EXT2 and Intellectual disability: A heterozygous deletion of 2.3 Mbp in chromosome 11p11.21 containing EXT2 causes Potocki-Shaffer-syndrome that is characterized by multiple osteochondromas, developmental delays, biparietal foramina, craniofacial abnormalities, and intellectual disability (Table 3; Swarr et al., 2010; Palka et al., 2012).