PARIS (AFP) -- Genetic scientists said on Sunday they could explain why Labrador retrievers, the most popular dog breed in the world, may be prone to suffering a collapse of their rear legs after having exercise.

The answer lies in a mutation of a gene called dynamin 1, or DNM1, on the dog's ninth chromosome that controls a key chemical in the nervous system, they said.
The syndrome, called exercise-induced collapse, was first spotted by vets in the 1990s among a group of Labradors who were undergoing training.
Some five to 15 minutes after getting strenuous exercise, some of the dogs would develop a wobbly gait and a high temperature, followed by a near-complete loss of control over their rear limbs. Most of the affected animals recovered after a rest of 30 minutes, but a few died.
University of Minnesota researchers carried out a gene scan of 96 dogs, 60 of which had the syndrome.
Up to 30 percent of Labrador retrievers carry the mutation, but the problem is concentrated among those dogs who have a double copy of the variant -- chromosomes comprise a string of gene pairs -- rather than a single copy.
In all, an estimated three to five percent of Labrador retrievers suffer from exercise-induced collapse, the scientists believe.
The team developed a gene test to see whether dogs have the normal or mutated form of DNM1, which could help dog breeders. DNM1 controls a chemical that facilitates signaling among adjacent cells in the central nervous system.
The flawed version of DNM1 has diminished function and during intense exercise blocks the communication, preventing muscle-controlling nerves from firing, even when they are instructed to by the brain.
The study appears in Nature Genetics, a journal of the British-based Nature Publishing Group.
""This is very exciting because it is the first naturally occurring mutation of this gene identified in any mammal,"" said James Mickelson, a professor of veterinary sciences at the university. ""Its discovery could offer insight into normal as well as abnormal neurobiology in both animals and humans.""