HECA, also known as headcase homolog, HDC, HDCL or HHDC, is a 543 amino acid mammalian homolog of the Drosophila headcase protein, a highly basic, cytplasmic peptide that plays a role in mitotic re-entry during adult morphogenesis. Expressed in a variety of tissues with highest expression in thymus, spleen and heart, HECA is thought to play a role in the development of epithelial tube networks in lung tissue and may also be involved in the pathogenesis of lung cancer. The gene encoding HECA maps to human chromosome 6, which contains 170 million base pairs and comprises nearly 6% of the human genome. Deletion of a portion of the q arm of chromosome 6 is associated with early onset intestinal cancer, suggesting the presence of a cancer susceptibility locus. Additionally, Porphyria cutanea tarda, Parkinson's disease, Stickler syndrome and a susceptibility to bipolar disorder are all associated with genes that map to chromosome 6.