Huntington's disease occurs when the cytosolic protein Huntingtin (Htt) has an additional 35 glutamine residues added to its amino terminal region. This modified form of Htt is called Htt. Htt makes Type 1 IP receptors more sensitive to IP, which leads to the release of too much Ca from the ER. The release of Ca from the ER causes an increase in the cytosolic and mitochondrial concentrations of Ca. This increase in Ca is thought to be the cause of GABAergic MSN degradation.