ANXA2R (annexin-2 receptor), also known as AX2R or C5orf39, is a 193 amino acid protein that is widely expressed and may act as an annexin II receptor on marrow stromal cells to induce osteoclast formation. In addition, ANXA2R is highly expressed in lymphocytes and is also found in resting CD4+ and CD8+ T cells. The gene encoding ANXA2R maps to human chromosome 5, which contains 181 million base pairs and comprises nearly 6% of the human genome. Chromosome 5 is associated with Cockayne syndrome through the ERCC8 gene and familial adenomatous polyposis through the adenomatous polyposis coli (APC) tumor suppressor gene. Treacher Collins syndrome is also chromosome 5-associated and is caused by insertions or deletions within the TCOF1 gene.