Jacobsen Synrome, also known as 11q deletion, is a rare congenital disorder resulting from deletion of a terminal region of chromosome 11 that includes band 11q24.1. It can cause mild mental retardation, a distinctive facial appearance, and a variety of physical problems including heart defects and a bleeding disorder. The syndrome was first identified by Danish physician Petra Jacobsen in 1973, and is believed to occur in approximately 1 out of every 100,000 births.