An excellent resource for anyone working with individuals with disabilities. A great place to begin your research about any disability, although I wouldn't stick just to this text.
Mark L. Batshaw is an M.D. and is currently the Chief Academic Officer for Children's National Medical Center.
This book contains a good deal of medical terminology, so it is not for the unfamiliar reader. If you're new to the world of disabilities/special education, I would recommend his other book, "When Your Child Has a Disability."
This was one of the textbooks I keep at my desk that I have from graduate school. It is very helpful when I am seeking refreshers about specific disorders or general problems like feeding. I use it often when coworkers or employees come to me with specific questions. Batshaw is able to explain things much more succinctly than I ever will.