Which cytogenic findings are characteristic of X-linked spinobulbar muscular atrophy (SBMA) (Kennedy disease)?

Updated: Apr 28, 2014
  • Author: Hidehiro Takei, MD; Chief Editor: Adekunle M Adesina, MD, PhD  more...
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Answer

Answer

X-linked spinobulbar muscular atrophy (SBMA) is an adult-onset recessive disorder. Female carriers of the mutation usually are clinically unaffected. The molecular basis of SBMA is the expansion of a trinucleotide cytosine-adenine-guanine (CAG) repeat, which encodes the polyglutamine tract, in the exon 1 of the androgen receptor gene on chromosome Xq11-12.

The CAG repeat ranges in size from 11 to 35 in normal individuals but ranges from 40 to 62 in SBMA patients. [46] Expanded CAG-repeat size is inversely correlated with age at onset and has a slight tend3ncy to further expansion in successive generations (ie, anticipation). [5] Molecular genetic testing for the CAG trinucleotide repeat expansion is available on a clinical basis.

The pathogenesis of this polyglutamine disorder is still unclear; however, there are strong indications that aggregation of the mutant androgen receptors within the nucleus or cytoplasm of motor neurons and visceral cells results in disruption of cellular functions in SBMA patients. [5]


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