We analyzed the ACTH, 11-deoxycortisol (11-DOC) and cortisol levels at different time-points during an overnight single-dose MTP test in 93 Dutch children with PWS and investigated whether the response to the single-dose MTP test changes with age, using two different cut-off points of acute stress-related CAI based on either the ACTH or 11-DOC peak. The gene discussed is POMC; the disease is Prader-Willi syndrome.