I know this subject has been do  to death, but  can anyone tell me the mode of inheritance  for HC.  I have been studying  the health tests on the kennel club website site and find   it interesting that you can get an affected dog from 2 clear parents,  even odder is an affected dog from 2 clear parents who have clear parents and  clear grandparents  themselves. Is there a DNA test we can do ?

I have researched this to death when choosing stud dogs to find pattern. I have noticed if a dog is affected there is quite often an AUNT or UNCLE that is affected.... It's as if it crosses over rather than comes down the lines.

No DNA test as yet sadly ..... I believe they are working on one,all we have for now is annual testing and checking back through lines....

In some breeds the DNA tests are available for hereditary cataracts, for example: French Bulldogs, Boston terriers, Staffordshire bull terriers and Australian shepherds. In other breeds, sadly, the markers have not been found yet. The inheritance is often homozygous recessive.

So is it like hip  problems in terms of inheritance  IE: you can do all the testing get you like have good hip scores for years and then suddenly  you breed a set of hips that are bad.?
A bit of back ground, I bred a litter which are now 5 months old,  one has been eye tested with possible  HC, to be retested in 6 months time.  I can't find anything in any of the  relatives back ground that  would suggest  it came via any of them.
All a bit confusing

> find   it interesting that you can get an affected dog from 2 clear parents,

If your talking CLINCALLY CLEAR then yes.

There is no physical difference between a clear dog, A Carrier dog, or even an affected dog with a late onset condition cleared before physical symptoms manifest.

If your talking specific DNA tests, as far as I am aware most/all HC cataract known genes are autosomal recessive inheritance, so to get an affected you need both parent to be carriers and or/Affected.

>even odder is an affected dog from 2 clear parents who have clear parents and  clear grandparents  themselves.

We have finally a DNA test for Glaucoma in my breed.

I have bred 8 generations of dogs and never produced an affected (as yet, though now know there is a litter now 5 years old that turns out to be carrier to carrier).

during the research I had all 6 of my girls sampled, (4 generations).

Oldest living generation turned out to be a Carrier.
Her daughter (next generation) Clear,
Next generation two of the clear bitches daughters, both Carriers,
final generation a daughter from each of the above both Clear.

Without DNA I would assume they were all clear!!

So if we didn't have DNA test and one of the at risk litter ends up with Glaucoma, it would appear to have come out of the blue.

> So is it like hip  problems in terms of inheritance

No Hips and Elbows are governed by multiple genes and environmental factors. 

It's estimated that HD has around 30% heritability whereas ED appears to be higher.

If you DNA test and breed from clear parents, there's no way you can have affected offspring.  It's the normal laws of inheritance: clear + clear = 100% clear offspring.  Clear x carrier = 50% clear, 50% carriers. Carrier x carrier = 25% clear, 50% carriers, 25% affected,  and affected x affected = 100% affected.

If there is no DNA test available,  then yes, clinically healthy dogs can produce anything.

The question is WHEN were the parents clear? HC, without a DNA test available, needs to be tested for every year. And a dog that was clear at say age 5 could be affected by age 10.

The fathers last eye test was done  at 10.2 years old, he died within that year so  that was his last test the bitch is almost 4 and has had a clear test every year , her   mother and father are both 6 and have had clear eye tests since 8 week old.
We have been using these lines for at least 10 years with nothing ever cropping up.

> We have been using these lines for at least 10 years with nothing ever cropping up.

but of course even if nothing has ever cropped up clinical eye testing will not differentiate between a genetically clear, dog, a Carrier or a later onset affected dogs.

All it can help eliminate is clinically affected dogs.

IF the mode of inheritance is recessive, the parents of ANY AFFECTED dog are both at least carriers.

So sadly when there is no DNA test available it's a shutting the stable door after the horse has bolted scenario.

So really until there is a DNA test for HC  in my breed we really are flying blind, you may have a popular  stud dog who is used many  times and doesn't develop  HC  till very old age,

> So really until there is a DNA test for HC  in my breed we really are flying blind, you may have a popular  stud dog who is used many  times and doesn't develop  HC  till very old age,

Virtually, you can only eliminate a dog after the event, though sometimes generations may well have been bred before it transpires a dog is a carrier, all you can do then is to ensure you do not have a known carrier on both sides of a pedigree, so careful pedigree research and knowledge is vital.

We had this with PRA in my breed, one well known dog didn't; produce an affected pup until he was 11 years old, and had produced 70 puppies.

By then he was sometimes in the 4th generation in pedigrees.

If a dog/bitch is used less often, have no/few offspring eye tested you may never know they are carriers, or producing affected offspring.

So what would happen if at least one  of the parents  was tested ( DNA) clear  but a pup was eye tested affected, I am really starting to  wonder  about the  mode of inheritance , and yes we know the parents are  correct.

Your dogs are DNA profiled for confirmation of parentage ?

If there is a DNA gene test then if it's an autosomal recessive and one parent is clear then none of the pups can test affected, if parentage is correct.

In all cases where this appears to have happened it turns out the sire was not that which was on the paperwork, (another dog mated the bitch in the same heat cycle), I know of one such case in Obedience circles, where a well known clear stud was used, but it turns out the bitch owners own dog also mated the bitch and was the sire of affected offspring.

It is of course possible that the clear eye test has detected another condition, not the one that the parent is DNA clear for.

For example in my own breed it is suspected that there are three forms of PRA historically found in the breed, there are now DNA tests for the most common prcd-PRA, erd (Early Retinal Degeneration) but there is not one for Rod Dysplasia. 

Both erd and rd haven't been seen in the breed in UK for decades, maybe even 40 - 50 years.  It took a long time for us to realise the PRA we had prcd-PRA because there were so few affecteds to research in order to develop a DNA test, or in our case find that we had the same form that a test already existed for in other breeds.

This is where the Panel testing that GEnescoper do with their MyDogDNA test panel is so useful every dog is checked for known hereditary diseases in the breed for which they have a test,b tu also EVERY DOG IS TESTED FOR EVERY OTHER DNA TEST IN THEIR PANEL.

In this way it has become apparent that Von Willebrands Type II, originally an issue in Wire Haired German Pointers, is actually found in far more breeds including my won where no-one has ever known of a case.

At first it was thought the gene mutation was only found in the Pointers, then it was found in rough and Smooth collies, and in May last year in my own breed the Norwegian Elkhound.  since then it ahs also been found in Old English sheepdogs, German Spitz Chinese Crested, Lagotta Romagnola and several other breeds.

The beauty of this approach is that gene mutations can be identified in a breed before they become common place.

Normally by the time a breed realises it ahs an issue, for every 1% affected animals there are likely to be around 20% invisible carriers.  To find a known gene mutation before a breed even knows it is there, means it can be managed and eradicated more effectively, without restricting the overall gene pool.