Segregation of melanocytic lesions in crosses among the Munich Miniature Swine Troll and German Landrace

Since 1986, a line of Munich Miniature Swine (MMS) Troll showing a high inc idence of spontaneous benign and malignant cutaneous melanocytic lesions ha s been established at the University of Munich. In order to study the inher itance of cutaneous melanocytic lesions in the Munich Miniature Swine Troll , we established the F-1-, F-2- B-IDL-, and B-ITroll-generations, starting with one melanoma-bearing MMS Troll boar and four non-affected sows of the German Landrace (DL) as founder animals. A total of 176 animals were availa ble, 27 in the F-1-, 111 in the F-2-, 19 in the B-IDL-, and 14 in the B-ITr oll-generation. Benign melanocytic lesions with two distinct forms of basal melanocytic hyperplasia or nests of hyperplastic melanocytes like in human junctional nevus were observed in 10 (41,7%) F-1-, 20 (18%) F-2-, 2 (10,5% ) B-IDL-, and 7 (50%) B-ITroll-animals. Malignant melanomas were found in f our (3,6%) F-2- and one (7,1%) B-ITroll-animals, but did not occur in the F -1- and B-IDL-generations. The observed segregation pattern suggests a diff erent mode of inheritance for benign melanocytic lesions and melanomas, res pectively. An influence of SLA haplotypes could not be observed. However, a significant influence of coat colour on the occurence of melanoma could be found in the F-2-generation. While around 65% of F-2-animals had the Germa n Landrace dominant white colour, melanomas were only found in black and re d animals. Benign lesions of the junctional nevus type, too, ware only foun d in black animals. A possible explanation is the lack of melanocytes in th e skin of dominant white pigs caused by a mutation of the KIT-gene, which l eads to a failure of melanoblast migration and development.