Thirteen chromosomal regions associated with 11 known disorders involving microdeletions and microduplications, including 1p36 monosomy, 1q21.1 (novel), 1q44 (novel), Wolf-Hirschhorn syndrome (WHS) (4p16.3), cri-du-chat syndrome (CDCS) (5p15.3), WBS (7q11.23), WAGR (Wilm's tumor, aniridia, genital/or urinary tract abnormalities, mental retardation) (11p13), Prader-Willi/Angelman syndromes (PWS/AS) (15q11.2), MDLS (17p13.3), CMT1A/hereditary neuropathy with pressure palsies (HNPP) (17p12), SMS (17p11.2), neurofibromatosis type 1 (NF1) (17q11.2) and DGS/VCFS (22q11.2). The gene discussed is NF1; the disease is Prader-Willi syndrome.