GENETIC ANTICIPATION - EXPANDING TANDEM REPEATS

The phenomenon of genetic anticipation, the progression of severity of an inherited disorder in successive generations, has not had a biolog ic explanation until recently. A new mutational mechanism of unstable trinucleotide (or triplet) tandem repeats in human genes has provided such an explanation. Several neurologic disorders including fragile X syndrome, myotonic dystrophy, Huntington's disease, spinocerebellar at axia type 1, spinal and bulbar muscular atrophy, and FRAXE mental reta rdation, are caused by this type of mutation. A recent approach to ide ntifying expanded repeats may simplify the process of finding candidat e genes for other disorders that show features suggestive of anticipat ion.