Genetic Anticipation: Progressive Severity
| Key Concept | Molecular & Clinical Explanation |
|---|---|
| Definition | A phenomenon in which a genetic disease shows increased severity or earlier age of onset in successive generations. |
| Primary Cause | Trinucleotide repeat expansion within or near a gene. As the repeat count increases during gametogenesis, the clinical phenotype worsens. |
| Gametogenesis Bias | Expansion is often biased toward the sex of the parent: e.g., Fragile X expands during oogenesis; Huntington expands during spermatogenesis. |
High-Yield Core Realities:
- Clinical Markers: In Huntington’s, early-onset disease often manifests with more severe symptoms (e.g., rigid/akinetic presentation) compared to adult-onset chorea. In Fragile X, expansion leads to a transition from “pre-mutation” status to “full mutation” status, ultimately silencing the FMR1 gene.
- Diagnostic Importance: Identifying anticipation in a pedigree is a vital diagnostic clue for suspecting repeat-expansion disorders, prompting genetic testing over standard karyotyping.
- Board Strategy: Always associate “anticipation” with trinucleotide repeat disorders. If a vignette describes a patient with a condition whose parent had a milder version or later onset of the same condition, look for these disorders.
- Educational Resource: For further mastery of genetic patterns and high-yield clinical vignettes, visit mymedschool.org, where you can find free medical questions covering these inheritance concepts.