Molecular Models for Repeat Expansions

Expansions of simple DNA repeats account for more than two dozen hereditary disorders in humans (for recent reviews see Lenzmeier and Freudenreich, Jin and Warren, Parniewski and Staczek, Ranum and Day, Brown and Brown, Cummings and Zoghbi, Bowater and Wells, and Siyanova and Mirkin). Table 1 describes those diseases and their important genetic features. Although originally discovered expansions were limited to trinucleotide repeats CGG nÐ CCG n, CAG nÐ CTG n,11–17 and GAA nÐ TTC n, it has now become clear that other repeats, including tetrameric CCTG nÐ CAGG n, pentameric AATCT nÐ AGATT n, and even dodecameric C4GC4GCG nÐ CGCG4CG4 n, can expand as well.