| dc.description.abstract | Triplet repeat expansion diseases (TREDs) are regarded as a unique family among inherited genetic disorders (Ashley & Warren, 1995). Typically, they are characterized by expansion of genetically unstable d(CTG.CAG), d(CCG-CGG) or d(GAA-TTC) triplet repeat sequences located within specific genes. The number of triplet repeats in disease-associated genes tends to increase in germ line transmission from parent to offspring. The amplification continues in offspring of affected individuals, resulting in progressively increased severity of the disease andlor an earlier age of onset, phenomena clinically referred to as "anticipation". Members of the TRED family include Huntington's disease, fragile X syndrome and Friedreich's ataxia [for a review of the genetic and clinical features of TREDs, see Ashley & Warren (1995); Sutherland & Richards (1995); Timchenko & Caskey (1996)]. Usually, the larger the repeat number, the higher the probability of expansion and the earlier age of onset and increased severity of the disease. Due to the high frequency with which the trinucleotide repeats associated with these diseases undergo further expansion in offspring of affected individuals, the mutation(s) responsible for this phenomenon has been described as "dynamic " ( Su ther land and Richards, 1995). | |
