- Appearance before the appointed time of a periodic symptom or sign.
- Progressively earlier age of manifestation of a hereditary disease in successive generations; may be factitious (because of heightened awareness of early signs of the disease or because these signs are more conspicuous in the young) or authentic (because of progressive loss of epistatic and modifier genes by recombination and segregation, or because of expansion of unstable alleles in successive generations).
- An increase in the severity of a phenotype in successive generations of a family, often associated with an increase in the number of trinucleotide repeats in a causative gene (e.g., fragile X syndrome, myotonic dystrophy, Huntington disease).
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