Expanded repeat sequences and disease

The clinical phenomenon of an earlier age of onset or a more severe phenoty pe in later generations of a family has been termed anticipation. In a numb er of neurological and neuropsychiatric disorders, the anticipation has bee n linked to expanded repeat sequences that increase in size upon transmissi on. This novel mutational mechanism has been demonstrated in more than 15 d isorders today. The repeat sequence motif (base composition), size, and loc alization of expanded repeats within the respective disease genes vary betw een disorders and influence the way the repeat causes disease. Here, we rev iew the occurence and properties of repeats in the genome. The different gr oups of disorders and possible pathogenic mechanisms are summarized. In add ition, methods used for detection and identification of expanded repeats an d the related disorders are discussed.