“Anticipation” describes a remarkable phenomenon in which a genetic disease appears earlier and with increased intensity with each succeeding generation. Anticipation was once thought not to exist in genetics. However, it has now been proven to occur in a large number of important genetic disorders, including Huntington’s disease and myotonic dystrophy. In molecular terms, anticipation is due to the expansion of a trinucleotide repeat sequence in the DNA. This phenomenon also occurs in the fragile X syndrome, the most common inherited form of mental retardation.