Jacobsen syndrome : four Korean children with thrombocytopenia or neutropenia. E.J. Seo, S.M. Ahn, J.Y. Lee, H.W. Yoo. Medical Genetics Clinic & Lab, Asan Medical Center, Seoul, Korea.
   Jacobsen syndrome is caused by terminal deletion of the long arm of chromosome 11. Patients with this syndrome have breakpoints in 11q23.3-11q24.2 and typical features including psychomotor and growth retardation, trigonocephaly, dysmorphic faces, ocular anomalies, cardiac defects, digit anomalies, and thrombocytopenia or pancytopenia. We have evaluated four Korean children with terminal deletion of 11q. Two patients had a breakpoint in 11q23.3 which may be related to the FRA11B fragile site. Remaining two patients showed a terminal deletion to distal 11q24. These patients had cardiac defects and dysmorphic facial features such as trigonocephaly, high-arched palates, and low-set ears. Strabismus, foot deformities, imperforated anus, and cryptorchidism were also found. Severe to moderate thrombocytpenia was observed in three patients. Neutropenia was detected in two patients. All patients revealed mild anemia. There are two candidate genes known to map to 11q24-25 that are likely to play some role in hematopoiesis: Ets-1 and nuclear-factor-related-kB (NFRKB) gene. Deletion of these genes appears to cause insufficiency for normal hematopoietic differentiation or development and result in thrombocytopenia or pancytopenia.