[Triplet repeat disease from the aspect of psychiatric disease]

Since 1991, about 20 triplet repeat expansion disorders have been reported. They are clinically characterized by anticipation, worsening severity or earlier age at the onset with each succeeding generation, and imprinting, a process whereby specific genes are differentially, marked during parental gametogenesis, resulting in their differential expression. The anticipation in psychoses was pointed out in the 19th century, but it was ignored because no one knew the mechanism at that time. The discovery of triplet repeat expansion diseases has reawakened interest in anticipation in psychiatric diseases. Anticipation has been confirmed in schizophrenia, mood disorders, and anxiety disorders. Molecular approaches have been taken to reveal the involvement of a triplet repeat expansion mechanism in psychoses. Most efforts have been made for CAG-type trinucleotide repeats. So far, most results did not support a trinucleotide repeat expansion mechanism also in psychoses. One plausable explanation for the "false positive" result is the presence of CAG trinucleotide repeats, which are highly polymorphic but not associated with an obvious abnormal phenotype. The screening for triplet repeats besides those of the CAG type remain to be performed.