The nuclear receptor superfamily describes a related but diverse array of transcription factors (nuclear hormones). Upon activation by glucocorticoids, mineralocorticoids, sex steroids (estrogen, progesterone, and androgen), thyroid hormones, or vitamin D3, the nuclear receptors can bind a highly specific DNA sequence. As a result, they regulate the expression of adjacent genes, thereby controlling the development, homeostasis, and metabolism of the organism. In the human genome, 48 different nuclear receptors are encoded, which can be classified into 6 evolutionary groups, based on their sequence alignment and phylogenetic tree. All NR proteins exhibit a characteristic modular structure that consists of five to six domains of homology on the basis of regions (A-F) of conserved sequence and function. The DNA-binding domain (DBD, region C), absent in DAX-1 and SHP, and the ligand-binding domain (LBD; region E) are the most highly conserved domains. These two regions are the most important and can function independently.