The huntingtin gene, also called the HTT or HD (Huntington disease) gene, is the IT15 ("interesting transcript 15") gene, which codes for a protein called the huntingtin protein. The gene and its product are under heavy investigation as part of Huntington's disease clinical research and the suggested role for huntingtin in long-term memory storage.It is variable in its structure, as the many polymorphisms of the gene can lead to variable numbers of glutamine residues present in the protein.