Novel therapeutic approach for spinal and bulbar muscular atrophy (SBMA)

Abstract

Spinal and bulbar muscular atrophy (SBMA) is a hereditary neuromuscular degenerative disease characterized by slowly progressive muscle weakness and atrophy. The cause of SBMA is the expansion of a trinucleotide CAG repeat encoding a polyglutamine tract within the first exon of the androgen receptor (AR) gene. The ligand–dependent nuclear accumulation of the polyglutamine–expanded AR protein is central to the gender–specific pathogenesis of SBMA. The pathogenic AR–mediated neurodegeneration is suppressed by androgen inactivation, the efficacy of which has been tested in randomized controlled trials. Decreases in serum creatinine, a biomarker of SBMA, occurred approximately 15 years before the onset of subjective muscle weakness. The mean serum creatinine concentration is ∼0.6mg/dl and ∼0.8mg/dl at the onset of weakness and hand tremor, respectively. The low serum creatinine concentration in subjects with SBMA is caused by impaired muscle uptake of creatine due to the pathogenic AR–mediated down–regulation of creatine transporter SLC6A8, in addition to being caused by neurogenic atrophy.