Caused by trinucleotide repeat expansion (CAG)n in the ataxin-3 gene (MJD, 607047.0001) [MOLECULAR BASIS] Onset in third to fourth decade [MISCELLANEOUS] Normal alleles contain up to 44 repeats [MISCELLANEOUS] Wide clinical variability [MISCELLANEOUS] Pathogenic alleles contain 52 to 86 repeats [MISCELLANEOUS] Genetic anticipation [MISCELLANEOUS] Incomplete penetrance with 45 to 51 repeats [MISCELLANEOUS] Progressive disorder [MISCELLANEOUS]
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