PYCARD and colitis: In studies using nonlittermate NLRP6 and ASC knockout animals, NLRP6 and ASC were reported to be regulators of the gut microbiome and influence the severity of colitis.21 However, subsequent studies using littermate controls find that NLRP6 and ASC do not regulate the composition of gut microbiota and that maternal inheritance and long-term separate housing are the biggest nongenetic confounders when studying the microbiome.22,23 These studies22,23 and our own argue the necessity of littermate-controlled experiments when studying mechanisms of innate immunity.