There is a test for that: Neurogenetic conditions breeders know about (Proceedings)

Over the last decade, the resources required to perform genetic studies in dogs have been developed and made available. Key amongst these is the high quality 7.5x canine genome sequence assembly (a Boxer) with automated gene annotation to other species [http://www.ncbi.nlm.nih.gov/genome/guide/dog/], and a detailed dog SNP library [http://www.broadinstitute.org/mammals/dog/snp2]. High-density canine SNP arrays offered by both Affymetrix and Illumina are now available, allowing rapid genotyping to be performed. As a result, there has been an explosion in the understanding of the genetic causes of canine traits and many neurological disorders have been investigated. As a result, a wide variety of genetic tests are now available and are frequently well known to breeders of a specific breed. This presentation will summarize some of the more important neurogenetic tests developed in recent years.

Degenerative myelopathy

One of the most exciting developments in neurology is the work performed by Dr. Coates' laboratory on the genetic basis of degenerative myelopathy1. Working on the Pembroke Welsh Corgi, they discovered a mutation in superoxide dismutase was associated with the disease trait. Genotyping of additional breeds demonstrated that the same mutation is associated with degenerative myelopathy in German Shepherd dogs, Boxers, Chesapeak Bay Retrievers and additional breeds. This genetic test is now available through OFA. Dogs have to carry two copies of this recessive gene to develop the disease, but it is extremely important to understand that age affects expression of the disease. Degenerative myelopathy is a disease of old dogs, and so a paraparetic young dog that is positive on the genetic test, is likely to have an additional disease causing signs at that time. The test is used by breeders to make breeding decisions, and is diagnostic for the disease if other causes of paraparesis have been ruled out.

Exercise induced collapse of labrador retrievers

This is an episodic disorder of Labrador Retrievers in which heavy exercise causes para and then tetraparesis. Signs reverse relatively rapidly with rest and often with cooling and water. Heat worsens the signs. Recently Dr. Patterson's laboratory identified the causative mutation to involve the gene dynamin 1 (DNM1)2. This gene encodes a protein that is vital for synaptic vesicle formation and therefore important in neurotransmission. The disease is autosomal recessive and the test is offered by the University of Minnesota. Animals with two copies of the mutant gene develop signs of the disease.

Myotonia congenita of miniature schnauzers

Myotonia is an autosomal recessive disease of muscle caused by a mutation in the chloride channel3. Clinical signs manifest at a few weeks of age and include muscle stiffness, a bunny hopping gait and hypertrophy of the tongue, causing difficulty swallowing. The dogs also have craniofacial morphological abnormalities. The genetic test is available at the University of Pennsylvania offered by Dr. Urs Giger's laboratory. Animals with two copes of the mutant gene develop signs of the disease.

Labrador retriever myopathy or centronuclear myopathy (CNM)

This is another autosomal recessive disease, this time causing signs of generalized muscle weakness in young Labrador Retrievers. The disease has been called many different names over the last 30 years, but most recently has become known as centronuclear myopathy. A mutation has been identified in the PTPLA gene that is associated with the disease4. The genetic test for this disease is offered by the French company Antagene through Optigen. Again, animals with two copies of the mutated gene will develop signs.

Neuronal ceroid lipofuschinosis

There are now several different recognized mutations for this storage disease and tests are offered for the American Staffordshire Terrier by Antagene through Optigen, and Dachshunds can be tested on a research basis by Dr O'Brien at Missouri.

Myoclonic epilepsy (Lafora's Disease) in wire haired dachshunds.

In this unusual form of epilepsy, auditory and visual stimuli can trigger myoclonus in Wire Haired Dachshunds. Onset of signs is usually between six and nine years of age, and is associated with the widespread presence of Lafora's bodies in the brain and other tissues. The disease is due to an expanded nucleotide repeat5. The test is not commercially available but the Hospital for Sick Children in Canada may be able to provide it on a research basis.

Cerebellar abiotophy in the Italian Spinone

Cerebellar abiotrophies are a relatively common disorder in pure-bred dogs, and many groups are working on the genetics of these diseases. A genetic test is available for the Italian Spinone, offered by the Animal Health Trust, although the underlying mutation has not yet been identified.

References

Awano T, Johnson GS, Wade CM, Katz ML, Johnson GC, Taylor JF, Perloski M, Biagi T, Baranowska I, Long S, March PA, Olby NJ, Shelton GD, Khan S, O'Brien DP, Lindblad-Toh K, Coates JR. Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis. Proc Natl Acad Sci U S A. 2009 Feb 24;106(8):2794-9.

Patterson EE, Minor KM, Tchernatynskaia AV, Taylor SM, Shelton GD, Ekenstedt KJ, Mickelson JR. A canine DNM1 mutation is highly associated with the syndrome of exercise-induced collapse. Nat Genet. 2008 Oct;40(10):1235-9.

Vite CH, Melniczek J, Patterson D, Giger U. Congenital myotonic myopathy in the miniature schnauzer: an autosomal recessive trait. J Hered. 1999 Sep-Oct;90(5):578-80.

Pelé M, Tiret L, Kessler JL, Blot S, Panthier JJ. SINE exonic insertion in the PTPLA gene leads to multiple splicing defects and segregates with the autosomal recessive centronuclear myopathy in dogs. Hum Mol Genet. 2005 Jun 1;14(11):1417-27.

Lohi H, Young EJ, Fitzmaurice SN, Rusbridge C, Chan EM, Vervoort M, Turnbull J, Zhao XC, Ianzano L, Paterson AD, Sutter NB, Ostrander EA, André C, Shelton GD, Ackerley CA, Scherer SW, Minassian BA Expanded repeat in canine epilepsy Science. 2005 Jan 7;307(5706):81.