--in which an isolated elevated transglutaminase IgG level might be associated with other autoimmune conditions, it is still most likely to point to either developing celiac or non-celiac gluten sensitivity.

The Gluten File in the Useful Websites section of this very forum has a lot of information on this and on celiac in general (and is very nicely indexed).

There is ALSO the possibility that the biopsied simply weren't taken from places that are experiencing villious atrophy, which can be patchy and widespread, especially in the early stages of celiac. If the high titres and/or symptoms persist you may want to get another intestinal biopsy at some point. (What's also important to point out is that doctors, even gastroenterologists, vary greatly in their biopsy skills.)