Thus, in this study, we have used a novel fluorescent reporter assay to investigate the molecular role of huntingtin in protein secretion using HeLa cells expressing HTT siRNA and homozygous primary embryonic fibroblasts isolated from the Htt140Q/140Q knock-in (KI) mouse as well as primary fibroblasts from an individual with HD who is heterozygous for 180Q at the HTT locus (HTT+/180Q). The gene discussed is HTT; the disease is Huntington disease.