tendency in certain genetic disorders for individuals in successive generations
to present at an earlier age and/or with more severe manifestations; often
observed in disorders resulting from the expression of a trinucleotide repeat
mutation that tends to increase in size and have a more significant effect
when passed from one generation to the next
Definition from: GeneReviews
from the University of Washington and the National Center for Biotechnology Information
Each generation of offspring has increased severity of a genetic disorder; e.g., a grandchild may have earlier onset and more severe symptoms than the parent, who had earlier onset than the grandparent.