The first model used was a PC12 cell line (derived from rat pheochromocytoma) that expresses an inducible EGFP-tagged exon 1 of huntingtin with 23 or 74 polyglutamine repeats (Q23 or Q74) (Wyttenbach et al, 2001). The gene discussed is HTT; the disease is hereditary pheochromocytoma-paraganglioma.