[1] NHGRI, Med Genet Branch, NIH, Bethesda, MD 20892 USA
[2] Childrens Hosp Philadelphia, Dept Pediat, Philadelphia, PA 19104 USA
[3] Childrens Hosp Philadelphia, Dept Genet, Philadelphia, PA 19104 USA
[4] Childrens Hosp Philadelphia, Dept Neurol, Philadelphia, PA 19104 USA
[5] Deutsch Krebsforschungszentrum, Div Mol Embryol, Heidelberg, Germany
[6] NHGRI, Med Genet Branch, Cytogenet & Confocal Microscopy Core, Bethesda, MD 20892 USA