In contrast to MHCII-competent controls, pIV−/− K14 CIITA Tg mice gained significantly less weight (Figure 1A), displayed significantly elevated fecal serum albumin levels reflecting augmented protein-losing enteropathy (Figure 1B), and developed a mild but prominent diarrhoea that was not observed in heterozygous control mice (not shown). The gene discussed is CIITA; the disease is Diarrhea.