However, taken together, the observations that reconstitution of Sash mice with mast cells eliminated susceptibility to ulcers and that ulcer susceptibility could be reproduced in WT mice by blockade of histamine H1-receptors provides definitive evidence that mast cells are the primary factor in the observed phenotype, rather than epithelial abnormalities induced from bile reflux from the KitW-sh genotype. The gene discussed is HRH1; the disease is bile reflux.