Fast and simple detection methods for the 4-base pair deletion of canine MDR1/ ABCB1 gene by PCR and isothermal amplification

Novel genotyping assay for the nt230 (del4) ABCB1 gene mutation and its allele frequency in Border Collie dogs in Mexico

A 4-bp deletion in the ATP-binding cassette subfamily B member 1 (ABCB1) gene, also referred to as the multidrug resistance gene (MDR1), produces stop codons that cause premature termination of P-glycoprotein 1 (P-gp) synthesis. Dogs with the homozygous mutation do not express functional P-gp, which increases their sensitivity markedly to many common veterinary drugs. We detected the nt230 (del4) ABCB1 mutation in Border Collie dogs in western Mexico with a simple and affordable primer-introduced restriction analysis PCR (PIRA-PCR). PIRA-PCR clearly identified all genotypes in our sample of 104 dogs. Genotype frequencies were 0.952 (wild/wild), 0.029 (wild/mut) and 0.019 (mut/mut). Allele frequencies were 0.033 (mutant alleles) and 0.966 (wild-type alleles). In this small subset of the Mexican dog population, we found a higher prevalence of the nt230 (del4) MDR1/ABCB1 gene mutation than reported in other countries.

Heartworm disease - Overview, intervention, and industry perspective

Dirofilaria immitis, also known as heartworm, is a major parasitic threat for dogs and cats around the world. Because of its impact on the health and welfare of companion animals, heartworm disease is of huge veterinary and economic importance especially in North America, Europe, Asia and Australia. Within the animal health market many different heartworm preventive products are available, all of which contain active components of the same drug class, the macrocyclic lactones. In addition to compliance issues, such as under-dosing or irregular treatment intervals, the occurrence of drug-resistant heartworms within the populations in the Mississippi River areas adds to the failure of preventive treatments. The objective of this review is to provide an overview of the disease, summarize the current disease control measures and highlight potential new avenues and best practices for treatment and prevention.

Two methods for genotyping a 4-base deletion in the canine ABCB1 gene

A 4-bp deletion (c.230_233delATAG) of the ABCB1 gene, frequently found in various dog breeds, results in intolerance to certain drugs routinely used in veterinary medicine, including many chemotherapeutic agents and macrocyclic lactones. The use of rapid and reliable genetic testing is fundamental for early detection of the mutation and prevention of undesirable toxicoses. We developed and compared 2 genotyping tests: PCR-high-resolution melting (PCR-HRM) and PCR-restriction-fragment length polymorphism (PCR-RFLP) to identify the 4-bp deletion in the ABCB1 gene of canine breeds. Amplified PCR products were sequenced in order to confirm different genotypes. Both techniques were efficient in discriminating homozygous wild-type, homozygous mutated, and heterozygous ABCB1 genotypes, and proved to be reproducible and economical methods. The HRM analysis, a sensitive and specific method for the molecular detection of genetic disorders, does not require labeled probes, processing, or separations after PCR.

Development of an oligonucleotide microarray for simultaneous detection of two canine MDR1 genotypes and association between genotypes and chemotherapy side effects

Canine MDR1 gene mutations produce translated P-glycoprotein, an active drug efflux transporter, resulting in dysfunction or over-expression. The 4-base deletion at exon 4 of MDR1 at nucleotide position 230 (nt230[del4]) in exon 4 makes P-glycoprotein lose function, leading to drug accumulation and toxicity. The G allele of the c.-6-180T>G variation in intron 1 of MDR1 (single nucleotide polymorphism [SNP] 180) causes P-glycoprotein over-expression, making epileptic dogs resistant to phenobarbital treatment. Both of these mutations are reported to be common in collies. This study develops a more efficient method to detect these two mutations simultaneously, and clarifies the genotype association with the side effects of chemotherapy. Genotype distribution in Taiwan was also investigated. An oligonucleotide microarray was successfully developed for the detection of both genotypes and was applied to clinical samples. No 4-base deletion mutant allele was detected in dogs in Taiwan. However, the G allele variation of SNP 180 was spread across all dog breeds, not only in collies. The chemotherapy adverse effect percentages of the SNP 180 T/T, T/G, and G/G genotypes were 16.7%, 6.3%, and 0%, respectively. This study describes an efficient way for MDR1 gene mutation detection, clarifying genotype distribution, and the association with chemotherapy.

Frequency of canine nt230(del4) MDR1 mutation in prone pure breeds, their crosses and mongrels in Israel - insights from a worldwide comparative perspective

Background

Sensitivity to macrocyclic lactones, which are commonly used in veterinary clinics, was first found in Rough Collies, and was attributed in 2001 to a 4 bp deletion in the MDR1 gene. The list of affected breeds currently includes 13 breeds. Researchers from different countries and continents examined the allelic frequencies of the nt230(del4) MDR1 mutation, emphasizing the clinical importance of this test not only to mutation-prone dogs, but also to their crosses and mongrels, since treatment of a deletion carrier with these compounds may lead to its death.

In this study, the allelic frequencies of nt230(del4) MDR1 mutation in affected breeds, their crosses, unrelated pure breeds and mongrels are reported for the state of Israel (n = 1416 dogs). The Israeli data were compared with reports from the US, Europe, UK, Australia and Japan.

Results

The allelic frequencies of nt230(del4) MDR1 mutation in Israel for Australian, Swiss and German Shepherds (31%, 17% and 2.4%, respectively) are similar to the corresponding frequencies worldwide, much higher for Border Collies (4.8%), twice lower for Rough Collies (28%, compared to 55% or more elsewhere), and ~1% for mongrels. The frequencies for crosses of Australian Shepherd and Border Collies in Israel are 4 and 1.6 times lower, respectively, compared to the frequencies for the respective pure breeds.

Conclusions

This work, that for the first time presents the frequency of nt230(del4) MDR1 mutation in Israel, along with a worldwide survey, has implications for clinicians, owners and breeders of sheepdogs and their crosses and supports the need for extra care in treatment and in future breeding. Of note, the relative proportion of affected breeds, in the overall tested dogs, might be higher than their actual proportion in Israel due to directed samples collection by veterinarians for clinical purposes, as these are mainly limited to certain affected breeds or dogs that resemble them.

Electronic supplementary material

The online version of this article (10.1186/s12917-017-1251-9) contains supplementary material, which is available to authorized users.