Primary Lens Luxation

Transcription

1 Primary Lens Luxation Cathryn Mellersh Animal Health Trust February, 2009

2 Collaboration & Acknowledgements David Sargan (University of Cambridge) David Gould (Davies Veterinary Specialists) AHT Ophthalmologists & BVA Eye Panelists Owners and breeders who have donated DNA samples from their dogs Kennel Club Charitable Trust, American Kennel Club Canine Health Foundation, Breed Clubs & individuals.

3 Talk Layout Brief overview of Primary Lens Luxation. DNA what it is, what it does, and how mutations in DNA cause inherited disease. How a mutation progresses through a pedigree. How a mutation is tracked down PLL mutation and DNA test what the results mean mutation frequency in the population general advice Vitreal leakage

4 Primary Lens Luxation Zonules In the normal eye the lens is held in place by numerous fibres, called zonules. Lens luxation occurs when all of these fibres are broken and the lens becomes loose within the eye, where it can move forwards or (less commonly) backwards in the eye.

5 PLL Primary Lens Luxation is a well-recognised, painful & potentially blinding condition known to affect many terrier and terrier-type breeds. Believed to be inherited as an autosomal recessive condition in all breeds studied. Difficult to eliminate from at risk breeds because: Clinically unaffected carriers can pass mutation on to offspring Condition is mid-late onset, so affected dogs often bred with prior to onset of clinical signs DNA test required

6 DNA DNA is a very long molecule & is found in virtually every cell of the body. The canine genome consists of approximately 2,500,000,000 nucleotides of DNA If each nucleotide was 1mm long the canine genome would stretch from Land s End to John O Groats and back. ALL the DNA is copied every time a cell divides DNA is responsible for every aspect of you and your dog that is not controlled by the environment.

7 Coding DNA DNA C G A T G T C A A T G C A C C G C T A C A G T T A C G T G G Transcription mrna G C U A C A G U U A C G U G G Translation Protein A T V T W

8 DNA DNA is a code/blueprint for every physical characteristic of a dog that is not determined by the environment. The code is determined by the order of nucleotides along the DNA. ALL 2,500,000,000 nucleotides are copied every time a cell divides. Mistakes that arise are called MUTATIONS. Most mutations that arise are repaired whereas a tiny minority persist. Most mutations have no effect, whereas some can be advantageous. Some mutations have a deleterious effect & cause inherited disease. *

9 Chromosomes Egg Sperm fertilization 38 autosomes & 1 X chromosome 38 autosomes & 1 X or Y chromosome X Y 38 pairs of autosomes & 1 pair sex chromosomes

10 Spontaneous Mutation X

11 Recombination X

12 Propagation X

13 Inheritance of Mutation Down a Pedigree Parents G-Parents G G-Parents G G G-Parents

14 Affected Shared Region of DNA

15 Mutation Identification Affected Unaffected

16 PLL research Research to identify mutation responsible for PLL initiated ~ 10 years ago. DNA from affected & unaffected dogs was analysed to identify region of the genome that was homozygous in all affected dogs, and different in the unaffected dogs. MBTS 40 cases & 11 controls LHs 22 cases & 18 controls X breeds 5 cases to cut a very long story short we identified the mutation responsible for PLL in Miniature Bull Terriers & Lancashire Heelers in summer It is a single nucleotide substitution. *

17 Breeds carrying PLL mutation Miniature Bull Terrier Lancashire Heeler Jack Russell Terrier Parson Russell Terrier Jagd Terrier Volpino Italiano Australian Cattle Dog Yorkshire Terrier Patterdale Terrier Sealyham Terrier Chinese Crested Dog Tibetan Terrier

18 Between Breeds

19 DNA Test Results DNA test developed and made available October 19th, Clear Carrier Genetically Affected

20 PLL DNA Test Kits for taking cheek swabs are available by phoning +44 (0) or via to Further information

21 PLL DNA Test Results CLEAR: these dogs have two normal copies of DNA. Our research has demonstrated clear dogs will not develop PLL as a result of the mutation we are testing for, although we cannot exclude the possibility they might develop PLL due to other causes, such as trauma or the effects of other, unidentified mutations. GENETICALLY AFFECTED: these dogs have two copies of the mutation and will almost certainly develop PLL during their lifetime. We advise that all genetically affected dogs have their eyes examined by a veterinary ophthalmologist every 6 months, from the age of 18 months, so the clinical signs of PLL are detected as early as possible.

22 Carriers CARRIER: these dogs have one copy of the mutation and one normal copy of DNA. Our research has demonstrated that carriers have a very low risk of developing PLL. The majority of carriers do not develop PLL during their lives but a small percentage do. We currently estimate that between 2% 20% of carriers will develop the condition, although we believe the true percentage is nearer to 2% than 20%. We do not currently know why some carriers develop the condition whereas the majority do not, and we advise that all carriers have their eyes examined by a veterinary ophthalmologist every 6-12 months, from the age of 2, throughout their entire lives. Current best estimate = 2.5% *

23 Mutation Frequency We collected DNA from random LHs to estimate the mutation frequency Samples from 98 dogs collected We removed all full & half-siblings left with 46 dogs that didn t share a sire or a dam Clear 28 (61%) Carrier 17 (37%) Affected 1 (2%)

24 LHs Tested Country Dogs tested Clear % Carrier % Affected % Finland % 28 50% 1 2% Netherlands % 0 0% 0 0% Norway % 3 60% 0% Sweden % 29 28% 0% UK % 33 38% 3 3% TOTALS % 93 36% 4 2%

25 TTs Tested (January 10) Country Dogs Tested Clear Clear % Carrier Carrier % Affected Affected % Australia % 0 0% 0 0% Belgium % 2 29% 0 0% Denmark % 0 0% 0 0% Eire % 2 18% 0 0% Finland % 5 23% 0 0% Germany % 48 17% 5 2% Holland % 4 67% 0 0% Ireland % 3 38% 0 0% Italy % 0 0% 0 0% Netherlands % 3 21% 0 0% Norway % 16 24% 0 0% Sweden % 3 60% 0 0% UK % 99 32% 7 2% USA % 3 30% 0 0% TOTALS % % 12 2%

26 PRTS Tested (February 2010) Country Dogs tested Clear % Carrier % Affected % Austria % 0 0% 0 0% Belgium % 0 0% 0 0% Czech Republic % 0 0% 0 0% Finland % 58 16% 7 2% Germany % 22 21% 1 1% Netherlands % 1 33% 0 0% Norway % 3 20% 0 0% Portugal % 3 75% 0 0% Slovakia % 1 50% 0 0% Sweden % 5 26% 0 0% Switzerland % 1 17% 0 0% UK % 30 28% 1 1% USA % 1 50% 0 0% TOTALS % % 9 1%

27 Advice Normally for recessive conditions we advise breeders to mate their carriers to tested, clear dogs. Puppies don t have to be DNA tested unless they will be bred with. NOT all the same advice for PLL. Owners DO need to breed with their carriers, because the mutation frequency is so high. But all puppies that are the offspring of at least one carrier parent should be DNA tested. Dogs carrying the mutation need to be clinically monitored throughout their lives. *

28 30% Carriers Males

29 30% Carriers Females

30 Breeding Outcomes Clear Clear x Clear 100% Carrier Genetically Affected Clear x Carrier 50% 50% Carrier x Carrier 25% 50% 25% Clear x Genetically Affected 100% Carrier x Genetically Affected 50% 50% Genetically Affected x Genetically Affected 100%

31 Vitreal Leakage As zonules rupture vitreous can leak into the anterior chamber of the eye vitreal leakage. In some countries evidence of vitreal leak age is sufficient for a dog to fail an eye examination and be classed as PLL affected We have analysed DNA from several dogs now, mainly Lancashire Heelers, that have clinical evidence of vitreal leakage but that are clear of the PLL mutation. Vitreal leakage might be a distinct condition from PLL in some dogs, and be caused by different mutation(s). Vitreal leakage alone is not diagnostic of PLL, although many dogs with vitreal leakage will progress to develop LL. Perhaps LL can be secondary to vitreal leakage????

32 LHs that Don t Fit Some dogs with clinical lens luxation are only carriers of PLL mutation explained by fact that small minority of carriers develop clinical PLL Some dogs with vitreal leakage (subluxation code 0) do not carry the PLL mutation - explained by fact that vitreal leakage might be a distinct condition from PLL in some dogs Some dogs with lens luxation are clear of the PLL mutation explanations include the possibility that LL can occur secondary to vitreal leakage OR there is another genetic form of PLL in the Lancashire Heeler. * Keep in mind that there are very few discrepancies of any breed

33 Samples for Future Research To help us understand the affected carrier phenomenon and vitreal leakage we need samples from from: carriers that develop PLL carriers that reach the age of 10 yo without developing PLL dogs diagnosed with vitreal leakage that reach 10 yo without developing PLL clear dogs with clinical LL All samples MUST be accompanied by full eye examination history

34 Thank You to all the owners who have provided DNA from their dogs and supplied us with information. to everybody who has made a financial donation to the research. We couldn t have done it without you.