Modulation of CYP3A4 activityhas a profound influence of the availability of synthetic GCs; CYP3A4 inhibition along withconcomitant synthetic GC administration frequently leads to the development of iatrogenicCushing’s syndrome (Mahlab-Guri etal. 2011, Bernecker etal. 2012). Here, CYP3A4 is linked to Down syndrome.