Canine genetics success stories
DNA TESTING FOR PRIMARY OPEN ANGLE GLAUCOMA IN THE PETIT BASSET GRIFFON VENDEEN GETS OFF TO GREAT START
The AHT DNA Testing Service has had an exceptional response from the Petit Basset Griffon Vendéen community for the DNA Test for Primary Open-Angle Glaucoma (POAG). This test was developed by geneticists at the AHT and subsequently launched at Crufts 2015, with great support from the breed community. Take up of the test has been very rapid, with 1,000 tests completed by November 2015, only eight months after the test was launched, in a numerically small breed.
The test is giving breeders the information they need to eliminate this terrible, blinding disease from their breed and testing for this form of glaucoma has been adopted all over the world, with tests submitted from Mexico, Japan and Singapore. The greatest numbers of samples received have been from the United Kingdom and the USA, with a strong representation from breeders in Scandinavian countries, The Netherlands and Australia.
5% of tests completed so far have identified genetically affected dogs. A further 43% of dogs tested have been identified as carrying one copy of the POAG gene, which they will pass on to around half of their pups.
The DNA testing programme means that breeders can now know exactly where the POAG genes are in their breeding stock to help the Petit Basset Griffon Vendéen community plan their breeding around this. The AHT updates results every month to The Kennel Club and also to clubs in Australia, Netherlands and USA.
CEREBELLAR ATAXIA IN THE SMOOTH-HAIRED HUNGARIAN VIZSLA
Cerebellar ataxia is a rare neurological condition which has been identified in a small number of smooth-haired Hungarian Vizslas. Cerebellar ataxia affects gait and coordination from around two to three months of age and is an aggressive and progressive condition for which there is no treatment. Affected dogs are euthanased on welfare grounds at the advanced stages of the disease.
The genetic mutation was discovered by researchers at the Kennel Club Genetic Centre at the Animal Health Trust in early 2016, in association with the neurology team at the Royal Veterinary College. A DNA test for this emerging disease was made available from the AHT DNA Testing Service on Monday 22 February 2016. The discovery of this genetic mutation was the first at the Animal Health Trust to use whole genome sequencing technology to identify the causative genetic mutation from just one DNA sample from an affected Vizsla.
Traditionally, a genetic investigation into a disease of this nature would require DNA samples from at least twelve affected dogs and the same number of healthy control dogs from the same breed. Now, advanced genome sequencing technology and the use of state-of-the-art computer analysis allows every letter of DNA from a single affected dog to be interrogated and compared to a bank of genome sequences of healthy dogs from different breeds, in order to find the change in DNA responsible for a specific inherited disease. This approach allowed the genetics of cerebellar ataxia in the Hungarian Vizsla to be investigated straight away, without collecting additional DNA samples.
The causal mutation was quickly identified as a single letter change in the 2.4 billion letter DNA code. Once this mutation had been pinpointed, it was confirmed by screening healthy Hungarian Vizsla DNA samples. Only the Hungarian Vizslas with cerebellar ataxia had two copies of the genetic mutation needed to cause the disease. Following further tests to validate the discovery, the DNA test was promptly launched.
This is the same technology at the heart of the AHT’s Give a Dog a Genome project to create the UK’s largest canine genome bank, to benefit all future inherited disease research at the AHT. The discovery of this mutation demonstrates the effectiveness of this technique.
PRIMARY OPEN ANGLE GLAUCOMA IN THE BASSET HOUND
Primary open angle glaucoma, also known as POAG, is a painful condition where the pressure in the eye(s) increases over time eventually leading to blindness. This is an emerging condition in the Basset Hound which is more commonly known to be affected by the other form on inherited glaucoma, primary closed angle glaucoma.
During eye examinations for a genetic research project into primary closed angle glaucoma an AHT vet discovered three Basset Hounds with primary open angle glaucoma - a form of the disease never previously recorded in the breed.
By working closely with the Kennel Club Genetics Centre, which recently developed a DNA test for POAG in another breed, the Petit Basset Griffon Vendeen, the genetic mutation responsible for the condition in Basset Hounds was swiftly discovered and a DNA test made available to order from the AHT DNA Testing Service from Monday 1st June 2015.
This mutation was verified against more than 200 Basset Hound DNA samples which had been collected as part of the initial research into primary closed angle glaucoma. From this sample set the carrier frequency rate was estimated to be 15% of the UK Basset Hound population.
It is hoped that by finding this condition early, and by promptly launching a DNA test, breeders will have the tools and knowledge to be able to get this painful and blinding disease under control in the Basset Hound before it becomes a widespread problem.
SENSORY NEUROPATHY IN THE BORDER COLLIE
Sensory neuropathy (SN) is a severe neurological disease affecting young Border Collies for which there is no treatment. Affected dogs progressively lose the sensation in their limbs due to the degeneration of sensory and motor nerve cells and have to be euthanised.
The onset of the disease is usually between two and seven months of age and clinical signs include knuckling of the feet, self-mutilation wounds (caused by excessive chewing or licking due to the lack of feeling in the limbs) and a progressive lack of coordination (ataxia). SN is currently a rare disease but cases have been seen worldwide in the UK, US, Belgium, Japan and Italy and it is impossible to know which lines contain carriers.
To help Border Collie owners and breeders combat this debilitating disease The Kennel Club Genetics Centre at the Animal Health Trust identified the genetic mutation responsible for SN in early 2015 and developed a DNA test, priced at £48, which will be available to order from the AHT DNA Testing Service from Monday 27 April.
A Border Collie combination test, testing for SN, trapped neutrophil syndrome and Vitamin B12 deficiency will also be available to order from Monday 27 April at a discounted price of £68 for all three tests to make health testing for SN more affordable.
PRIMARY OPEN ANGLE GLAUCOMA IN THE PETIT BASSET GRIFFON VENDEEN
Primary open angle glaucoma, also known as POAG, is a painful condition where the pressure in the eye(s) increases over time eventually leading to blindness. With funding from the Waltham Foundation, the AHT have been investigating an inherited form of this disease which affects the Petit Basset Griffon Vendeen dog breed. The research programme has progressed extremely well and we are delighted to report that the causal mutation for this disorder was identified towards the end of 2014.
A DNA test for POAG in the Petit Basset Griffon Vendeen was launched at Crufts 2015. Our aim, together with breeders, is to completely eradicate POAG from this lovely breed.
MACULAR CORNEAL DYSTROPHY IN LABRADOR RETRIEVERS
Macular corneal dystrophy (MCD) is a hereditary eye disease and although it is a painless condition, it causes severe visual impairment in affected dogs. Dogs affected with MCD will develop cloudy eyes, due to an abnormal accumulation of carbohydrates (known as glycosaminoglycans) in their corneas. The only treatment for the disease in people is to surgically perform a corneal transplant; however this has not yet been performed successfully in the dog for the treatment of MCD.
In 2014, scientists working in the Kennel Club Genetics Centre at the AHT, identified a mutation responsible for the development of MCD in Labrador Retrievers. From 26 January 2015, the AHT will offer a DNA test for MCD which will identify dogs which are clear of, or are carriers of, the genetic mutation.
Primary Lens Luxation (PLL) is a well-recognised, painful and blinding inherited eye condition that affects many breeds of dog, particularly Terrier and Terrier-type breeds including (but not restricted to) Miniature Bull Terriers, Tibetan Terriers, Jack and Parson Russell Terriers, Lancashire Heelers and Chinese Crested dogs. In affected dogs the zonular fibres that support the lens break down or disintegrate, causing the lens to fall into the wrong position within the eye. If the lens falls into the anterior chamber of the eye, glaucoma and loss of vision can quickly result.
In 2009 the Canine Genetics team at the AHT, in collaboration with Dr David Sargan (University of Cambridge, UK), Dr David Gould (Davies Veterinary Specialists, UK) and Gary Johnson’s team at the University of Missouri, USA, identified a mutation that is responsible for the development of PLL in many different breeds of dog. The AHT now offers a DNA test for PLL that examines the DNA from each dog being tested for the presence or absence of this precise mutation.
An ADAMTS17 Splice Donor Site Mutation in Dogs with Primary Lens Luxation
Farias FH, Johnson GS, Taylor JF, Giuliano E, Katz ML, Sanders DN, Schnabel RD, McKay SD, Khan S, Gharahkhani P, O'Leary CA, Pettitt L, Forman OP, Boursnell M, McLaughlin B, Ahonen S, Lohi H, Hernandez-Merino E, Gould DJ, Sargan D, Mellersh CS Investigative Ophthalmology and Visual Science 2010 51: 4716-4721
ADAMTS17 Mutation Associated With Primary Lens Luxation Is Widespread Among Breeds
Gould D, Pettitt L, McLaughlin B,Holmes N, Forman O, Thomas A, Ahonen S, Lohi H, O'Leary C, Sargan D, Mellersh C Veterinary Ophthalmology 2011 14:378-84
Cataracts are a leading cause of blindness in dogs. Using a candidate gene approach, scientists in the Canine Genetics team at the AHT have successfully identified the mutation that causes both hereditary cataract (HC) in Staffordshire Bull Terriers and early onset hereditary cataract (EHC) in Boston Terriers. This is the first mutation to be associated with HC in dogs and is an important breakthrough from both genetics and breeding viewpoints. A DNA test, exclusive to the AHT, is now being offered which will determine the genetic status of dogs, with respect to this mutation, and inform breeders which dogs can be mated together safely, without the risk of producing affected puppies.
Further investigation of the discovered HC causal mutation highlighted a dominant variant in the same gene which conclusively proved to be an increased risk factor for the development of cataract in the Australian Shepherd. A DNA test is also available for this breed.
Identification of mutations in HSF4 in dogs of three different breeds with hereditary cataracts
Mellersh CS, Pettitt L, Forman OP, Vaudin M, Barnett KC Veterinary Ophthalmology 2006 9: 369-378
Mutation in HSF4 associated with early but not late-onset hereditary cataract in the Boston Terrier
Mellersh CS, Graves KT, McLaughlin B, Ennis RB, Pettitt L, Vaudin M, Barnett KC Journal of Heredity 2007 98: 531-533
Mutation in HSF4 is associated with hereditary cataract in the Australian Shepherd
Mellersh CS, McLaughlin B, Ahonen S, Pettitt L, Lohi H, Barnett KC Veterinary Ophthalmology 2009 12: 372-378
L-2-hydroxyglutaric aciduria (L-2-HGA) is a devastating disease that affects the nervous system. Clinical symptoms appear between the ages of six months and one year of age, and include seizures, incoordination (ataxia or wobbly gait), tremors and altered behaviour. Towards the end of 2004, two scientific papers were published announcing the identification of the gene involved with L-2-HGA in humans. We sequenced the same gene in affected and unaffected dogs and identified the mutation causing L-2-HGA in Staffordshire Bull Terriers. A DNA test for L-2-HGA is currently being offered at the AHT to diagnose L-2-HGA in Staffordshire Bull Terriers.
L-2-hydroxyglutaric aciduria: characterisation of the molecular defect in a spontaneous canine model
Penderis J, Calvin J, Abramson C, Jakobs C, Pettitt L, Binns MM, Verhoeven NM, O'Driscoll E, Platt SR, Mellersh CS Journal of Medical Genetics 2007 44: 334-340
Progressive retinal atrophy (PRA) is a well-recognised inherited condition in many breeds of dog. The condition is characterised by bilateral degeneration of the retina which causes progressive vision loss that culminates in total blindness. There is no treatment for PRA - the most successful way to combat the disease is to identify dogs that carry the mutation and develop informed breeding strategies.
In 2010 we developed a DNA test following the identification of the mutation which causes the most common form of PRA among Golden Retrievers in Europe – known as GR_PRA1. In 2012 we developed a second DNA test for PRA in the Golden Retriever, based on a different mutation we identified that causes a genetically different form of PRA in this breed. We named this form of the disease GR_PRA2. The two forms of PRA are clinically identical, but are genetically distinct diseases caused by independent mutations.
Gordon Setters suffer from a late onset form of PRA that doesn’t typically affect dogs until they are around eight years of age. Owners report that their affected dogs develop night blindness in the first instance, which is indicative of a rod-cone degeneration, so we have termed this mutation rcd4 (for rod-cone degeneration 4) to distinguish it from other, previously identified, forms of rod cone degeneration. In 2011 we identified the mutation for rcd4, which we believe is the most common form of PRA in the Gordon Setter, but our investigations indicate that there might be another, genetically distinct, rarer form of PRA in this breed. The rcd4 mutation is also present in Irish Setters and Tibetan Terriers. A DNA test is available for all three of these breeds.
In 2013 we discovered a mutation that causes a different form of PRA in Tibetan Spaniels and Tibetan Terriers. This form of the disease is called PRA3 to distinguish it from other, genetically distinct, forms of PRA that are caused by different mutations, including the rcd4 mutation that is also known to cause PRA in some Tibetan Terriers (described above). A DNA test for PRA3 is available.
Genetic analysis of both a large inbred pedigree and outbred dogs from the worldwide pet population enabled the AHT to identify a mutation that is associated with PRA in Miniature Long-Haired Dachshunds. A DNA test for this mutation is currently being offered at the AHT. We have also found the identical mutation present in English Springer Spaniels and, in collaboration with Dr Gary Johnson at the University of Missouri, USA, we have confirmed that dogs that carry two copies of the mutation have a significantly increased risk of developing PRA. A DNA test for PRA in the English Springer Spaniel was launched in April 2007.
In collaboration with Dr David Sargan (University of Cambridge), we are continuing to investigate the genetic basis of PRA in the Miniature Long-Haired Dachshund, and in particular why there is considerable variation in the age at which Miniature Long-Haired Dachshunds that carry two copies of the PRA mutation develop clinical disease.
A frameshift mutation in golden retriever dogs with progressive retinal atrophy endorses SLC4A3 as a candidate gene for human retinal degenerations
Downs LM, Wallin-Håkansson B, Boursnell M, Marklund S, Hedhammar Å, Truvé K, Hübinette L, Lindblad-Toh K, Bergström T, Mellersh CS PLoS One 2011;6:e21452
Late-onset progressive retinal atrophy in the Gordon and Irish Setter breeds is associated with a frameshift mutation in C2orf71
Downs LM, Bell JS, Freeman J, Hartley C, Hayward LJ, Mellersh CS. Anim Genet. 2013 44: 169-77
Genetic screening for PRA-associated mutations in multiple dog breeds shows that PRA is heterogeneous within and between breeds
Downs LM, Hitti R, Pregnolato S, Mellersh CS Vet Ophthalmol. 2013 Nov 21. doi: 10.1111/vop.12122. [Epub ahead of print]
Canine RPGRIP1 mutation establishes cone-rod dystrophy in miniature longhaired dachshunds as a homologue of human Leber congenital amaurosis
Mellersh CS, Boursnell ME, Pettitt L, Ryder EJ, Holmes NG, Grafham D, Forman OP, Sampson J, Barnett KC, Blanton S, Binns MM, Vaudin M Genomics 2006 88: 293-301Phenotypic variation and genotype-phenotype discordance in canine cone-rod dystrophy with an RPGRIP1 mutation Miyadera K, Kato K, Aguirre-Hernández J, Tokuriki T, Morimoto K, Busse C, Barnett K, Holmes N, Ogawa H, Sasaki N, Mellersh CS, Sargan DR Molecular Vision 2009 15: 2287-2305
Ophthalmic and cone derived electrodiagnostic findings in outbred Miniature Long-haired Dachshunds homozygous for a RPGRIP1 mutation
Busse C, Barnett KC, Mellersh CS, Adams VJ Veterinary Ophthalmology 2011 14: 146-152
A Frameshift Mutation in Golden Retriever Dogs with Progressive Retinal Atrophy Endorses SLC4A3 as a Candidate Gene for Human Retinal Degenerations
Downs LM, Wallin-Håkansson B, Boursnell M, Marklund S, Hedhammer A, Truvé K, Hübinette L, Lindblad-Toh K, Bergström T, Mellersh CS PLoS ONE2011;6:e21452.
Copper toxicosis in Bedlington Terriers is a genetic disorder causing elevated liver copper levels. Affected dogs suffer from hepatitis and progressive cirrhosis of the liver. The gene causing this disorder had been discovered previously, and a large deletion was shown to be the causal mutation for the disease. Additional work at the AHT has enabled the mutation to be fully characterised, allowing development of a robust DNA test.
Above: DNA test results for a Bedlington Terrier that carries the copper toxicosis mutation.
Identification of a new copper metabolism gene by positional cloning in a purebred dog population
van De Sluis B, Rothuizen J, Pearson PL, van Oost BA, Wijmenga C Human Molecular Genetics 2002 11:165-173
Characterization of the COMMD1 (MURR1) mutation causing copper toxicosis in Bedlington Terriers
Forman OP, Boursnell ME, Dunmore BJ, Stendall N, van den Sluis B, Fretwell N, Jones C, Wijmenga C, Rothuizen J, van Oost BA, Holmes NG, Binns MM, Jones P Animal Genetics 2005 36: 497-501
Episodic Falling (EF) in the Cavalier King Charles Spaniel (CKCS) is a serious, debilitating, inherited condition that is distressing for both affected dogs and their owners. EF is an inherited 'exercise-induced hypertonicity disorder' meaning that there is increased muscle tone and the muscles are unable to relax. Episodes usually occur in response to excitement, exercise, or frustration, except in severe cases in which symptoms may be chronic or happen with no apparent cause. Clinical signs usually appear before one year of age and both male and female dogs are affected.
Dry Eye Curly Coat Syndrome, known clinically as Congenital Keratoconjunctivitis Sicca and Ichthyosiform Dermatosis, affects a dog’s eyes and skin. Affected dogs produce no tears making their eyes incredibly sore. Their skin becomes very flaky and dry, particularly around the foot, and this can make standing and walking difficult and painful. This syndrome appears to be a problem unique to CKCS and most dogs diagnosed with the condition are put to sleep.
With funding from the Waltham foundation (Pedigree Masterfoods) and the Kennel Club Charitable Trust we have identified mutations associated with both of these conditions, and DNA tests for CKCS are now available. We have also investigated the frequency of the two mutations in the CKCS population in the UK; a copy of our report can be found by clicking here.
Parallel mapping and simultaneous sequencing reveals deletions in BCAN and FAM83H associated with discrete inherited disorders in a domestic dog breed
Forman OP, Penderis J, Hartley C, Hayward LJ, Ricketts SL, Mellersh CS PLoS Genet. 2012 8:e1002462
Late onset ataxia (LOA) in Parson Russell Terriers (PRT) is a disease of incoordination of gait and lack of balance. The onset age for the disease is usually between six months and one year of age, when owners may start to notice that their dog is showing changes in gait pattern, (often weaving of the hind limbs), and some difficulty balancing.
The disease is progressive and affected dogs become increasingly uncoordinated with difficulty balancing, which makes moving around and everyday tasks such as going up and down stairs difficult. There is no treatment or cure for LOA and affected dogs are often euthanized, typically around two years after onset, on humane grounds, as their quality of life diminishes.
We undertook extensive investigations of LOA in the PRT and successfully identified the mutation responsible for the disease; in November 2012 we launched a DNA test for this mutation in this breed.
Missense mutation in CAPN1 is associated with spinocerebellar ataxia in the Parson Russell Terrier dog breed
Forman OP, De Risio L, Mellersh CS. PLoS One. 2013 May 31;8(5):e64627
Neonatal cerebellar cortical degeneration (NCCD) is a hereditary disease that can affect Beagle puppies. Affected puppies start showing clinical signs around three weeks of age. They are slower and less coordinated than their littermates, fall more often and are unable to regulate a normal gait.
This disease has minimal progression, but currently there is no cure. The clinical signs are due to damage in their cerebellum, which is the part of the nervous system that controls the movement and the equilibrium. In 2012, together with the AHT’s own veterinary neurologists, we used a novel technique to identify the mutation for NCCD in the Beagle and make a DNA test available.
Genome-wide mRNA sequencing of a single canine cerebellar cortical degeneration case leads to the identification of a disease associated SPTBN2 mutation
Forman OP, De Risio L, Stewart J, Mellersh CS, Beltran E. BMC Genet 2012 13:55