Hypochondroplastic dwarfism in the Irish setter

Short and sweet: foreleg abnormalities in Havanese and the role of the FGF4 retrogene

Background

Cases of foreleg deformities, characterized by varying degrees of shortened and bowed forelegs, have been reported in the Havanese breed. Because the health and welfare implications are severe in some of the affected dogs, further efforts should be made to investigate the genetic background of the trait.

A FGF4-retrogene on CFA18 is known to cause chondrodystrophy in dogs. In most breeds, either the wild type allele or the mutant allele is fixed. However, the large degree of genetic diversity reported in Havanese, could entail that both the wild type and the mutant allele segregate in this breed. We hypothesize that the shortened and bowed forelegs seen in some Havanese could be a consequence of FGF4RG-associated chondrodystrophy.

Here we study the population prevalence of the wild type and mutant allele, as well as effect on phenotype. We also investigate how the prevalence of the allele associated with chondrodystrophy have changed over time. We hypothesize that recent selection, may have led to a gradual decline in the population frequency of the lower-risk, wild type allele.

Results

We studied the FGF4-retrogene on CFA18 in 355 Havanese and found variation in the presence/absence of the retrogene. The prevalence of the non-chondrodystrophic wild type is low, with allele frequencies of 0.025 and 0.975 for the wild type and mutant allele, respectively (linked marker).

We found that carriers of the beneficial wild type allele were significantly taller at the shoulder than mutant allele homozygotes, with average heights of 31.3 cm and 26.4 cm, respectively.

We further found that wild type carriers were born on average 4.7 years earlier than mutant allele homozygotes and that there has been a gradual decline in the population frequency of the wild type allele during the past two decades.

Conclusions

Our results indicate that FGF4RG-associated chondrodystrophy may contribute to the shortened forelegs found in some Havanese and that both the wild type and mutant allele segregate in the breed. The population frequency of the wild type allele is low and appear to be decreasing. Efforts should be made to preserve the healthier wild type in the population, increase the prevalence of a more moderate phenotype and possibly reduce the risk of foreleg pathology.

Canine chondrodysplasia caused by a truncating mutation in collagen-binding integrin alpha subunit 10

The skeletal dysplasias are disorders of the bone and cartilage tissues. Similarly to humans, several dog breeds have been reported to suffer from different types of genetic skeletal disorders. We have studied the molecular genetic background of an autosomal recessive chondrodysplasia that affects the Norwegian Elkhound and Karelian Bear Dog breeds. The affected dogs suffer from disproportionate short stature dwarfism of varying severity. Through a genome-wide approach, we mapped the chondrodysplasia locus to a 2-Mb region on canine chromosome 17 in nine affected and nine healthy Elkhounds (p_raw = 7.42×10⁻⁶, p_genome-wide = 0.013). The associated locus contained a promising candidate gene, cartilage specific integrin alpha 10 (ITGA10), and mutation screening of its 30 exons revealed a nonsense mutation in exon 16 (c.2083C>T; p.Arg695*) that segregated fully with the disease in both breeds (p = 2.5×10⁻²³). A 24% mutation carrier frequency was indicated in NEs and an 8% frequency in KBDs. The ITGA10 gene product, integrin receptor α10-subunit combines into a collagen-binding α10β1 integrin receptor, which is expressed in cartilage chondrocytes and mediates chondrocyte-matrix interactions during endochondral ossification. As a consequence of the nonsense mutation, the α10-protein was not detected in the affected cartilage tissue. The canine phenotype highlights the importance of the α10β1 integrin in bone growth, and the large animal model could be utilized to further delineate its specific functions. Finally, this study revealed a candidate gene for human chondrodysplasias and enabled the development of a genetic test for breeding purposes to eradicate the disease from the two dog breeds.

Bone disorders in the dog: a review of modern genetic strategies to find the underlying causes

In man, the genetic defects of more than 600 inherited diseases, of which at least 150 skeletal diseases, have been identified as is the chromosomal location for approximately 7000 genes. This rapid progress has been made possible by the generation of a genetical and physical map of the human genome. There is no reason to believe that for the dog not a similar development may occur. This review is therefore focussed on the use of novel tools now available for comparative molecular genetic studies of skeletal dysplasias in the dog. Because the genomes of mammals at the subchromosomal level are very well conserved, likely candidate disease genes known from other species might be considered. In this review, formation of the bones and the most important canine disorders of the skeleton influencing locomotion will be discussed first. The canine disorders discussed are canine hip dysplasia, the three different forms of elbow dysplasia (fragmented coronoid process, ununited anconeal process, osteochondrosis dissecans and incongruency) and dwarfism. Where possible a link is made with similar diseases in man or mouse. Then, the molecular biological tools available to analyse the genetic defect will be reviewed and some examples discussed.

Evaluation of flea control strategies using fipronil on cats in a controlled simulated home environment

Three groups of six cats were kept in similar carpeted pens in which a self-replicating population of Ctenocephalides felis had been established. One group was left untreated, but the other groups were treated every 28th day with 0.5 ml of a 10 per cent fipronil spot-on formulation, and the cats in one of the treated groups also wore a methoprene collar. No fleas were found on any of the treated cats, either during the first 13 weeks of the study, when heavy flea burdens were developing in the control pen, or over the next 11 weeks when a declining number of fleas was present on the control group.