Bulbar and spinal muscular atrophy (Kennedy's disease): a review

Bulbar and spinal muscular atrophy (BSMA) is an adult-onset, X-linked recessive trinucleotide, polyglutamine disorder, caused by expansion of a polymorphic CAG tandem-repeat in exon 1 of the androgen-receptor (AR) gene on chromosome Xq11-12. Pathogenetically, mutated AR accumulates in nuclei and cytoplasm of motor neurons, resulting in their degeneration and loss. Phenotypically, patients present with amyotrophic, proximal or distal weakness and wasting of the facial, bulbar and limb muscles, occasionally sensory disturbances, and endocrinologic disturbances, such as androgen resistance, gynecomastia, elevated testosterone or progesterone, and reduced fertility. There may be mild hyper-CK-emia, abnormal motor and sensory nerve conduction studies, and neuropathic and myopathic alterations on muscle biopsy. The golden standard for diagnosing BSMA is genetic analysis, demonstrating a CAG-repeat number >40. No causal therapy is available, but symptomatic therapy should be provided for tremor, endocrinologic abnormalities, sensory disturbances, or muscle cramps. The course is slowly progressive, the ability to walk lost only late in life, only few patients require ventilatory support, and life expectancy only slightly reduced.