Etiological aspects on craniofacial morphology in twins with cleft lip andpalate

The craniofacial morphology of 39 Finnish twin pairs concordant or discorda nt for cleft of the lip (CL), unilateral cleft tip and palate (UCLP), or cl eft palate only (CP) was studied by means of lateral cephalometric radiogra phs. The intrapair differences between various cleft and twin subgroups wer e compared by means of univariate analysis; multivariable analysis of cleft discordant pairs and the variance components were estimated with the TWINA N program. Larger values for intrapair differences were found, especially i n linear measurements in older twin pairs. Heritability estimates for the c ranial base measurements and, to a lesser extent, for the mandibular measur ements were high. Comparisons on the basis of cleft type revealed more diff erences between twin pairs when clefting was more severe. Concordant and di scordant CP twin pairs showed similarity in their intrapair craniofacial mo rphology, indicating that surgery seemed to have no major effect on their c raniofacial morphology. A similar comparison in discordant UCLP showed that , in addition to clefting itself, external factors, i.e., the repaired clef t's direct effects on craniofacial morphology, have a strong influence on c raniofacial morphology, especially in the maxillas of the UCLP twins. The c raniofacial morphology in these Finnish twins supports the hypothesis of di fferent genetic behavior for cleft lip and cleft lip and palate (CL(P)) and CP in Finland.