Spinal and bulbar muscular atrophy (SBMA), popularly known as Kennedy's disease, is a rare, adult-onset, X-linked recessive lower motor neuron disease caused by trinucleotide CAG repeat expansions in exon 1 of the androgen receptor (AR) gene, which results in both loss of AR function and toxic gain of function. In men, the disease slowly progresses over decades with bulbar and lower motor neuron loss, muscle denervation, and direct skeletal muscle involvement. The disease causes progressive muscle loss with weakness, fasciculations, and cramps. Weakness of the bulbar muscles follows causing difficulties in speech (dysarthria) and swallowing (dysphagia). Female carriers do not show symptoms. Although there is no cure, supportive intervention can improve mobility and reduce complications. The prevalence of SBMA has been estimated at 2.6:100,000 males.
