1. Department of Organic and Macromolecular Chemistry; Ghent University; Krijgslaan 281 S4 9000 Ghent Belgium
2. Current address: Dept. of Molecular Biology/; Massachusetts General Hospital; Simches Research Center 185 Cambridge Street Boston MA 02114 USA
3. Center of Medical Genetics; Ghent University; Medical Research Building De Pintelaan 185 9000 Ghent Belgium