of expanded glutamine repeats in neurodegeneration - - current situation and new possibilities

Tandem repeats, that is simple sequence repeats, occur commonly in the human genome, and they have long been used as markers in linkage studies. In this decade, it has also been found that tandem repeats underlie an entirely new class of human mutations. The expansion of a group of trinucleotide repeats is now known to cause several inherited diseases, all of which are neurological disorders. These trinucleotide repeat diseases share several common features: 1. Inheritance is autosomal dominant or X-linked. 2. Disease severity correlates directly with increasing repeat length. 3. Expansions arise from CG-rich triplet repeats that are polymorphic in the normal population. 4. The expanded trinucleotide repeats are unstable and change in size when transmitted to successive generations. 5. The diseases show anticipation, that is, disease severity increases in successive generations of a family. 6. Parent-of-origin effects are common, where the most severely affected individuals usually inherit the disease from the father.