Why can we just find the defective gene in familial histiocytic diseases and breed unaffected dogs to eliminate these diseases?
Both forms of familial histiocytic disease (reactive and neoplastic) likely are polygenic disorders. That is there are multiple genetic defects involved in the development of these diseases. It is likely that combinations of abnormal genes lead to disease. Hence, even outwardly normal individuals could carry altered genes that are only manifest when they coexist with other critical altered genes necessary for disease development. Hence, 2 totally unaffected parents can produce dogs with high susceptibility to disease development if the right mix of genes is present. Clearly this is a far more complex situation than simple single recessive or dominant genetic traits. The existence of multiple silent genetic abnormalities is difficult to exclude on an individual basis until all genes contributing to development of histiocytic disease have been identified. Identification of disease susceptibility genes and gene mapping efforts are currently not very advanced in the canine genome. So there
