Among genes with X-linked transmission, defects in DAX1 determine a syndromic association between CHH and congenital adrenal hypoplasia; although penetrance is near-complete (48, 49), phenotypic variability is seen both in the severity of CHH (48–52) and in the age at onset of adrenal insufficiency (48–50, 53, 54). This evidence concerns the gene NR0B1 and cartilage-hair hypoplasia.