Kennedy's disease: clinical significance of tandem repeats in the androgen receptor.

Kennedy's disease (KD) or spinobulbar muscular atrophy is a hereditary X-linked, progressive neurodegenerative condition caused by an expansion of the CAG triplet repeat in the first exon of the androgen receptor gene. The phenotype in its full form is only expressed in males and presents as weakness and wasting of the upper and lower limbs and bulbar muscles associated with absent reflexes. Sensory disturbances are present. Various endocrine abnormalities including decreased fertility and gynecomastia are common and amongst the first features of KD. Animal models of KD have demonstrated improvement on withdrawal of testosterone, indicating that this agonist of the androgen receptor is required for the toxic effect. Potential therapies based on testosterone withdrawal in humans have shown some promise, but efficacy remains to be proven. Potential clinical factors, pathogenesis and future approaches to therapy are reviewed in this chapter.