Kennedy syndrome a pathological expansion of the AR gene CAG repeats

X-linked spinobulbar muscular atrophy (X-SBMA) or Kennedy syndrome, is a rare inherited neurodegenerative disease characterized by progressive neuromuscular weakness being caused by a loss of motor neurons in the brain stem and spinal cord. Disease onset developing in the third to fifth decade of life is likely to be preceded by muscular cramps on exertion, tremor of the hands and elevated muscle creatine kinase. The initial description of one of the individuals affected with Kennedy syndrome also includes gynaecomastia, a hypoandrogenic symptom (Kennedy et al. 1968). Subsequent reports emphasized the presence of symptoms indicating the development of androgen insensitivity in men with X-SBMA exhibiting varying degrees of gynaecomastia, testicular atrophy, disorders of spermatogenesis, elevated serum gonadotropins and also diabetes mellitus (e.g. Arbizu et al. 1983). Thus, the AR was regarded as candidate gene for X-SBMA and the expansion of the polyglutamine repeat within the N-terminal region was furtheron recognized as the cause (La Spada etal. 1991). The longer the CAG repeat in the AR gene, the earlier the onset of the disease is observed and the more severe the symptoms of hypoandrogenicity are (Choong and Wilson 1998; Dejager etal. 2002; Doyu et al. 1992; Mariotti etal. 2000; Mhatre etal. 1993). The absence of any neuromuscular deficit or degeneration in patients with complete androgen insensitivity (CAIS) (Quigley et al. 1995) suggests that neurological deficits in XBSMA are not caused by a lack of androgen influence but rather by a neurotoxic effect associated with the pathologically elongated number of CAG repeats, which causes irregular processing of the AR protein and accumulation of end products (Abdullah etal. 1998).

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