Yes diarrhea can be quite a problem with APS-1 and it has several causes. Celiac disease is one. This can be screened for by antibodies (both IgA and IgG subtypes) in the blood for tissue transglutaminase (TTG). Sometimes there is IgA deficiency which can be screened for by a blood test. In the latter case, giardia or bacterial overgrowth of the upper small intestine may be the cause and can be helped by antibiotics or metroniadazole. Patients can also develop autoimmunity to the serotonin rich endocrine cells of the intestine (antibodies against tryptophan hydroxylase which are markers for this problem are I believe not commercially available). The latter may respond to immunosuppressive therapy. In any event, potassium needs to be replaced meantime. Calcium supplements which she needs may help also. Probiotics may be useful. Avoidance of fatty or oily foods will help until the diarrhea has lessened.

Noel Maclaren MD