Androgen receptor<unk>  is caused by expansion of a CAG repeat in the first exon of the androgen receptor gene (trinucleotide repeats). The CAG repeat encodes a polyglutamine tract in the androgen receptor protein. Patients with longer CAG expansions tend to develop more severe disease manifestations and earlier disease onset. The repeat expansion likely causes a toxic gain of function in the receptor protein, since loss of receptor function in androgen insensitivity syndrome does not cause motor neuron degeneration.<unk>  may share mechanistic features with other disorders caused by polyglutamine expansion, such as Huntington's disease. For example, the polyglutamine expanded androgen receptor is known to misfold and aggregate. This aggregation of the mutant protein is dependent on the presence of testosterone, the ligand for the androgen receptor. As a result, though female carriers of the CAG repeat expansion express the polyglutamine androgen receptor protein, due to lower levels of testosterone they do not develop disease. Similarly, in animal models of<unk>  castration dramatically reduces disease phenotype. Polyglutamine expansion of the androgen receptor has a number of known cellular and molecular consequences, including disrupting cellular signaling pathways, protein homeostasis, and cellular trafficking.
Spinal and bulbar muscular atrophy
Infantile progressive bulbar palsy
Ataxic cerebral palsy
Madras motor neuron disease
Multiple system atrophy
Spinal muscular atrophy
Spinal muscular atrophy with lower extremity predominance 1
Babinski–Nageotte syndrome