FAM58A (family with sequence similarity 58, member A) and FAM58B (family with sequence similarity 58, member B) are 248 amino acid and 252 amino acid proteins, respectively, that belong to the cyclin-like FAM58 subfamily. Existing as multiple alternatively spliced isoforms, FAM58A interacts with Sall1 and is thought to play a role in cellular proliferation. Defects in the gene encoding FAM58A are associated with toe syndactyly, telecanthus, and anogenital and renal malformations (STAR syndrome), which is characterized by renal and anogenital malformations. FAM58B, a protein that is related to FAM58A, is expressed in healthy retina and breast tissue, as well as in retinoblastoma and breast cancer cell lines, suggesting a role for FAM58B in tumor transformation and metastasis.