[Disease-modifying therapy for spinal and bulbar muscular atrophy (SBMA)]

Neurodegenerative diseases have long been construed as incurable disorders. However, therapeutic developments for these diseases are now facing a turning point, that is, analyses of cellular and animal models have provided insights into the pathogenesis of neurodegenerative diseases and have indicated rational therapeutic approaches. Spinal and bulbar muscular atrophy (SBMA) is an adult-onset motor neuron disease characterized by slowly progressive muscle weakness and atrophy. This disease is caused by the expansion of a trinucleotide CAG repeat within the androgen receptor (AR) gene. The results of animal studies suggest that testosterone-dependent nuclear accumulation of the pathogenic AR protein is a fundamental step in the neurodegenerative process. Androgen deprivation with a luteinizing hormone-releasing hormone (LHRH) analogue suppresses the toxicity of the mutant AR in animal models of SBMA. In a phase 3 trial, 48 weeks of treatment with leuprorelin acetate, an LHRH analogue, tended to improve swallowing function in a subgroup of SBMA patients with disease duration less than 10 years but did not significantly affect the total population. Disease duration might influence the efficacy of leuprorelin acetate, and therefore, a further clinical trial that involves sensitive outcome measures is in progress. Advances in basic and clinical research on SBMA are now paving the way for the clinical application of pathogenesis-targeting therapies. To optimize translational research related to the process of testing candidate therapies in humans, it is important to identify biomarkers that can be used as surrogate endpoints in clinical trials for neurodegenerative diseases.