Canine Chondrodysplasia is an inherited bone and cartilage disorder and in Norwegian Elkhound and Karelian Bear Dog. It is an autosomal recessive disease. Wider, complex group of bone and cartilage disorders is known as skeletal dysplasias. Forms of the disorder within this bigger group vary in modes of inheritance, symptoms and causative mutations. They affect humans and dogs. Canine chondrodysplasia, other than in Norwegian Elkhound and Karelian Bear Dog, has been reported in the Alaskan Malamute, Miniature Poodle, Samoyed, Labrador Retriever, Scottish Deerhound, English Pointer, Great Pyrenees and the Irish Setter. Among these dog breeds, the disorder is inherited in an autosomal recessive inheritance pattern in Alaskan Malamutes, Great Pyrenees, Irish Setters, and, as previously mentioned, Norwegian Elkhound and Karelian Bear Dog. The disorder’s phenotype was first described in 1980’s in a Norwegian Elkhound dog.
Characteristics and Symptoms
Bone formation takes place in the epiphyseal growth plates of the long bones. The cartilaginous growth plates are composed of extracellular matrix and of differentiating chondrocytes. They are organized into different zones, zone of resting, proliferating, mature and hypertrophied cells, which are with time replaced by trabecular bone. Mutations in genes encoding proteins that affect growth plates can lead to various pathologies. As significant cause of chondrodysplasia are genes encoding extracellular matrix proteins and also genes encoding receptors that regulate growth plate chondrocyte differentiation and proliferation.
Radiographic findings in affected dogs show curved front limbs, carpal valgus, shortening of vertebral bodies, delayed ossification of carpal bones and increased metaphyseal width and flaring. The stature appears as short and standing can be troubling in case of present hip dysplasia. In growth plates unusual wide bards of extracellular matrix is evident, as well as abnormally large chondrocytes with unusual morphology.
Canine Chondrodysplasia in Norwegian Elkhound and Karelian Bear Dog is associated to mutation in the ITGA10 gene, which results in encoding of truncated integrin subunit alpha 10 protein. Integrins are membrane proteins composed of two chains, alpha and beta. They have a role in cell adhesion as well as cell-surface signaling. Integrin subunit alpha 10 protein combines with the beta chain in order to form a collagen type integrin which is expressed and needed in cartilage tissues.
Chondrodysplasia in Norwegian Elkhound and Karelian Bear Dog is inherited in an autosomal recessive manner. 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 skeletal dysplasia. 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.
Kyostila K, Lappalainen AK, Lohi H (2013:) Canine Chondrodysplasia Caused by a Truncating Mutation in Collagen-Binding Integrin Alpha Subunit 10. PLoS ONE 8(9): e75621. doi:10.1371/journal.pone.0075621