Description of Japanese twins with cleft lip, cleft palate, or both

Cleft lip and palate is relatively common among congenital external malformations; however, the pathogenesis of this condition remains unclear. Cleft lip and palate has long been considered to be a multifactorial hereditary disease in which not only genetic factors, but also environmental factors, may be related in a complex manner. We have been studying the pathogenesis of cleft lip and palate in Japan and report here on some recent findings. We reviewed 32 pairs of Japanese monozygotic twins who had cleft lip and palate and compared these twins with non-twins who had cleft lip and palate in order to elucidate genetic factors that may cause this malformation.