Trinucleotide repeat expansion and anticipation
How unstable repeats expand between generations, the repeat thresholds for Huntington disease, myotonic dystrophy and fragile X, parent-of-origin effects, and why standard sequencing misses them.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Short tandem repeats (most often three bases) become unstable above a threshold and tend to lengthen when passed on.
- Longer repeats cause earlier onset and worse disease. That is the molecular basis of anticipation.
- Parent of origin matters: Huntington disease expands through fathers; congenital myotonic dystrophy and fragile X full mutations arise through mothers.
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Sources
- GeneReviews: Huntington DiseaseUniversity of Washington, Seattle (NCBI Bookshelf NBK1305)
- GeneReviews: Myotonic Dystrophy Type 1University of Washington, Seattle (NCBI Bookshelf NBK1165)
- GeneReviews: FMR1 DisordersUniversity of Washington, Seattle (NCBI Bookshelf NBK1384)
- GeneReviews: Friedreich AtaxiaUniversity of Washington, Seattle (NCBI Bookshelf NBK1281)
- Nolin SL et al. Expansion of the fragile X CGG repeat in females with premutation or intermediate alleles. Am J Hum Genet 2003;72:454-64American Journal of Human Genetics, 2003
- Reproductive carrier testing for cystic fibrosis, spinal muscular atrophy and fragile X syndrome (MBS items 73451 and 73452) factsheetAU/NZAustralian Government Department of Health, MBS Online, 2023
- MBS Online: items 73451 and 73452 (reproductive carrier and partner testing)AU/NZAustralian Government Department of Health, Disability and Ageing, 2023
- Thompson & Thompson Genetics and Genomics in Medicine (9th ed.)Elsevier (Cohn, Scherer and Hamosh, eds), 2023
- Last updated
- 14 November 2026
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