Context: DAX1 (for dosage-sensitive sex reversal, adrenal hypoplasia congenital critical region on the X chromosome, gene 1; also called NROB1) mutations are responsible for adrenal failure and hypogonadotropic hypogonadism in patients with adrenal hypoplasia congenita (AHC), through a loss of trans-repression of SF-1 (for steroidogenic factor-1)-mediated StAR (for steroidogenic acute regulatory protein) and LHβ transcriptional activities and a reduction of GnRH expression. The correlation of clinical features with genetic and functional alterations of the gene was investigated in detail in AHC patients. Objective: The present study aimed at identifying DAX1 mutations in Chinese AHC patients and investigating the functional defects of detected novel mutations. Patients and Methods: Nine patients with AHC were recruited from eight families. DAX1 mutations were screened, and the transcriptional activities of the identified mutations were assessed in vitro. Results: DAX1 mutations were detected in all nine patients enrolled in the study, with eight different mutations. Among the latter, seven are novel mutations, including two missense (L262P and C368F), one nonsense (Q222X), and four frame-shift (637delC, 652-653delAC, 973delC, and 774-775insCC) mutations. The functional studies showed that the mutant DAX1 was impaired by nuclear localization, loss of trans-repression of StAR and LHβ transcriptional activities, and reduction of GnRH expression. Conclusion: These findings provide insight into the molecular events by which DAX1 mutations influence the hypothalamus-pituitary- gonadal and hypothalamus-pituitary-adrenal axis and lead to AHC and hypogonadotropic hypogonadism. Copyright © 2010 by The Endocrine Society.