Identification of a nonsense mutation in feline ABCB 1

The aim of this study was to sequence all exons of the ABCB 1 ( MDR 1) gene in cats that had experienced adverse reactions to P‐glycoprotein substrate drugs (phenotyped cats). Eight phenotyped cats were included in the study consisting of eight cats that experienced central nervous system toxicosis after receiving ivermectin ( n = 2), a combination product containing moxidectin and imidacloprid ( n = 3), a combination product containing praziquantel and emodepside ( n = 1) or selamectin ( n = 2), and 1 cat that received the product containing praziquantel and emodepside but did not experience toxicity ( n = 1). Fifteen exons contained polymorphisms and twelve exons showed no variation from the reference sequence. The most significant finding was a nonsense mutation ( ABCB 1 1930_1931del TC ) in one of the ivermectin‐treated cats. This cat was homozygous for the deletion mutation. All of the other phenotyped cats were homozygous for the wild‐type allele. However, 14 missense mutations were identified in one or more phenotyped cats. ABCB 1 1930_1931del TC was also identified in four nonphenotyped cats (one homozygous and three heterozygous for the mutant allele). Cats affected by ABCB 1 1930_1931del TC would be expected to have a similar phenotype as dogs with the previously characterized ABCB 1‐1Δ mutation.