Test Detail

MDR1 / ABCB1-1Δ (drug sensitivity)

Metabólico · Dog

Loss-of-function mutation in the ABCB1 gene (formerly MDR1) that encodes P-glycoprotein, a drug efflux pump present in the blood-brain barrier. Without this pump, certain drugs (ivermectin and other endectocides, loperamide, some chemotherapeutic agents such as doxorubicin/vincristine and certain anaesthetics) accumulate in the central nervous system, causing neurotoxicity that can be fatal. It is not a structural disease: it is an inherited pharmacogenetic condition, and knowing about it prevents severe iatrogenic poisonings.

Inheritance pattern	Autosomal recessive with a dose effect (heterozygotes show intermediate sensitivity at high doses)
Gene / Mutation	ABCB1-1Δ (4-bp deletion in ABCB1/MDR1)
Penetrance	Homozygotes Δ/Δ: fully sensitive phenotype (typical neurotoxicity with ivermectin at high doses and with other drugs even at usual doses). Heterozygotes Δ/N: documented intermediate sensitivity to high doses — they must be managed clinically as if they were sensitive. Outside exposure to P-glycoprotein substrate drugs, the dog is healthy.
Code	samk
Turnaround time	7 days
Price	34,22 €

Incidence

Historically high mutant allele frequencies in long-haired Collie, Shetland Sheepdog, Border collie (low but present), Australian Shepherd, Old English Sheepdog (Bobtail), long-haired Whippet, Silken windhound, white Swiss shepherd, Mc Nab and Elo; also described in Walliser-Sennenhund. Systematic screening in organised breeds has greatly reduced the frequency of homozygotes. The specific percentages per population are not cited here: limited data.

Breeder management

- Test ALL breeding lines of affected breeds before the first mating.\n- Clear × carrier: acceptable, progressively replacing offspring with clear animals.\n- Carrier × carrier and affected × anything: avoid (risk of Δ/Δ puppies exposed to everyday drugs).\n- Record the status in health booklets and communicate it to every veterinarian who attends the animal throughout its life.\n- In breeds with a high frequency (Collie, Sheltie), keep updated lists of breeding dogs and use clear males whenever possible to accelerate the reduction of the allele.

Specialist notes

Official list of problematic drugs maintained by WSU (P-gp substrates): avermectins/milbemycins at high antiparasitic doses, loperamide, acepromazine and butorphanol (caution), quinidine, doxorubicin, vincristine, vinblastine, Actinomycin D, mitoxantrone, emodepside. Diagnostic alternative to the DNA test: fluorescence functional test (does not replace genotyping for breeding). Consider pre-anaesthetic and pre-chemotherapy genotyping in at-risk breeds even if the owner does not request it.

References

1. Mealey KL, Bentjen SA, Gay JM, Cantor GH. Ivermectin sensitivity in collies is associated with a deletion mutation of the mdr1 gene. Pharmacogenetics. 2001.. PMID: 11692082
2. Mealey KL. Therapeutic implications of the MDR-1 gene. J Vet Pharmacol Ther. 2004.. PMID: 15500562

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