Which gene mutation causes susceptibility to toxic neurological reactions in dogs and cats?

The MDR1 gene mutation is indeed associated with increased susceptibility to toxic neurological reactions in both dogs and cats. This mutation results in a defect in the multidrug resistance protein 1 (MDR1), which plays a crucial role in the transport of various drugs and toxins across the blood-brain barrier. When an animal has this mutation, the protective barrier becomes less effective in preventing harmful substances from entering the central nervous system, leading to potentially severe neurological reactions.

Certain breeds, particularly herding breeds like Collies, are known to be more affected by the MDR1 mutation, which makes them particularly sensitive to certain medications, such as ivermectin. This sensitivity can result in severe neurological symptoms, including seizures, ataxia, and even coma, when exposed to normal doses of these drugs.

Other gene mutations listed, such as BRCA1, TP53, and CFTR, are associated with different health issues and conditions but do not have the same implications for drug and toxin susceptibility in dogs and cats as the MDR1 mutation does.