Canine mdr1 gene mutation in Japan

Frequency of the 4-bp deletion mutant in canine mdr1 gene was examined in 193 dogs of eight breeds in Japan. The mutant allele was found in Collies, Australian Shepherds, and Shetland Sheepdogs, where its respective frequencies were 58.3%, 33.3%, and 1.2%. The MDR1 protein was detected on peripheral blood mononuclear cells (PBMC) from a MDR1/MDR1 dog, but not on PBMC from a mdr1-1 delta, mdr1-1 delta Collie. Rhodamine 123 was extruded MDR1/MDR1 lymphocytes. That excretion was inhibited by a MDR1 inhibitor, verapamil. On the other hand, Rh 123 excretion was not observed from lymphocytes derived from a mdrl-1 delta/mdr1-1 delta Collie. These results indicated that the mutant mdrl allele also existed in Collie-breed dogs in Japan at high rates and that mdrl-1 delta/mdrl-1 delta dogs have no functional MDR1.