Nuclear receptors in disease: thyroid receptor beta, peroxisome-proliferator-activated receptor gamma and orphan receptors

The nuclear receptor superfamily comprises a group of proteins that includes the molecular targets for classical steroid hormones such as glucocorticoids, androgens and vitamin D, together with a number of so-called 'orphan' receptors whose ligands and/or function remain to be determined. Many of the world's most commonly prescribed drugs act via nuclear receptors, attesting to their importance as therapeutic targets in human disease [for example, the novel anti-diabetic thiazolidinediones rosiglitazone and pioglitazone are high-affinity ligands for peroxisome-proliferator-activated receptor gamma (PPARgamma)]. The study of transgenic mice harbouring global and tissue-specific alterations in nuclear receptor genes has greatly enhanced our understanding of the roles that these receptors play in mammalian physiology. In many cases, these findings have been complemented by the study of human subjects harbouring naturally occurring mutations within the corresponding receptor, whereas in others, such studies have served to highlight important differences that exist between human and mouse physiology especially, for example, in relation to aspects of metabolism. Here we review the diverse clinical phenotypes that have been reported in subjects found to have germline mutations in thyroid hormone receptor beta, PPARgamma, hepatocyte nuclear factor 4alpha, small heterodimer partner, steroidogenic factor 1, DAX1, photoreceptor-specific nuclear receptor and NUR-related factor 1, and consider the molecular mechanisms through which aberrant signalling by mutant receptors might contribute to the pathogenesis of the associated disorders.