The present invention provides a method of determining the susceptibility of a dog to liver copper accumulation, comprising detecting the presence or absence in the genome of the dog of (a) a polymorphism in the GOLGA5, ATP7a or UBL5 gene that is indicative of susceptibility to liver copper accumulation and/or (b) a polymorphism in linkage disequilibrium with a said polymorphism (a). The invention also provides a method of determining the likelihood that a dog is protected from liver copper accumulation comprising detecting the presence or absence in the genome of the dog of one or more polymorphisms selected from (a) SNP ATP7a_Reg3_F_6 (SEQ ID NO: 142) and (b) one or more polymorphisms in linkage disequilibrium with (a).
