I'm assuming since dwarfism was ruled out that he was tested for being a little person (non-PC term -midget)? There are differences in dwarves and "midgets" -sorry -I'm not sure what they prefer to be called now except for little people. They are proportionate and basically look normal except they're very short. My 4.5 year old encountered a lady at the grocery store last week, who was fortunately very kind, because before I could catch him he was staring at her in her face! They were the same height, but of course she was an adult woman, so he was quite intrigued. Maybe your son is the same way? Good luck!