SLC6A18 and Hartnup disease: Additionally, the formation of large membrane complexes in the intestinal/renal epithelial transporters B0AT1 and B0AT3 and IMINO (SLC6A19, 18, and 20, respectively) and their complex interactions with the ancillary proteins ACE2 and collectrin in the small intestine and kidney, respectively participate in the etiology of Hartnup disorder (Kowalczuk et al., 2008; Camargo et al., 2009; Fairweather et al., 2012; Fairweather et al., 2015).