Anticipation is a phenomenon where the signs and symptoms of a particular genetic condition can become more severe and appear at an earlier age, when compared to the previous generation that had this condition.

Anticipation is more often seen with certain genetic disorders of the nervous system, example: Huntington disease, myotonic dystrophy and fragile X syndrome.

Anticipation occurs with disorders that are caused by an unusual type of variant, called the trinucleotide repeat expansion. A trinucleotide repeat is a sequence of three DNA building blocks (nucleotides) that is repeated a number of times in a row. Usually, DNA segments with an abnormal number of these unstable repetitions cause errors during cell division. The number of repetitions can change as the gene is passed from parent to child. If the number of repetition increases, it is known as a trinucleotide repeat expansion.

There is not a definite explanation for this variability to occur. However, researchers believe a combination of genetic, lifestyle, and environmental factors could cause this genetic variation.