Xanthine stones in Drosophila Malpighian tubules (analogous to human hereditary xanthinuria) can be reproducibly generated by mutating the rosy (ry) gene, encoding xanthine dehydrogenase (XDH) (Mitchell and Glassman, 1959; Bonse, 1967; Figure 7—figure supplement 1A–C), or by feeding adults the XDH inhibitor allopurinol (Chi et al., 2015; Figure 7—figure supplement 1D). Here, XDH is linked to xanthinuria.