SINGLE GENE DISORDERS
Our recommendations for Screening for testable Autosomal Recessive Disorders
Single gene disorders become relevant if a dog carries two copies of a disease-related allele.
It should be stressed that overly restrictive breeding recommendations have historically been very harmful for pedigree dog populations. It is important to screen only for conditions where a true threat to health exists.
The following testing recommendations apply to Finnish Lapphunds:
prcdPRA (progressive rod-cone degeneration) Progressive Retinal Atrophy
We recommend that the prcdPRA status should be known for all breeding dogs.
GSD II (Pompe's disease)
Knowledge of GSD II status is highly desirable. A validated, affordable and accessible test for GSD II must be commercially available to Australian breeders before the FLCNSW will formally recommend testing for all breeding dogs.
SOD1-associated Degenerative Myelopathy (DM)
CMR1 Multifocal Retinopathy
These tests are commercially available but the importance of testing all breeding stock for these conditions is not established.
Single gene inheritance disorders are relatively simple to screen for once the mutant allele has been identified. The number of commercial genetic tests is increasing. The mere availability of a commercial test does not mean that testing in all dogs is mandatory for breeders. Only conditions that have significant disease burden within the breed should be critical to test for. Unfortunately commercial entities may encourage breeders and the general public to consider that testing is mandatory for many more conditions than is useful or necessary for breed health.
prcdPRA is the only gene status that the FLCNSW would formally recommend for breeding dogs. prcdPRA is an autosomal recessive single gene disorder. It has been known for many decades that there is clinical PRA disease within the breed. The disease onset of prcdPRA is late and mild in most cases. The testing of every breeding dog is not necessary if documentation of clear-by-parentage status is available. As testing becomes cheaper, breeders may prefer to retest “clear by parentage” dogs every few generations. There is no harm in this practice and does make documentation of carrier status across generations easier.
GSD II (Pompe’s Disease) is an early onset disease and is fatal. It is a rare condition that is present in only a few lines of the breed. A commercial test became available internationally in 2013. As the commercial test for GSD II becomes validated and reliable within Australia, breeders should ensure that the GSD II status of their breeding stock is known. A significant proportion of Australian dogs are expected to be clear by parentage.
A test for CMR1 Multifocal retinopathy has recently become commercially available. This condition affects Lapponian Herders and does very rarely affect Finnish Lapphunds. The Finnish Lapphund carrier frequency is unknown but is likely to be very low. Until better data on the test performance becomes available, clinical eye examination by an approved vet (see recommendation G) is currently still the recommended screening strategy. Testing for CMR1 is optional for this breed at this time.
There has been recent interest in the commercially available genetic test for Degenerative Myelopathy (DM) conferred by a mutation in the SOD1 gene. Dogs with two copies of the mutation are best described as ‘at risk’. This mutation is present in the Finnish Lapphund gene pool. Exact carrier frequency is not yet established, but is likely to be between 25% and 40% of the Finnish Lapphund population. DM is a condition with both reduced penetrance and variable expressivity. Multiple other genes are at work to affect expression of the disease. Some breeds with extremely high rates of DM allele frequency have long lives but are not known to be affected by the disease. Other breeds with low DM allele frequency are well known to be affected. It is possible that DM has not been recognised in Finnish Lapphunds because it is a late onset disease where the manifestations of disease in dogs at risk have been attributed to very old age. It is also possible that the disease does not manifest very frequently in Finnish Lapphunds. Nevertheless, at time of writing (Jun 2017) there have been two older dogs in Finland who were ‘at risk’ of DM and who have manifested clinical symptoms consistent with DM disease. One of these dogs has died and has displayed findings at autopsy consistent with DM.
For the Finnish Lapphund breed, The SOD1 mutation is the first ‘susceptibility gene’ that has been found where the health consequences for ‘at risk’ dogs are not certain. It is inevitable that the dilemma of whether to screen for different susceptibility genes will recur many times in the future as the genetic basis for more health conditions are revealed.
Healthy dogs suitable for breeding programs should never be excluded merely because of their SOD1 carrier status. Where voluntary testing has occurred and the SOD1 status of breeding dogs is known, breeders should:
avoid carrier-to-carrier matings.
choose a known clear mate if the dog is homozygous/ ‘at risk’
(Supported by FCI-IBS 5, JTO, LBC.)