RB1 and Prader-Willi syndrome: DNA probes selected were: Prader-Willi Syndrome (PWS) on 15q11-13 (Vysis); Retinoblastoma (RB1) on 13q14 (Vysis); whole painting probes specific for chromosomes 1, 3, 9, 13, 14, 15, 18, 19 (Metasystems, Altlussheim, Germany); α-satellite probes for centromeres of chromosomes 13/21 (Q-BIOgene, Illkirch, France).