Consistent with its function, duplication of the X region containing NR0B1 is associated with male-to-female sex reversal in XY individuals, and loss-of-function mutations in NR0B1 are responsible for X-linked adrenal hypoplasia congenita, a disorder characterized by hypogonadotropic hypogonadism (Fig. 1) [18]. This evidence concerns the gene NR0B1 and alternating hemiplegia of childhood.