Pathophysiology
As reported in 1991, SBMA 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. The greater the expansion of the CAG repeat, the earlier the disease onset and more severe the disease manifestations. 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. Spinal and bulbar muscular atrophy may share mechanistic features with other disorders that are caused by polyglutamine expansion, such as Huntington's disease. There is currently no treatment or cure for SBMA.
It is a lower motor neuron disease.
Read more about this topic: Spinal And Bulbar Muscular Atrophy