[Kennedy's disease: expansion of the CAG trinucleotide].

Kennedy's disease is a rare X-linked spinal and bulbar muscular atrophy (SBMA). A degenerative process of the motor neurons is associated with an increase in the number of CAG repeats encoding a polyglutamine stretch within the androgen receptor. Despite a distinctive clinical phenotype, SBMA can be misdiagnosed, usually due to the lack of clear family history. Accurate diagnosis is important for genetic counseling and because alternative diagnosis of amyotrophic lateral sclerosis usually means much worse prognosis. We report 2 unrelated patients with Kennedy's disease in whom the clinical diagnosis was confirmed by showing the CAG repeat expansion.