Landseer Muscular Dystrophy
Landseer Muscular dystrophy is a genetic disorder that causes progressive deterioration of the muscles in Landseer dog breed. Generally, muscular dystrophy (MD) is a group of heterogeneous muscle diseases that weaken the muscoskeletal system and disrupt walking or moving abilities. Other than progressive skeletal muscle weakness, these disorders are characterized by defects in muscle proteins, and the death of muscle cells and tissue. Muscular dystrophy is known to affect dogs, cats and humans. Among dogs, it is the most common among Golden Retriever breed, but it differs in genetic background and mode of inheritance from muscular dystrophy in Landseer dogs. Other dog breeds affected with X-linked muscular dystrophy are Irish terriers, Pembroke Welsh Corgi, Samoyed, Rottweiler, Belgian Shepherd, Miniature Schnauzers and others.
Characteristics and Symptoms
Collagen VI myopathies are a group of muscular dystrophies that are relatively less studied and understood than other groups od MDs. Collagen VI is an extracellular matrix protein, composed of three chains. The three chains together compose collagen VI molecule that further binds in complexes of dimers and tetramers. Through further binding, such molecules surround the basement membranes of fibers, binding components of the extracellular matrix and transferring mechanical and biochemical signals from the extracellular matrix to the muscle cell. The three subunits, or chains, that compose the collagen VI molecule are encoded by three genes, the COL6A1, COL6A2, and COL6A3 gene. Mutations within these genes can cause specific forms of muscular dystrophies.
Some of the common symptoms of Landseer Muscular Dystrophy are muscular weakness, excessive drooling, difficulty breathing, muscle spasms, difficulty moving tongue, limb deformity, tremors and gait abnormalities. Manipulation of the joints seems to be painful for the dog. Gait abnormalities include short, strided gait in the thoracic and pelvic limbs. While standing dog’s back seem arched and the pelvic limbs are placed under the abdomen. On palpation, the muscles of the limbs seem to be atrophied. Articulations of elbow, carpus, hip, and tarsus have a decreased range of motion. Elevated body temperature is possible and auscultation of the lungs can reveal hard sounds. Neurologically, the gag reflex seems to be reduced. Other neurological abnormalities have not been identified and affected dogs seem mentally alert. Creatine kinase activity is elevated, as well as leukocyte cell count in more severely affected dogs. Radiographic examination reveals generalized megaesophagus and aspiration pneumonia in the severely affected dogs.
Affected dogs usually are euthanized due to severity of the disorder at 5 months of age.
Landseer Muscular dystrophy is associated to a mutation in COL6A1 gene.
The disorder is inherited in an autosomal recessive manner. Dog can be clear, carrier or affected. Healthy parents of an affected puppy are obligate heterozygotes, and therefore carry one mutant allele. Heterozygotes have no symptoms. Dogs homozygous for the mutation will display the symptoms of the muscular dystrophy. At conception, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
Steffen, F., Bilzer, T., Brands, J., Golini, L., Jagannathan, V., Wiedmer, M., Drögemüller, C., Drögemüller, M. & Leeb, T. (2015). A nonsense variant in COL6A1 in Landseer dogs with muscular dystrophy. G3: Genes| Genomes| Genetics, 5(12), 2611-2617.