Assistance or service dogs help the disabled. They are generally broken down into three categories, guide dogs, hearing dogs and service dogs (which are for disabilities other than blindness or deafness). There are many kinds of service dogs, almost as many as there are kinds of disabilities.
Some service dogs are mobility dogs for the physically disabled who pick up dropped items, open and close doors, and turn on lights among other things.
There are also dogs that assist with medical-related disabilities, such as neurological, developmental, psychiatric, and diabetic disabilities.
Service dogs are about any breed you can imagine, depending on what job they perform. Larger dogs are used to pull wheel chairs, while smaller dogs might be more convenient for medical alert purposes. It all depends on the specific needs of the person with a disability.
Just about any type of disability might be mitigated by an appropriately trained service dog.