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Editor’s note: X-linked spinal and bulbar muscular atrophy (SBMA) is caused by an expansion of the CAG repeats in the first exon of the gene that encodes the androgen receptor (
AR). It is a slowly progressive disorder in which there is degeneration of the lower motor neurones. However, in some cases gynecomastia, pain, cramps, and postural tremor precede the development of muscle weakness.