What we know - what we are trying to find out.
And an alert to the fancy about the continuing importance of puppy eye exams.
Catherine McMillan, Minuteman Miniature Schnauzers
Please bear with me for a moment while I outline the history behind the discovery of this disorder. I offer it for a couple of reasons - the first, to establish that it is not a new mutation, and the second, to try to dispel any misinformation that may be circulating.
Since I started breeding Miniature Schnauzers in 1983, I have faithfully examined eyes on my puppies prior to placement - pets as well as show stock. I considered it a routine procedure, as taken for granted as their vaccinations. Until a few months ago, no puppy bred under my kennel name had had anything of a serious, inherited nature diagnosed in a puppy eye exam.
I shall back up a few years. In September of 1997 I recieved a call from a breeder in Indiana. She had taken 4 puppies for routine eye checks with disturbing results. One female had mild retinal folds and a male had retinal detachments. He was blind, and had probably been so from birth. We discussed the results at length, as the pedigree contained 25% of my breeding on the dam's side. At the time we knew not what to make of the test results - retinal dysplasia is a known genetic problem in many breeds - but not the Miniature Schnauzer. It may also be caused by viral infections while a bitch is pregnant (including toxiplasmosis, herpesvirus and parvovirus) - so diagnosis of the defect is not an automatic indication of a genetic cause. However, all the puppies and both parents were subsequently removed from breeding.
The second case came to my attention in June of 2000. A daughter of one of my males had been bred to an unrelated sire in the USA. The resulting pedigree was a second generation outcross and contained no common ancestors in 5 generations. All four puppies were examined and it was discovered that one bitch had severe folds and a male had detaching retinas. The male was euthanized, and his eyes sent for pathology. No obvious signs of viral infection could be found. The breeder of the dam had made a routine practice of puppy eye exams, with no previous incidence of this defect. The sire's breeders, however, reported that they had not done routine puppy tests for some years, so data was incomplete. However,through my dog, the maternal grandsire, there was a loose thread of pedigree relationship to the litter in Indiana.
Janet Corpin and I decided to do an inbreeding between my male and a different daughter. This bitch was an older, normal eyed daughter of the bitch who had produced RD in Indiana. When the 4 puppies were examined, a female was found with minor folds. Retinal dysplasia, again - a mild case. Then, a surprise. Three weeks later, another litter he had sired for Janet was examined, and one male puppy out of the 7 was found to have complete retinal detachments.
A pattern was emerging, but - both bitches had been pregnant in the same household at the same time - environmental/viral influences could still not be ruled out. To complicate matters, data on many of the dam's ancestors and their littermates was unavailable. While it appeared to act as simple recessive, lack of data meant one could not rule out a sex linked defect or incomplete dominant mode of inheritance.
Then, this past July a litter that doubled up on the suspected "carrier" male was examined in Ontario. Three of the four puppies are affected with retinal dysplasia. One bitch has retinal folds, the second bitch has severe folds and areas of detachment, and a male has detached retinas. For the first time, we have a litter in which a good deal of data has been gathered on the siblings of dogs in the pedigree, with three forms of the defect in varying severity. While not the original purpose of the breeding, it accomplished two things - it added further weight to the suspicion that the defect is caused by an recessive gene action of some sort, and that there is a wide variation of expression. (This variability of expression is consistant with RD in a number of other breeds.)
I had already taken possession of the affected bitch and dog from Janet's earlier litters, and a test breeding is planned under the supervision of Dr.Bruce Grahn ACVO at the University of Saskatchewan. (Dr. Grahn is also involved in related dna research.) However, my oldest affected bitch is still just a baby, and the only affected breedable adult is in the possession of a breeder who declines to participate in the official program, so we are obliged to wait until 2002. When the affected to affected breeding is completed we hope to bring more evidence to the table to support or refute the theory that it is a simple recessive trait.
Some will surely question whether it is prudent to present this information to the fancy at this midway point in the research, but there is a growing body of evidence that suggests that the time to make haste is now - before the defect weaves its way into the dna of a future (or present) popular sire, to become a widespread breed problem.
What do we know so far?
(1) Each year for the past 4, retinal dysplasia has been reported in the breed by CERF. Last year, RD cases outnumbered those of PRA.
(2) In the Purdue University database of the top 100 diagnosis made in the breed in the past 11 years, are included 44 cases of retinal detachment. We can account for only 2 of those.
(3) We cannot make a definitive statement about mode of inheritance, although simple recessive is highly suspected. However, in the 11 cases to date, all 6 males have had detached retinas, while the females ranged from minor folds to geographic dysplasia. There may be sex linked influences or it may be co-incidental. Also of note - many of these affected animals also have defects of the vitreous, notably PHPV. (Persistent Hyperplastic Primary Vitreous).
(4) Minor folds may disappear with age! As the current evidence suggests that the dog with folds and the dog with detachments may be equally affected genetically, this has important implications for breeders.
(5) If you are not examining all of your puppies prior to sale, you cannot assume your dogs are clear of this defect. In only once case in 6 litters, did the breeder suspect visual deficits in her puppies - and she was prewarned about the condition. So, do not be complacent or dismissive of retinal dysplasia and the importance of puppy eye exams.
(6) CERF does not recognize retinal folds as a condition that would preclude a Miniature Schnauzer from being certified. In other words, a dog affected with mild retinal dysplasia would in all likelihood, obtain a CERF number. This MUST change, and it can, if the AMSC makes a request for the condition to be added to the list of non-certifiable ones for the breed.
If there are any silver linings in this cloud, they are these; this is a breeder's issue - much like myotonia, cleft palate or congenital cataracts, no buyer should ever purchase a puppy affected with RD, if the breeder practices routine screening. The defect occurs during fetal development, and is present at birth. Thus, it is a managable defect. And dogs with mild dysplasia have little or minor vision loss - they can live normal lives as pets. Even our blind test dogs have an amazing ability to cope with their disability.
On a personal note, and to halt speculation, the dogs here at Minuteman and Sandcastle who are known carriers are not at public stud. This does not mean that breeding from the line will discontinue. Some breedings will be for research/test purposes, and some aimed at preserving the best of the family until test breeding or dna research shows us the way out. This may include the controlled breeding of known carrier dogs. If you see that an outside breeder has used a known carrier or high risk dog, be assured that it was with done in knowledge of the risks, and our satisfaction that offspring will be bred carefully and responsibly, while answers are sought.
I have not yet named the dog that the research revolves around, and it would be an incomplete report if I did not. The dog in question is Am.Can.Ch.Benalta Batman ROM. He himself, is normal eyed, and has not produced any other inherited eye defects or major health disorders that I am aware of. However, before the reader jumps to conclusions - be reminded that one of his daughters produced two affecteds when bred to an unrelated dog. In researching the pedigrees of all dogs known to have produced this defect, we have found the earliest common ancestor in a dog born in 1973, suggesting that, if recessive, this gene has been in existance for at least that long. Consider the information from Purdue and CERF, and the unsettling fact that minor folds may resolve and appear normal by adulthood. Batman is not the first, nor is he the only dog who has produced Retinal Dysplasia. He is simply the first one to be recognized and disclosed publicly.
Catherine McMillan (c - 2001)