Hmm. I am not aware of anyone in my family that has an auto-immune disease. The exception would be my first cousin once removed, who, I just recently found out (we are approximately the same age) also has T1D. This is a rather obscure connection, though. I thought it was strange when I found out about him, but I cannot think of any common relatives with auto-immune conditions.
Also, I had heard the vitamin D deficiency theory before, and related that it is most common for T1D to be diagnosed in the winter. I don't know how true that is, but I was diagnosed in June. I played sports in school and had spent a lot of time outdoors just prior to my diagnosis. I have no idea if I was sick - it's too long ago to remember.