Chapter ST.6, Problem 1DQ

There are nine known progressive neurodegenerative disorders that all share expanded numbers of the CAG codon, which inserts extra glutamine residues into the coding regions of specific genes. Genes carrying such mutations are typically gain-of-function mutations and often share a common mechanism of pathogenesis. Why would such genes be gain-of-function? Speculate on why such diseases may be caused by a common mechanism.