe that the dog is unable to get of them and simple dies because of them. The seizures can sometime be confused with other behaviours and other diseases. Epilepsy can though always be recognized by lose of contact to the world and the dog will not responding towards calling and touch. It is rare that the dog will start seizure like described above, Grand mals as they are called. The dog will normally have Petit mals, small seizures that the owner hardly detects for years. Such seizures can be seen as lightly shaking on the head, like a fly that anois it or just sitting and stirring for several minutes. Epilepsy can be cause by other than genetic inheriting, like trauma, toxics, organ failure and so on. This type of epilepsy is also called secondary epilepsy; the hereditary kind is call primary epilepsy. There has unfortunately been observed a dramatically rise in Aussies suffering from primary epilepsy the last couple of years. This is due to two tings:
1) that epilepsy can be caused by other factors than heredity and 2) that epilepsy properly is inherit polygenetic (under the influence of several genes/loci)
Some breeders does unfortunately take the above as a excuse for continue breeding dogs that carries epilepsy. Denial is something you often hear in connection with this diesease, instead of admitting does such breeders hide the truth by saying things like "he must have eat poison", "He had a injury to his head" or "He was damaged during birth". Such a dog is often put to sleep quickly, so they don't have to be diagnose it with hereditary epilepsy. Epilepsy is inherit in a complex way and is believed to be under the influence of several loci. This means that the dog needs to carry all the defect alleles in order to develop the diseases. Lets say that 5 loci are involved in epilepsy: A, B, C, D and E. The wild type alleles is named a, b, c, d and e and the mutated alleles (the ones that cause epilepsy) A, B, C, D and E. A dog suffering from epi will therefore have the genotype ABCDE. A dog with the genotype BCD can produce epi if it is mated to a dog with the genotype AE, but not with ABCD, CDE and so on. This means that a huge number of dogs can carrie epilepsy with detecting it for years or generations. It is estimated that about 80% of the Aussie population is carrier of one or several loci of epilepsy. It is the breeders job to minimize any chance of combining loci that can cause epi. It should be obviously that dogs with epilepsy, which has produced it or is related to a producer never should be used for breeding. Dogs with a risk of 40% or higher should not be bred before the age of 4 and only to dogs with a lower risk.
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