Reduced expression of CD99 and functional disturbance in anencephalic cortical thymocytes

In a significant proportion of cases, anencephaly is associated with thymic enlargement, suggesting a possibility that anencephalic fetuses have a fun ctional disturbance in thymocyte differentiation and development. In this r eport, we demonstrated that CD99 expression was consistently reduced in cor tical thymocytes of all anencephalic fetuses. In addition, the CD99-depende nt aggregation of immature cortical thymocytes was almost completely impair ed and apoptosis of thymocytes was markedly reduced in several cases. These results are in agreement with previous findings that CD99 regulates the ag gregation and apoptosis of various types of cells. These data strongly sugg est that functional disturbance of thymocytes and thymic hyperplasia are re lated to the reduced expression of CD99 molecule in anencephalic fetuses.