Review on canine elbow dysplasia: pathogenesis, diagnosis, prevalence and genetic aspects.

Elbow dysplasia (ED) is a progressive skeletal disease, which may comprise osteoarthrotic changes, incongruity of the joint, a fragmented medial coronoid process (FCP), osteochondrosis dissecans of the trochlea humeri (OCD), and an ununited anconeal process (UAP). Disturbances of enchondral ossification, as well as asynchronous growth of the antebrachial bones and an increased growth rate may provoke abnormal stresses on specific locations such as the medial coronoid process, the anconeal process of the ulna or the humeral trochlea, which may result in ED. Overnutrition with calcium, vitamin D and energy had important influence on rapidity of growth and proneness to ED. ED manifests most often in young dogs less than 1 1/2 year, causing clinical signs such as (intermittent) lameness, pain on movement and altered posture of the affected limb, and radiographically secondary osteoarthrotic changes such as osteophytes or the aforementioned primary lesions. As radiographic projection of the primary lesions FCP and OCD may be difficult in the commonly used mediolateral flexed and craniocaudal views, additional projections such as mediolateral extended or anteroposterior oblique views and alternative diagnostic means such as computed tomography (CT) may be worth considering. Cases of ED are reported in various breeds, though some breeds are especially predisposed and seem to be prone to specific primary lesions. For the German shepherd dog, a breed-predisposition for UAP may be explained by broad chondral junction in association with an accelerated pattern of skeletal maturation. Heritabilities were estimated in a variety of studies, depending strongly on the type of model used. The mode of inheritance is not yet ascertained, but recently the common assumption of a polygenic mode of inheritance for ED is doubted. Instead, genetic independence was supposed between different primary lesions, and also for ED as well as for FCP major gene influence was discussed. So long, phenotypic mass selection was accomplished in different countries most often resulting in a reduced prevalence of ED. The use of best linear unbiased prediction (BLUP) methods including information on relatives and separate evaluation of genetically independent primary lesions may further improve selection against ED.

Inheritance of canine hip dysplasia: review of estimation methods and of heritability estimates and prospects on further developments.

Canine hip dysplasia is a long-known, widespread degenerative skeletal disease. A hereditary component of hip dysplasia was assumed early, although attempts to explain hip dysplasia with known Mendelian modes of inheritance did not sufficiently fit the data observed. Nevertheless, both recessive and dominant modes of inheritance were proposed. Later on, it was proposed that CHD was determined in a multifactorial way. Both the influence of many genes and environmental effects were assumed to affect the development of CHD. More recently, this thesis was supplemented and refined, as a major gene was detected as a cause of CHD in addition to a polygenic component. Nowadays, projects are under way with the aim to locate quantitative trait loci (QTL) significantly linked to CHD, and ultimately to develop gene tests to identify carriers of genes responsible for CHD.

Genetic analysis of three different classification protocols for the evaluation of elbow dysplasia in German shepherd dogs.

OBJECTIVES: Three different scoring systems for elbow dysplasia and its radiographic signs were genetically evaluated in 2645 German shepherd dogs. METHODS: An animal model was used to estimate heritabilities and additive genetic and residual correlations for the three scoring systems: ED-SV, which is recommended by the International Elbow Working Group; ED-LA, developed by Lang and others; and ED-TH, proposed by Tellhelm. RESULTS: The effects of sex, age at examination and the correlation between the two factors were significant for all three scoring systems. Heritability estimates (se) were 0.18 (0.04) for ED-SV, 0.11 (0.03) for ED-LA and 0.16 (0.04) for ED-TH. The additive genetic correlations among the different single criteria for elbow dysplasia and the different elbow dysplasia scores were between 0.68 and 0.98, except for the criteria ununited anconeal process and osteochondrosis dissecans of the trochlea humeri, which were mostly genetically negatively correlated to the other radiological criteria. CLINICAL SIGNIFICANCE: The elbow dysplasia scores were determined by two genetically different traits. The possibilities for selecting German shepherd dogs with respect to elbow dysplasia might be improved by taking into account these two traits in the prediction of breeding values.

Complex segregation analysis of canine hip dysplasia in German shepherd dogs.

Complex segregation analyses were carried out to clarify the mode of inheritance of canine hip dysplasia (CHD) in German shepherd dogs. Data were used from 8,567 animals examined for CHD from 20 families with three to four generations. The existence of a major gene in addition to polygenic gene effects was detected. In the present study, a mixed model with a dominant major gene effect seemed to be most probable for dichotomous encoding (0: dogs without signs of CHD; 1: dogs with borderline/slight to severe CHD). In addition, mixed major gene inheritance was shown for a binary trait where borderline was assigned to dogs scored free from CHD and for a trichotomously encoded trait (0: dogs without signs of CHD; 1: borderline CHD; 2: mild to severe CHD). Although only small frequencies were found for the unfavorable homozygotic genotype AA, the probability of the AB genotype was high in affected animals. Selection schemes to reduce the frequency of the allele A should therefore efficiently improve existing breeding programmes in German shepherd dogs.

Genetic evaluation of elbow angles as predictors of elbow dysplasia in German shepherd dogs.

Elbow angles were measured in X-rays of both elbows to elucidate the usefulness of such data for selecting against elbow dysplasia (ED) in German shepherd dogs. These measurements record the size, proportions and alignments of the anconeal process (PA), the radius (RA), the olecranon (OL), and the ulnar trochlear notch (UL). The reference system for evaluating the information content of the measurements was the score for ED (ED-SV) as recommended by the International Elbow Working Group. Data from 2645 X-rayed dogs born from 1998 to 2001 in 1331 kennels were analysed by using residual maximum likelihood procedures to estimate heritabilities, additive genetic correlations and residual correlations. The pedigree file included 11,426 dogs and contained ancestors for up to six generations. ED-SV was significantly influenced by sex, by age within sex and by month of birth. The elbow angles were significantly influenced by the month and year of birth, X-ray positioning of the dog's forelimbs, angle of elbow flection, litter size and number of dogs X-rayed by the veterinary practitioners. The following heritability estimates were found: h2=0.18+/-0.04 for ED; h2=0.76+/-0.04 for OL; h2=0.52+/-0.05 for PA; h2=0.50+/-0.04 for UL; and h2=0.39+/-0.04 for RA. The additive genetic correlations of ED-SV with three elbow angles (OL, UL and RA) were close to zero. A higher additive genetic correlation to ED-SV was found only for PA, for which r(g)=0.31. The distributions of predicted breeding values for susceptibility to ED were not affected by regarding the elbow angles as additional traits in the multivariate prediction procedure. Measurements of elbow angles were thus shown to be unsuitable for use in selection programmes against ED in German shepherd dogs.