A. Edwards, A. Civitello, H.A. Hammond, C.T. Caskey, "DNA typing and genetic mapping with trimeric and tetrameric repeats," American Journal of Human Genetics, 49:746, 1991.
C. Thomas Caskey (Baylor College of Medicine, Houston): "Tandem repeats of three or four nucleotides are common in the human genome and frequently contain different numbers of repeated units. They are, therefore, extremely useful for genetic linkage studies, personal identification, and, most recently, for diagnosis of disease-producing mutations for spinal and bulbar muscular atrophy (SBMA), fragile X syndrome, and myotonic dystrophy. In the case of disease-producing mutations, the repeat sequences can be unstable in germline and somatic tissues once the number of repeats reaches 50-60. Further expansion of the repeat region leads to the disease. The extent to which expansions of triplet repeats are associated with other genetic diseases is currently under investigation.
"These simple tandem repeats are very useful for genetic linkage...