Observations across studies that examined mice with additional Irgm deficiencies indicate that the three genes (Irgm1, Irgm2, and Irgm3) have nonredundant functions and complex interregulatory relationships, as evidenced by mice displaying differential susceptibilities to infection with various intracellular pathogens depending on which Irgm genes are inactivated (1). The gene discussed is IRGM; the disease is infection.