The aberrant surface phenotype of the thymic epithelium is magnified in Foxn1+/−;Foxn1:Noggin mice, in which the thymus consists of a large cyst; keratin 5-positive epithelial cells occupy a basal location and only few, if any, haematopoietic cells are present (Fig. 3e). The gene discussed is KRT5; the disease is cyst.