Cephalometric analysis of the Prader-Willi syndrome

The Prader-Willi syndrome (PWS) is characterized by short stature, mild mental retardation, and a characteristic face. Approximately 75% of all patients have a del (15q). Cephalometric roentgenograms of 20 PWS patients of both sexes (12 adults, 8 children, age 4.5-50.0 years) were analyzed to determine if the facial appearance is reflected in changes in the bony architecture, a characteristic which might be useful in diagnosis and/or dental treatment of these individuals. PWS subjects were compared with chronologic age and sex-matched control individuals derived from the Denver Growth study using 52 point computer analyzed lateral head-plate tracings performed by the same individual (RS). The mean Z-score differences for mandibular and maxillary total length, ramus height, mandibular corpus length, posterior facial height, and mid-facial height were all significantly smaller in greater than 65% of the PWS subjects; this was more evident in the PWS children. The Z-score difference for posterior cranial base was very large in most PWS adults and children whereas lower facial height was small or normal in all subjects. No statistical difference in mean Z-score measurements was found for all these measures in PWS subjects with or without the 15q chromosome deletion. The overall small bony structures contrast with the relatively large soft tissue draping seen especially in obese adults. The data suggest that a characteristic bony model might be created for PWS which could be of use in diagnosis and in the treatment of PWS patients by their orthodontist.