HOX genes have been implicated in the regulation of Sf-1 transcription in the developing adrenal.14 Transgenic mice with increased foetal Sf-1 expression showed extra-adrenal formation and mice with a Sf-1 sumoylation mutation have a persistent X zone, suggesting that the bigger foetal derived X zone seen in the adrenal of the transgenic Sf-1:Hoxb9 mice could be due to the higher Sf-1 levels.40,41 Whether this pathway is active in adrenal tumours is unclear as we did not observe an increase in Sf-1 protein in the adrenals of double-mutant mice. Here, HOXB9 is linked to adrenal gland neoplasm.