Dopey-1 is a 2,465 amino acid protein that is thought to be involved in protein trafficking between the late golgi and early endosomes and may be involved in neurological alternations and mental retardation associated with Down syndrome. The gene encoding Dopey-1 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.