Medscape just put this article out which is a reasonable overview. At least they are beginning to realize that there can be different causes. PR
Normal TH metabolism and action require adequate cellular TH signalling. The last decade has witnessed the identification of several novel syndromes resulting from defects in TH transport, deiodination and receptor function. Because the clinical consequences can be severe, it is of utmost important to develop adequate treatment strategies for these different clinical syndromes. These important recent discoveries may hold the promise that the route of TH signalling will turn out to be even more exciting in the near future.