Intracellular inclusions, pathological markers in diseases caused by expanded polyglutamine tracts?

The largest group of currently known trinucleotide repeat diseases is caused by (CAG)n repeat expansions. These (CAG)n repeats are translated into polyglutamine tracts from both mutant and wild type alleles. Genetic and transgenic mouse data suggest that the expanded polyglutamines cause disease by conferring a novel deleterious gain of function on the mutant protein. These mutations are associated with the formation of intracellular inclusions. This review will consider findings from necropsy studies of human patients and transgenic mouse models of these diseases, along with in vitro models, in order to try to synthesise the current understanding of these diseases and the evidence for and against inclusion formation as a primary mechanism leading to pathology.