Sunday, December 14, 2014

Ivermectin Sensitivity in Nine Herding Breeds

This is from an article I wrote for The Bark. You can read the entire piece, Deconstructing Gene Pools: Dr. Mark Neff and his team uncover the surprising origin of a potentially deadly mutation (The Bark, issue 34, Jan/Feb 2006).

“Recent research has shown that a single mutated gene, unnoticed for over a century, is responsible for sensitivity to several modern medicines. These adverse drug responses can cause illness or death in dogs that harbor the mutation, including nine herding breeds.”

The ubiquitous working collies and spaniels of Europe spawned a number of the breeds created during the prosperous, class-conscious Victorian era. In the age of upward mobility, those on the way up claimed many of the privileges of the upper class, including the luxury of breeding, showing and “creating” pedigreed animals.
Clockwise: Four of nine affected herding breeds with frequency of mutation:
Silken Windhound (17.9%), Long Haired Whippet 41.6%),
Miniature Aussie (25.9%), and Collie (highest frequency - 54.6%)
More than one-quarter of the world’s estimated 375 breeds were created between 1859, when the first dog show was held in the UK, and 1900, when Westminster and Crufts were well established; even the most subtle differences in weight or color were enough to allow registry of a new breed type. In many cases, the subdivision of farm dogs was an unintended consequence of competitive exhibition in dog shows.

Responding to the shows’ strict criteria for body type, size and color, breeders drew from an increasingly smaller number of founder populations to create dogs who conformed to these standards. Breeding closely related dogs to one another became a popular way to refine a breed, which today means a group of dogs with a common gene pool and characteristic appearance and function.
Unfortunately, the down-side of homozygosity (having two identical genes at a specific location on the DNA strand) can be disease and unsoundness. Partly as a consequence of this intense concentration on form, modern dogs suffer from more than 350 genetic illnesses, and today’s breeders bear the burden of restoring their lines to health.


There are no easy answers. Removing affected individuals from breeding populations may decrease the incidence of a particular disease, but smaller gene pools create opportunities for other congenital problems. In cases where an entire breed is afflicted, out-crossing with other breeds may mean running the risk of losing truly unique traits.

Recent research has shown that a single mutated gene, unnoticed for over a century, is responsible for sensitivity to several modern medicines, ranging from ivermectin (a common ingredient in heartworm preventatives) to anticancer agents such as vincristine. These adverse drug responses can cause illness or death in dogs that harbor the mutation, including nine herding breeds.
Top to Bottom: Five affected herding breeds with frequency of mutation:
McNab (17.1%), Shetland Sheepdog (8.4%), English Shepherd (7.1%), 

Aussie (16.6%), and Old English Sheepdog (3.6%).

A team of researchers led by Professor Mark Neff at UC Davis expanded the results of earlier research by demonstrating that the mutation probably originated in a single generic herding dog who lived in Great Britain in the mid-1800s. This dog must have been a common ancestor of founding dogs for nine different breeds, all of which were found to possess the mutation. Moreover, scientists involved in this study were able to describe the frequency of the mutation in these various breeds, further defining the inherited risk of adverse drug response.

Dr. Neff talked to me about his research and the implications of genetic testing on the health and well-being of dogs. Read the interview in the 2006 winter edition of The Bark.

1 comment:

  1. I never realized that certain breeds of dogs and cats carry genetic problems until I got a maine coon from our pound. She had a heart defect and didn't know until it was too late. One of the things I like, is to see breeders who breed out the defects by testing their dogs before breeding.

    Debbie

    ReplyDelete