Triplet repeat

In this situation, a triplet of nucleotides increases in number within a gene. A mutation especially occurring in central nervous system disorders is the increase in the number of normally occurring triplets repeats. Examples include myotonic dystrophy, Huntington's disease and fragile X mental retardation. Expansion may be greater depending on the transmittiong parent (eg, the mother in myotonic dystrophy, the father in Huntington's disease); thus, a parent-of-origin effect and genetic anticipation can be observed.