A genome-wide scan was performed to detect quantitative trait loci (QTLs) for osteochondrosis (OC) and osteochondrosis dissecans (OCD) in horses. The marker set comprised 260 microsatellites. We collected data from 211 Hanoverian warmblood horses consisting of 14 paternal half-sib families. Traits used were OC (fetlock and/or hock joints affected), OCD (fetlock and/or hock joints affected), fetlock OC, fetlock OCD, hock OC, and hock OCD. The first genome scan included 172 microsatellite markers. In a second step 88 additional markers were chosen to refine putative QTLs found in the first scan. Genome-wide significant QTLs were located on equine chromosomes 2, 4, 5, and 16. QTLs for fetlock OC and hock OC partly overlapped on the same chromosomes, indicating that these traits may be genetically related. QTLs reached the chromosome-wide significance level on eight different equine chromosomes: 2, 3, 4, 5, 15, 16, 19, and 21. This whole-genome scan was a first step toward the identification of candidate genome regions harboring genes responsible for equine OC. Further investigations are necessary to refine the map positions of the QTLs already identified for OC.
BackgroundCerebellar abiotrophy (CA) is a rare but significant disease in Arabian horses caused by progressive death of the Purkinje cells resulting in cerebellar ataxia characterized by a typical head tremor, jerky head movements and lack of menace response. The specific role of magnetic resonance imaging (MRI) to support clinical diagnosis has been discussed. However, as yet MR imaging has only been described in one equine CA case. The role of MR morphometry in this regard is currently unknown. Due to the hereditary nature of the disease, genetic testing can support the diagnosis of CA.Therefore, the objective of this study was to perform MR morphometric analysis and genetic testing in four CA-affected Arabian horses and one German Riding Pony with purebred Arabian bloodlines in the third generation.ResultsCA was diagnosed pathohistologically in the five affected horses (2 months - 3 years) supported by clinical signs, necropsy, and genetic testing which confirmed the TOE1:g.2171G>A SNP genotype A/A in all CA-affected horses.On MR images morphometric analysis of the relative cerebellar size and relative cerebellar cerebrospinal fluid (CSF) space were compared to control images of 15 unaffected horses. It was demonstrated that in MR morphometric analyses, CA affected horses displayed a relatively smaller cerebellum compared to the entire brain mass than control animals (P = 0.0088). The relative cerebellar CSF space was larger in affected horses (P = 0.0017). Using a cut off value of 11.0% for relative cerebellar CSF space, the parameter differentiated between CA-affected horses and controls with a sensitivity of 100% and a specificity of 93.3%.ConclusionsIn conclusion, morphometric MRI and genetic analysis could be helpful to support the diagnosis of CA in vivo.
SummaryIn this study, we refine a quantitative trait locus for equine osteochondrosis (OC) on horse chromosome (ECA) 2 to a genome-wide significant interval at 20. 08-30.94 Mb. The marker set contained 27 newly developed microsatellites equidistantly distributed over ECA2 and 44 nucleotide polymorphisms, located in 16 positional candidate genes for OC. Genotyping was performed in 211 Hanoverian horses from 14 paternal half-sib groups. A NCDN-associated SNP and haplotype were significantly associated with OC in fetlock and/or hock joints. This study is a further step towards the identification of genes responsible for OC in horses.Keywords association, horse, neurochondrun, osteochondrosis.Osteochondrosis (OC) is an inherited orthopaedic disorder frequently detected radiographically in young horses (Stock et al. 2005;Wittwer et al. 2006). Heritabilities for OC have been estimated in different horse breeds in a range of h 2 = 0.10-0.37 (Schober 2003;Stock et al. 2005;Wittwer et al. 2007;Van Grevenhof et al. 2009). A focal disturbance of chondrocyte differentiation and maturation during the enchondral ossification, most commonly seen in fetlock, hock and stifle joints, is causing OC in horses. Osteochondrotic lesions include subchondral bone cysts, fissures, cartilage flaps and osteochondral fragments. Osteochondral fragments are present in case of an osteochondrosis dissecans (OCD). The clinical manifestation of OC may lead to premature retirement of the animal as a result of chronic or recurrent lameness (Stock & Distl 2006).A chromosome-wide significant quantitative trait locus (QTL) was identified for fetlock and hock OC in Hanoverian warmblood horses at 22.0-49.0 cM (this corresponds to 17.80-32.50 Mb on ECA2). These chromosome-wide significance levels were empirically determined using 1000 replicates (Dierks et al. 2007). The objective of this study was to confirm and refine the position of this QTL using a dense marker set based on newly developed microsatellites and single nucleotide polymorphisms (SNPs) and to identify significant associations of candidate gene-associated SNPs with OC.We used genomic DNA from 211 horses including 104 foals, 99 mares and eight stallions of 14 paternal half-sib families that were not closely related (Table S1). A detailed description of these families and the scheme for diagnosis of OC and OCD can be found elsewhere (Dierks et al. 2007).We supplemented the previously employed marker set for ECA2 with a total of 37 informative and evenly spaced microsatellites. From previously published equine linkage maps, 10 microsatellites could be selected for improvement of the marker set. For a uniform coverage of ECA2, 27 microsatellites had to be newly developed (Table S2).Genotyping of microsatellites was performed as described by Dierks et al. (2007), and details can be found in Table S2. Screening and genotyping for candidate gene-associated polymorphisms was performed by sequencing all PCR products in both directions on a MegaBACE 1000 capillary sequencer (GE Healthcare) for all ...
In this report, we provide 29 new informative microsatellites distributed over a region of 21 Mb on horse chromosome (ECA) 5 and refine a quantitative trait locus (QTL) for fetlock osteochondrosis dissecans (OCD) to a genome-wide significant interval between 78.03 and 90.23 Mb on ECA5. Genotyping was performed in 211 Hanoverian warmblood horses from 14 paternal half-sib groups. Within this OCD-QTL, collagen type XXIV alpha 1 was identified as a potential functional candidate gene for equine osteochondrosis. This report is a further step towards unravelling the genes that cause equine osteochondrosis.
Osteochondrosis (OC) is an inherited developmental disease in young horses most frequently observed in thoroughbreds, trotters, warmblood and coldblood horses. Quantitative trait loci (QTL) for equine OC have been identified in Hanoverian warmblood horses employing a whole genome scan with microsatellites. A QTL on ECA16 reached the genome-wide significance level for hock osteochondrosis dissecans (OCD). The aim of this study was to refine this QTL on ECA16 using an extended marker set of 34 newly developed microsatellites and 15 single nucleotide polymorphisms (SNPs). We used the same 14 paternal half-sib groups as in the above-mentioned whole genome scan. The QTL for OCD in hock joints on ECA16 could be delimited at an interval between 17.60 and 45.18 Mb using multipoint non-parametric linkage analyses. In addition, six microsatellites and one SNP were significantly associated with hock OCD in the QTL region between 24.26 and 42.41 Mb. Furthermore, our analysis revealed a second QTL for fetlock OC between 6.55 and 24.26 Mb on ECA16. This report is a further step towards unravelling the genes underlying QTL for equine OC and towards the development of a marker test for OC in Hanoverian warmblood horses.
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