EXT2 and Intellectual disability: In our patient, the lack of exostoses and parietal foramina is in agreement with the presence of two copies of the causative genes EXT2 and ALX4. Conversely, the deletion includes the PHF21A gene, which has been recently implicated as contributing to the intellectual disability and craniofacial anomalies typical of PSS, such as brachycephaly, midfacial and mandibular hypoplasia [20].