As Nppb−/− survival declined, autopsy of moribund animals revealed a significant incidence of mesenteric vasculitis with enlarged and tortuous mesenteric arteries (Fig. 3A,B, indicated by black arrows), similar to polyarteritis nodosa (PAN); a phenotype not observed in Nppb−/− males19. This evidence concerns the gene NPPB and polyarteritis nodosa.