CLDND1 (claudin domain containing 1), also known as C3orf4 or HSPC174, is a 253 amino acid multi-pass membrane protein that is expressed at high levels in adult brain and at lower levels in adult heart. Existing as two alternatively spliced isoforms, CLDND1 is encoded by a gene that maps to human chromosome 3, which houses over 1,100 genes, including a chemokine receptor (CKR) gene cluster and a variety of human cancer-related gene loci. Key tumor suppressing genes on chromosome 3 include those that encode the apoptosis mediator RASSF1, the cell migration regulator HYAL1 and the angiogenesis suppressor SEMA3B. Marfan Syndrome, porphyria, von Hippel-Lindau syndrome, osteogenesis imperfecta and Charcot-Marie-Tooth Disease are a few of the numerous genetic diseases associated with chromosome 3.