Correlation between the CAG repeat size and electrophysiological findings in patients with spinal and bulbar muscular atrophy

ABSTRACT Introduction Spinal and bulbar muscular atrophy (SBMA) is caused by the expansion of a CAG repeat in the androgen receptor gene. The relationship between the CAG repeat size and electrophysiological findings is not completely understood. Methods We retrospectively analyzed 62 SBMA patients to assess the correlation between their CAG repeat size and electrophysiological findings. Results In multiple regression analysis including age at examination and disease duration, we identified a negative correlation between the CAG repeat size and the compound muscle action potential (CMAP) amplitude. No significant correlation was found between the CAG repeat size and sensory nerve action potential (SNAP) amplitude. Discussion Contrary to previous reports of motor‐ and sensory‐dominant phenotypes correlating with CAG repeat sizes, the CAG repeat size was negatively correlated only with CMAP amplitude, and not with SNAP amplitude. Muscle Nerve 57: 683–686, 2018