Craniofacial morphology in twins with cleft lip and palate

The craniofacial morphology of 11 pairs of monozygotic (MZ) and 28 pairs of dizygotic (DZ) Finnish twins, discordant or concordant for cleft of the lip (CL), unilateral cleft lip and palate (UCLP), or cleft palate only (CP) were investigated by means of lateral cephalometric radiographs. The results were compared to those of age-, sex-, and cleft-type matched single-birth cleft subjects, and also with normative data from the Nordic population. The co-twins with no cleft lip or palate (NONC) showed only slightly more obtuse gonial and steeper mandibular angles compared to normative data. Twins with CL, UCLP or CP had a more retrusive mandible, a wider cranial base and mandibular angle, and a wider angle between the maxilla and mandible than did the single-birth cleft subjects. Comparison of the noncleft twin group with the CL, UCLP, and CP twin groups for the CL twins showed no significant differences. For the UCLP twins, a more retrusive and down- and backward rotation of both jaws, a wider gonial angle, and a wider cranial base angle was seen. The CP twins had their maxillae slightly retrusive, the down- and backward rotation of both jaws was apparent, and the gonial angle was more obtuse. A comparison between the noncleft MZ and noncleft CDZ twins showed no significant differences. The MZ CP twins had a more retrusive mandible and more down- and backward rotation of both jaws than did DZ CP twins. It thus can be suggested that twinning itself does not seem to have an effect on maxillofacial morphology, but the features of the mandibular structure, the cranial base angulation, and the inclination of the jaws are at least partly genetically induced.