CAG repeat length in androgen receptor gene is not associated with amyotrophic lateral sclerosis

Background: Epidemiological and clinical studies show higher prevalence of amyotrophic lateral sclerosis (ALS) in males than in females and more severe lesions in androgen receptor (AR)-expressing tissues. The AR gene contains a polymorphic CAG trinucleotide repeat, whose expansion over a certain threshold is toxic to motor neurons, causing spinal and bulbar muscular atrophy (SBMA). Purpose and methods: We tested the hypothesis that the AR CAG repeat linked to SBMA is a risk factor for ALS. We analyzed AR CAG expansions in 336 patients with ALS and 100 controls. Results: We found a negative association of AR CAG expansions with ALS susceptibility, clinical presentation, and survival. Conclusions: Our findings do not support a role of the AR CAG repeat length in ALS.