Classifying common oral clefts: a new approach after descriptive registration.

OBJECTIVE: Using the Dutch Oral Cleft Registration, which records the morphology and topography of common oral clefts, a new classification based on the (patho)embryology of the primary and secondary palates was tested. DESIGN: Prospective observational study. SETTING: The fifteen cleft palate teams in the Netherlands register patients to the national registry. PATIENTS: All unoperated patients with common oral clefts reported between 1997 and 2006 inclusive were included. MAIN OUTCOME MEASURES: The classification is based on the pathoembryological events that ultimately result in various subphenotypes of common oral clefts. PATIENTS within the three categories cleft lip/alveolus (CL/A), cleft lip/alveolus and palate (CL/AP), and cleft palate (CP) were divided into three subgroups: fusion defects, differentiation defects, and fusion and differentiation defects. A timetable was constructed to relate the type of clefting to the time of derailment during embryonic development. RESULTS: 3512 patients were included. PATIENTS with CL/A showed 22% fusion defects, 75% differentiation defects, and 3% fusion and differentiation defects. CL/AP patients and CP patients mostly showed fusion defects (70% and 89%, respectively). We were able to relate almost all (over 90%) cleft subphenotypes to specific weeks in embryonic development. CONCLUSIONS: This classification provides new cleft subgroups that may be used for clinical and fundamental research. The subphenotypes of these subgroups originate from different time frames during embryonic development and different cell biological mechanisms, thereby enabling more accurate data for, e.g., gene identification and/or environmental factors.