Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Jacobsen Syndrome, 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.
- Closely-set eyes caused by trigonocephaly
- Folding of the skin near the eye (epicanthus)
- Short, upturned nose (anteverted nostrils)
- Thin lips that curve inward
- Displaced receding chin (retrognathia)
- Low-set, misshapen ears
- Permanent upward curvature of the pinkie and ring fingers (bilateral camptodactyly)
- Hammer toes
In addition, patients tend to be shorter than average and have poor psychomotor skills.
Patients with this disorder can often live relatively normal lives within the limitations of their disability, although this varies from person to person, and congenital heart disease that does not manifest itself until adulthood is common. There is a greater incidence of various forms of cancer among Jacobsen patients. The vast majority of patients have a bleeding disorder called Paris-Trousseau Syndrome, which causes reduced blood platelet counts and an impairment of platelets' normal blood clotting function. Platelet counts increase during childhood and can eventually reach normal levels, but many patients still have poor clotting due to abnormalities in platelet function. Unless their platelet function has been tested and shown to be normal, Jacobsen patients should be assumed to have a bleeding disorder.
The majority of Jacobsen syndrome cases are not familial in nature, resulting from a spontaneous mutation occurring in a single parental gamete. However, some instances of familial disease resulting from local chromosome fragility or an unbalanced translocation have been described.
- 11q.org - Note: PDF file
- Orthoseek - Specializes in pediatric orthopedics and pediatric sports medicine