Contents

1. Introduction	2. Further Investigation
3. Clinical Picture	4. The Incidence of Primary Ciliary Dyskinesia
5. Where do we go from here?	6. How are disease-causing genetic mutations identified?
7. What about PCD in Newfoundlands?	8. Questions & Answers

1. INTRODUCTION

Two years ago, Mrs Watson noted similarities in the symptoms of three Newfoundland's that had been referred to her. Each dog had had a succession of chest infections, a mucous discharge and areas of consolidation (infection) on their chest x-ray. Infections would clear with antibiotics and steam treatment, only to recur some time later. She also noticed that in two of the dogs, the heart lay towards the right side of the chest, not the left as is normal. These features, together with reduced fertility in males, are also found in Humans with a hereditary condition called ‘Kartagener’s Syndrome’. The basic problem in this syndrome is an abnormality of the cilia which prevents them from moving correctly.

(Cilia are microscopic, hair-like projections on the surface of some cells. (Singular = cilium). The are usually grouped in large numbers and beat in a co-ordinated wave to move a fluid film over the surface of the cells. They are numerous on the cells lining the respiratory tract, where bacteria and debris are trapped in the fluid film. The beating of the cilia transports the fluid upwards until it can be coughed out. They are also present in the male and female reproductive tracts. The tail of a sperm is basically a very long cilium.

Normal cilia consist of groups of very fine tubes, rather like a bundle of drinking straws, with two single tubes in the centre, and 9 pairs of tubes arranged symmetrically around them. Cilia move by virtue of the tubes sliding relative to each other, using a ratchet-type mechanism involving arm-like projections from the paired tubes, called Dynein arms. Cilia are anchored in the cell by special structures, which are precisely aligned.)

2. FURTHER INVESTIGATION

Mrs. Watson then obtained a semen sample from an affected adult dog. Analysis showed the sperm had poor forward motility with a high
proportion of abnormal forms – was this a canine form of Kartagener’s syndrome?

Examination of the cilia by electron microscope showed they had missing Dynein arms, abnormal numbers of tubes and some of the paired tubes were separated. The anchoring structures were randomly aligned. All these abnormalities mean that the cilia would be unable to beat in a
co-ordinated wave and so would be unable to move the fluid film in the lungs. This means bacteria and debris would be trapped and the dog would develop repeated chest infections.

The condition in these dogs was therefore identified as Primary Ciliary Dyskinesia or PCD (dys = abnormal, kinesia = movement).

3. CLINICAL PICTURE

Newfoundlands with PCD first show symptoms as young puppies. They have copious, sticky nasal discharge within a few days of birth. They soon develop a moist cough and recurrent chest infections. Typically, the infection clears up with antibiotics, but soon recurs. Of the three cases
studied, one died at 5 following repeated chest infections that were gradually becoming more severe; one is stable and the other was euthanised at 9 months due to the severity of the condition and poor response to treatment.

Reports of Newfoundlands showing these symptoms were sought and three more were found, two of them in Australia.

4. THE INCIDENCE OF PRIMARY CILIARY DYSKINESIA

PCD is seen in about 1 in 16 000 humans. It has also been described in a cat, pigs, mice, rats and 14 other breeds of dog, including Golden Retrievers, English Springer Spaniels, Old English Sheepdogs and Border Collies.

PCD is the result of a genetic abnormality. In Newfoundlands, this abnormality is inherited as an autosomal recessive defect. Most cases are inherited in this manner, but in some species, PCD is due to a dominant gene. There are many genes involved in the inheritance of ciliary structure, and different gene defects are probably responsible for PCD in different species.

Pedigree analysis of the affected dogs showed the same common ancestor on both sides 4 – 5 generations previously. However, this sire has been used extensively as a stud dog and appears in the pedigrees of approximately 40% of current dogs – this means he is probably not the
source of the abnormality.

It is surprising that more cases of PCD are not seen, this may be due to several reasons:

i. There may be under recognition and under reporting of the problem by both breeders and veterinary surgeons due to problems with diagnosis. (Affected dogs may be mis-diagnosed as ‘fading puppies’, cases of pneumonia due to inhalation of maternal fluids, or cases of ‘neonatal respiratory virus infection’.)
ii. There may be a different common ancestor, much further back in the pedigrees of the affected dogs, which is featured in the pedigrees of a much smaller proportion of current Newfoundlands than the sire implicated.
iii. Carriers of this condition may be less fertile than normal individuals. The average litter size of the parents of the affected Newfoundlands is 3.25, whereas the overall average litter size is approximately 6.
iv. Affected puppies may die before or shortly after birth, thereby reducing the number of cases seen by veterinary surgeons.

5. WHERE DO WE GO FROM HERE?

Can the gene responsible for PCD in Newfoundlands be eradicated from the gene pool?

If no affected individuals are bred from, the incidence of the gene responsible will be reduced. However, after 7 – 8 generations, the incidence will plateau and it will be almost impossible to find the remaining carriers.

If the abnormal gene can be identified by molecular genetic techniques and a DNA test can be devised (so-called DNA finger printing), ALL carriers can be identified. The abnormal gene could then be eradicated within 1 generation, if all breeding individuals were tested and carriers
were not bred from.

6. HOW ARE DISEASE-CAUSING GENETIC MUTATIONS IDENTIFIED?

This is rather like searching for a needle in a haystack.

There are approximately 3 000 000 000 base pairs in the DNA of the dog, and the mutation may affect just one of these.
Things are made more complex by the fact that normal variation between individuals means there are between 10 and 30 million different genes that could potentially be present.
The identification of the single abnormality responsible for a recessive defect usually takes several man-years of work.

There are 2 ways to identify the culprit gene

i. Guess where to look. For example, the mutation is likely to affect one of the proteins present in the cilia. Therefore, if the genes known to be related to ciliary proteins are examined first, only 1 – 200 genes need investigation not 80 – 100000.
ii. Search sequences of DNA using a technique called ‘Linkage Analysis’ to direct the search to the relevant part of the affected chromosome. Possible candidate genes can be identified in several ways, making the search easier.

The advent of a canine genome map has made this type of research much quicker (a genome map identifies where particular genes lie on each chromosome). A vast amount of research effort has gone into this in 20 different countries and genetic ‘markers’ now exist for ‘areas’ of all chromosomes. These ‘markers’ can be used to identify groups of genes, and if an individual inherits a particular marker with a genetic disease,
the gene responsible must lie close to the marker on the same chromosome. The nearer a marker lies to the mutated gene, the more likely they are to be inherited together. Once a close marker has been identified, the mutated gene becomes easier to find. (Note, a genetic marker is not the same as a gene).

The dog has a very complicated genome, with 78 chromosomes, but fortunately, the human genome is very widely mapped and the two are fairly
similar. This makes the search for genetic markers in the dog much quicker than it otherwise would be.

Once the mutated gene responsible for a genetic disease has been identified, a simple, reliable test can be developed which will identify the presence of that gene on an affected individual’s ‘DNA fingerprint’, or in a carrier. This means carriers can be identified before they are bred from, with the potential for several tests to be performed for different diseases on only one blood sample or cheek swab. The disadvantages with this type of DNA test are that it can only be performed in specialist centres and each test is usually specific to only one disease in one breed.

7. WHAT ABOUT PCD IN NEWFOUNDLANDS?

Mrs. Watson and her team are keen to hear of any future affected puppies, to determine whether this is a significant problem in the breed.

It is theoretically possible to identify a marker for PCD in Newfoundlands. It is also possible to identify the culprit gene and develop a DNA test for it. However, this would be very time consuming and expensive. It would take a researcher at least 1 year, full-time, and cost at least £30 000 to £40 000 to investigate a genetic marker, with no guarantee that the mutation would be identified. A test based on a genetic marker would only be 95 – 98% accurate. A DNA test to identify the mutation would be 100% accurate, but would take another 1 – 3 years.

Breed enthusiasts will need to ask whether the severity of the problem within the breed justifies the expenditure of this amount of time and money. If yes, funding will be needed (the work to date has been funded by Waltham). Outside funding would only be possible if breed enthusiasts showed a high level of commitment, and were willing to investigate parents and littermates of affected individuals, even if normal themselves. To be worthwhile, at least 6 – 10 affected individuals and 60+ relatives (including those not affected) would need to be examined.

8. QUESTIONS & ANSWERS:

Q: At what age does the condition become manifest?

A: (Mr. Vincent) There have now been 4 authenticated cases, two of which were puppies he has bred himself. At birth, the first puppy had a nasal discharge and was wheezy. It progressed well, apart from the very sticky nasal discharge but developed a chest infection at 5 weeks which did not improve with treatment. The second puppy had no nasal discharge until 3 weeks old, but did have a chest infection. Both puppies characteristically lay with their heads vertically up the wall of the whelping box within a few hours of birth, in order to catch their breath.

It is very difficult to spot adults with the condition. They have repeated bouts of pneumonia which are difficult to clear, but are not always due to the same type of bacterium. If an adult has repeated chest infections, the owner should suspect PCD.

Q: How is the diagnosis made?

A: A firm diagnosis can only be made by examining the cilia with an electron microscope.

The puppies are not physically big enough for samples to be taken until they are about 5 weeks old.

Local anaesthetic is sprayed up the nose. A special brush is passed up the nostril and rubbed against the wall of the nose in order to obtain some of the cells lining the nasal passages. The brush (plus cells) must then be sent to Mrs. Watson.

Q: Would mass screening at a show be feasible?

A: A show of hands indicated people would be willing to have their dogs tested at a show. This would be a good way to get samples from many different breed lines, but only healthy dogs would be available at a show.

Q: If the possibility of identifying a genetic marker were to be examined, what samples would be needed?

A: Blood collected into an EDTA tube (your vet will know what this is) and sent through the post would be suitable. However, there are ethical considerations in taking blood from a healthy individual.

Q: Would it be possible to use blood samples that have already been taken for genetic analysis of a different condition?

A: Yes.