To investigate the role of wild-type huntingtin in protein secretion, the authors use a combination of tissue culture cell lines, including primary fibroblasts isolated from homozygous Htt140Q/140Q knock-in mice, HTT-knockdown human HeLa cells and primary fibroblasts obtained from a heterozygous individual with HD (HTT+/180Q). This evidence concerns the gene HTT and Huntington disease.