Programmed neuronal cell death is a feature of neurodegenerative disorders such as Alzheimer's and Huntington's disease, which occur later in human life. Huntington’s disease at the molecular and cell level is characterized by polyglutamine expansion of the protein huntingtin (Htt) that leads to apoptotis-mediated neurodegenerative loss of medium spiny neurons throughout the striatum. Polyglutamine expansion reduces the level of association between Hip-1 and Htt, thereby increasing levels of free Hip-1 that then can be the candidate protein Hippi (Hip-1 protein interactor). The Hippi-Hip-1 heterodimer is a pro-apoptotic complex that recruits procaspase-8 and initiates caspase-8 activation, which may contribute to the neuronal cell death observed in individuals diagnosed with Huntington’s disease. The human hippi gene maps to chromosome 3q13.13 and encodes a 429 amino acid protein.