Good to see your awareness about type 1 diabetes
and related immunological diseases. I hope your son is receiving standard care for both type 1 diabetes and thyrotoxicosis
. Well as far as the common concomitant autoimmune disorders
are concerned, you get serum cortisol tested early in the morning (8 am) along with IgG, serum sodium and potassium to rule out adrenal insufficiency
, then anti-tTG to rule out celiac disease
. Other diseases like autoimmune vitiligo, autoimmune deficiency of reproductive hormones (autoimmune hypogonadism) are really very rare. Serum RA factor and Vit B12 is something you must get it done as the tests are easy and easily available everywhere. All the very best.