Test Detail

MDR1 defect (ivermectin sensitivity)

Metabólico · Cat

The ABCB1 gene (formerly MDR1) encodes P-glycoprotein, an efflux pump of the blood-brain barrier that prevents numerous drugs from reaching the central nervous system. When the gene does not function, certain medications (ivermectin and other macrocyclic lactones, loperamide, some chemotherapeutic agents) reach toxic concentrations in the brain, with severe neurotoxicity that can be fatal. In the cat, the evidence on specific ABCB1 variants is more limited than in the dog.

Inheritance pattern	Considered recessive; in other species an incomplete dominant inheritance is debated.
Gene / Mutation	ABCB1: 2-base-pair deletion c.1930_1931delTC (OMIA:001402-9685), which produces a truncated non-functional protein. The feline variant described is rare.
Penetrance	Homozygotes for loss-of-function variants lack functional P-glycoprotein at the blood-brain barrier and are at greater risk. In the cat the deletion does not explain all cases of toxicity, so the test should be interpreted with caution.
Code	hvel
Turnaround time	7 days
Price	36,05 €

Incidence

In the dog the classic deletion reaches high frequencies in the Collie and related breeds. In the cat the population frequency is not established: in the original study the deletion was rare (1 affected homozygous cat and 4 non-phenotyped cats).

Breeder management

- Communicate the result to all veterinarians involved and note it in the health record.\n- Avoid or adjust the dose of ivermectin and macrocyclic lactones in general, loperamide and chemotherapeutic agents that are substrates of P-glycoprotein (e.g. vincristine, doxorubicin), always under veterinary protocol.\n- For deworming, choose alternatives with a proven safety margin in cats and at labelled doses.\n- It is not grounds for reproductive exclusion in itself: it is a pharmacogenetic trait managed clinically.

Specialist notes

Differentiate ABCB1 neurotoxicity from other causes of acute neurological signs: pyrethroid or permethrin poisoning (common in cats), metabolic encephalopathies and epilepsy. Permethrin is toxic to all cats because of their glucuronidation deficit, regardless of ABCB1: never use dog antiparasitic products on cats. In case of exposure, urgent decontamination and supportive treatment.

References

1. Mealey KL, et al. Ivermectin sensitivity in collies is associated with a deletion mutation of the mdr1 gene. Pharmacogenetics. 2001;11(8):727-733. PMID: 11692082
2. Mealey KL, Burke NS. Identification of a nonsense mutation in feline ABCB1. J Vet Pharmacol Ther. 2015;38(5):429-433. PMID: 25660379
3. Mealey KL. Canine ABCB1 and macrocyclic lactones: heartworm prevention and pharmacogenetics. Vet Parasitol. 2008;158(3):215-222. PMID: 18922637

Add to cart

← Back to the search