The World Canine Organization recognizes 332 breeds of dogs, as of 2015. However, there are many different definitions for what constitutes a dog breed. Some consider it to be what your dog looks like - after all, a cocker spaniel or a poodle can be visually told apart - while others might consider the breed to be what its parents were. If a dog is a mix of a poodle and a labrador, that is its breed to some people.
No matter how one defines a dog breed, a purebred dog can have health issues later in life. This is simply due to the fact that by keeping the dogs purebred, the breeders are limiting the genepool to a specific breed and to specific genes.