Osteochondrosis (OC) is a developmental disease in horses with a significant impact on the horse's welfare and performance. Previously, differentially expressed genes in leukocytes of OC-affected have been identified and were differentially expressed in horses of different ages when compared to their age-matched controls.As the time course of the development of OC lesions seems to be joint dependent,the aim of this study is to compare in young OCaffected horses (between 8 to 12 months), the different expression of selected genes depending the joints involved.The expression of OC-related genes were analysed by rt-PCR and subsequent statistical analysis (ΔΔCT) in the leukocytes of 30 Belgian Warmblood horses aged between 8 to 12 months divided in groups depending the affected joints (fetlock, hock and stifle).In the three groups, expression of ApoB-3G, MGAT4A, B4GALT6 and PRKCG genes were significantly higher in the OC-affected foals compared to the healthy foals. Based on the profiles of expression ofApoB-3G, Dsh1/Dvl1, Foxl1, Hp, ISG15, Mark2, PPR2A, RUSC2 and WASH1 genes,the localization of the disease can be determined: expression levels of ApoB3G, WASH1 and FOXl1 to identify fetlock, ApoB3G, PPR2A to identify OC-development in the hock and ApoB3G, Dsh1/Dvl1, WASH1, PPP2R1A and Mark2 geneto identify OC-development in the stifle. However at this moment, the rt-PCR analysis of the identified genes as biomarkers gives only diagnostic information. For the future, the profile of expression of these genes could give also some predictive information on the evolution of the disease such as remission or permanent OC-lesions.