The CNM Project in France recently released an update on their research into Centronuclear myopathy (CNM) in Labrador Retrievers. You can read the very scientific update at http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046408
In a nutshell, CNM is a collapsing disorder. Symptoms generally develop between two to five months of age and include gait abnormalities, generalized weakness and tiring easily, a lack of "knee cap" reflexes and muscle wasting. CNM can affect both sexes and all three recognized colors.
It's a genetic disorder and requires two copies of the CNM gene - one from each parent.
Puppies with only one copy of the gene are carriers and don't develop symptoms, but if they are later bred they can pass the CNM gene on to their puppies. The researchers estimate one dog in seven is a carrier so all breeding animals should be tested (unless both parents are tested clear).
Dogs that are affected or carriers can be bred, but must be bred to a dog clear of the CNM gene to prevent producing more affected dogs. And that's in addition to testing for dysplasia and eye problems, at the very least!
In the past seven years the researchers tested samples from over 7,400 Labs and found 80 affected dogs. They believe it started with a single mutation about 50 years ago and has rapidly spread to at least 18 countries through the use of popular sires.
Although it is not fatal, it is a debilitating disorder and an affected dog will require a supportive caretaker.
Here is a video of a 5 month old affected puppy. Note the general weakness and body position, particularly the head and neck.
Here is a video of another Lab having a particularly tough day although she's determined to get her bumper.
Here is a video of an adult Lab who has been able to overcome many of the symptoms of CNM with the help of his caregivers. According to his owners, "As a puppy, he couldn't hold his head up, control his tongue, hold a tug toy, walk for more than a few feet without having to crawl, or climb stairs."
And, no, CNM is not the same as Exercise Induced Collapse (EIC), although both disorders are genetic. CNM is a muscle weakness whereas EIC is a neurologic dysfunction.
Here is a video from the University of Minnesota where they are doing research on EIC.