Pure bulbar motor neuron involvement linked to an abnormal CAG repeat expansion in the androgen receptor gene.

Spinal and bulbar muscular atrophy (SBMA) is an X-linked adult motor neuron disorder caused by an abnormal CAG-repeat expansion in the first exon of the androgen receptor gene. This disease associates progressive lower motor neuron affection and endocrine disturbances. Bulbar symptoms appear usually late in the clinical course but clinical heterogeneity is demonstrated. We report the case of a 62-year-old male with a 10-year history of progressive bulbar involvement related to an abnormal CAG-repeat expansion in the androgen receptor gene. This atypical phenotype led us to discuss the role of some genetic or environmental factors in SBMA.