RAD21 and developmental disability: Cornelia de Lange syndrome (CdLS) is a rare genetic disorder that affects multiple organ systems and is characterized by distinctive facial features, growth retardation, and developmental disabilities. The syndrome is caused by mutations in genes (<i>NIPBL</i>, <i>RAD21</i>, <i>SMC3</i>, <i>HDAC8</i>, and <i>SMC1A</i>) involved in the cohesin complex, which plays a critical role in chromosome segregation and gene expression regulation.