IGFBP2 and Prader-Willi syndrome: They proposed that this genomic area was a susceptibility region for neurological dysfunction, impaired development and characteristic phenotypic features which was initially raised by Butler et al. [5] in a study of PWS individuals with the larger 15q11–q13 type I deletion including the four genes in the BP1 and BP2 area and having a more severe behavior phenotype compared with those with the smaller type II deletion.