There is no official miniature Irish wolfhound dog breed. Dogs that appear to be a miniature Irish wolfhound are mixed-breed dogs that may be part wolfhound or that may be some completely different combination of breeds.
Mixed-dog breed dogs known as "designer dogs" are two different purebred dogs bred together. For example, a labradoodle is a Labrador retriever bred with a standard poodle. Some dogs that look like a miniature version of a giant breed dog such as the Irish wolfhound are actually designer dogs.
There are no designer dogs, however, that breed an Irish wolfhound with a smaller dog to produce a miniature Irish wolfhound. Most designer dogs involving the Irish wolfhound are crosses with another large-breed dog.